i was under the impression from way back when that the main purpose of TVC was to help with high-altitude high-speed maneuvering because the air is too thin at 60k+ for the control surfaces to be very effective
No there is a code one article – with Paul Metz – if I recall correctly. That stated the TVC is not used in the supersonic regime – for a turn. I also believe Dozer confirmed this at fencecheck. However this is still classified material – but at high high altitudes the F-22s TVC might indeed be used in a manner to help the control surfaces change the jets angle of attack – the control surfaces are totally sufficient at doing this down in thicker air – but way up at say 60k foot +, the TVC might indeed be used to quicken the process of AoA change – perhaps even at supersonic speeds. But the wing still turns the jet at those altitudes. So as I have said previously – it has some utility up there. But it is at the very edge of the jets envelope. I doubt an F-22 supercruising at 36k is going to engage TVC in a “crank”.
I was actually referring to the angle (a’) between thrust vector (t) and its velocity component (v).
Ahhh, ok, I see what you are saying now. You had me confused because you used the term “velocity vector”. Which is indeed as I have explained it earlier. That “v” is represented by the component of “horizontal thrust” but not the “velocity vector”.
So you are saying if we canted the jets thrust with TVC “t” – to make it parallel with “v” – the horizontal thrust component. We could combat the form drag (brown) drag of the jet – fully (as in all of the thrust is directed against the form drag) – and inturn raise the lift of the jet. The answer to that I think is no – due to the fact that all this will be doing is increasing the alpha/AoA of the jet that the canard is maintaining. So all this does as a result is increase the form drag and increase the vortex induced drag. Thus slowing the jet down – therefore decreasing lift and as such turn ability. There is no need really to do this as the control surfaces in 95% of the flight regimes it will be used in have enough authority on any Fighter Jet to maintain the best AoAs to induce the jets maximum turn rate.
If an advanced FBW were to be used where it uses the canard and the TVC to achieve a perfect balance – where the canard is used less – say to a lower angle – therefore resulting in less drag – and the TVC is as such pointed in the direction of the “horizontal thrust vector” to maintain the AoA needed for a specific turn. Then yes it has a benefit of dropping control surface drag and fully counteracting the form drag of the jet – without increasing the jets overall AoA and therefore overall drag. HOWEVER – this in the case of the Typhoon would probably only give it a 5 % or less thrust advantage in its best sustained turn – and that is probably being overly optimistic – for the fluid mechanics of the nozzle at the deflected angle would most likely result in a total thrust drop of more than 5% thrust due to the draggier geometry inteference – with perhaps some small control surface drag advantage – which is unclear aswell, as the deflected TVC nozzles + canard deflection might actually increase the overall drag. While this method can’t be used in a vertical loop as it drops thrust performance vs gravity. So pretty much zero utility in my opinion – not worth the effort + extra weight + complexity and hence why I don’t think this is actually used.
It should be noted the Typhoons canards are not used to make the aircraft pitch up quite the reverse.
The airframe is unstable and really wants to pitch up very fast indeed all the time, the canards are continually fighting this tendency with tiny movements.
If a rapid pitch up is commanded by the pilot then the canards take a break of a few milliseconds and the aircraft pitches up rapidly, the FCS then commands the canards to arrest the pitch at a level that doesn’t stress the airframe.
You can actually see the canards pointing downwards against the loop which is counter intuitive to the way normal canards behave.:eek:
Cheers
This is all pretty much semantics as I have said before – they are still the surfaces that control the pitching moment about the jet. Whether they do the work or merely temper it is irrelavent. The fact that the EF wants to pitch up naturally is testement to the fact that the canards are negative lift surfaces – in the subsonic regime – as shown in the diagram. While in the supersonic regime they become positive lift surfaces and actually do the work.
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The basic idea is that the canards will increase AoA up to maximum possible and then instead of relaxing to keep AoA steady, the TVC would compensate increasing overall lift. Why is this impossible, can you pls elaborate?
Your second paragraph, though, was more than clear.
It is perfectly understandable that the wing is much more efficient in producing lift, than TVC, except possibly from the extreme ends of the flight envelope.
Having that in mind, is it possible to do the exact opposite?
That is, inside a sustained turn, the TVC could keep thrust parallel to the velocity vector, thus increasing this effect?
Ok to explain what you ask in your first paragraph… I have attempted to model a pretty poor Eurofighter in paint – as it turns. In this model we assume it makes a 360 degree loop from straight and level flight – as it simplifies the explanation and applies to a banked turn aswell.
Explanation to follow.
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