The F-35 and the Infamous Transonic Acceleration ‘Spec’ Change:

Part 2:  Top-Level Analysis of F-35 Transonic Performance

(Part 1 Here, Part 3 Here, Bonus Block 60 Comparison Here)

Analytical Approach

To make the next part of our exploration as widely accessible and understood as possible, our goal will be to continue to minimize the amount of math and physics to the greatest practical extent: keeping things as simple as we can without doing violence to the phenomena. Think of it as a ‘studies’ approach. 

Therefore, I will try to base analyses upon relative differences in ‘sum totals’ and relative percentages or fractions to some baseline. We can’t get away from a minimal discussion of the nature of acceleration versus drag, but we can illustrate the things about drag and acceleration that we need to grasp without crunching too many of the numbers. Which is a good thing, because without the need to know, we don’t have the actual F-35 numbers (ex: drag values) available to us in the public domain for plugging into any calculations anyway.

First we’ll summarize the relevant things we now know-- or think we know-- about the F-35’s Transonic Acceleration KPP and overall performance. We will focus on the F-35A model in examining the relevant physics of accelerating through the transonic region and how they affect all aircraft and in particular the F-35A. We’ll then follow with a discussion examining just one likely ‘workaround’ that the F-35A might operationally employ (if it is even needed), and discuss the ‘tactical’ impacts and whether or not what may obviate or mitigate whatever the ‘popularly-perceived’ operational challenges the F-35 variants endure passing through the transonic region.

What we know or think we know

Here is what we know or has been reported as stated by the F-35 Program Participants including the user communities that will help guide the discussion.  Note: We’re numbering the references for easing later analysis and possible discussion.

1. The 2012 DOT&E report mentioned the following about the F-35 acceleration from .8M to 1.2M:

A.) A Model: Extended the time for acceleration from 0.8 Mach to 1.2 Mach by 8 seconds

B) B-Model: Extended the time for acceleration from 0.8 Mach to 1.2 Mach by 16 seconds

C) C Model: Extended the time for acceleration from 0.8 Mach to 1.2 Mach by “at least” 43 seconds

2. A Lockheed Martin representative was quoted in Air Force Magazine (cached) as stating the F-35 can maintain Mach 1.2 for a dash of 150 miles without using afterburners. Adding: "Mach 1.2 is a good speed for you, according to the pilots,".

(3, 4,and 5 are all from the same source)

3. “Based on the original spec, all three of the airplanes are challenged by that [acceleration] spec,” said Tom Burbage, Lockheed’s program manager for the F-35. “The cross-sectional area of the airplane with the internal weapons bays is quite a bit bigger than the airplanes we’re replacing.”…

4. …“We’re dealing with the laws of physics. You have an airplane that’s a certain size, you have a wing that’s a certain size, you have an engine that’s a certain size, and that basically determines your acceleration characteristics,” Burbage said. “I think the biggest question is: are the acceleration characteristics of the airplane operationally suitable?”…

5. …U.S. Air Force Lt. Col. Eric Smith, director of operations at the 58th Fighter Squadron at Eglin Air Force Base, Fla., and F-35 test pilot, said that flying the aircraft is a thrilling experience.

“I can’t even explain the adrenaline rush you get when you light the afterburner on that thing,” Smith said. “The acceleration is much better than an F-16.”

6. The F-35′s acceleration is “very comparable” to a Block 50/52 F-16. “Again, if you cleaned off an F-16 and wanted to turn and maintain Gs and [turn] rates, then I think a clean F-16 would certainly outperform a loaded F-35,”Kloos says. “But if you compared them at combat loadings, the F-35 I think would probably outperform it.”   The F-16, Kloos says, is a very capable aircraft in a within visual range engagement–especially in the lightly loaded air-to-air configuration used during training sorties at home station. “It’s really good at performing in that kind of configuration,” Kloos says. “But that’s not a configuration that I’ve ever–I’ve been in a lot of different deployments–and those are the configurations I’ve never been in with weapons onboard.” – 

7. The weight purge of a few years ago was so “intensive,” Crowley said, that “there’s not thousands of pounds” of weight left to be saved on the F-35. However, even with a three percent annual weight growth, the key performance parameters, or KPPs, won’t be affected.

“All of our predictions for performance are based on an end-of-life, worst-case” scenario relative to the F135 engine’s power capacity, “so the true performance of the jet, throughout its life, will be much better.”

8. PARLIAMENTARY JOINT COMMITTEE ON FOREIGN AFFAIRS, DEFENCE AND TRADE 20 MARCH 2012 (Tom Burbage) Transcript: 

For any performance-related requirements, we artificially penalise [sic] the engine by five per cent fuel flow and two per cent thrust. Those margins are given back as we mature the design and get more and more solid on exactly what it is going to do. They are there for conservative estimation up front. We have not taken back any of those margins yet so, when those margins are taken back, the airplane will continue to be well in excess of its basic requirement.

Information from ‘other’ sources.

9. The baseline transonic acceleration specifications for the three variants prior to the spec change are believed to be:

A) A Model: The original “threshold” Key Performance Parameter (KPP) specification time for transonic acceleration (.8 to 1.2 Mach) was ≤ 55 seconds at 30Kft Altitude.

B) B Model: The original “threshold” Key Performance Parameter (KPP) specification time for transonic acceleration (.8 to 1.2 Mach) was ≤ 65 seconds at 30Kft Altitude.

C) C Model: The original “threshold” Key Performance Parameter (KPP) specification time for transonic acceleration (.8 to 1.2 Mach) was ≤ 65 seconds at 30Kft Altitude.

These times were asserted in an oft-referenced Air Command and Staff College paper authored in 2008 by a then-Lt Commander Geoffrey P. Bowman (USN). These numbers have been repeated in the popular aviation press (example) and Australian Air Force Air Vice Marshall Osley came close to ‘anecdotally’ confirming the F-35A KPP as asserted in the ‘Bowman Paper’ in testimony before an Australian Parliamentary Committee in 2013. The aircraft gross weights and fuel loads for the KPPs have not been revealed, though the Bowman Paper observes they are for internal-only weapons load configurations.

***********

APC Quotes added 20 Apr 15 (because the Australian Parliamentary Committee link seems to be a 'moveable' feast):

Dr JENSEN: Air Vice Marshal Osley, in a previous hearing you responded to APA's criticism of the F35's aerodynamic performance and you said that it is inconsistent with years of detailed analysis undertaken by Defence, the JSF program office, Lockheed Martin and eight other partner nations. Given that the Director of Operational Test and Evaluation has indicated that the JSF program office, the JPO, has asked JROC to reduce the sustained turn and the acceleration performance essentially to exactly the numbers that APA was predicting years ago, what does that say about the detailed analysis by Defence, the JSF program office, Lockheed Martin and the eight partner nations? 

Air Vice Marshal Osley: The points that the Director of Operational Test and Evaluation made there about the manoeuvrability, as you point out it was the sustained turn and the transonic acceleration. He pointed out that the targets that have been set for those parameters were not going to be met by the F35. The figure of I think it was 55 seconds for transonic acceleration, the F35 was going to take 63.9 seconds to do that. That is obviously at a certain altitude, I think it was 30,000 feet, and a range of mach 0.8 up to mach 1.2.
The point to make about those is that that acceleration by the F35 is in a combat configuration. If you look at the legacy aircraft and we talk about comparable performance, a legacy aeroplane would require weapons and, obviously, external fuel tanks to be in combat configuration.

**********

10. …This next reference is included because I believe the article that it is from was at the root of the comment that provided me with the impetus for these posts. It also hints at a way forward within 

An interesting factoid, one of the USMC test pilots mentioned this little tidbit—they have to use a modified Rutowski profile in order to get the F-35B and C up to Mach 1.6. Basically, you do one push over, unload the jet and accelerate, get up to 1.2, turn and repeat until you hit 1.4 Mach, turn and repeat till you hit Mach 1.6. It just barely gets there and barely has any gas left over afterwards. The kinematics are basically F/A-18C-like, though that was apparently exactly what was expected….

FYI and FWIW, here’s one of the more decent explanations of a “Rutowski maneuver” that I’ve found online: 

If the final speed is near the aircraft’s maximum speed, the large speed increase necessary renders the conventional method of using the peaks of the Ps curves useless. However, the energy method works well. Note in this example the optimum climb path includes an acceleration in a dive. This optimum energy climb path is also known as the Rutowski climb path, after its developer. The path (Figure 7.14) [at the link] consists of four segments to reach energy state E in minimum time. Segment AB represents a constant altitude acceleration from V = 0 to climb speed at state B. The subsonic climb segment follows a path similar to the one illustrated to the tropopause at state C. This subsonic climb is usually a nearly constant Mach number schedule. An ideal pushover or dive is carried out at constant Eh from C to D. The acceleration in the dive is actually part of the optimum climb path.

 (It's better at the source with the graphic)

11. There’s a Block 50/52 (F110-GE-129 or F100-PW-229 powered) Dash-1 supplement (Hellenic Air Force) out on the web that provides significant insight as to the F-16 performance baseline used to set the original F-35 transonic KPP.  

Deduced Transonic Acceleration KPP Times Analysis of the Variants

The most important performance ‘data’ in our hands are the believed-to-be-actual acceleration times

From References #1 and #9 above, we find evidence that the F-35 variants are currently expected to perform the transonic dash from .8 to 1.2 Mach in the following times:

Model Original KPP Time (secs) Exceeded by (secs) New KPP Time (secs)

F-35A   55                                                  8 63

F-35B 65                                                 16 81

F-35C 65                                                 43 (minimum) 118

Why the differences, and why by ‘that’ much?

IMHO these differences would make an excellent case study for an introductory course on aircraft design if only to just illustrate how much even small differences in design can affect aspects of performance in large ways. I can’t think of any other case where there are three ‘operational’ combat designs that are so close to each other but still different enough to tease out likely drivers of performance differences. (I am excluding aircraft that have had all sorts of various bulges and blisters scabbed on post-manufacture). The first question that springs from observing these differences is how much of the variation is due to variation in aerodynamic shape, propulsion efficiency, and weight?  

