F-35A vs B vs C

The F-35 compared with other modern jets.
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lbk000

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Unread post11 Nov 2018, 22:37

Really good points Xander, especially about F-35 losses. The F-35 is designed to be a juggernaut -- it keeps on rolling. That's why there's so damn many of them. The US has always liked to maintain an undercurrent of few vs many, quality over quantity, "Alamo holdout" narrative but when you look at the number it's kind of funny because the US has always rolled over its opposition with both quality AND quantity. It's so damn unfair that I think if some people were more aware of it they would declare it a crime -- but that's the point, to be unfair.

So I'm gonna finally bite and get on the kinematics train since at the end of the day we don't seem to ever want to get away from talking about it (just means we know even less about the other stuff like EW). The F-35C's better energy retention capabilities are what I would call a sidegrade. It's a sidegrade because the concept of what constitutes agility has long become more abstract than how long time it takes to do a flat turn.
Now what I'm gonna say is just from my internalization of how things work, so it's very much in my own words. Maybe it will touch off some understanding, maybe not.

In the past, energy conservation was considered a good thing. It is a good thing the weaker your engine is, because if you think about energy like income, the worse your income, the more thrifty you have to be.
Cool, but there is absolutely such a thing as "too much energy". You can think of every coordinate point in the air as having a set "energy value" (this isn't exactly the right term but Steve :D is already tired enough). If you don't have that energy value, you won't be at that coordinate. If you are "saddling up" on a guy, you are trying to hit all the energy values as he does. Your aircraft's kinematic characteristics determine how well you can sustain nailing those energy values. If your aircraft lacks power or you're pissing your energy away in drag, etc., your energy points won't reach up to the needed value (determined by your opponent) and your nose will start to drop to hit lower energy values that you can reach, and so your coordinates series (aka your flight path!) will deviate from his. If you have too much energy, you will be forced to hit higher energy values, changing your coordinates again, which manifests as the overshoot. Thus, differently engined aircraft need to be managed in different ways. A relatively underpowered aircraft keeps the throttle jammed in all the time, but an "overengined" aircraft (ex. late war WW2 jobs like the 190D, and big boys like the F-15) may actually require the pilot to cut the throttle to avoid over-energizing.
So how does aerodynamics come into play with energy? The traditional approach to aerodynamic energy management is drawn from the premise that the powerplant is of relatively low TWR. Propeller aircraft and early jet aircraft all can be said to have low energy income. Therefore the focus has always been to conserve what little energy could be gained as much as possible, by cutting into the air as cleanly as possible, to which end you desire as low AoA as possible.
Earlier airfoils being designed to work at low AoAs, weren't very good at dealing with high AoAs. Once Humpty Dumpty fell off the wall and the airflow separated, they weren't really able to put Humpty Dumpty back together again until the AoA was reset to smooth it all out again. So to make sure the airflow was always smooth, one had to constantly groom the airspeed to ensure it was within the wing's "AoA capacity" else if you exceed it, the wing chokes and you can basically consider it the aerial equivalent of snagging a pothole and getting thrown off your bike.

nrg.png
For older fighters, you got to "slot the airfoil" peg into the slot on the airspeed scale, which is really the doghouse chart that I've turned on its side.

So with an aircraft like... the MiG-15, if you wanted to make a good turn, you had to first ensure you started at the right energy level: you hit that speed brake to get you down to 600kph or so, at which then your wing really bites into the air and slides you around. If you tried to hoik the stick at 900kph, your wing got a mouthful of energy that it failed to convert into mechanical motion and the aircraft yells at you by buffeting a bunch and dipping a wing and all that good jazz.

For a long time though, especially with American (and practiced by Germans) ACM doctrine, there was absolutely no reason to reduce your energy level down to the enemy's. American doctrine was rooted in combining offense with defense, in avoiding the turnfight (which requires energy matching) by maintaining an insurmountable energy difference by flying faster and higher than the opponent.

This was alright back in the age of propellers where relatively speaking, a large absolute energy differential was not needed to be tactically significant. But as aircraft technology advanced, the scale also grew, until the necessary scale to prosecute skirmish boom and zoom tactics became so great as to be wholly impractical. Simple logic suggested WW2 fights would just be magnified to supersonic speeds (and some planners thought this), yet the range of the human eye and the range of the cannon had not kept pace with the capabilities of aircraft and that changed the balance of the equation significantly. Basically, air forces no longer knew what to do with all this energy that they were capable of attaining.

So here's the problem that was discovered in Vietnam: keeping a large energy gap between you and your opponent is good for keeping yourself safe, but now in jets you basically need to slow down to get anything done outside of BVR. Unfortunately there is no way you're going to instantaneously brake fast enough to saddle in. To do that, you'd need massive airbrakes the size of wings (hold on to that thought). It's as troublesome as jumping off a building and landing in the saddle Zorro-style.

