Aerodynamics thread

[Engineer]

Posting diagrams from marketing brochure doesn't help you. That is especially so when rolling isn't the same as turning. Nice try though. Real-world exercises don't see the advantages being claimed.

 

[Engineer]

I don't have time for this, but Engineer should rather be named Lawyer for his style of argumentation; it's sophistic par excellence.

My arguments are excellent. Or may be yours are not as good because they are not backed up by real-world observation.

When I say that TVC reduces drag compared to canards, the point is cruising drag, not maneuvering drag. If the aircraft is moving level, putting canards in front will necessarily create drag. This is why the Su-35S doesn't have canards; the Russians decided that with TVC, the aircraft was already sufficiently maneuverable and that canards reduced the range of the aircraft.

To that I already replied while it may be so, the claimed benefit was proposed for traditional configuration with tail-plane like the Su-35, instead of canard-delta configuration. The latter has more control surfaces for trimming to begin with.

Second, TVC creates little to no RCS increases when the aircraft is cruising and in proper orientation. Canards, on the other hand, tend to create RCS issues simply because they're in front. "Engineer" seems to think that TVC will cause diffraction from traveling waves more than canards, but in cruise mode, the diffraction is almost entirely covered by the fuselage of the aircraft and the diffraction actually reduces RCS.

When the aircraft actuates TVC, though, the nozzles may extend outside the blocking shape of the fuselage body, but that's not a given and it's dependent on the design of the aircraft.

Diffraction reduces RCS? Diffraction is uncontrollable radar return, so it wouldn't matter if the diffraction happens at the tail end. Now, the issue here isn't whether frontal RCS got bigger as a result, but by how much, and the same goes for canard. When canard doesn't break stealth, then talk of improvement is no better than trying to make a glass of water more wet.

Third, TVC is not just for rotation. Depending on the design of the aircraft and where the center of gravity lies, TVC can be used to directly change the vector of the aircraft simply because it's changing the direction of thrust. Some of the changed thrust vector may go into rotation, but not all of it.

You are assuming those effects will be favourable. NASA did a study on F-18 and found out that thrust-vectoring introduces adverse force during turns. That is, a force which opposes lift when lift is needed the most. This is extracted from a paper titled Thrust Vectoring on the NASA F-18 High Alpha Research Vehicle.

Not only that, but changing the aircraft's vector in the way you proposed is not the purpose of thrust-vectoring. The paragraph above explicitly stated that vectoring is intended primarily as a moment-producing effector.

Fourth, both TVC and canards are means of improving instantaneous turn rates. I misspoke when I said that canards can do TVC; what I meant is that canards do ITR. Canards are large control surfaces that can radically move the direction of air, and canards also help the aircraft to achieve control authority at high AOAs. TVC can do something similar; both by redirecting the direction of thrust and by rotating the aircraft, TVC can allow the aircraft to sustain a higher AOA than normal, while not necessarily stalling, giving it better ITR.

I have nothing against ITR. This isn't about ITR. The USAF lecturer was very clear that the F-22 and Su-30MKI pilots made the mistake of going post-stall. Post-stall manoeuvrability, also known as super manoeuvrability, was touted as an advantage of thrust-vectoring. However, using it only got the pilot lose faster.

 

[b787]

Posting diagrams from marketing brochure doesn't help you. That is especially so when rolling isn't the same as turning. Nice try though. Real-world exercises don't see the advantages being claimed.

Studies have shown that equipping a fighter aircraft with thrust-vectoring nozzles can increase its survivability by enhancing its maneuverability and turn rate (ref. 2).

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3. Turn rate enhancement at speeds below corner speed. If the thrust is vectored towards the centre of the turn, then the turning force will be increased, leading to a higher turn rate. Above the corner velocity the aircraft will be load factor limited, and no advantage from TVC will be gained.

Herbst[5] concluded that turn rates of 25/s (high in the early 1980’s) could only be surpassed using new technology like thrust vector control

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in few words STR or sustained turn rate is highly increased by using TVC nozzles, ITR is only increased below corner Speed

 

[Engineer]

in few words STR or sustained turn rate is highly increased by using TVC nozzles, ITR is only increased below corner Speed

Those are examples of what thrust-vectoring promised but didn't quite materialized in the real-world. Fact: F-22 engaged TVC, F-22 lost dog fight. Fact: Su-30MKI engaged TVC, SU-30MKI lost dog fight. See the following talk about lesson learned from F-22 and Su-30MKI in exercises.

This is why fighter aircraft is not built based on studies of CFD alone, but include wind-tunnel testings and some half a decade of test flight. Even after the aircraft is introduced into service, there is on going tactic development.

 

[SamuraiBlue]

This is why aircraft is not built based on studies of CFD alone, but include wind-tunnel testings and some half a decade of test flight.