To help us investigate, we now need to take a look at the possible relevant differences. Those would be the differences between aerodynamic shapes, the engine installations, and relative weights: elements affecting the drag equation (Figure 3 from Part 1) which we now modify to remind us that the drag coefficient is but one element in the drag equation:

Figure 8 (Numbering Continued From Part 1

   

As the range of airspeed from .8 Mach to Mach 1.1 is the same, and the same air density (same altitude) are common to all variants, this reduces the number of variables on the drag side of the thrust-drag equation to two: the Drag Coefficient and the Cross-Sectional area. On the thrust-side of the equation, we will have less to work with but not so much less as to prevent us from making several observations and ‘educated’ estimations. Since this little exercise is about ‘understanding’ and not ‘quantifying’, I am comfortable working within these limitations.        

Relative Weights

We’ll model some likely weights (based upon the ‘Bowman Paper’ and acknowledged fuel and weapons carriage plans). Why ‘weight’? Because it is an excellent proxy for examining relative lift differences between the variants which “weight”, in level flight, must equal “lift”—the major constituent driver of ‘drag’.

If we take the empty weights, add half-internal fuel weight and the basic ‘day-one’ combat weapons load weight (with a wedge ‘rounding-up’ to account for the weight of weapon interfaces of each of the three variants), we arrive at a ‘likely’ set of aircraft weights for the Transonic Acceleration KPP:

            Empty Wt     50% Fuel Wt Weapons Load (2 JDAMS, 2 AIM-120s)     Total

F-35A 29300 9240 5000                                       43540

F-35B 32300 6750 3000                                       42050

F-35C 34800 9875 5000                                       49675

These configurations, whether exactly those used for the Transonic Acceleration KPP or not, are at least representative of the aircraft weights before release of air-to-ground stores and at the mid-mission point. They are therefore ‘realistic’ for use as a baseline for our explorations. They also cannot be too far off relative to each other to make too much of a difference in our search for understanding, as the only variable is fuel weight and the lower F-35B model JDAM carriage capability.
Using the F-35A Model weight as the basis, we find that over a range of mid-mission fuel loads, the F-35C weight, and therefore lift needed to be generated in level flight to be around 13-14% higher than the F-35A. 

Figure 9. Relative f-35 Variant Weights

We also see that largely due to a smaller total fuel load and lower weapons payload, the F-35B needs to generate approximately 3-4.5% less lift to maintain level flight. (This also again illustrates a point made in the Sustained G discussion about the lighter an aircraft, the more sensitive its performance is to weight changes.)

We can therefore conclude that the wing wave drag coefficient  percentage contribution to the total drag coefficient that is due to lift for the F-35B is less than the F-35A (under the same flight conditions in the speed region we are looking at of course), and that the F-35C’s wing wave drag coefficient contribution due to lift is significantly higher than for the F-35A. Further, we can conclude there is little, if any, difference between the wing wave drag contribution due to volume for the F-35A and B because the F-35A and F-35B wings are identical in area: they have the same fixed length (chord), and span. We  also know the area of the A and B wings are identical and their cross-sectional volumes very nearly so (more on this in the next section).  

We can also conclude that there is a large difference between the F-35A and F-35C in wave drag contribution as a percentage of the total drag due to both lift and volume. This is because the F-35C has a much bigger wing and control surfaces (more on this too in the next section). The overall coefficient of drag for the F-35C might theoretically be smaller than the A or B at some points along the curve, but that would have to come from reduction in the total drag via other means. For all we know, the total volume distribution of the F-35C comes closer to an ideal Sears-Haack distribution than the other two variants. We cannot definitively rule this out without more data, but given the differences between the F-35A and C in transonic acceleration, I believe we can assume with some relative confidence the F-35C has an overall drag coefficient much, much, higher than the A model, and even if the F-35C drag non-wing coefficient was lower than the A model, it certainly does not overcome the F-35C’s larger cross-sectional area. If the differences in drag coefficient due to wing lift were the only effective differences between F-35 models, we would expect the F-35B to have better transonic acceleration more on a par with the F-35A due to it weighing less when loaded, and we would expect the F-35C to be much slower in accelerating in level flight than either the A or B model. Since the A model has the best transonic acceleration, we should assume there is some other factor (or factors) affecting the F-35B performance beyond wing wave drag. Also, while it appears the C is the worst performer in transonic acceleration, it is almost certainly NOT due solely to wing wave drag contribution to total drag coefficient. This leads us to the next discussion, Aerodynamic shaping.

Aerodynamic Shaping 

Even this kind of comparison without hard data would be impossible if we were comparing completely different aircraft, or if we were seeking to quantify the differences instead of just understanding them. The good news is our limitations will make this section mercifully short.  

Cross-sectional area comparison 

First, we find that the cross-sectional differences between the F-35A and C are different in nature and scale than the differences between the F-35A and F-35B.

  

Figure 10. Cross-sectional Are Differences

The differences between the F-35A and B are more in the 'non-direct' lift regions of the cross-sectional area and are obviously due to the B model lift fan installation (#7). The wing profile is slightly increased at the lower wing root (#6) due at least in part to the STOVL roll-control system installation. 

The shape differences between the F-35A and F-35C are far greater. First, wing (#3) and horizontal stabilizer (#2) extensions as well as the taller vertical stabilizers (#1) add significant cross sectional area to the C model. Further, it appears the C model wing cross-section is indeed thicker (#5) than the F-35A’s to support the greater wingspan, but this could be an illusion from a longer curved under-surface and/or wing twist (either way, this presents an increased cross-section perpendicular to the airstream versus the A or B model). The F-35C wings also present an effectively increased cross-section to the airstream at the wing-folds (#4).  The F-35A and C do have a slightly increased cross-section versus the B model in the area of the tail hook enclosure (#8) but unlike the other cross-sectional areas, it is unclear how much of this is area that is presented perpendicular to the airstream in level flight.  Not known is if there are unseen relative differences in inlet design that affect not only installed thrust but also effective cross-sectional area, bur I believe we've captured the dominant difference drivers.

The Impact of Lift Surface Area on Wave Drag 

As already noted, Wave Drag due to ‘volume’ as a contributor is characterized in terms of a cross-sectional area for some fixed length. The F-35C is overall slightly longer than the F-35A and B, but its lift surfaces also have a significantly longer “fixed length” than the near identical F-35A and B surfaces. The F-35C’s wing and tail surface wave drag contribution due to ‘volume’ is therefore significantly greater than that for the F-35A and B. As a result we would expect the total drag of the F-35C in level flight to be much greater than the F-35A or F-35B due to having both a higher wing wave drag coefficient and greater cross-sectional area. 

     

Figure 11. Extended Vertical surfaces on C model not shown

Engine Installations

Whereas the first two topics of weight and aerodynamic shape dealt with the drag side of the acceleration equation, the engine installation aspect is relevant more on the thrust side of the equation. This is actually a pretty simple thing to compare on the F-35, as all three engines are essentially the same, with the major differences (performance wise) being between the F-35A/C engines and installations being highly common and the F-35B engine installation being very different from the other two. The physical differences of the F-35B installation-- the integrated lift-fan at the front of the system, the articulated exhaust duct with a different afterburner and nozzle installation at the other end, as well as a roll control nozzle system tapping flow off of the core engine in the middle cannot ‘help’ the conventional-mode of operations. Any significant performance differences between the F-35A and C engines would have to be due to any installation differences that are not apparent/acknowledged. 

For all practical purposes, we should then expect the F-35A and F-35C engines to have “the same” installed thrust and efficiencies. On the other hand, with the F-35B we would expect installed thrust penalties due to the added mass of the lift fan drive shaft and open roll-control ducting, the shaft passing through the bifurcated air inlets where they meet, as well as the different exhaust nozzle. We don’t know for certain, but it makes sense to believe the F-35B engine installation may be somewhat less efficient than the A or the C model in the conventional operation mode.

A Summary of Thrust vs. Drag

To summarize the relative differences between the variants that would affect transonic acceleration in a table:

Figure 12.  Factor Differences  between variants, F-35A Baseline 

In these same factors and relationships we find the seeds of understanding the operational implications of the F-35’s performance relative to each other in regards to the Transonic Acceleration KPPs. 

Transonic Acceleration: What is it good for?

The first thing to understand about the transonic acceleration KPPs is that they are proxies for the reasons WHY a fighter aircraft would want to accelerate quickly through the transonic region in the first place. The (obvious) answer is to gain a position advantage against an enemy in the air or on the ground by reaching that position to achieve an advantage before an enemy can position themselves to counter it. In the Air-to-Ground scenario this might mean simply getting to a high speed sooner to reach a time-critical target before it disappears or for some similar reason. We will ignore the air to ground aspect in thinking about the F-35s transonic acceleration KPPs and assume that because they are set at a 0K ft altitude, there wasn't a lot of Air-to-Mud consideration behind them. In the Air-to-Air combat it is about either closing some distance to gain a superior position on an opponent or opening some distance to gain position or keep the opponent from gaining a position on you. So the key thing to remember, and I hope the reader finds this an irritatingly obvious point, is that an acceleration KPP is about the ability to cover some distance over a set time when starting at a relatively lower speed. A transonic acceleration KPP is about being able to cover some distance as quickly as possible while moving ever faster through the particularly challenging transonic speed region.  This seems to beg the question: how significant it is really that the F-35A is projected to exceed its KPP by 8 seconds? (Note: We’ll get to the B and C KPPs in passing as we proceed.)         

F-35A Transonic Acceleration Performance

It has been determined by the F-35A program’s analyses that the original Transonic Acceleration KPP for the modeled F-35A will be exceeded by 8 seconds, taking 63 instead of 55 seconds. But considering we have multiple sources (#5, #6 above) citing excellent acceleration characteristics compared to an F-16 that imply superior initial acceleration, and the analyses are based upon degraded engine performance (#7, #8 above) how likely is it that the 8 second difference is even operationally relevant? Take a look at a second hand on your watch or clock. Watch it for 8 seconds.  If you were going M1.2 at the end of eight seconds, how fast were you going at the start of the eight seconds? M1.19? M1.18? 

