“Fighter Aircraft” Design: Driven by Operational Requirements (Part 3)

With the world about to bear witness at the Paris Air Show (#PAS17) this week that the F-35 is NOT the 'pig' aircraft that the propagandist critics (all of whom have NO material knowledge of the F-35) have claimed, I decided it was time to finally publish this post and close out the series. All the contrived elaborate and ignorant ‘stories’ assembled from twisted factoids  that have surfaced over the years, are about to fall flat, and will trigger much denial, wailing and gnashing of teeth from those quarters.
Now is also an especially good time for me to close out the series because it will be a handy reference for later smacking down a piece of anti-JSF Dezinformatsia that surfaced (as a metaphorical rotting dead cetacean) this week.

Behold! O haters and doubters.....and weep.

Super-manueverability without Thrust Vectoring, Check...

And so we proceed…

The entire point of this series has been and is to illustrate that fighter design isn’t driven by opinions, whim, or fashion; nor is the implementation of it either the least bit capricious. To recap, Part 1 of this series was just an initial outline of what I intended to cover/accomplish overall. Part 2 was an extended ‘two-parts in one’ review of the evolution of fighter design requirements from the earliest days and up through the emergence of ‘supermaneuverability’. We reviewed the developments that influenced fighter designs up through to the ‘fourth-generation’ of fighters and we could even say included design trends that influenced the earliest aerodynamics of fifth generation design: the F-22.

This brings us up to the starting point for Part 3, still somewhat in the past, but not so far as to prevent us from getting to the present from there. In the introduction of this series, I had originally envisioned that in Part 3 we would:

..."break down a 1 vs. 1 air combat scenario into a high-level conceptual model of constituent phases and associated combatant states. Then we will apprise the F-35’s potential advantages and disadvantages”...

As it turns out, we can leverage one and a half decades of expertise from professionals to accomplish the first objective and do so in fewer words than I had initially planned. We will also use the same for framing the discussion to meet the second objective: quickly ‘apprising’ the “F-35’s potential advantages and disadvantages”. It should shock only those with less than a passing interest in, and/or superficial knowledge of the subject, that by the time the first Part 3 objective is met, the second objective will become largely self-evident.


“Aircraft Maneuverability” or “Agility” research probably reached its zenith (in the West anyway) with the extremely successful X-31 Enhanced Fighter Maneuverability Demonstrator program.

Before the X-31 even flew, it was already viewed as a key investigative tool for ‘applied agility’ research, and the only effort at the time to span all “applied” research areas of interest.

Figure 1. X-31 Spanned Applied Agility Research Interests

I was TDY to Edwards AFB for one program or another and we had just landed (it had to have been sometime in 1992 or January-ish 1993 at the latest) and while sitting on the ramp waiting for a crew van, we watched the X-31 return from a mission and work the pattern with its chase plane. The discussion, led by our own test pilots and flight test engineers, turned to wondering: Just how much any additional maneuverability that might come out of the X-31 program would actually translate into any REAL additional combat capability? This is a question of the same kind of ‘asymptotic limits’ that were addressed in Part 2.

As it turns out, we still can’t quantify an answer to that question because nothing about that time on up through to the present day was, or is, “static”. Changes and developments in all the other fighter aircraft capabilities and technologies kept evolving long after we hit peak ‘supermaneuverability’ with the X-31. But from Part 2 and what we are about to review, we can answer the question in general:

1) Maneuverability beyond the F-16/F-18 characteristics doesn’t really get you all that much more capability (effectiveness and survivability), and  

2) When costs involved are considered, there are cheaper/better ways to increase combat offensive capability and survivability than improving AoA, turn rates, or g-loads past the present state of the art.

We know these are the answers because those involved in fighter design and development have known them for a long time. From 1986 through at least 1995, the NATO member countries of France, Germany, the United Kingdom, and the United States collaborated on a major study1 to determine where future fighter design efforts should be targeted.

Note:  

While I’ve been too busy to engage in substantial posting for a lot of reasons, another reason this post was so long in coming is the open source data has been fickle. I first typed out about 4K words (longer than this post) I had put to electrons just to go over the gory details in the study we are about to discuss. But after all that work trying to do justice to the contents of the study I found a copy of the original without a paywall in place. I slashed what I had written to leverage the source without saving the earlier version. Then the source disappeared again. If access reappears, I'll link to it.