The solution is BFM. By packaging your excess potential energy as mechanical motion, BFM manages and grooms your energy and geometry until they are in a desirable state. BFM is the aerial equivalent of taking the stairs down the building to the ground floor where your horse is waiting.

However, taking the stairs is slow. The dream is to be Zorro and leap off the building right onto your horse to ride off into the sunset. That's where high alpha really comes into play. The new wave of aerodynamics in the 80's allowed the wing to be the airbrake. Wings that used to choke on too much air are now able to smoothly put separated flow back together again as the airspeed slows down and AoA drops. If we go back to that diagram above, now instead of looking and guiding your peg into the hole, now you can start at the top and slide yourself down until you catch the slot and grease it right in. Or like, now you got a mountain bike and you go right over the pothole without a hitch. To go back to the visualization that coordinate points in space are of set energy states, now you get to chop off all excess energy very quickly that previously you had to gradually get rid of with extra BFM choreography.

So the real breakthrough realization was the importance of spending energy. That's why TWR became emphasized since the 70's. You make a lot so you can spend a lot. The aircraft that is more dynamic at gaining and losing energy gets to "buck" the other guy off the WVR rodeo.

That's why I think the F-35A is the preferred design over the F-35C, even in WVR, because the smaller wing and higher energy bleed allows for faster braking, because excess energy can be opted to not be converted into mechanical motion. Conversely, the lower parasitic drag and attendant better acceleration of the A allows for a better energy recovery/income. With its more dynamic energy states, the F-35A can nail coordinates in space in sequences that older designs aren't going to dream about matching.

But that's what Dolby Hanche already told us.
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Unread post11 Nov 2018, 23:51

Appreciate your insights and analogies lbk000.
"When a fifth-generation fighter meets a fourth-generation fighter—the [latter] dies,”
CSAF Gen. Mark Welsh
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Unread post12 Nov 2018, 07:47

lbk000 wrote:
That's why I think the F-35A is the preferred design over the F-35C, even in WVR, because the smaller wing and higher energy bleed allows for faster braking, because excess energy can be opted to not be converted into mechanical motion.


I agree with this, it continues the long standing rivalry between the USAF and the USN in this area. The AF always had the better energy fighter (F-16 and F-15) while the Navy had the better slow speed maneuvering fighter (F/A-18).

Although the Viper has the clear advantage in income (energy generation) there are Hornet pilots that still claim they are better in dogfight scenario. I've never lost to a Viper I saw was the statement of 1 Hornet pilot here.

https://fightersweep.com/4210/dogfighti ... 18-hornet/
But there are many other aspects of aircraft performance besides thrust-to-weight ratio and turn rate. Specifically, turn radius is a very important component to BFM as well. In fact, I would say the Hornet has arguably the best turn radius of any fourth generation fighter.

The Hornet, like the Viper, has a very high level of maneuverability. However, there are some advantages inherent in the Hornet design. It’s Leading Edge Extensions (LEX’s) combined with advanced flight control laws in the computers allow for carefree handling. This is especially important for flight at high angles of attack (AOA). This high AOA advantage is manifested in many ways, but two of the most important ways are in the form of slow speed handling and nose authority. The pilot has no AOA limiter and does not need to worry about any nasty stalls or departures from controlled flight.
most BFM engagements will get slow at some point as pilot’s spend their energy to take shots or gain a positional advantage. This is where the good Hornet pilot will look to force his adversary and go 1-circle and turn inside his opponent with the superior tight turn radius.

Another capability is the ability to execute a rapid energy excursion, and trade energy for nose position. All fighter pilots understand this and use this technique in their own jets, but the Hornet does this exceptionally well. Since the nose position can be pointed well past the jet’s flight path (the definition of high angle of attack), the jet can sell a large amount of energy quickly to point the nose at will. In the vertical, the jet can take advantage of its high AOA abilities with a maneuver called The Pirouette.

It looks like a zero airspeed hammerhead reversal, and can quickly yield a positional advantage when done correctly. Combine this with the high-off-boresight abilities of the JHMCS and AIM-9X, and you have a very lethal platform.


Problem is, now the USAF has access to superb slow speed, high AoA capabilities as well in the F-22 and F-35A.
But with regards to the A vs C, I think the C will still retain the smaller turn radius advantage due to the fact that it can turn at the same G as the A at a much slower speed. In fact, if the KPP revision is to be believed, the C will sustain a higher G at the specific set of conditions that they placed.

