F-35 TVC

[chuck4]

It appears that Boeing Y-32 had a F-22 style 2D stealthy vectoring nozzle. But F-35 only has a normal axial symmetric non-venctorying nozzle with rudimentary stealth treatment. Why were F-35 not fitted with vectoring 2D nozzles? Can F-35B move its nozzle in flight for purposes of inflight maneuver other than transition to landing and takeoff?

 

[F-14D]

It appears that Boeing Y-32 had a F-22 style 2D stealthy vectoring nozzle. But F-35 only has a normal axial symmetric non-venctorying nozzle with rudimentary stealth treatment. Why were F-35 not fitted with vectoring 2D nozzles? Can F-35B move its nozzle in flight for purposes of inflight maneuver other than transition to landing and takeoff?

F-35 vectoring: Probably decided it wasn't worth the cost.

F-35B: To the best of my knowledge, no

 

[chuck4]

For a compact, dense fighter of questionable aerodynamic maneuverability for its generation, TVC would seem to atone for a few agility sins.

 

[Kryptid]

Questionable aerodynamic maneuverability? I think it's plenty agile for its design mission. It has an angle of attack limit of 50 degrees; literally twice that of the F-16. TVC would improve nose-pointing authority and post-stall control but it wouldn't necessarily help that much. A TVC system would make the plane a bit heavier and more complicated actually. With HOBS of the degree that the Lightning II will possess, improved nose-pointing authority isn't that much of a help anyway.

Also, if the F-35 met the agility requirements set forth, then it's not the F-35 you should be arguing about; it should be those requirements.

 

[F-14D]

Questionable aerodynamic maneuverability? I think it's plenty agile for its design mission. It has an angle of attack limit of 50 degrees; literally twice that of the F-16. TVC would improve nose-pointing authority and post-stall control but it wouldn't necessarily help that much. A TVC system would make the plane a bit heavier and more complicated actually. With HOBS of the degree that the Lightning II will possess, improved nose-pointing authority isn't that much of a help anyway.

Also, if the F-35 met the agility requirements set forth, then it's not the F-35 you should be arguing about; it should be those requirements.

Plus, TVS helps you point the nose more, but it doesn't let you turn tighter. Besides, it's often academic if there's a missile capable of 60g turns tracking you.

 

[chuck4]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate. If you need to sustain a turn to dodge a 60G missile, then means you are persistently in the missile's field of view, and you are probably dead. But if you snap 12g turn for a instant at the right moment, then if the missile approach speed is high, you might just escape its field of view, or yourself out of its envelope due to high approach speed. No?

 

[saintkatanalegacy]

err...

but there's a trend of lower wing loading for most fighters with air superiority requirement...

that tells you something about sustained turns

 

[bobbymike]

From a longer article by Loren Thompson of the Lexington Institute (he is a known proponent of the F-35) so take it as presented:

The electronic edge F-35 enjoys over every other tactical aircraft in the world may prove to be more important in future missions than maneuverability -- although test pilots say it matches or surpasses the aerial agility of every fighter other than F-22.

 

[Abraham Gubler]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate.

Well that flies in the face of the entire history and practise of air combat manoeuvring.

Instantaneous turn rate or roll rate and capture turn is by far the most important agility metric because this is how you initiate action and counter action in a dogfight. The ability to jink and match that jink is what decides dogfights before all the speed is bleed off.

 

[F-14D]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate. If you need to sustain a turn to dodge a 60G missile, then means you are persistently in the missile's field of view, and you are probably dead. But if you snap 12g turn for a instant at the right moment, then if the missile approach speed is high, you might just escape its field of view, or yourself out of its envelope due to high approach speed. No?

Not as much as you'd think, you've still got the momentum of your course vector to overcome and TVC won't help you with that.

Regarding the 12g turn, it has to be only for an instant. Any longer, you stress the aircraft structure, will probably experience G-LOC ( which makes you an easy target) and will bleed off so much energy you'll be a sitting duck for the 2nd missile fired a few seconds after the first.

Plus, it won't work. During the instant (if) you manage to do 12g, you aren't going to change the angle enough to defeat the missile. Besides you're still facing something that can hack the vector change a lot better than you. I used 60g because I've heard that AIM-9X can do at least that. ASRAAM and Iris-T may actually do better, and there's some talk that A-Darter can do 100g. Have no idea regarding R-74. Even AIM-120 can do well over 20g in the terminal phase. All of these weapons have dramatically expanded no escape zones over previous generations. Basically, if you are in the missile's no-escape zone there is no aerodynamic maneuver alone you can make to defeat the missile.