The study had two major objectives:

• Through analysis and simulation, determine whether supermaneuverability is operationally useful in future air combat scenarios.  

• If operationally useful and technically feasible, determine the practical limits of supermaneuverability and full envelope agility.

The context of the study was obviously about the benefits of supermaneuverability in WVR combat. The authors referred to it as “Close In Combat” (CIC), of which choosing to engage in a turning fight is only one possibility. After all there’s not much point in doing a Danse Macabre if there’s no opponent within visual range to ‘appreciate’ it.

The study participants used the following definitions:

“Supermaneuverability is defined as very high levels of maneuverability and agility throughout the flight envelope of a fighter aircraft, especially beyond maximum lift.”  

“Agility is defined as the ability to change states rapidly with precision.”   

“Full envelope agility contains airframe, missile, and avionics attributes.”

It is important to observe here the recognition by the actual “experts” involved that the broadest definition of agility was important going in to the study. The definition of 'weapon system agility'  has become a somewhat standard one:

Figure 2. Weapon System Agility = Total Agility

(See also my backgrounder on modern Energy-Maneuverability,)

The study’s ‘statement’ of purpose was:

Previous analyses and manned simulations for close-in-combat (CIC), primarily emphasizing 1 v. 1, have indicated substantial improvements in air combat effectiveness when supermaneuverability (in particular, post-stall technology) was incorporated in advanced fighter designs. Recognizing that air combat scenarios are likely characterized by rapid transition from beyond-visual-range (BVR) to CIC involving multiple aircraft, the effect of supermaneuverability technologies on the outcome of this type of engagement needs to be determined.

This multi-national NATO-sponsored study began with manned simulation at Industrieanlagen-Betriebsgesellschaft (iABG), involving two piloted aircraft and three computer generated aircraft. Four pilots were trained on the baseline post-stall aircraft including avionics, weapons, and scenarios. After the training phase, the pilots jointly determined possible starting conditions (geometry, speed, weight, weapons load, number of runs, etc.).
The purpose of the manned simulation was to create a database to develop a digital pilot reaction model. The application of a batch model was necessary in order to generate the large number of computer runs needed to accomplish the project goals. The batch simulation strategy involved three different programs. First, the ‘Arena’ war simulation program was used to model a beyond-visual-range, many-on-many air battle and generate within-visual-range starting conditions. This was a valuable technique that got the study group past the ‘How do we set up realistic WVR combat starting points?’ question. Second, the Air-to-Air System Performance Evaluation Model (AASPEM) was used to model one-versus-one (1 v 1) engagements that were initialized under the Arena-derived starting conditions. Third, the Abductory Induction Mechanism (AIM™) was used to link AASPEM results to Arena as depicted in Fig. 3.
 

Figure 3. Source: Practical Limits of Supermaneuverability and Full Envelope Agility

As you can see by the parsing of function among different models, it wasn’t easy to do complex scenario modeling back in the 80’s-90’s. The primary models had to be linked because neither one could answer the questions ask if used as standalone devices. An evolved MIL-ASSPEM II was part of the USAF’s standard analysis toolkit as late as 2005. It might still be.

The study identified and used probability of kill, probability of survival, and exchange ratio as “the key parameters” using two types of weapons: missiles and guns. For each weapon type they assigned a probability of a kill (Pk) given a ‘hit’. Under a ‘massive-number-of-trials’ modeling effort, they established an average Pk of a (AIM-9L ‘like’) missile of 0.8 for each simulated missile fly-out. The Pk (given a ‘hit’) of the missiles being held constant may have made some of the long-term study quantifiable results more conservative ‘offensively’ and more optimistic ‘defensively’ than optimum, given the lethality enhancements seen with AIM-9 and AIM-120 developments ongoing at the time and later. The advantage of using a constant Missile Pk value is that it prevents missile lethality from dominating the calculations and masking nuances in outcomes due to other variations in the aircraft/missile (as a system) combinations. ‘Pk’ for the gun was more complex, and was based upon a function of the maximum burst length for one firing and the time duration of the gun hits within that burst.

