J-15 carrier-borne fighter thread

[Blitzo]

Yano guys, it could just be that launching with MTOW from a ski ramp is impractical, and thus operationally untenable.

Oh, I don't disagree, but that is why I've been trying to use the phrase "heavily loaded" instead. That is to say, I expect that the safe operationally viable max take off weight of a fighter from a ski jump compared to a catapult under all possible operational conditions is probably lower, but the question is how much lower it is, and under which operational conditions, and also depends on how often those operational conditions are likely to occur.

 

[Blitzo]

A link to those charts and figures would be nice. Also are we talking control environment or real world application?

I think he's talking about these charts -- I deliberately saved these onto my hard drive a few years ago because they kept getting brought up when we talked about take off weight of fighters from ski jumps.

 

[Blitzo]

Continued....

 

[snake65]

Link. I don't know Russian and can't find the Russian version.


Obviously, when Soviets did their tests, Kuznetsov was new and so was everything else. And of course, launch weight depends on the weather conditions at the time, as well as the launch position.

Not only the Soviets have done their tests

 

[snake65]

Not only the Soviets have done their tests

Even Spanish

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[delft]

I haven't yet read the Spanish paper but I saw it didn't consider the take off with engine failure.
With engine failure the acceleration will be much less and so will be the speed at the end of the ski ramp. If you are taking off with MTOW for the circumstances you will calculate with engine failure at the moment of release, drop the external stores one second after leaving the ramp and let the aircraft accelerate in the air at low AoA so that the aircraft will not end up in the drink. If you take an aircraft characteristic and an engine characteristic, chose an ambient atmosphere and wind speed and a ship with a ski ramp at some chosen speed it is not difficult to simulate take off with and without engine failure at several take off weights.

If you build an EM cat in the ski ramp it can compensate for the engine failure up to the aircraft leaving the ramp so if you found some speed with engine failure to be sufficient to take off safely under the worst design circumstances you can choose that speed to be the design speed for the cat and you can calculate the cat length from the acceptable acceleration. Design all other aircraft you want to use with the cat to need no more than that length. The propeller aircraft are of course needing a lower speed and so accept a lower acceleration.

 

[delft]

Btw The energy to be provided to and by a ski ramp cat is much lower than for a flat cat and the space needed is also smaller so such an installation is more suitable for a smaller flattop than the steam cats that are functioning so well in the large US carriers.

 

[kwaigonegin]

No Kwaig, it is the way to launch aircraft at a low AoA and so with a low induced drag. It enables you to launch at a low speed compared with using a cat because the aircraft doesn't need flying speed when it leaves the ramp as it can accelerate further in the air. It needs adequate control of course.

Low speed is still a crutch in skip ramp launches which directly affect lift and TOW afterall isn't that's what we are talking about here... can the Flankers launch off the skip ramp with maximum combat load? I thought the entire argument isn't about the launching of aircraft but about how much weight the lift coeficient can be for non vertical thrust takeoffs.

• g - Gravity
• T - Thrust adjusted according to α - AoA to air speed V direction
• L - Lift = Lcoef * V2 - perpendicular to the air speed - V
  Note: Lcoef is calculated under assumption that engines are at maximal thrust giving some vertical lift, i.e.:
  g = Lcoef * V2req + T*sin(α)
• D - Drag = Lift / (Lift-to-Drag ratio) in the opposite direction of the air speed V

 

[delft]

Low speed is still a crutch in skip ramp launches which directly affect lift and TOW afterall isn't that's what we are talking about here... can the Flankers launch off the skip ramp with maximum combat load? I thought the entire argument isn't about the launching of aircraft but about how much weight the lift coeficient can be for non vertical thrust takeoffs.

• g - Gravity
• T - Thrust adjusted according to α - AoA to air speed V direction
• L - Lift = Lcoef * V2 - perpendicular to the air speed - V
  Note: Lcoef is calculated under assumption that engines are at maximal thrust giving some vertical lift, i.e.:
  g = Lcoef * V2req + T*sin(α)
• D - Drag = Lift / (Lift-to-Drag ratio) in the opposite direction of the air speed V

These matter were discussed, pretty summarily, in a lecture series about STOL and VTOL aircraft during my study some forty years ago, long before Adm. K. was built. The lecturer spend about a half hour on the ski ramp. He said that you would naturally build airfields with these ramps if you could depend on the wind always blowing from the same direction.
The contribution of engine thrust to lift will be important even after the failure of one engine. You would then optimize the angle of attack and so lift and acceleration to achieve flying speed at a safe altitude. I suppose some of the pictures reproduced a few posts back show the flight altitude during such a take off with engine failure. A pity that I can't read Chinese. No video we have seen show such a take off.

 

[Engineer]

Low speed is still a crutch in skip ramp launches which directly affect lift and TOW afterall isn't that's what we are talking about here... can the Flankers launch off the skip ramp with maximum combat load? I thought the entire argument isn't about the launching of aircraft but about how much weight the lift coeficient can be for non vertical thrust takeoffs.

That guy thinks slow take off speed is a feature, not a bug. Hence why you were totally confused. His reasoning violates Laws of Conservation of Energy when you think about it.