Just from the drag equation and the drag coefficient charts we know that acceleration will be much greater at the start of the acceleration run than at the end. Is it possible the F-35A exceeds the initial predicted acceleration but just barely misses the full expectation?  Answers to these questions could have bearing as to whether or not extending the KPP by 8 seconds was even operationally relevant.  As it stands, it should still be viewed as superior to a Block 50/52 F-16. As we will see, Kloos (Ref #6) understates the F-35A’s abilities compared to the Block 50/52, at least at the 30K ft KPP altitude (Ref #10). 

How the F-35A new KPP standard stacks up against the F-16 Block 50/2 

If we examine the F-16’s ‘Combat Max AB’ transonic acceleration data (Ref #11, Table A8-12), and compare it to the F-35A’s newest transonic KPP time (63 seconds) we find the F-35A loaded with two AMRAAMs and two 2KLb JDAMs has better acceleration than the F-16C/D in 20 of the 30 possible weight/drag index combinations shown in the tables (weights from 20K lbs to 41K lbs, and Drag Indexes from 0 to 250).

Figure 13. F-35A KPP Superior to most F-16C Weight/Drag Combinations

Figure 14: External Stores start adding drag quickly

The F-35A KPP is on par with the F-16 in one of the possible F-16C load-outs. At least three of the remaining nine F-16 load-out combinations I would characterize as ‘highly impractical/improbable’ (for those you can have a few hundred pounds of usable fuel, or you can have two AMRAAMs but you cannot have both).






This is about as much as a Block 50/52 F-16C can weigh/carry without increasing the drag count:

Figure 15. Max 'Clean' Block 50/52 weight.( Source Ref 11)

Figure 16: Empty Fuel Tanks and Store Stations Still Add Drag 

Three more F-16 combinations involve simply carrying two more 600 gallon fuel tanks with various degrees of ‘fullness’ along with just two AMRAAMs and no other weapons other than the ever present 20mm cannon.

On the other hand, for 6 of the 20 load-outs where the F-35 KPP performance meets or beats the F-16C, the F-16 can’t even GET to Mach 1.2 (for three combinations the F-16 performance is ONLY subsonic).

In short, even if the F-16 is running on fuel fumes carrying wingtip AMRAAMs and
LANTIRN pods, it can only carry just a little more internal fuel before the F-35A's latest transonic acceleration KPP standard can be said to be ‘better’ than an F-16C Blk50/52 in transonic acceleration.

Figure 17: F-35A KPP performance vs. F-16 w/ DI=100

  

Figure 18: Only 2 AIM-9s greater load than F-35 Internal Load Out. It'll need those AIM-9s long before te F-35 will. 

Even the F-35B and F-35C transonic KPP times meet or beat a similarly-loaded but much lighter weight Block 50/52 F-16s:

Figure 19: With comparable war loads: F-35A and F-35 B beats all & F-35C beats most F-16 configurations.   

 The ‘meaning’ we can derive from the revised F-35A transonic dash KPP is this: It still represents the stated ‘F-16 Like’ performance goals and overall, it exceeds them. Other than that, everything else is guesswork. 

BUT!  The ubiquitous 'some' might ask.... 

‘What If’ Operational needs require the F-35A/B/C to get rid of all or part of those extra darned seconds enroute to Mach 1.2?  

THAT topic we will address in closing the series in Part 3.

The F-35 and the Infamous Transonic Acceleration ‘Spec’ Change:

Part 1: The Basics

Flashback...

About two years ago, F-35 critics were agog over the news that the F-35 was reducing its “Sustained G” and “Transonic Acceleration” Key Performance Parameters. As (the once-but-no-longer-promising-and-now -‘Punk’) ‘Journalist’ Dave Majumdar reported on FlightGlobal.com:

Turn performance for the US Air Force's F-35A was reduced from 5.3 sustained g's to 4.6 sustained g's. The F-35B had its sustained g's cut from five to 4.5 g's, while the US Navy variant had its turn performance truncated from 5.1 to five sustained g's. Acceleration times from Mach 0.8 to Mach 1.2 were extended by eight seconds, 16 seconds and 43 seconds for the A, B and C-models respectively…

Soon thereafter, I posted a short series where in the first part it was highlighted that the only truth one could conclusively draw from the Sustained G Spec change was that the F-35s would have slightly reduced sustained turn bank angles than planned. Anything else, including the relevance/significance of the change, would be speculation without additional knowledge.

We then explored what such a bank angle reduction MIGHT mean by performing parametric ‘what if’ exercises based upon certain assumptions. What we discovered was, is that the most important unknown appears to be aircraft total loaded weight and that the “baseline standard used [in developing the F-35 Spec] for the comparison was a clean Lockheed F-16 Block 50/52 with two wingtip Raytheon AIM-120 AMRAAMs”. 

In other words, the Sustained G spec was based upon an F-16 in a lightly loaded, and operationally-limited and therefore very non-typical ‘lightweight’ configuration. When an F-16A was loaded in a manner similar to the F-35’s ‘stealth’ weapons load, we found the F-35 may very well be significantly better than the F-16 in the ‘sustained turn’ category: It all depends on how heavily loaded each aircraft is relative to the other. 

For fun, we also showed that for the ‘spec’ F-35A to ‘turn like an F-4’ the F-4: 

1) had to be a late-model F-4E ‘slat bird’, 

2) had to be given every benefit of the doubt wherever there was any performance ambiguity, AND

3) it had to be loaded so lightly that it could only have a little over 8 minutes of fuel on board to achieve its maximum Sustained G turn performance. 

I also note here, once again, that ‘Sustained Turn’ is not now seen as important of a maneuverability parameter in the post-‘All Aspect’ missile era as it was before the all-aspect attack guided missile: Sustained Turn was more important when it was essential to get right on your enemy’s tail for a ‘kill’ while keeping him off yours.

Flash Forward: Today

I had left the transonic acceleration spec changes alone at the time it was ‘all the news’ because when I finished the ‘Sustained G’ posts, all the F-35 haters, anti-defense weak sisters, faint-of-heart, and the Joe Public mouth-breathers had pretty much moved on to complaining about something else. Also by the time I finished the Sustained G discussion, I didn’t really have the free time to quickly distill an explanation about transonic acceleration—or at least do so such that most people could understand the phenomenon if they put a little effort into understanding. After all, you can’t really simplify transonic acceleration with the same ease that you can with ‘sustained G’ because the former is about dynamic ‘change’ while the latter is about representing different states of equilibrium: nice and easy ‘steady state’ conditions.
A while ago though, I was reading a comment thread ‘someplace’ where there was ‘someone’ mixing claims about acceleration performance with top speed performance for the F-35C and complaining about the F-35 having to ‘dive’ to get to its top speed. I’m pretty sure he was referring to a comment made by a test pilot at PAX River (Naval Air Station Patuxent River)--also a while back--who talked about having to “accelerate, turn, unload, and accelerate” repeatedly within PAX’s range space to get the F-35C up to its top sustained speed of M1.6 using a ‘modified Rutowski’ procedure. I believe the commenter was incorrectly translating the ‘unload’ into a need to dive, versus the need to preserve speed during turns, just to make going through the exercise worth the effort within the limited range airspace allotted. This poor person’s mental flailing-about on something he clearly did not understand (alternatively, I suppose he could have been disingenuously misleading others--whatever) got me thinking again as to how we could best give some perspective as to what the announced changes to the transonic acceleration performance of the different F-35 variants might actually ‘mean’ without having someone pulling a synapse and then mentally limp right past the ‘Eureka!’ moment. Having thought about the subject for a while now, I now don’t think it’s too ‘hard’ of a write-up to produce – It’s just a tedious one.

Terminology Housekeeping

Because the media and others tend to use a shorthand to describe Key Performance Parameters (KPPs) as ‘specs’ or ‘Specifications’, we shall reluctantly do the same. KPPs are selected based upon their relevance to top level program requirements such as survivability, lethality, supportability, etc. The KPPs are the basis, as former F-35 PM Tom Burbage noted in 2012, “from which lower level detailed engineering specification are derived and Lockheed's job is to meet as many of those specifications as possible within the laws of physics”. In other words, KPPs are a vehicle used for deriving detailed engineering requirements from top-level operational requirements. They are initially established before the first design iteration comes out and it is not uncommon for them to be adjusted as more information about operational requirements and/or understandings of technical feasibility are refined. Though we will treat KPPs as requirements for the sake of simplicity, we need to understand that they are not immovable goals (or thresholds) that must be individually or collectively met, but instead are guideposts that show the way toward defining and then meeting engineering requirements that will support overall top-level program requirements. I’ve touched on this subject before, and this link still leads to the DoD Manual for the Operation of the Joint Capabilities Integration and Development System (JCIDS) which, with the references listed within the document, describe how requirements are determined and used, including the role of KPPs in the requirements process and the required steps/approvals to change KPPs.

Drag, Thrust and Acceleration

If you know all this already, go ahead and skip the discussion about aerodynamics. If you know his stuff and read this part anyway, you will see there will be a lot I’m leaving out or perhaps oversimplifying. But I do so on purpose. Once again we’re conveying enough information to get an idea across, and not enough to go design an aircraft. These are just the ‘basics’, on the ‘basic concepts’ needed to understand what we’re going to discuss.

Drag: Subsonic and Beyond!

The most important things to remember about ‘drag’ for this discussion are that not only does drag increase due to friction the faster an object moves through the air, but that the ‘nature’ of drag changes as the object moves through the air at ever increasing speed. The airstream over the object begins transitioning from a ‘compressible flow’ to an ‘incompressible flow’. This occurs even before the object reaches Mach 1, as it enters the ‘transonic speed region’, with some surface areas of the object going ‘Mach’ (Critical Speed) before other areas on the object (aircraft). The transition from subsonic to the supersonic region is typically described as .8 Mach to Mach 1.2. [Note: Above Mach 1.2 is considered ‘supersonic’ until much higher Mach Speeds where the nature of the flow changes again and is then viewed as ‘Hypersonic’ with the object moving through a ‘Plasma’ flow beginning at around Mach 5.]

This change in the interaction between the aircraft and airflow results in a change to the relative contributions of various contributors to total aircraft drag:

Figure 1: Drag Contributors, Subsonic vs. Supersonic

Remember, not only do the relative contributions of the drag components change going from subsonic to supersonic, but the resultant drag for nearly all the ‘contributors’ increase as well. For example, here is a reconstruction of a typical straight wing drag profile, expressed in terms of drag coefficient (Cd): a dimensionless value used in calculating total drag (force). 