The baseline “good-guys” (Blue aircraft) were assumed to have the ‘agility’ of the X-31, and the baseline “bad-guys” (Red aircraft) represented an “F-18 type aircraft”. Given the study timeframe we can probably assume the “F-18 type” aircraft comparisons were based upon the F-18C/D versions.

The study group ran multiple excursions of the 'sort-of-a-metamodel' they created, exploring the relative impacts of increasing aircraft and weapons capabilities on the outcomes of air combat engagements. A recreation of the contents in the matrix of different test cases explored and as summarized in the study’s Table 8 is shown in Figure 4.

Figure 4. Cases studied in "Practical Limits of Supermaneuverability and Full Envelope Agility"

The engagements were run under set conditions to control the number of variables. The following are the rules of engagement used for 1 v. 1 engagements:

• 120 second duration  

• No kill removals  

• Each aircraft started with same fuel load  

• Each aircraft had 4 missiles and a gun  

• Conditions for gun firing:  

- Minimum range = 500 ft  

- Maximum range = 3500 ft  

- Tracking delay = 0.2 seconds  

- Pipper size = 3.5 MIL (±2°)

All of these criteria were controls based upon expert analysis and historical records except the “No Kill Removals”. The ability to count wins and losses in a test run without ‘kills’ that would remove the killed aircraft from the equation allowed for many more engagements (trials) to add up within each computer simulation run. This approach in modeling was akin to the process of re-spawning adversary aircraft in Red Flag or similar exercises, though with a somewhat different purpose. Today, we would run more trials with actual removals because computer time is cheaper and the runs are faster.

What was learned

Figure 5. The Bottom Line of  Modern WVR Combat

In trying all the various combinations of possible enhancements (and degradations) the authors produced many relevant ‘findings’ associated with each of the design changes and combinations thereof.

1. Aircraft Agility Changes: Blue’s losses were serious, but Red Losses were even worse. Blue losses were seen as high (around 45%) for the baseline case; aircraft agility increased the red losses by 20%, while blue losses increased slightly.  

2. Enhanced Missile Capability: Blue’s losses were still serious, but Red Losses were even more severe. Blue losses were high (around 45%). However, red losses increased drastically to near 70% against the most capable missile option.  

3. Enhanced Avionics: Just improving avionics didn’t help Blue’s effectiveness or survivability. Overall, there was virtually no effect on exchange ratio or losses (which, once again, were around 45%) for the Blue Force.  

4. Combined Short-Range Missile (SRM) and Avionics Enhancements. Blue losses are again high (40-45%). Red losses were slightly lower than that for the same missile using baseline avionics, but still significant approaching 70%.  

5. Aircraft Agility with SRM Enhancements. Losses remained high (up to 52% for blue and up to 66% for red).  

6. Aircraft Agility with Avionics Enhancements. Red losses were again higher than blue losses (20% higher), but both remained high (above 45%).  

7. Combined Enhancements. Again, blue losses were high (48% for the "best" system). Red losses increased to beyond 70%.

The biggest benefit of EFM that could be drawn from the study was that EFM pays off significantly IF the A2A fight STARTS very ‘close in’ under 1 v. 1 situations AND inside the minimum range (Rmin) of the ‘then-era’ of Short Range Missiles with limited OBC (Off-Boresight Capability up to 30°), AND IF no further aircraft enter the combat (remains a 1 vs 1 engagement). Within the study, EFM largely enhanced gun firing opportunities that come well after the initial ‘long-game’ has been played and those outcomes settled. That advantage is now questionable with SRMs that have very high OBS capability. No one has to actually point anywhere near the opponent in WVR combat anymore to be able to take offensive action against that opponent.

And for the readers who just skimmed the WVR engagement outcomes above and didn't see Figure 5, let us now explicitly state that the WVR ‘short game’ IF it comes at all, during the course of this study was determined to be an unsustainable “loser’s game” between comparable opponents. This has now been known for decades, and findings such as these had to have influenced the definition of the F-35’s requirements.

Given that 1) ‘modern’ low observability predates this study significantly-- at least in the U.S.—and 2) low observability makes a foe far more lethal to 4th generation and earlier aircraft as well as more dangerous surface to air systems, it should speak volumes to any reasonable person as to why the design thrust of the F-22 and F-35 (and now others) emphasizes the reduction of susceptibility to being targeted in the first place, while (as in the case of the F-35) also emphasizes the ability to sense, discern, and assist the pilot in dealing with external threats as effectively and efficiently as possible.

