Interesting questions from a thread at AVSIM...

  • At altitude at the stable maximum speed, a very gentle 2 degree pitch down (-4000 fpm on autopilot) results in a buffet free smooth acceleration past the 'sound barrier', reaching a remarkable Mach 1.19. This is with a simple fuselage, a wing aerofoil section previously used in the 1940s North American P-51 and a tiny engine derived from a remote control target drone. This is a performance which would have delighted the team initially trying to develop the Convair F-102 delta winged supersonic interceptor in the 1950s. The Aermacchi is simpler and cheaper than the Alpha Jet trainer and the Alpha Jet will never go supersonic. The stability and controlibility in the transonic transition requires considered and dedicated aeroengineering which certainly was never considered in the case of the Aermacchi. I do not mind this as if I try a vertical power dive in an Aerofly Aermacchi I can make it more authentic by just pulling back the throttle.

  • Ok, I think see your point "Overloaded"...


    Same applies to the present damage model, and lack of accelerated stall when you pull out of one of those dives, at 600+ KIAS, by pulling all the way back on your stick...


    Other aircraft exhibit a more plausible bahavior though, so I think / hope it can be fine tuned.


    And I can think of many more details to ask for, when the product achieves more stability and nears release, such as fine tuning of conventional, turboprop and jet engines, etc...


    I really haven't even tried to figure out how engine modeling is presently done.

    1983 ......……....2012.…………….......2018...

    fs1 ===>     MS FLIGHT ===>   WT 1.83

    Start ... Hope ... Realization ...

  • I can just give the MB339 higher drag on the fuselage to slow it down. I had a version that was stalling much faster but it wasn't really easy to fly corners anymore. If I just decrease the stall angle for the airfoils it should be much harder to fly. Also I could reduce the lift in the stall, that would make the wing drop much stronger.


    The thing you call accelerated stall doesn't exists :p
    You can stall at any airspeed, in fact the stall point is defined at the angle of attack at which the flow seperates and not the stall speed. That is angle constant (for high enough Reynolds numbers and reasonable Mach-numbers). The speed at which the airplane stalls can be calculated when you know the stall angle and the lift force that you are trying to achieve. But the stall itself still comes at the same angle of attack, therfor there isn't a difference in the physics here, its the same stall when you pull more g's as if you make your airplane heavier... What does change with higher speeds are higher pressure differences and greater forces acting. Hence an "accelerated stall" will be quicker because the intertia of the aircraft remains constant (apart from fuel mass).


    So what you are saying is that the airplane doesn't really drop a wing in the stall, that is a correct observation :-)
    And yes the wings of the aermacchi should be braking off when you do 600+ kias and full up elevator :D
    Or elevator and/or aileron could show flutter at higher than design speeds...


    Cheers,
    Jan

  • Jan,


    thx for your thoughts :-) and I do know what stalls and, "accelerated stalls" ( indeed ... ) are... Been fying for more than 36 yrs... and I'm very interested in aerodynamics, even if I am not an aeronautical engineer :-)


    I believe the Aermachi can be fine tuned indeed, and the approaches you suggest look interesting.


    Really have to read your Wiki page - lot's of info there.


    And... since you mention flutter, I got the idea it was modeled in Aerofly FS 1, at least in the Swift ? Can it happen in Aerofly FS 2 ?

    1983 ......……....2012.…………….......2018...

    fs1 ===>     MS FLIGHT ===>   WT 1.83

    Start ... Hope ... Realization ...

  • The P-38 doesn't Mach tuck and the Aermacchi behaves like an area ruled razor blade winged 1950s trans-sonic X plane. Does it really matter though?


    Well, if AeroflyFS wants to aim at the (let's call it) "complex flight simulator" market, implementing Mach effect is necessary to accurately model subsonic and supersonic aircrafts.


    Mach effects include multiple aspects:


    Parasite drag increase (Mach drag rise);
    Compressibility effects on indicated airspeed;
    Increase in lift slope;
    Aft shift in center of pressure (Mach tuck / trim changes);
    Decrease in max Cl (Mach buffet -> Coffin corner);
    In some cases, variation of flight controls effectiveness;


    Most of this are necessary to accurately model airliners or supersonic aircrafts, if they are to be considered "study aircrafts".


    Mach "physics" is something we will consider in the future. We already bugged our main physics developer to add support for this. Wouldn't it be great one day to fly with the Concord in Aerofly FS?


    That's great news! I hope it's high in the priority list. Of course, as I explained above, it's necessary not only for the accurate modeling of supersonic aircrafts, but also airliners. :)