Figure 2; 'Straight Wing' Drag Coefficient increases through transonic region

From Figure 2, it is obvious that the wave drag contributors, particularly the contribution due to the effects of the wing wave drag, are the overwhelmingly dominant factors. I’m going to risk oversimplifying wave drag somewhat here and just note that wave drag is composed of two contributors: Wave drag due to volume (cross-sectional area for some fixed length), 

and wave drag due to lift . One of the earliest advances in overcoming wave drag was the recognition that there were two contributors, which allowed designers to methodically attack the wave drag problem. (Though the occasional spark of genius didn’t hurt)
The graphic above is scaled to reflect all values as a percentage of the maximum value. From this example we see that at Mach 1, the drag coefficient is but 75% of the maximum value reached around Mach 1.1, and that by Mach 1.6 the total Cd is less than 50% of the peak value. If we wished to calculate the total drag
force at any given speed, we could plug in the Cd value into the ‘Drag Equation’:

Figure 3: Drag Equation

The only mysterious-to-some element in this equation should be the Cross-Sectional Area. This is the cross-sectional ‘slice’ of aircraft area presented to the air stream, and is perpendicular to the airflow passing over the aircraft. As the equation indicates, given the drag coefficient and cross-sectional area of any aircraft, drag increases as airspeed increases and when air density increases (density altitude decreases). Keep this equation in mind as we go forward: we will be relying on and referring to it from this point forward.
While we do not know what the Drag Coefficient is for any of the F-35 variants at any of speed, we may have a general idea of what the ‘shape’ of the probable curve for each looks like. Here is a reconstruction of a typical swept wing aircraft drag profile, also expressed in terms of drag coefficient:

Figure 4: Swept Wing 'Drag Rise' Curve

Note the effect of using the swept wing configuration. It delays the rapid onset of drag rise and also pushes the peak drag coefficient to higher Mach numbers. Remember also that this graph is scaled against peak drag coefficient at around Mach 1.55, with horizontal gridlines spaced at ‘25% of peak’ increments.

Figure 5. F-35 'Straight Wing', Extracted from a photo at www.JSF.mil 

The F-35 wing is a straight wing with swept leading edges. I suspect the F-35’s drag curve may be shaped something like a hybrid of the sample straight and swept wing curves shown, with a bias towards the straight wing drag rise curve shape. The acknowledgement that the F-35 can go some distance above Mach 1.2 without afterburner (to be shown in ‘What we know or think we know’, Ref #2 in Part 2 coming up) is a good indicator of the F-35A's drop in drag coefficient after Mach 1.1 as shown in the straight-wing graph vs a peak at Mach 1.55 as shown in the swept wing example.

Why Straight Wing?

In case someone is asking the question, a simple NASA graphic drives home the point that a [swept] wing is ‘the way to go’ if a primary design concern is to reduce drag coefficient below about Mach 1.8. But there are other concerns, when it comes to fighter aircraft (such as 'maneuverability' and 'g-loading') that a straight wing provides certain advantages--such that a 'compromise' is often sought by sweeping the leading edges on an otherwise straight wing.

Figure 6: Straight vs Swept Wing Decision 

Thrust and Acceleration

To accelerate at any speed, the thrust must be greater than the drag opposing the thrust. Jet engine thrust also decreases as the aircraft speed increases, because the difference between the aircraft velocity and the velocity of the engine exhaust becomes smaller as the aircraft accelerates. This isn’t a complete explanation, but it is the conceptual ‘bottom line’ and I don’t want to get wrapped around variability of air mass and internal engine drag among other things. For a more detailed discussion on the topic, NASA’s K-12 site has a pretty good overview (some high school math and physics employed).

In closing Part 1...

The most important point to remember going forward is the obvious one: At a given altitude, when airspeed is lower, the thrust is higher and drag is lower. Therefore, acceleration is greater. 

Figure 7. (Updated/Corrected 21 Mar 15)

As the aircraft moves faster through the airstream, the thrust/drag ratio decreases (Figure 7). Therefore the rate of acceleration will becomes less and less as the aircraft approaches the end of an acceleration run through the transonic region. If we can reduce drag and/or increase thrust between the beginning and the end of an acceleration run, then the rate at which acceleration (rate of increasing speed over time) will be lower (still accelerating, just doing so at an ever-slowing rate) as the jet passes through the transonic region. (Paragraph corrected/revised 21 Mar 15)

In Part 2, we will have a go at a top-level analysis of F-35 transonic performance.

Tyler Rogoway on F-35 Fuel Trucks

Sometimes,.... when it’s really, really hot..., you don’t want to heat soak your fuel trucks. So What? 

Hat tip:KamenRiderBlade at F-16.net 

Tyler Rogoway writes for a living. He’s got to write about something, and the latest ‘something’ is all about telling the American, nay, The World’s Low-Information crowd that not only the Air Force has found out that in really, really hot, weather, it doesn’t want to 'heat soak' the fuel trucks servicing your F-35s, but also that this development is, apparently in Rogoway’s opinion, a ‘BAD!’ thing.

His ‘article’ is about what we've come to expect from him, and the entire treatment of the subject matter is an excellent example (yet one more in a line of many) of how F-35 critics will highlight something they don’t understand as being a flaw or deficiency. The next step will be to add that one little mis-characterization to a litany of previous mis-characterizations, and then use them in their totality to continuously criticize and condemn the aircraft, program, technology,and hell, when you get right down to it, even the ‘National Defense Strategy’ that drives the selection and fielding of weapon systems in the first place.

The ardent F-35 critics generally fall into two camps: Those that do so while really understanding NONE of it, as I suspect in Rogoway’s case, or alternatively, those who do so as an intentional manipulation of the facts to distort reality for nefarious purposes (P.A.C.E. anyone?). I am indifferent as to what brand of delusion drives the contrived criticisms, but believe while the latter is incurable, there is always hope for disabusing the former of their delusions through information. (Kreuger-Dunning Effect notwithstanding, there is always hope). I could go into Rogoway’s GAWKER piece and dissect it into itty-bitty chunks of tautological floatsam, but to me the comment thread is far more interesting.

Rogoway’s façade of being a disinterested observer slips somewhat, and probably reveals more about where he is ‘coming from’ than he really would have wished. To his credit, he did not immediately wash these exchanges down the memory hole like a lot of people would have.

I’m now going to place one of my favorite quotes here for later reference. I think I will be pointing to it later in this post:

Novices in mathematics, science, or engineering are forever demanding infallible, universal, mechanical methods for solving problems. 

–J.R. Pierce 

------------

Here we go. My observations in [square brackets] and boldface emphases in Rogoway’s responses are mine. No typos are corrected. The selected (because it was more succinct than another) exchange of interest is:

‘Dastim’ to Tyler Rogoway 

Having decades of experience with LockMar's military products (Submarine sonar), I can honestly say this is par for the course. It is VERY common for a new weapons system to have faults out of the gate and the more complex/expensive they are, the more faults possible. Moving forward they prove themselves invaluable but the start is always ugly. When they took the submarine sonar contracts in the early 90s we had a plethora of problems, some mission limiting, but in the end, their systems proved to be the best in the world. Be patient, this shit is far more complicated than most of you have any idea about.

[Other than not being a ‘fault’, but an emergent requirement based upon the press release wording, the need for fuel not to exceed some very high temperature when it is loaded is almost certainly driven by the aircraft using the fuel system as a heat sink for its environmental control system (ECS). If the fuel is already hot, it will not be an effective heat sink, will it? This again, is not a ‘fault’, but at worst it is an “operational requirement”. All aircraft have specific operational requirements, and there’s no requirement that they all be the same that I’ve ever heard of. So What? If one is familiar with advanced aircraft or avionics systems design, one might speculate--and then ask for confirmation either way—that perhaps the additional heat controls placed on the fuel that is loaded and the effect on the ECS cooling system is related to the closely controlled gaps and openings on the F-35 outer mold line (OML) in order to meet LO requirements. For whatever reason, the requirement can be perceived as problematic only if it will require some onerous workarounds to overcome. Clearly this isn’t about an F-35’s systems intolerance of normal military operating temperatures and requirements, though the ‘stories’ written to-date might lead one to believe it were so. This has to be about fuel temperatures after the fuel has been heat-soaked for hours (or days), and reducing the heat soak by either reducing the amount of heat absorbed directly (paint the truck tank a light color) or indirectly (shelter the truck to prevent direct sunlight from beating down on the fuel tank). Not being a panic-prone F-35 hatercritic, I would also wonder if then perhaps the F-35 might also expect fewer problems with very cold fuel in arctic climes? Dastim’s point about complexity is well founded and well made, but it is only half the story. Combine an aircraft in development experiencing the normal issues one would expect if one knew what they were doing, with the apparent legions of technically deficient souls who have NO understanding of the challenges AND BENEFITS that make those challenges worth the effort in pursuing advanced technology systems, and you get a technically illiterate response...such as:]

Tyler Rogoway to ‘Dastim’ 

You sir are a part of the problem. Major systemic issues led to the F-35 being in the place that it was, including ridiculous sell job on concurrency and laughable cost goals and timelines. We cannot sustain the best fighting force in the world like this, it will economically break us.

You may feel just at home with this sort of nonsense and after writing well over 200 pieces on this program I am insulted when you say myself and others probably have no idea what we are talking about. We need a new approach with fresh minds that will come up with new ways so that this sort of program never happens again. And finally, the F-35 program, the largest weapons program in history, is not new sonar arrays for submarines.