To be fair you can't do a comprehensive analysis of TVC through simulation either computer or actual wind tunnel testing since you have no basis on how TVC and air fluidity will mix at various velocities.
Basically there are too many conflicting variables changing the results.

 

[Engineer]

To be fair you can't do a comprehensive analysis of TVC through simulation either computer or actual wind tunnel testing since you have no basis on how TVC and air fluidity will mix at various velocities.
Basically there are too many conflicting variables changing the results.

Good point. Due to that, the real-world result is more valuable than results on paper.

 

[Inst]

dingyibvs, do you have the exact RCS map of the F-22, F-35, PAK-FA, or J-20 on hand? It's somewhere in the NSA archives, I'm sure, but civvies don't have access to the quantitative material. As to canards vs LEVCONs, the qualitative argument is simple. Canards create discontinuities in the airframe, meaning that you will have to use RAM, radar transparent materials, or shaping to minimize its effect on RCS. LEVCONs are just a giant control surface; they are connected to the main wing.

 

[Inst]

Along with b787, I'm happy to say that we've gotten Engineer to admit that TVC does more than enable post-stall. The video he keeps on reposting is an argument about how post-stall is stupid, which is not entirely true; there are circumstances where post-stall is advantageous, like in a 1v1 where post-stall enables a sure kill. However, the point that is being made is that post-stall is not a be-all end-all, it simply bleeds too much energy.

I'll let b787 take over; I'm busy.

 

[b787]

Those are examples of what thrust-vectoring promised but didn't quite materialized in the real-world. Fact: F-22 engaged TVC, F-22 lost dog fight. Fact: Su-30MKI engaged TVC, SU-30MKI lost dog fight. See the following talk about lesson learned from F-22 and Su-30MKI in exercises.


This is why fighter aircraft is not built based on studies of CFD alone, but include wind-tunnel testings and some half a decade of test flight. Even after the aircraft is introduced into service, there is on going tactic development.

good try but already has been proven on aircraft flying, not computer models that turn rates are enhanced

Introduction
Thrust vectoring technology has been successfully demonstrated on several previous programs to provide tactical maneuvering advantages in the very slow speed, very high angle-of-attack (AOA) flight regime

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The YF-22 was a technology demonstrator and prototype of the F-22 Raptor aircraft. The aircraft had the capability to switch its TVC on and off from within the cockpit. An experiment was undertaken to measure the STR at a supersonic flight condition, without TVC. The STR was then flown at the same flight condition, but this time with TVC switched on. It was found that the YF-22 had an increased supersonic STR when using TVC[5]


5. Barham R.W., “Thrust Vector Aided Manoeuvring of the YF-22 Advanced Tactical Fighter Prototype”, Paper Number 5, AGARD Meeting on “Technologies for Highly Manoeuvrable Aircraft”, October 1993.

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[Engineer]

As to canards vs LEVCONs, the qualitative argument is simple. Canards create discontinuities in the airframe, meaning that you will have to use RAM, radar transparent materials, or shaping to minimize its effect on RCS. LEVCONs are just a giant control surface; they are connected to the main wing.

LEVCON introduces discontinuity to aircraft's structure too. How else do you think they can move?

Along with b787, I'm happy to say that we've gotten Engineer to admit that TVC does more than enable post-stall. The video he keeps on reposting is an argument about how post-stall is stupid, which is not entirely true; there are circumstances where post-stall is advantageous, like in a 1v1 where post-stall enables a sure kill. However, the point that is being made is that post-stall is not a be-all end-all, it simply bleeds too much energy.

I'll let b787 take over; I'm busy.

That's like saying there is advantage to buying lottery when you are sure to win. The so call "advantage" isn't an advantage when it is almost never going to be exercised.

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Moreover, Thrust Vector operation requires the pilot to “create the opportunity” for its usage, spending valuable time in manoeuvring the aircraft to achieve a suitable condition and managing the activation of the Thrust Vector Control.

If you are “defensive” and your aircraft has Thrust Vectoring, you can possibly outturn your enemy, but that most likely won’t prove to be a great idea: an energy fighter like the Typhoon will conveniently “use the vertical” to retain energy and aggressively reposition for a missile or gun shot. Also the subsequent acceleration will be extremely time (and fuel) consuming, giving your opponent the opportunity to tail chase you for ever, exploiting all its short range weapon array.

If you are “neutral”, when typically vertical, rolling and flat scissors would accompany the progressive energy decay, similarly performing machines would remain closely entangled, negating the opportunity for Thrust Vector activation.

If you are “offensive”, probably stuck in a never ending “rate fight”, Thrust Vector could provide the opportunity for a couple of shots in close sequence. Make sure nobody is coming to you from the “support structure”, otherwise that could be also your last move.