We can be certain that the responsible agencies involved conducted manifold similar studies involving the effects and limits of low observability in combination with all other design drivers to produce the latest fighter designs. I can’t imagine what kind of thinking is required by the uninvolved to imagine the professionals make these kinds of analyses and force structure decisions without due diligence.

How many more pilots, planes, and support assets would ‘blue’ forces need to win a war of attrition if only WVR-capable “day fighters” and/or non-‘stealth’ aircraft are involved? This is an important question. After all, simple ‘less capable’ fighters are what all those earnest and/or Faux Reform critics advocate to varying degree when they are insisting the actual experts are doing fighter acquisition “wrong”. Advocates of less capable systems are advocates for a strategy of Wars of Attrition.

The frequency--how often WVR conditions would occur between aircraft (again, they were all non-LO aircraft) -- was to be a subject of the Arena runs of the future. I’ve not found the results of this effort in unclassified sources, but given what we’ve learned from all air combat that has occurred since that time, and experiences in major exercises such as in recent Red Flags, I would suspect WVR encounters, and certainly 'extended turning' fights, will become even more of a rarity.

Given the improved min-range performance of short-range missiles and future non-kinetic weapon solutions on the horizon, extended maneuvering fights might become extinct. At the very least, they could become ‘black-swan’ encounters not worthy of driving aircraft design in the future nearly as much as in the past, that is, at least for the foreseeable future.

How potential enemies see the future is indicated in how hard they work to either follow the US lead in design trends or in attempting to devise ways to mitigate the advantages sought by the U.S. and its allies. “Advantages” such as those that come from the capabilities of the Fifth Generation fighters.

The entirety of EFM-AASPEM work performed during the study was devoted to within-visual-range 1 v. 1 combat. Comparisons were made based on firing opportunities, exchange ratio, and losses. One really needs to read the study to understand the nuances of the findings, but by way of introduction to the findings, let us observe what key conclusions were drawn. [ My comments in brackets]:

• The most significant contribution to operational effectiveness was increased OBC coupled with enhanced avionics (mainly due to helmet mounted displays). Further improvements were possible when Rmin [Minimum Range] was reduced. [Missile Rmins have been getting smaller, and off boresight capabilities have expanded wildly beyond any assumptions in the study since the report was published. The utility of an advanced HMD has been recognized as far back as the earliest F-15 requirements list. It’s good to see technology has finally advanced enough for the concept to have come of age in the F-35.]  

• Missile and avionics enhancements have to be harmonized to fully make use of the improvement potential. It should be noted that missile/avionics OBC enhancements will provide even higher impacts in the many-on-many environment. [And the F-35’s integrated avionics/sensor fusion are now the epitome of this idea made real.] 

• Aircraft agility contributes to a certain extent, although not as significantly as missile/avionics enhancements. To make full use of agility, new aircraft designs might be required concerning aircraft kinematics and aerodynamics. [‘Agility’ as defined by the research pointed to just the kind of design philosophy used for the F-35.]  

• Conventional aircraft performance enhancements do not improve system effectiveness. If envisaged, they would also require new aircraft designs. [Asymptotic limits of maneuverability have been reached. Perhaps it is a plateau for the current technology available, but I would suspect there will have to be a breakthrough no one has yet identified as needing to happen first.]  

• Degraded aircraft performance [Aero efficiency and Thrust to Weight for the most part] can hardly be compensated by enhanced agility. The degradation decreases the conventional turn capability which is a "defensive" potential. A decrease of this potential enables the opponent to generate increased firing opportunities. [In a WVR world fighters will still need to be able to turn and burn. Think of it as the lower limit of maneuverability isn’t going away just because the practical upper limit has been reached.]  

• Degraded aircraft performance might be compensated by suitable missile/avionics enhancements. Although the same degradation concerning "defensive" potential applies, more firing opportunities can be generated earlier. [This is actually not a new thought. If Glenn Bugos’ history of the F-4 is to be believed (and I believe most of it is quite on target), much of the F-4 Phantom design was philosophical: driven by how best to divide the ‘capability’ between the missiles carried and the aircraft carrying missiles and to a lesser extent fleet radar support.]