Sprts's operational comparison chart also showed that C had a higher sustained G rate than the A IIRC

So the rivalry continues
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Unread post12 Nov 2018, 07:58

Whether or not you believe this: Both the F-18 (both) and F-35C are designed to carrier land. This necessitates certain limitations upon these carrier capable aircraft caused by the limitations of things such as the arrestor gear then throw in how the carrier aircraft need to be toughened up for carrier landings in sometimes slightly adverse conditions and you have a requirement to be SLOW & maneuverable in these circumstances. A big thread about this for the F-35C exists whilst some of it may be summarized in a oft cited PDF about designing the F-35C (& B) for flat deck operations. Hence a difference from the beginning of development of a NAVAL aircraft compared to conventional fighter aircraft (not bomber).

The Influence of Ship Configuration on the Design of the Joint Strike Fighter 26-27 Feb 2002 Mr. Eric S. Ryberg, http://www.dtic.mil/cgi-bin/GetTRDoc?Lo ... =ADA399988 (1.1Mb)

Search on RYBERG to find lots of references in this forum to this PDF however there is lots of other info nearby these URLs.

My 'ryberg' search had 27 hits: search.php?keywords=ryberg&terms=all&author=&fid%5B%5D=65&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=-1&t=0&submit=Search
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Unread post12 Nov 2018, 09:51

Things sometimes change over time. Loved this article. I've always wondered if the USN adopted the YF-16 instead of the -18, would there still be an F-35C today or an F-36 instead.

https://www.defensemedianetwork.com/sto ... t-wasnt/2/

Most accounts state that a primary reason for rejection of the F-16 was that the Navy preferred its aircraft to have two engines, because of the added over-water safety factor.


Admiral, the Air Force is the program manager for the F-16, and I can promise you we are not going to screw up the design and performance by adding a lot of stuff that the Navy wants. It’s an Air Force lightweight fighter, and we are going to keep it that.”
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Unread post12 Nov 2018, 09:58

^^ It's not that I don't believe it Spaz, I understand that carrier borne aircraft will have requirements that will make it heavier and slower. But they will also have requirements that will have the byproduct of being better in the slow speed arena.

Now the argument here is why did the Navy request for higher maneuverability. A requirement that forced Boeing to implement major design revisions and could have played a major factor on their loss.

Was it simply for carrier approaches? If so, they have grossly over estimated the required maneuvering performance needed for the JSF's maneuverability because the resulting F-35C is arguably the most maneuverable Naval fighter ever built.

Has there ever been a US naval fighter that can go beyond the 7.5G ball park (I know they can go beyond with the G override switch). According to QS, the C also has a higher G onset rate than the A. Thats pretty big considering that the A is definitely no slouch. And lastly, the C rivals or may even be better than the SHornet in the post stall region.

Are these all unintentional byproducts of the flight handling requirements for carrier approaches? Theres also a long lecture on this thread explaining that Billy Flynn was actually praising the handling of the C and not necessarily max maneuvering performance. So I don't think improving handling will directly translate to better maneuvering performance because they are not the same. So the fact that the C has such good maneuvering performance tells me that it was intentional in the design and not just a byproduct of carrier approach requirements
Last edited by zero-one on 12 Nov 2018, 10:14, edited 2 times in total.
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Unread post12 Nov 2018, 10:08

Naval Fighters are limited to 7-7.5 G's to extend their service life. Has nothing to do with the number of G's they can sustain.

As a matter of fact the Hornet and Super Hornet has a switch to override the G Limit. I believe the F-35C has the same system. Yet, haven't found a source online....
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Unread post12 Nov 2018, 10:50

F-35 test pilots have switches to over ride the CLAW/limits "paddle on / off". I don't believe ordinary pilots will have this.

'zero-one' all of your text means a lot to you - keep in mind the naval hornet aircraft are 'strike fighters' whilst all the F-35 variants are 'strike fighters'. What came first - I would have to do research that I'm not willing to perform because I'm not interested in your assertions as such. However I am interested in how the USN strike fighters were designed for carriers.
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Unread post12 Nov 2018, 10:54

So the fact that the C has such good maneuvering performance tells me that it was intentional in the design and not just a byproduct of carrier approach requirements


It can be explained totally by the greater wing lift area which was mandated by the carrier approach requirements. Your argument would only have validity if you can step back and say there would have been a better/equivalent way of meeting those requirements without having a bigger wing.
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Unread post12 Nov 2018, 11:57

spazsinbad wrote:F-35 test pilots have switches to over ride the CLAW/limits "paddle on / off". I don't believe ordinary pilots will have this.