 

[Avimimus]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate.

This is only true for attempts to outmaneuver short-range missiles (if and when it works), however sustained turn rate is far more important in BVR.

Missiles have small wings and rarely have sustaining motors. If a fighter can change its heading the missile will have to make a much larger correction (since the missiles is using a lead approach - and any heading change made by the fighter moves the location "where it would be when the missile intercepts it" considerably more than the actual change in course of the fighter). If the fighter can maintain a high speed while making these heading changes the change in intercept trajectory will be even greater.

As a result, the ability to maintain speed during moderate supersonic turns can massively reduce the effective range of BVR missiles (regardless of sensor capabilities). The PAK-FA is engineered specifically for maintaining supersonic turns with this goal in mind.

The F-35, as a medium fighter with relatively limited total thrust and limited maximum speed is already at a considerable disadvantage for this purpose (when compared to any heavy fighter). Any gains to the thrust-to-weight ratio will help compensate for this. Relying on off-boresight missile capabilities and removing in order TVC to save weight makes perfect sense.

 

[sferrin]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate.

This is only true for attempts to outmaneuver short-range missiles (if and when it works), however sustained turn rate is far more important in BVR.

Missiles have small wings and rarely have sustaining motors. If a fighter can change its heading the missile will have to make a much larger correction (since the missiles is using a lead approach - and any heading change made by the fighter moves the location "where it would be when the missile intercepts it" considerably more than the actual change in course of the fighter). If the fighter can maintain a high speed while making these heading changes the change in intercept trajectory will be even greater.

As a result, the ability to maintain speed during moderate supersonic turns can massively reduce the effective range of BVR missiles (regardless of sensor capabilities). The PAK-FA is engineered specifically for maintaining supersonic turns with this goal in mind.

This is also what enabled the Blackbird to avoid so many SAMs.

 

[F-14D]

Nose pointing helps with instantaneous turn rates, No? Instantaneous turn rates seems more important in shaking off a 60G missile with high head-on approach speed than sustain turn rate.

This is only true for attempts to outmaneuver short-range missiles (if and when it works), however sustained turn rate is far more important in BVR.

Missiles have small wings and rarely have sustaining motors. If a fighter can change its heading the missile will have to make a much larger correction (since the missiles is using a lead approach - and any heading change made by the fighter moves the location "where it would be when the missile intercepts it" considerably more than the actual change in course of the fighter). If the fighter can maintain a high speed while making these heading changes the change in intercept trajectory will be even greater.

As a result, the ability to maintain speed during moderate supersonic turns can massively reduce the effective range of BVR missiles (regardless of sensor capabilities). The PAK-FA is engineered specifically for maintaining supersonic turns with this goal in mind.

The F-35, as a medium fighter with relatively limited total thrust and limited maximum speed is already at a considerable disadvantage for this purpose (when compared to any heavy fighter). Any gains to the thrust-to-weight ratio will help compensate for this. Relying on off-boresight missile capabilities and removing in order TVC to save weight makes perfect sense.

One of the considerations in facing a modern BVR missile coming at you from the forward sector (assuming you detect it in time) is when to make the turn. Start it too early, while the missile is still a good distance away, and the angle-off doesn't change that much as the missile can make a relatively small course change to counter. Make it too late, and you don't travel that far during the available time and the missile still has enough energy to counter with its much higher turn capabilities. When you're in the "no-escape" zone, you're pretty much stuck.

Remarkable progress has been made in expanding said zones for BVR missiles. Starting withe the aborted AIM-152, results have steadily increased that zone's size partly by finding ways to increase energy for the end game. Both Meteor and AIM-120D will have the capability to be under power in the terminal phase, which counters a lot of aircraft maneuvering (and they're both capable of turns well exceeding 20gs). Meteor accomplishes this through ramjet technology, of course, while AIM-120D has the capability to fire its rocket again in the endgame. I don't know about Derby or R-Darter. What this means for aircraft is that defense will have to move more towards countermeasures and defeating the seeker.


Regarding the SR-71 and SAMs, the Blackbird had a number of things going for it. One was that it flew so damn high. The SAM had to spend a significant amount of time and energy climbing to its altitude which really impacted acceleration, speed and available energy. Now the SR at speed couldn't turn all that quickly and never had really high g limits, but it was going so fast that the geometry of the intercept changed significantly. Plus, when it needed it, the SR had probably he best ECM in the Air Force. The DEF was large, and designed specifically for it. When you only have to build a few systems, you can spend a lot of money on them.

