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    S-70 "Okhotnik" UCAV

    flamming_python
    flamming_python

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    Post  flamming_python on Sun Mar 03, 2019 5:42 pm

    Another amateur aerodynamics expert here

    The problem I see with using TVC to correct for unneeded lift is that it's only one engine/nozzle, and one that's exactly inline with the longitudinal axis of the aircraft. A lot of force will be generated on afterburner and with a downward momentum, and under such conditions even a slight bit of turbulence underneath one of the wings can cause the aircraft to roll to one side because such an arrangement is not stable. And afterwards the UAV will careen out of control in a big spiral, as the TVC nozzle will still be inclined downwards, causing massive stress to the airframe.

    You'd want at least 2 engines with TVC side-by-side, with enough of a gap between them to provide stability. Same arrangement as the moving tail surfaces on either side of the engine(s) on normal supersonic aircraft.
    marcellogo
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    Post  marcellogo on Sun Mar 03, 2019 11:45 pm

    flamming_python wrote:Another amateur aerodynamics expert here

    The problem I see with using TVC to correct for unneeded lift is that it's only one engine/nozzle, and one that's exactly inline with the longitudinal axis of the aircraft. A lot of force will be generated on afterburner and with a downward momentum, and under such conditions even a slight bit of turbulence underneath one of the wings can cause the aircraft to roll to one side because such an arrangement is not stable. And afterwards the UAV will careen out of control in a big spiral, as the TVC nozzle will still be inclined downwards, causing massive stress to the airframe.

    You'd want at least 2 engines with TVC side-by-side, with enough of a gap between them to provide stability. Same arrangement as the moving tail surfaces on either side of the engine(s) on normal supersonic aircraft.

    I would call your post an absolutely needed callback to realism, _python.


    I don't know if it possible to overcome all-wing transonic limit thank to TVC and I am even less secure if it would end up to be advantageous (I mean: if it would limit into attaining a max speed of 1.2/1.3 doubling the cost and development time, no thanks).

    Even in the best scenario it would be a very difficult task dunno but if someone could EVER get trough it, I'll bet on Sukhoi! unshaven
    In any case let's give a cut to all unsubstantiated speculations and wait almost until its first take off or, even better, until they shown up a second, more refined prototype.
    GarryB
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    Post  GarryB on Mon Mar 04, 2019 5:28 am

    TVC is actually a good thing for a flying wing... if you have any familiarity with boats the angle of the propeller in a small boat is critical... when you start off it is angled down to lift the boat out of the water... once at speed and riding on the water you change the angle of the propeller because it not longer needs to lift the boat... the speed of the boat will hold it out of the water, so once you get up to speed you angle the propeller again so that it directs the thrust backwards which increases the speed of the boat because no energy is wasted trying to lift it any more.

    With a modern flying wing it should have surfaces on the leading edge and trailing edge to change its level of lift... max lift for takeoff and landing, while minimum drag low lift for very high speed flight.

    At different speeds different angles of thrust will improve performance and reduce drag.

    At very high speed having the control surfaces in neutral means less drag but changing the angle of attack of the wing surface can also reduce drag too and a TVC engine should allow the aircraft to do that without adding the drag of a control surface deflection.

    (Note the thrust angle is called trim...)

    The problem I see with using TVC to correct for unneeded lift is that it's only one engine/nozzle, and one that's exactly inline with the longitudinal axis of the aircraft. A lot of force will be generated on afterburner and with a downward momentum, and under such conditions even a slight bit of turbulence underneath one of the wings can cause the aircraft to roll to one side because such an arrangement is not stable. And afterwards the UAV will careen out of control in a big spiral, as the TVC nozzle will still be inclined downwards, causing massive stress to the airframe.

    The control surfaces on the wing still work and could keep the wing level... a single TVC nozzle really just changes the angle of attack of the engine thrust and can be used to pitch the nose up or down or yaw it left or right. With just one TVC nozzle the only thing it cant do is roll around its central axis which is critical for a dogfighter in a dogfight in a superstall with no airflow over the wings, but a near supersonic flying wing would have enormous roll control using its wing mounted control surfaces...

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