Called “flight test aids” in F-35 program.
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Unread post12 Nov 2018, 11:58

marsavian wrote:
So the fact that the C has such good maneuvering performance tells me that it was intentional in the design and not just a byproduct of carrier approach requirements


It can be explained totally by the greater wing lift area which was mandated by the carrier approach requirements. Your argument would only have validity if you can step back and say there would have been a better/equivalent way of meeting those requirements without having a bigger wing.


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Unread post12 Nov 2018, 12:03

01 — “A requirement that forced Boeing to implement major design revisions and could have played a major factor on their loss.”

The design revision was for carrier approach requirements which required them to switch to a more conventional wing/tail arrangement.
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Unread post12 Nov 2018, 12:19

Not really, If you can provide links that prove the US Navy's increased maneuvering requirement was due to carrier approach retirements then I'd be happy to rest my case. I have no problem accepting if I'm wrong.

Right now, I'm just afraid that most of us here have become so bent on ruling out dogfights that we'd rather believe it was never a factor in the F-35's design phase.
To me that could be dangerous, because its been done before and the lessons were painful. And even if we're certain the F-35 will almost never reach the Merge, I think designers still incorporated dog fighting performance into the design for that unlikely scenario.

To be clear I too think that most F-35 kills will be BVR and most of the few WVR kills will not involve maneuvering. But if it should come to that, then the F-35 is well capable for it. Thats the response I give whenever some says "The F-35 was not built to dog fight"
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Unread post12 Nov 2018, 12:25

These footnotes from LM Test Pilot about F-35 CLAW have been mentioned a few times so perhaps to mention them again.
Semper Lightning: F-35 Flight Control System
09 Dec 2015 Dan “Dog” Canin

"...[4] What’s NzW? The airframe structural limit isn’t just a function of g – which the pilot can sense – but the actual lift force imposed on the airframe, which is the product of gross weight (W) and g (also known as Nz, the normal acceleration in the z direction). At light weight (low W) we can pull more Nz with the same structural load (Nz*W). That said, there’s still a maximum g the F-35 is allowed (9g for the F-35A, 7g for the B, and 7.5g for the C), and CLAW will let us pull that anytime the weight is less than the Basic Flight Design Gross Weight (BFDGW). Above that weight, the allowable g decreases to keep the total lift – Nz*W – constant. . Fortunately, CLAW figures that out for us.

[5] An OVER G advisory will trip if you exceed the book symmetric or asymmetric maneuvering limits by more than 0.5g. For the purposes of this ICAW, the airplane defines as “asymmetric” any roll rate over 50 deg/sec, so there’s a 25 deg/sec buffer there as well. So if you stick to the flight manual roll rate limit, you should never see this ICAW. What you might trip, though, is an “overload” HRC, which has a much more sophisticated algorithm behind it and will only trip when you’ve exceeded an actual limit on some component of the structure. CLAW should in all cases prevent actual overload to failure, but during rolling maneuvers it may allow one of these indications to trip, requiring a maintenance inspection...."
&
Photo caption & explained in main text: "What about g? We’re mostly protected, but not completely. Interestingly, the protection is least where the maneuvering limits of the F-35 are the lowest: in powered approach (PA) and aerial refueling (AR).
&
The limits in powered approach and aerial refueling modes are 3g and 2g, respectively, and there’s nothing to keep pilots from exceeding them. Why not? Because, while those limits are more than adequate for normal ops, there might be times when we need to exceed them to avoid hitting something – such as the ground, or the tanker – and our CLAW engineers have wisely decided that running into things would probably be worse than busting the g limit. So they let us bust the limit.
&
The pilot-observed [G] limits were decreed to make sure the airframe delivers its contractually specified life. If we exceed them, the wings won’t fall off, but we might reduce some of that life."

Source: http://www.codeonemagazine.com/article.html?item_id=187
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Unread post12 Nov 2018, 12:32

zero-one wrote:Not really, If you can provide links that prove the US Navy's increased maneuvering requirement was due to carrier approach retirements then I'd be happy to rest my case. I have no problem accepting if I'm wrong.

Right now, I'm just afraid that most of us here have become so bent on ruling out dogfights that we'd rather believe it was never a factor in the F-35's design phase.
To me that could be dangerous, because its been done before and the lessons were painful. And even if we're certain the F-35 will almost never reach the Merge, I think designers still incorporated dog fighting performance into the design for that unlikely scenario.

To be clear I too think that most F-35 kills will be BVR and most of the few WVR kills will not involve maneuvering. But if it should come to that, then the F-35 is well capable for it. Thats the response I give whenever some says "The F-35 was not built to dog fight"


NOW you’ve back-slid into the BVR thing again. You’ve been here before zero — ad nauseam. You argue with your own straw man. :roll:
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