 

[bobbymike]

AF COS Schwartz was asked a question by a B-1 pilot, "Why spend billions on a new bomber, why not put a laser on my B-1?" Schwartz said the preference "today" is not to be seen but defensive DEW is a capability that we want in the future.

 

[Maro.Kyo]

It appears that Boeing Y-32 had a F-22 style 2D stealthy vectoring nozzle. But F-35 only has a normal axial symmetric non-venctorying nozzle with rudimentary stealth treatment. Why were F-35 not fitted with vectoring 2D nozzles? Can F-35B move its nozzle in flight for purposes of inflight maneuver other than transition to landing and takeoff?

It's an old thread from more than a decade ago but I think it's an interesting topic so I'm digging this up.

To answer this question, we should first acknowledge the very apparent advantages of the lift-plus-lift/cruise has over lift or cruise approach, that of Harrier and X-32 in terms of reliability/stability and lift thrust. So Lockheed (and MD as well for JAST, and all the other preceding examples using L+L/C to the VTOL fighter jets) went with a vectoring nozzel at the end.

When it comes to a vectoring nozzel that can vector 90°, there's nothing much better than the 3BSN. Before Lockheed dug up the 3BSN documents from their Convair cabinetts, they've tried out various other approaches like SERN or MADEN to realize nozzel vectoring for L+L/C and if you've seen those drawings, you'll notice that those designs, especially MADEN looks way more suited for a 2D TVC than 3BSN with some alterations to the nozzel drive design. Compared to that, it aould be an absolute disaster to fit a 2D vectoring nozzel at the end of the 3BSN mechanism, when one of the biggest advantage of 3BSN is its relatively light weight.

Then also comes the question of "if its not possible to fit it on STOVL model, why not on CTOL and CV?". The answer would be that they don't need to, as others have explaines above. As we know with YF-23 and F-35 itself, modern flight models ever since the advent of CCV can do wonders in terms of pointing the aircraft where we want them to. I don't necessarily see the point of adding TVC for the F-35.

 

[njiiaf]

The one thing the F-35 is actually good at from a maneuverability point of view is low speed, high aoa nose pointing.
Adding TVC to improve that capability is a massive waste of money, especially considering that it would come with a weight penalty which would harm its already mediocre sustained turn performance.
Multiple pilots, both publicly and anonymously, have stated the 35 struggles to maintain energy in a turn fight. It’s too heavy at combat weights and simply produces too much drag when turning.
I’ve heard it compared to the F-15E in this respect, you pretty much get one good turn and that’s about it. If you haven’t killed the enemy by this point, you’re in a bit of trouble.

So yes, it really has no use for TVC.

 

[red admiral]

To answer this question, we should first acknowledge the very apparent advantages of the lift-plus-lift/cruise has over lift or cruise approach, that of Harrier and X-32 in terms of reliability/stability and lift thrust. So Lockheed (and MD as well for JAST, and all the other preceding examples using L+L/C to the VTOL fighter jets) went with a vectoring nozzel at the end.

Please could you explain this differently? I'm having problems understanding

The main advantage of the lift+liftt/cruise shaft driven lift fan was in terms of aircraft sizing. In hover you need Thrust/Weight >1.3. If your up and away performance requirements (e.g. sustained turn rate) don't need T/W of 1.3 then the hover conidition sizes the engine and hence aircraft. The SDLF provides a mass/space-efficient way of creating additional thrust in the hover condition from a smaller engine more suited to the up and away performance condition.

 

[Maro.Kyo]

Please could you explain this differently? I'm having problems understanding

The main advantage of the lift+liftt/cruise shaft driven lift fan was in terms of aircraft sizing. In hover you need Thrust/Weight >1.3. If your up and away performance requirements (e.g. sustained turn rate) don't need T/W of 1.3 then the hover conidition sizes the engine and hence aircraft. The SDLF provides a mass/space-efficient way of creating additional thrust in the hover condition from a smaller engine more suited to the up and away performance condition.

What you're saying doesn't contradict what I'm saying.