[Rogoway’s first paragraph, aside from the abstract, unsupported, and unwarranted accusation made against his commenter, is a series of claims made without supporting evidence and with the presumption that they are indisputable facts when in reality they are a series of claims that are not only debatable but have been and are continuously debated. Rogoway, apparently happens to believe these claims are true. This is his first logical fallacy: “Begging the Question”. He layers on top of this fallacy, via assertions of “ridiculous”, “sell job” and “laughable” (without falsifiable support) the additional logical fallacy of “Appeal to Ridicule”. The second assertion that he has written “well over 200 pieces on this program” in defense of his knowledge base is clearly a Fallacious Appeal to Authority, and it is one built upon another fallacy: The Non-Sequitur. Just because someone ‘writes’ about something, particularly ‘opinion pieces’ it “does not follow” that they must understand, much less be an authority on what they are writing about. How we judge someone knows or knows not what they are talking about is based upon the CONTENT and the 'verifiability' of the writing. Rogoway digs deeper with a rhetorical ploy you don’t see every day: Righteous Indignation (“I am insulted”) over his being ‘doubted’. Rogoway begins his fadeout with more ‘Begging the Question; (‘need fresh minds’) with another Non Sequitur (‘so it will never happen again’). Rogoway’s last sentence is a throwaway line but he should have thrown it farther. As he slung it, “the F-35 program, the largest weapons program in history, is not new sonar arrays for submarines” misses Dastim’s point: It takes time to develop and field complex systems. If Rogoway is willfully ignoring this point, his assertions that ‘one of these is not like the other’ could very well be thought of as a Composition Fallacy in his denial.]

------------

I wonder... 

If Rogoway cut down on his logical fallacies to nil, would the next 200 articles on the F-35 gain him the  'cred' he thinks he already deserves? Personally, I think he won't get any better until he realizes he is one of those Novices' old J.R. warned us about. (Told you I would refer back to J.R.)

I worked a 12 hour day today (now 'yesterday'-yikes), so I don’t feel like taking down his Magnum Opus of Circumstantial Ad Hominem that occurred in his exchange with ‘ashkelon’ tonight/this morning.

But here's some food for thought, 

What happened the last time a bunch of naysayers, some 'expert', but all OUTSIDERS who were looking in at a revolutionary weapon system program and then made all kinds of criticisms they just knew 'had to be true'?
Answer: Hilarity ensued.

Hello GAO? About that F-35 ‘Report’

Next time maybe you could bring some experts in something other than ‘bean counting’.

It appears that the GAO attempted to structure their latest F-35 ‘Report’ “F-35 SUSTAINMENT: Need for Affordable Strategy, Greater Attention to Risks, and Improved Cost Estimates”, to deliver a certain message, a certain way, and with a certain flourish. But with only the most cursory professional eyeballing, gaps in the report’s observations, argumentation, and conclusions quickly appear. Viewed more closely and put into perspective with past F-35 reports, the gaps become gaping chasms and the document devolves to merely another example of the GAO ‘defense’ report archetype: a rather subjective, deeply flawed and--of course--superficial GAO product.

As with most GAO reports of this genre, this particular GAO product, ‘Incompetence’ comes to mind more than ‘malevolence’. Ultimately we cannot fault the GAO for attempting to audit and write about that which they know little, they do what they are told to do. But I do hold them responsible for their total pretension of authority and the Hybris they display in asserting their ignorance as authoritative.

We place a spotlight on the GAO’s most damning sins committed within this report. It will become readily apparent why this GAO product gained very little traction in the popular media once it was actually released: It confirms the beliefs of those who want the reports ‘findings’ to be true so they don’t really bother to critically review it, and the rest who care about the issue enough to take the time to really read and understand the content will just dismiss it. The majority of people simply remain disinterested. I happily observe that to date, with sporadic interest and promotion even by the lowest forms of media habitués (example: the Puffington Ho’s of this world), the report has not gathered much audience or furor.

There’s quite a bit the GAO missed in that ‘Comparison’ (P.2 and P. 12)

The following graphic appears twice in the report. Once in the front matter and once within the body proper. I’d say that makes the subject of the relative O&S costs of legacy aircraft to the F-35 one of their major ‘points’. I further assert they are completely bonkers if they think their reasoning and evidence supports, in any manner, the point they attempted to make—the point they expect others to believe.

GAO 2014 Comparison of Apples and Oranges

To paraphrase myself elsewhere:

Q1: Notice any aircraft type and associated costs missing from the list of aircraft being ‘replaced’?

Hint for those who need help: It starts with an "A" and ends with "-10".

So even IF this were an ‘apples-to-apples’ comparison, the GAO did not count the right apples, and it looks like there are not even the right number of ‘legacy’ apples to be counted within the equation. I should not have to point out to anyone, that even if the GAO substituted the same number of aircraft, since they were not the same type and number of aircraft with the same mission lists in the same relative proportions, that the F-35 is replacing, any such ‘adjustment’ only introduces error.

Q2: Notice the different cost number sources for the F-35 compared to the 'others'?

The legacy aircraft listed have had a theoretical inflation added to their 2010 O&S costs and applied for the years shown (2036-2040—when peak numbers of F-35s will be operating) in the comparison. 

BUT on the other side of the comparison, the F-35 cost estimates are known--from previous reports and other publications (see page ‘XX’ footnote here for an example)--to include not only inflation, but to also include estimated Cost Growth ABOVE Inflation (CGAI). CGAI is another ‘guess’ that gets compounded (not just added) on top of the ‘guesstimated’ inflation, and can be expected to be part of F-35 program cost accounting until at least the baseline Block 3F configuration aircraft designs are finalized and/or fielded.

Given the crudeness of the GAO comparison, I seriously doubt the GAO was sufficiently thorough to also include CGAI in the legacy aircraft cost estimate. But even IF they did, they are still not comparing ‘apples-to-apples’. I’m not even the first one to observe this discrepancy BTW, for within the first leaked news of this document we find:

“A source close to the program pointed to this comparison as one example of how GAO was “comparing apples and oranges.” 

Quite true. TOO true.

More Content: More Missing Oranges.

This is not even real news. But it has been observed that whenever these sort of lame comparisons are made, those making the cost comparisons are particularly thorough in ignoring the fact that whatever F-35 costs are, they include the cost of more ‘content’ than legacy aircraft costs. For example, in testimony before the Senate just this year (pg 5) , it came out that for F-18 legacy aircraft, the Department of the Navy will need to keep buying some of the capabilities that are similar (but still less advanced) to the capabilities the F-35 already has just to keep F-18A-Ds relevant into the near future: 

In order to maintain warfighting relevancy in a changing threat environment, we will continue to procure and install advanced systems such as Joint Helmet-Mounted Cueing Systems (JHMCS), High Order Language (HOL) Mission Computers, ALR-67v3, ALQ-214v5, Multi-Function Information Distribution System (MIDS), APG-73 radar enhancements, Advanced Targeting FLIR (ATFLIR) upgrades, and LITENING for the Marine Corps on selected F/A-18A-D aircraft.

We observe now that for the F-35, there are several counterparts of the items listed in the testimony above, such as the Helmet Mounted Display System , as well as all the necessary sensors and targeting systems that are accounted for not only in the F-35 production costs, but also in the costs for the upkeep of same--captured as part of the F-35’s sustainment costs. For legacy aircraft, these sustainment costs for all the additional systems they need to operate, along with the external fuel tanks I might add, are relatively ‘hidden’: they are  accounted for on accounting ledgers that are separate from the host aircraft’s. These ‘hidden’ costs are not trivial.

Finally, the entire F-35 Autonomic Logistics Information System is in the F-35’s cost estimate as well. This system is a streamlined logistics support network, global in scope. Imagine the network support costs alone! NONE of the legacy systems’ support infrastructure is included in their O&S costs.

We could go further and expand the scope of comparison to total force employment costs. We could discuss how the F-35 is expected to require fewer mission support assets (transports, jamming aircraft, aerial refueling aircraft, etc) or talk about how the value of the F-35’s ‘stealth’ features certainly far outweigh the additional system support costs not found with non-low observable aircraft. But why bother? The cost comparison the GAO attempted fails within its own set boundaries.

GAO Shows Us Some Goodness…Was this some kind of a slip-up? (PP. 17-18)

Excerpt:

• Mean Flight Hours between Failures (Design Controllable) is the average amount of flight hours achieved before a design-controllable failure occurs. As of March 2014, this metric was progressing in that the number of flight hours before a failure occurs was increasing for all three variants. For example, the average flight hours between failures for the F-35A—the variant with the most flight hours to date—was 5.2 in March 2014, surpassing the expectation at its current flight hours by about 1.2 and growing toward its requirement at maturity of 6.0. Moreover, this was an increase of about 1.8 average flight hours between failures since September 2013, as reported by GAO.

I find how MFHBF(DC) was framed this time around ‘interesting’. This data is absolute “goodness”, but it is delivered so deadpan you’d hardly know it without reading it twice. The graphic the GAO used two years ago (Figure 9, pg 30) to then illustrate the F-35 being ‘behind’ in MFHBF (the ‘DC’ was left off in 2012) looked like this:

2012 GAO Report Chart of MFHBF (Really MFHBF(DC))

In the 2012 report, the GAO was all over this metric for all the variants as ‘lagging’. I noted at the time that it was a premature analysis.

This year, the positive performance for the same metric just gets a ‘paragraph’. Here’s the same MFHBF(DC) info from this report in a graph similar to back in 2012 when the GAO was more interested in selling a negative story. 

2014 GAO MFHB(DC) Data in Chart Format

Even though the metric indicates good reliability performance (ahead of where it is supposed to be at the point in time it was measured), it shouldn’t be taken any more seriously than in the past without more perspective and data behind it including knowledge of the long term trend. But guess what?

MFHBF(DC) 2012 & 2014 Data Merged 

Putting the 2012 and 2014 report data we get enough data to call it ‘better’ and to note the trend is—encouragingly--positive, so we can call this unquestionably good news. Keep the trend line (it is calculated and not simply drawn by the way) in mind for later use--when the GAO whips out a fallacious Appeal to Authority on us.

But we observe again that it is still ‘early’ in the grading period. The trend could reverse if ‘something’ pops up, though the longer the F-35 goes with a positive trend, the less likely something will pop up until it starts reaching its end of life at the other end of the ‘bathtub’ curve. We must remember that in June 2014, the fleet was only .085 (8.5%) complete towards maturation to be measured/graded at 200,000 flight hours. The data stops in March in this report, so it is based upon probably no more than 7% of flying hours towards maturity. 

Still, it is interesting -- mostly as an illustration to contrast how the GAO delivers information that supports their message and how they deliver that which doesn’t support the message.

In passing, I also add that in light of the positive news above, we should remember the manner in which the report was ‘leaked’ to gather negative headlines before the release, to support the mystery leaker’s purposes. That too is interesting.

