Wednesday, January 18, 2017

Not the 'Second Engine for the F-35' Cr*p Again!

Oh dear, if only the world was this simple.

Breaking Defense has an advocacy piece up at Breaking Defense titled: "Trump Wants Lower F-35 Costs, He Should Compete F135 Engine" from Retired USAF Colonel John Venable (who is now with the Heritage Center). In it, Venable tries to make a case for reviving a second engine effort for the F-35. But in typical AF 'advocacy style guide' fashion, elides right by many key factors to consider while throwing all possible arguments at the wall trying to make one stick. I wanted to just make a comment at BD, but since they've invoked the ads among the commenters in their comment threads their web page tends to crash on me for all but the shortest comments. Could be the times, could be my system (Adobe updater is always a suspect). In any case, here are my observations on the sales pitch Venable makes.  Read the whole BD article first to see the targets of my counterpoints.    

RE: Competition

‘Competition!’ is almost always a good thing in an open commercial and ‘free’ market, the kind of market most of us deal with every day. However, it is only a good idea sometimes, under certain conditions, in a monopsonistic (such as ‘defense’) market. At the risk of oversimplifying almost as much as the author, in a defense market a competition is generally ‘good’ for reducing risk and improving technical outcomes, but generally NOT good for reducing ‘cost’.
The body of defense acquisition research is awash with the whys and wherefores of when and how a program should invoke competition. Though people like to point to the Great Engine War history in this instance, they tend to forget that most of that ‘narrative’ was written before the history had fully played out. Later views on the utility and relevance of that competition to the F-35 are far more nuanced than simple invocation of the Great Engine War can convey. 
Not to put too fine a point on it, there are certain requirements for a successful (cost lowering) competition (see here for starters) and one of the most important set of conditions has to do with the total volume of work competed AND the rate to which it is to be performed. Two operations running at reduced capacity are NOT cheaper than one running at full capacity. So if the author and Heritage want to advocate competition in this case, they need to caveat that advocacy with a requirement to ramp up the F-35 production rates sufficiently and far enough ahead of any doubling of the number of engine suppliers to ensure sufficient and worthwhile demand for same.

Finally, given the program is looking to refresh F-35 engine technology, you better have the second engine supplier qualified and production ramped up yesterday if you don’t want it competing with the effort that now appears to be on the F-35's horizon (mid 2020s). How much so-called 'savings' can possibly accrue if there's only a couple of years production involved?

RE: F-35 Weight

Is the author aware that the F-35 variants are all at or below their target weights for the end of SDD? Is he aware that those target weights were set with an allowance for further weight growth already factored in? Is the author aware that weight growth in past aircraft (both the F-16 and F-18 spring immediately to mind) was driven primarily by scabbing kinds of needed systems (sensors, EW, etc.) onto them that are already integral to the F-35 design and already installed or have their weight already accounted for in the target weights?

RE: Thrust

Is the author aware that increased thrust has been available from the F135 for some time if is needed, but increased thrust will require changes/differences in the F-35B along with associated program cost increases to incorporate?

While we’re on the subject of cost, no doubt the author also has a plan to add a couple of $B to the program in order to finish development of a second engine, to include getting everyone on board with the idea AND happy about the extra cost involved including the cheapskates budget conscious and the faux military reform industry.

RE: 'Transonic Acceleration' and 'Sustained G' KPPs

Is the author aware that the transonic acceleration and sustained turn KPPS are only factors in the trade space below Lethality and Survivability requirements, and that their values are only relevant as contributors to the overall requirements? If the program is not concerned, the author ought to first find out 'why' before engaging in public handwringing. I've examined these KPPs before (here and here) so I get why the program isn't too concerned. As the KPP values were established with a mid-mission weight and payload involved, and assuming some degraded engine performance towards end of life, perhaps some of the author's concerns will be allayed knowing that similarly equipped F-16s in most cases couldn't do any better?


Since the author is a recognized top fighter pilot and ‘patch wearer’ who came of age in the aftermath of all-aspect short-range IR missiles, he surely must be cognizant of the fact that these two parameters have taken a backseat to instantaneous turn rate, time to corner speed, and low speed nose pointing: three measures of agility that from what the pilots are saying are where the F-35 excels.

Table 3 Reconstruction from “Advanced Fighter Agility Metrics
Andrew M. Skow, Willlam L. Hamilton, John H. Taylor; AIAA-A85-47027
10 = most important 
We won’t go into it here, but even these measures of agility may have been rendered less important with higher off-boresight and 'shorter minimum' range missiles (that's probably going to come in the next part or part after of my fighter design series by the way--still working on it).

In any case, advocating more thrust to improve these metrics is pretty hapless if one thinks about the speed regions involved. It's probably more important that the F-35 variants are meeting/beating their  weight targets.

So all the arguments for adding the second engine into the F-35, at least for the factors above, seem to be rather unconvincing. As to the decision to stop the GE engine effort, which was very immature, it made sense. How immature? As I observed in 2014:
In the spring of 2010, the F136 was only 700 hours into a 10,000 hour test program and had not been flight tested. No one knows what problems it would have encountered had it been fully developed. But in its cancellation, the F136 has become the mythical 'success-that-could-have-been-but-never-was' to the proverbial ‘some’ in the backbenches.
Let's keep the F136 the mythical success it is, at least as far as the F-35 is concerned.

3 comments:

Seal Of Lion said...

I wish the air force or the companies had just continued with development of the F120/136 engines even if they aren't used on the F-35. The variable cycle concept is interesting. It sounds like GE/Rolls Royce had figured out a way not to make it overly complicated.

SMSgt Mac said...

The GE approach would have been invoked in the F-22 or F-23 if the Cold War had not gone so well for us when it did. The GE engine gave better performance to both ATF fighters, and the AF picked the lowest supercruising combo to develop for lower risk and "producability". Whether or not GE succeeds in the future with their advanced engine remains to be seen, but the engine tech itself is coming.

DigitalFilm JamesT said...


Sea of Lion. I believe the F-136 does not feature the variable cycle concept. However, I was informed that one of the reasons the F-136 was cancelled (aside from cost cutting) was because the DOD was more interested in GE moving forward in developing next Generation Engine that had the variable cycle feature. Am I correct in this?