F-35B's SDLF + 3BSN based L+L/C was and is a better solution than a MFVT based direct lift solution of the X-32 (or the SFVT of Harrier) when it comes to stability, especially considering hot gas ingestion that was still a problem despite the bleed air jet screen. When it comes to ground effects MFVT could've casued suck-down force as well but to my knowledge that was not the case with X-32 (conversly with SDLF fountain forces could have been a problem but was not to my knowledge). X-32 being a MFVT also needs a more complex ACS compared to that of F-35B, which can control its yaw authority with 3BSN and pitch with the lift fan VAVBN.

Also, any offtake based system causes pressure loss potentially greater than that of 3BSN. Obviously I shall not forget the losses induced from the SDLF but such losses are in itself smaller than the net advantage of total lift thrust achieved by employing a SDLF and this was very well demostrated by the greater lift thrust margins of the X-35 compared to X-32.

 

[sferrin]

To answer this question, we should first acknowledge the very apparent advantages of the lift-plus-lift/cruise has over lift or cruise approach, that of Harrier and X-32 in terms of reliability/stability and lift thrust. So Lockheed (and MD as well for JAST, and all the other preceding examples using L+L/C to the VTOL fighter jets) went with a vectoring nozzel at the end.

Please could you explain this differently? I'm having problems understanding

The main advantage of the lift+liftt/cruise shaft driven lift fan was in terms of aircraft sizing. In hover you need Thrust/Weight >1.3. If your up and away performance requirements (e.g. sustained turn rate) don't need T/W of 1.3 then the hover conidition sizes the engine and hence aircraft. The SDLF provides a mass/space-efficient way of creating additional thrust in the hover condition from a smaller engine more suited to the up and away performance condition.

The engine in the X-32 was massive because of this. 34,000lbs+ DRY and 51k in afterburner.

 

[red admiral]

The engine in the X-32 was massive because of this. 34,000lbs+ DRY and 51k in afterburner.

Quite, and Up and Away performance was similarly enhanced over the threshold requirements

 

[red admiral]

F-35B's SDLF + 3BSN based L+L/C was and is a better solution than a MFVT based direct lift solution of the X-32 (or the SFVT of Harrier) when it comes to stability, especially considering hot gas ingestion that was still a problem despite the bleed air jet screen. When it comes to ground effects MFVT could've casued suck-down force as well but to my knowledge that was not the case with X-32 (conversly with SDLF fountain forces could have been a problem but was not to my knowledge). X-32 being a MFVT also needs a more complex ACS compared to that of F-35B, which can control its yaw authority with 3BSN and pitch with the lift fan VAVBN.

I don't think that is the case. The number of nozzles and their relative positions has the largest impact rather than the propulsion "cycle". There's also a load of dependency on specific aerodynamics of the configuration.

In terms of "best" for stability in jet-borne flight, then I'm pretty sure that the P.1216 configuration is: 2 fore + 1 aft nozzle arrangement is one of the best, booms add roll inertia which reduces impacts of gusts

There was a special AIAA / Cranfield course on STOVL aero-propulsion back around 2000 which is a great source of info if you can find it

 

[Maro.Kyo]

I don't think that is the case. The number of nozzles and their relative positions has the largest impact rather than the propulsion "cycle". There's also a load of dependency on specific aerodynamics of the configuration.

In terms of "best" for stability in jet-borne flight, then I'm pretty sure that the P.1216 configuration is: 2 fore + 1 aft nozzle arrangement is one of the best, booms add roll inertia which reduces impacts of gusts

There was a special AIAA / Cranfield course on STOVL aero-propulsion back around 2000 which is a great source of info if you can find it

No, you're talking about flight control authority and dynamic stability of the aorcraft while in hover while I'm talking about the potential possibility of loss of control/stability, eg stall caused by hot gas ingestion. Like I've said, I don't think we're talking about something that contradicts the other. Maybe it was my wording and I should've said "dependancy" rather than "stability".

SDLF with its jet of cold air screens the hot gas more effectively than the jst screen on X-32 ever did, combined with the fact that the intake is more spaced from the exhaust. Also like I've said, ACS design of X-32 is quite a bit more complicated than that of X-35/F-35B. Also, I don't disagree with what you're saying.

I'll try to find the AIAA course that you've mentioned. Thank you for the information. A refommendation from my side would be NASA's research and evaluation regarding STOVL concepts from the 90s and early 2000s. They were specifically evaluating concepts outlined for the ASTOVL program. Their evaluation, although preliminary at the time, also pointed out that a mixed flow exhaust through main nozzel during wing-borne flight and a lift mechanism separate from the main engine exhaust while jet-borne flight was the most suitable.