Now try and remember what we’ve just covered and use it to judge the importance of what the GAO has to say about the next two metrics. It is particularly important to remember in light of what the GAO says about MFHBCF, which for the most part can be considered a SUBSET of the MFHBF and MFHBF(DC). I say ‘for the most part’ because MFHBCF can contain the results of induced (think self-inflicted) failures that are not "design controlled".

Enjoyed The Goodness?… It’s followed by drivel (PP. 17-18)

Excerpt:

•Mean Flight Hours between Critical Failures is the average amount of flight hours achieved before a failure occurs that results in the loss of a capability to perform a mission-essential function. As of March 2014, this metric was lagging well below its requirements at maturity, meeting an average of 42 percent of those requirements across all three variants.

“…this metric was lagging well below its requirements at maturity”? That is an interesting turn of the phrase there: as if it should be significant that it is not near full expected value, with only about 93% of the fleet flying hours missing and need to be flown before we are to actually ‘grade’ the performance. I view this as a logical parallel to berating a 10-year old for having not yet finished college.

So where is the MTBCF relative to where it was planned to be AT THIS EARLY POINT on the road to maturity? This info is curiously absent, given how past GAO reports made a big deal of being ‘below the curve’ when the data was even less meaningful. I strongly suspect it is no longer below the ‘should be’ curve because, among other reasons, the GAO conveniently leaves this information out.  In addition, there is absolutely ZERO significance to throwing out an ‘average’ MTBCF value that runs across all variants—each at different stages of maturity in their development. What are the values for each variant? Why did the GAO not tell us? Was the GAO trying to make a point without revealing something about a sensitive or classified program spec? I doubt it.

The relevant information we need, and yet the GAO does not provide (if they even know) is:

1. Where is the value compared to where it was predicted to be at this time? 
2. What is the trend?
3. Is the reason the value is ‘what it is’ understood?
4. Is there an adverse impact that needs to be eliminated/mitigated to meet the spec at ‘maturity’? 

The GAO has actually been boneheaded enough in the past to also raise a question in my mind as to even the significance of how they use the term MFHBCF itself. I question it, because as I noted above, MFHBCF is often a catchall that includes induced failures. It can also contain the effects of misdiagnosis of non-existent faults using not-yet-mature tech data: also known as normal ‘growing pains’ experienced in learning to operate and maintain the system.

What percentage of MFHBCF hits are the result of Airman Doofus breaking something or Lance Corporal Slacker not following repair direction correctly, or of either misinterpreting the troubleshooting directions? How about the aircrew botching his evolving, maturing checklists? A better measures to judge the reliability progress would be MFHBF(DC) as we saw above. As an aside, I suspect what the GAO means by MFHBCF is really “Mean Flying Hours Between Operational Mission Failure” (MFHBOMF). 

And AGAIN, we note (can’t repeat it enough) the F-35 fleet had accrued only about 7% of the total flying hours needed (where the reliability targets are supposed to be met) at the time the report’s data was collated, yet the GAO still has the temerity to assert that it was ‘only’ operating at an ‘average’ of 42% of the ‘maturity’ spec is (somehow) 'significant'? 

If the F-35s were really ‘breaking bad’ we’d hear about it from the pilots screaming about ‘availability’ and the maintainers about too many maintenance man-hours per flying hour (MMH/FH). We hear nothing about these performance metrics from the GAO. Surprise.

The GAO then brings up MTTR:

Mean Time to Repair is the average time it takes a maintainer to repair a failed component or device. Currently, this metric is not improving in that as flight hours increase, it is taking maintainers longer to repair failed components for the F-35A and F-35C, and the amount of time it takes to repair failed components for the F-35B remains unchanged. Specifically, GAO reviewed R+M growth curves provided by DOD showing the historical growth of this metric from 2009 for the F-35B and 2010 for the F-35A and F-35C to March 2014, and we observed that the metric is trending in the opposite direction of its predicted path for the F-35A and F-35C, and the metric is remaining steady, without improvement, for the F-35B.

I have suspected for some time higher MTTR was due to Outer Mold Line (OML) restoration cure times. If so, I would also suspect a good portion of that is driven by For Other Maintenance (FOM) actions. I still suspect it is a factor, but perhaps not as significant as I previously believed. What is nagging me is the missing commentary on Maintenance Man Hour Per Flight Hour (MMH/FH) numbers.

OML restoration would probably have a significant (but lesser) impact on the MMH/FH metric however. But with the GAO the norm is ‘no news is good news’. I therefore see missing complaints about MMH/FH as indicative of relatively lower OML restoration activity than I previously believed. The longer things go without us hearing about MMH/FH, the less I think OML restoration has a major impact. This has caused me to turn my thinking to new directions as to why the F-35 is experiencing higher than expected MTTR.  It now seems there are a couple of really interesting unknowns that could better explain the higher than desired MTTRs.

First there is the distribution of actual task repair times. IF the F-35 designers did a good job driving out all the typical ticky-tacky maintenance actions of the past, there would be fewer short duration maintenance events than seen on legacy systems, this would skew the average (Mean) repair time to the high side very quickly, not because more tasks were taking longer, but because longer tasks are harder to drive out of the equation. The MFHBF(DC) trend and the lack of details concerning MFHBCF would support this possibility. 

Second, I would be very interested in the internals of the data to see if there were discriminants by operating location and LRIP lot buys for each variant. I would expect Edwards, Eglin and Pax River to have more MTTR hours because they have more early jets ( how much planned mod activity is impacting this metric?) and/or are more aggressively trying to break the plane. But inversely, I would expect Yuma and Luke to have better numbers with the newer jets and more ‘operational-like’ environments than Eglin, Edwards or Pax River. Further, I would expect the Operational Test F-35s at any location to have even better numbers due to their flying of later LRIP jets and flying programs with a greater emphasis on more ‘operational’ maintenance paradigms.

There are also any number of reasons that the high MTTR could be deceptive or even unimportant. For all we know, it could even have nothing to do with the jet: some of this might be merely an issue with the maintenance process closeout and ALIS development/maturation (yes, I’ve done maintenance data collection: NO system is perfect). There is also the question of what percentage of this metric is also due to maintainers working on the plane when there is ‘No Fault Found’ or work caused by ‘Induced’ actions? We need the GAO to tease out the relevant bits if only to improve their own sorry analyses. But if they are going to highlight something as a problem in a public report, they need to let the public know the ‘whys’ behind the MTTR and MMH/FH data to justify their claims. That is, unless the purpose of the report is to just dupe and spin up the rubes. 

In passing, I note once again, knowledge of crew sizes would also be helpful. I suspect they too are meeting the F-35’s needs. 

If there were valid reasons to be concerned about the MTTR at this time, it would show up in the other data the GAO isn’t showing. What data the GAO does give us sufficient information on, doesn’t support the idea anyone should be concerned: the missing data needed to further evaluate the seriousness of the high MTTR hints at the MTTR as not being a serious problem at all. When the GAO is involved, I’ve consistently found that ‘absence of evidence IS indicative of ‘evidence of absence’. 

As it stands, even IF the F-35 does takes longer to fix than spec (and it very well could be even the spec was overly ambitious) then it only becomes important if it is failing too often (availability issue), or taking more manpower to fix (cost issue). Without knowing the relationship, which lets us determine actual availability and cost impacts, our knowing the MFHBCF and MTTR is pretty meaningless. It is however, something for the GAO to air out just so others can b*tch about it.

Does the GAO even know what ‘troubleshooting’ or ‘learning curve’ mean? (Pgs. 18-19)

For that matter, do they understand how ‘engineering’ works? As a long-time ‘tester’ this section cracks me up:

To identify some software issues as they arise, users in the field use an internal system to submit requests to the contractor, but these requests are submitted on an individual basis and may not always be addressed immediately as it takes time to determine whether the issue is related to hardware or software. For example, officials told us that the Electrical Optical Targeting System, which is used to track a target, continues to fail. In this instance, testers reported the problem, and officials attempted to improve the capability with hardware changes. However, not all issues with the Electrical Optical Targeting System were fixed with the hardware changes, and officials have decided to also try to address the issue with software changes, causing users to identify workarounds in the meantime. 

This is either illustrative of the GAO's general unfamiliarity with how troubleshooting and engineering is done OR how the GAO is oriented to bring up issues without any consideration or understanding as to the relevance of the problems they highlight. The GAO reports this bit as if the F-35 program was taking some kind of a 'hobby-shop' approach to solving the issue mentioned. If experience is any guide (and it usually is) the F-35 engineers probably 'racked and stacked' options to remedy the problem as quickly and cost-effectively as possible. In analyzing the options, it was probably determined that the hardware changes would be the most beneficial and easiest to employ, knowing all along that there was either a possibility OR certainty they would need to implement the software changes afterwards. Stating "officials have decided to also try to address the issue with software changes" makes employing standard engineering management tools sound like ad hoc (“try”) guesswork, and also tells me the GAO really has no idea how engineering works. Does the GAO understand that maturing fault isolation software involves learning what the faults look like and how they manifest in an operational system? Does the GAO realize that until the system is fielded, the knowledge will always be imperfect beforehand?
The GAO continued:

As another example, officials discussed instances in which the diagnostics system signals to a maintainer that the landing gear failed, but it was actually a sensor near the landing gear that failed. Because software for isolating these types of failures is not yet mature, operators and maintainers on the ground may continue to check the landing gear without discovering the sensor issue and reporting it. Finally, officials stated that with the release of the next increment of software in 2015, a number of new issues may arise, and these issues may be related to software because the new software includes new processors that can affect mission systems on the aircraft.

What the GAO is describing in the second half of the section concerning the ‘landing gear’ anecdote is what is usually thought of as a 'nuisance' software problem. It is standard (and sound) program management to triage your design (hardware or software) development issues so that the most important problems (those impacting flight safety are highest priority) are dealt with first. Without knowing how well the F-35 program as a whole is managing all the issues, singling out something like this is pretty pointless: it has no programmatic utility. It is, however a good scare story.

The GAO ‘Need More Control’ Over Tech Data Rant (Pgs 22-23)

It would be too much reading for most people, so I’m not going to post all the GAO’s ramblings lamenting the F-35 program tech data strategy. My response as to ‘why’ the lamentation is pernicious and only an invitation to trouble and more costs-- is long enough.