Some of the last findings in the study report can be said to have become even MORE true since it was written [Brackets still mine]:

During the last 10-12 years, [and now two decades since the study report] there has been significant improvement in missile technology. Next generation missiles [ASRAAM, AIM-9X, etc.] have better seekers and more sophisticated fly-out capabilities to make successful use of better thrust vector control, thereby improving missile agility in the close-in environment as well as endgame performance. [The missile performance realized in today’s generation of missiles exceed that ever envisioned in the study]. In addition, [aircraft] avionics have improved to make use of high OBC. [And of what the study authors would have considered impossibly-high OBC.] These developments [through and past 1995 and that were and are ongoing] make the new generation SRM/avionics attractive; however, the high mutual loss rates [expected to increase further] with all type of enhancements will "stress" the recommendation to urgently improve situational awareness as well as beyond-visual-range effectiveness to avoid WVR/CIC. [And unsurprisingly has been incorporated into the F-35 design.]

“Fighter Aircraft” Design as Always is STILL Driven by Operational Requirements

(Bumped)

Operational requirements have evolved continuously since the first fighters flew. It would be as large a folly to insist that a fleet of 4th generation fighters could meet the needs of current and foreseeable operational requirements as to insist a WWI aircraft could meet the requirements of a WWII operational environment.

Compare what we know now about ‘where’ air-to-air combat is going with the kinds of capabilities built into fighters like the F-35 and F-22, and what potential ‘near-peers’ are trying to build. Given the study findings, 5th generation fighter capabilities, and actual air combat history, WVR combat is now something to be even avoided more; something any A2A combatant would seek to avoid if at all possible and only to be endured if unavoidable.

Defense planning and foresight informed by experience and research, such as that embodied in the study we just reviewed, produces the requirements for future weapon systems that resulted in the F-35. I marvel at how much hybris the uninformed must possess to shamelessly assert alternate realities while second guessing legions of actual subject matter experts who have done the work day-in and day-out for decades to deliver viable solutions to defense requirements, and who have access to the kind of data and history needed to actually carry out such responsibilities.

The future of fighter design and design requirements will change as the operational environment changes. This is why as soon as one ‘generation’ of fighters is being fielded, work begins to define what will be needed in the next generation. Work on what became the F-15 began as soon as the AF got the F-4. The F-22 is descended from the first efforts to define what would be needed after the F-15 as the first F-15s were in development. Yes, we can envision some of these future changes (lasers anyone?) and can imagine how strategists and designers will cope with them. But the entire battlespace will continue to be reshaped beyond any analyst’s imagination and prevent them from peering too far into the future just as it always has been.

NOTE:

Nowhere in this series of posts, or in any other posts the reader will find here, is the assertion made that ‘maneuverability’ (however one defines it) is "unimportant"-- in the past, modern day or immediate future. This must be stated unambiguously up front because I've seen the tiresome broad-brush accusation of same made too often when anyone dares challenge some closely held belief as to maneuverability’s relative importance to fighter design, or dares challenge the vague reasons why many of the uninitiated think “maneuverability” is important.

A Request in Closing: If history repeats itself, when this post is referenced on a ‘board’ or comment thread somewhere, some yahoo is probably going to contest what I have written as “SMSgt Mac is wrong…”. As if their disagreement is with ‘me’-- when they’re really expressing their disagreement with…y’know…the ACTUAL experts I cited. I usually trip over these weak statements. while looking for something else, ages (sometimes years) after the mischaracterization of what I typed is displayed: long after the disinformation damage is done and everyone has since moved on to other topics. Soooo…If one finds this happening somewhere after this post, it would be much appreciated if a reader or two would reply in response that “SMSgt Mac said you would try that B.S. deflection”. Feel free to use the direct quote.



1. Practical Limits of Supermaneuverability and Full Envelope Agility; B.A. Kish, D.R. Mittlestead, G. Wunderlich, J.M. Tokar, T. Hooper, R. Hare, H. Duchatelle, P. Le Blaye; Proceedings from the AIAA Flight Simulation Technologies Conference, San Diego, CA, July 29-31, 1996; PP 177-187; AIAA Paper 96-3493.