Bottom line: The F-35 program was undertaken using one strategy for tech data. In the last few years (and well after the F-35 program was started) the DoD has changed their preferred strategy. 

Now the GAO is b*tching about the F-35 program not being in ‘compliance’ with a newer strategy. The original F-35 strategy was to only pay for the tech data the F-35 operators and maintainers would actually use. Pretty smart huh? Unless you are working in certain parts of the USG and believe EVERYTHING should be under the direct control of the USG.

When the government decided to buy only the tech data they needed, it does not mean the rest of the tech data they desire is just sitting there for the asking. I doubt in most cases it even exists, much less is already in hands of the suppliers ready to go. And it most probably does not exist (yet) for the simple reason that no company these days can afford to expend effort on tasks that for which they are not contracted to deliver. The proprietary KNOWLEDGE needed to create the data exists in the hands of the suppliers, but there probably is no USG-grade (deliverable) tech data extant beyond what the F-35 Program is already paying for. 

On acquisition contract programs, the government: 

1. By law owns the data it pays to own under the contracts, 
2. Has limited rights to related contractor data that allows the USG to use that data for the DoD’s own purposes but cannot be shared with a third party, and 
3. May include a mechanism reserving rights to buy more data from the contractors that contains the tribal knowledge they want…but they still have to pay for it to be developed and delivered. 

To change the strategy NOW to buy more data would cost bigger bucks than anyone involved would ever be willing to talk about.  The GAO may get to whine about this for decades.  

If the F-35 program, GAO, or other agency managed to get a wild hair up the ‘nethers’ and insist the contractors produce data over and above that already agreed to be delivered, and then turn it over to the Government for free, It would cost the taxpayers even MORE money to settle the lawsuits (perhaps dozens that could last decades) over what would, in essence, be the USG compelling the contractors to turn over their property (proprietary data) for use by competitors. This information would not only allow those competitors to compete against the incumbent contractors using the incumbent’s own trade secrets on the F-35 program but also on any number of future competitions as well.  

If this GAO ‘whine’ gains political traction, it will be ‘Stupid’ on steroids.

Life Cycle O&S Cost B.S. (P. 24)

The most important thing to take away from this section is that the ‘huge’ O&S cost numbers being contrasted are:

1.  Costs over a “56 year operational life” and 
2.  Based upon premature and incorrect judgments being made as to the relevance of immature data. 

Let that sink in for a moment. What could go wrong in relying on ‘estimates’ ONLY a half-century into the future? (/sarc)

Could you see anyone in 1943 sitting down with a rational expectation they could characterize a reasonable (or even remotely credible) O&S cost estimate for the P-51 Mustang through to the year 19969? In decrying and calling for ‘resolving’ the 56 year O&S cost estimate ambiguity, the GAO is apparently seeking more certainty in their uncertainty. They aren’t looking for better information. They are looking for information they will feel better about.

As 'Neptune’ at F-16.net summarized:

GAO was mandated to review DOD's F-35 sustainment planning efforts... 

GAO recommends that DOD develop better informed affordability constraints… 

DOD concurred with all... 

and partially concurred with the recommendation… 

GAO continues to believe that the recommended analysis would provide a more comprehensive sense of the uncertainty in the estimates... 

It never hurts to have someone, else, to look over your "most favored" program…Glad to hear they can provide a more comprehensive sense of uncertainty…

Here’s my take on "Certainty".

If the GAO wants “certainty”, tell them to first have someone build them a time machine (they can write ‘reports’ about it too!), and then get back to us with their numbers when they return. Until the GAO can get that time machine fielded, then EACH, ANY and EVERY “56 YEAR” cost estimate that is produced isn’t just ‘uncertain’. It is a SWAG.

 

Are there no aviators in the GAO? Pg 26

In this particular report the GAO treats Fuel Burn Rates in cartoonish fashion, and from the first sentence it is clear they are working back from a conclusion to justify their 'uncertainty'.

•Fuel burn rates: The JPO and CAPE estimates do not use a reasonable assumption for the Marine Corps fuel burn rate across the life cycle of the aircraft. Both estimates use a fuel burn assumption of 1,493 gallons per flying hour for the Marine Corps variant. While the rate used in the estimates was calculated based on service-planned missions at maturity and DOD-validated physics-based models, this burn rate is an almost exact match of the burn rate being observed at the operational sites. This may be a reasonable assumption for the short term, but it is likely that the fuel burn rates will increase in the long term. The burn rate of 1,493 gallons per flying hour used in the JPO and CAPE cost estimates reflects fuel burn data from aircraft flown using limited capabilities—at slower speeds and at lower altitudes than the F-35 will eventually fly. After 2015, the Marine Corps is planning on using the aircraft’s increased capability, which will likely result in more fuel being used. In addition, shortly after 2015, the Marine Corps is planning on deploying the F-35 to ships, where the aircraft’s fuel-intensive vertical landing capability will be used more frequently, which will likely increase fuel usage. Consequently, the use of lower fuel burn rate across the entire life cycle of the Marine Corps variant is not a reasonable assumption.

Perhaps if the GAO took a broader view as to the possible factors affecting fuel burn rates?
Afterburning turbofan engines LIKE to fly faster and higher. Up to ~35-40K feet and about Mach .95, they tend to get more efficient the higher and faster they fly. The F-35, like all aircraft, is a design that is optimized to perform best in a bounded range of speeds and altitudes. If the F-35 is flying lower and slower now than it will be flying later, this suggests speed and altitude as drivers for LOWER fuel consumption in the future. I find it interesting that the GAO thinks it is worthy of observation that the DOD-validated physics models closely track actual data but then it discounts the model and methodology for future fuel consumption predictions. Did the GAO look at the internals of the model being used?
We should probably also note here, that as the F-35 F135 engine has a rather high thrust rating at military power (no-afterburner) relative to its thrust rating with afterburner, and the F-35 has been acknowledged as being able to ‘supercruise’ (by definition ‘without’ afterburner) some distance at around M1.2. Therefore, the F-35 fleet may spend less net flight time in afterburner than the legacy aircraft. It would also take very few seconds of reduced afterburner time to save more fuel than that burned at 'high' throttle settings (without afterburner) in STOVL mode. Maybe the F-35 will spend more time in AB if the pilots find it advantageous and eat up the fuel savings. Who knows until they get their hands on the jet in numbers?
While the GAO is specific as to one change that may increase fuel consumption: the short mission segment involving (sometimes) vertical landings. The GAOers are evidently oblivious to the relative effects of being able to spend significant percentages of flight hours at more economic fuel burn settings on the other side of the balance of things. Consequently, the GAO's dismissal of the possibility of lower fuel burn rates in the future was not a reasonable assumption. I think the GAO may have been alluding to more afterburner time in the future when they talk about speed, but the GAO did not specify afterburner time as the discriminant, and GAO’s crude approach to comparing fuel costs does not permit the needed granularity to compare costs anyway.

More Fuel Fun (Pg 27)

The GAO wasn't done with this bone yet:

Similarly, the JPO estimate lowered its fuel burn rate assumption to 1,480 gallons per flight hour from 1,558 gallons per flight hour for the Air Force variant. However, the Air Force stated that the more conservative assumption of 1,558 gallons per flight hour should be used across the life cycle because the F-35 has yet to use its full flight capabilities, weapons, or mission systems, which will likely increase the fuel burn rates in the long term. The higher fuel burn rate assumption for the Air Force would represent a $4.0 billion cost increase in base year 2012 dollars across the life cycle of the aircraft.

This comes closer to making sense, if the implication is that the AF's F-35s will be flying at higher weights and yanking-and-banking than it currently does. But even IF the USAF's ~5.27% higher than the program's estimate of total fuel consumption is a ‘better’ estimate, it may not be ‘right’ either. It all depends upon how closely the internal model ground rules and assumptions will match future use. There is also a VERY good chance both models make incorrect (and high) assumptions as to afterburner use. 
Finally, the amount of fuel burned isn’t nearly as important as the cost of fuel burned, and not all fuel ‘costs’ the same; cost depends largely on delivery method and location. With typical planned F-35 payloads, carried internally, the range without refueling is comparatively longer than the legacy aircraft it is replacing for all the variants. This indicates less fuel will be delivered by mid-air refueling than for legacy aircraft the F-35 is replacing. Fuel delivered by aerial refueling was shown (circa 2001) to cost about 13.8 TIMES the cost of refueling via ground refueling (Pg. 8).

I imagine fuel delivery via ship lies somewhere in between ground and air delivery, and probably closer to ground refueling since it is moved and delivered in greater bulk than by air. But my point is made: it’s not the number of gallons that is important. What is important is the cost of the gallons delivered. Just something for the GAO to consider for their next SWAG.

The absolute bottom line on the fuel story is that the GAO did not present proper justification for their assertion that “The JPO and CAPE estimates do not use a reasonable assumption for the Marine Corps fuel burn rate across the life cycle of the aircraft”. Additionally, the GAO including the statement of “ the Air Force stated that the more conservative assumption of 1,558 gallons per flight hour should be used across the life cycle because the F-35 has yet to use its full flight capabilities, weapons, or mission systems, which will likely increase the fuel burn rates in the long term” should be a clear indication that there is great ambiguity in any long-term estimate of future fuel use. The AF position makes sense, if the implication is that the AF's F-35 s will be flying at higher weights than it currently does and nothing else changes. But even if the USAF's ~5.27% higher than DoD's estimate of total fuel consumption is a better estimate, it may not be right either depending upon internal model ground rules and assumptions. There is a VERY good chance both models make incorrect (on the high side) assumptions as to afterburner use. 
However, it appears the main objectives of the GAO to include this point it is to use it to question the USMC’s fuel estimates and to warn “The higher fuel burn rate assumption for the Air Force would represent a $4.0 billion cost increase in base year 2012 dollars across the life cycle of the aircraft.” I particularly enjoy the GAO’s penchant for obfuscating cost impacts by rolling them up into the largest possible numbers over the longest possible times. The “$4.0 billion” figure is a good example. $4.0 billion over 56 years is a very small number when thought in terms of cost per aircraft per day. I expect it to be even smaller than the savings to be had from the fuel consumption reduction that will come from the progressive engine improvements already in planning.


Why do I expect it?
In July, A Pratt and Whitney official was reported on as saying some very interesting things:

Mr. Croswell said Pratt & Whitney also is starting to explore how to upgrade the F135 powerplant in coming years. "We see real opportunities to continue to improve the F135 over time," he said. Fuel consumption could be cut 7% by around 2020 and a combined 15% to 20% around five years later, he said. The life of the engine could be increased around 50% within the next decade, he said. Those effort could be a key element in the wider push within the F-35 program to cut the long-term costs of the Pentagon's most expensive weapons program. (link)

Yeah, that probably explains why the program's internal fuel estimates aren't as high as the others, but don’t tell the GAO. To them the world is static. Planned and programmed change  just sounds like “crazy talk” as far as they’re concerned.

Part Replacement: The GAO really goes off the rails (Pg.28)

This is where the GAO really displays a lack of knowledge, And they do it SO effusively...

Part replacement:The JPO estimate does not include reasonable assumptions for part replacement. Based on data from the Air Force and Marine Corps F-35 variants at testing and operational sites, parts are being replaced, on average, 15 to 16 times more frequently than the assumptions used.

The GAO report makes no case for the first sentence, and the second sentence is Garbage Out as the result of Garbage In. Their characterization of the data they present is so awful I find it hard to believe any ill intent, but I also find it not hard at all to observe that analytically, they are WAY out of their depth. What the GAO shows us immediately after the passage above is that they improperly correlate ‘part removals’ to ‘failure rate’ Nothing could be further from the truth.
The GAO confounds Mean Time Between Removals (MTBR) with time between failures. They presume that all ‘part removal’ was due to a failure (reliability issue) and then it was replaced with a different part. The table the GAO showed provides some insight as to what the list is really about, and it isn’t just about failure rates.

Sorry, Removal Rates Do Not equal Failure Rates

‘Removal rates’ include a variety of ‘causes’ that have nothing to do with reliability or failures.
The GAO ignores that possibility (more like probability in some cases) that the same removed part was reinstalled for any of several reasons. Most likely among those reasons are to get at another part (For Other Maintenance’ or FOM) or to perform a precautionary inspection or correct a miss-installation (Ejection Seat Module?). Since the program is actively bringing early LRIP jets into baseline Block 3 configurations, it should be no surprise if this list contains parts removed to be upgraded and replaced by a previously upgraded part (HMD system?).
I would also note here that the ‘multiples of times than expected’ figures themselves are almost certainly misleading for at least some components. The given time frame for the removals was from March 2013 to March 2014. As the removal rates are in flight hours, using the F-35’s ‘Fast Facts’ updates for source data (March 2013 Here and February 2014 Here, both in PDF) we see the entire fleet flight hours for that timeframe was about 6000 or so flight hours. The F-35 A and B model flight hours would be some subset of the 6000+ hours. If any of those components listed has a high predicted MFHBR rate and only handful of them are removed for any reason, the ‘multiples of times’ could be very high though the number of actual removals for were small.       

Even IF the GAO’s list of removals actually reflected failure data (which it doesn’t) they still wouldn’t be correct in assuming them as representative of the entire F-35 system reliability. They would be basing their conclusions on just data for the current high drivers, and extrapolating it to effects on the entire aircraft. It is one thing to pick a small sample, it is another thing to pick a pseudo-random sample, and yet another thing altogether to pick ALL items intentionally only because they are the ‘high drivers’.
In doing so the GAO effectively ignores the removal rate of perhaps several hundred (at least and perhaps a thousand at most) components when they admit that they looked at fewer than 200 of the ‘high drivers’ for each of the F-35A and F-35B models. As far as overall reliability, the impact of the reliability of the components that are NOT failing at ‘higher multiples’ could easily outweigh the impact accounted for in evaluating the high drivers the GAO cherry-picked for the report.

Ummm...About those component ‘costs’

The ‘costs’ presented caught my eye first when looking at the table above. They are clearly unit costs, but when a part is actually failed, then unit cost for replacement is only suitable when the component is non-reparable. Looking at the list, and based upon unit cost, I would estimate only one, perhaps two of the components on this list would normally be non-reparable. The number of spares required to cover the repair items in the pipeline would cost as much as the numbers provided but the number of spares would be a very small number compared to the number of actual repairs over the same timeframe and is dependent upon repair turnaround time and transport/processing time. Some small percentages of failures would require scrapping and replacement, but the rest would have repair costs that would be only fractions of the replacement costs. So even if all the parts removed were repairs, the implication that the costs the GAO presented were relevant to their costs conclusions is hogwash.

The Curious Case of the Fallacious Appeal to Authority (P. 29)

The GAO attempts to wrap this section up in some semblance of authority but fails miserably:

However, according to officials from the Institute for Defense Analysis, who conducted a study of the F-35’s R+M for DOT&E, the F-35 program would have to achieve a higher reliability-growth improvement rate than has been observed in almost all other aircraft in order to meet the anticipated reliability by 2020. As a result, it is likely that the depot maintenance hourly cost used in the JPO’s 2013 estimate is not a reasonable assumption. As previously stated, reliability improvement efforts are under way that could reduce these costs, but it is unlikely that these efforts will bring significant results in the near term because the current F-35 fleet must be modified into the configuration necessary for reliability improvement.

Treating a DOT&E sponsored ‘analysis’ by IDA (by the way I’m familiar with a bomber ‘study’ IDA did once that stunk so bad it got buried before the ink was dry) as somehow more authoritative is a form of fallacious appeal to authority. The GAO’s preferred source is in disagreement with the JSFPO’s source. this is an area where experts can be expected to disagree. So What? It doesn’t make the GAO’s pet ‘authority’ any more authoritative than the JSFPO’s sources, but it sure does make the GAO’s favored pet farther away from the data, experience and knowledge base needed to understand it. The trend line we noted above for MFHBF(DC) certainly doesn't support the GAO's Doubting Thomases. Therefore, we can conclude disagreement between the two sources certainly doesn’t warrant the GAO’s specious conclusion: 

As a result, for the next 10 years, the F-35 fleet will not represent the configurations necessary for reliability-growth improvement.

One of These is Not Like the Others (Pg. 30)

The GAO now declares:

To develop its hourly cost, the JPO used F-16 data from Lockheed Martin contractors that had been adjusted for the F-35. According to the JPO’s current assumptions, materiel costs would be 30 percent of the labor costs, but data for the AV-8 and F/A-18 depot inductions used in the previous year’s estimate indicate that depot induction materiel costs have historically been closer to 45 percent of labor costs.

Here the GAO reveals its ignorance about what aircraft depots do and how they work. All depots are not all the same. The 'Depot' type and activities are determined by the aircraft requirements. The first thing that comes to mind in reading this passage is to wonder if the GAO is aware as to how material-intensive the F-18 and AV-8 depot operations are here at the end of their service lives? Think structural repairs for starters, and obsolescing components follow in thought. Is the GAO aware of the different types of Depot maintenance? That is to say: The F-18A-D and AV-8B have entirely different depot constructs than the F-35, but the F-35 has the same depot construct as the F-16.

Fortunately, I did an in-depth aircraft depot maintenance analysis a couple of years ago and so I DO know the differences (see figure below) and can explain them to you.

Know Your Depot Types and Activities

There are currently three major types of U.S. fighter aircraft ‘depot’ operations. Depot activity may be conducted at one of the Military Service Depots, or they may occur ‘in the field’. The Department of the Navy conducts Periodic Maintenance Intervals (PMIs) as shown. A simple explanation as to what occurs during a PMI is that ‘discovery’ repairs are completed when discrepancies are found during the inspections, aircraft are upgraded to the latest configurations and structural durability (life) modifications are performed. In addition, selective preventative maintenance is performed to ensure reliability (Reliability Centered Maintenance). It can easily be shown that the F-18A-D has lately required increased maintenance attention in the field and up to the depot level, and the GAO itself knows it is no different for the AV-8B.

As the PMIs of the Navy Fighters are ‘maintenance’ centered, so is the F-15’s Programmed Depot Maintenance. There is a lot of programmed maintenance for the F-15, and I suspect it is getting even more attention these days.

These other depots are designed to perform regular maintenance actions. Programmed maintenance  however, IS NOT part and parcel with depot work for the F-16 paradigm, which is the Modification or 'Mod' Depot. By ‘chance’ (I joke) would have it, the Mod Depot is the construct for the F-35. That’s right, the F-16 and F-35 Depots are for performing modifications to the aircraft, because the airplanes themselves are designed such that regular PDM/PMI is not necessary. The Mod Depots still perform the extraordinary and discovery repairs as needed, but these are O&S costs over and above the ‘depot’ costs. They’re still accounted for, but in a different ‘pot’ of money. The GAO should have at least known how depots differ if they were going to attempt to draw a credible line around depot costs.

I will offer one 'depot' consideration for the GAO to factor into their next quest for “certainty in their uncertainty”. And that is they should keep a watchful eye out for changes to the F-35B and C depot constructs to more closely fit the Navy depot mold versus the Navy adapting their depots to the planes they work on. I say this because, 1) it is the Navy we’re talking about, and 2) the overarching driver in timing and durations of PMI activity for naval aircraft is the timing and workup to full readiness in order to support planned ship deployments rather than to meet the aircraft requirements themselves. It is a Navy-unique ‘cost of doing business’ .

Therefore, when the GAO concludes…

“As a result, it is likely that the depot maintenance hourly cost used in the JPO’s 2013 estimate is not a reasonable assumption.”

…simply because they prefer F-18 and AV-8 depot cost numbers over the F-16 numbers as a planning basis, even though the F-16 depot construct is closer to the F-35's construct, they are most certainly talking out of their a**.

We left some small stuff on the table, but I think we've now adequately covered the GAO's flailing about in their desire to 'feel good about their uncertainties'. Good night!

Bonus Fun

If you want to hear the GAO bray about their ‘watchdog’ role, catch this short podcast on this report. The transcript is there, but in the podcast you get to hear the Valley Girl (Imitation?)interviewer grilling her words away as she questions the interviewee-- a seriously earnest, if hapless, protector of the American taxpayer.
It's a hoot.

Note: minor changes made 5 Nov. for clarity, readability, and in defiance of Bill Gates; spellchecker.