Originally Posted by
yoko1
BTW, there if no "if" about the g-forces. They are included in the published FDR data. The aircraft registered nearly negative 2 g's near the end of the flight. If the pilots had not been strapped in, they surely would have hit the ceiling. At a minimum, the Captain lost some leverage against the yoke as he was attempting to pull back.
You have to keep in mind that in this flight region beyond Vmo, the aircraft would be reacting very differently than normal to control inputs. There were already plenty of signs that the ET302 Captain was not particularly comfortable with hand flying, and that was with an aircraft within the flight envelope. If you've ever been an instructor pilot and seen a student pilot make very tentative control inputs because they are nervous about what will happen, then that's the closest example I could give of why the Captain was not more assertive with making the necessary trim adjustments.
The recorded g is measured at a station near the mid section of the wing. Under either negative or positive accelerations other than 1g, the flightdeck load experienced can be much greater in either sense than recorded. Conventional simulators are limited in achieving the forces experienced under pitching conditions. Where the pitching rate is high, the difference can be noticeable. The vibration at the cockpit can be very noticeable as well, it may be low amplitude but can uncage your eyeballs.
At high MACH there is a tendency to a pitch down coming from the development of normal shock on the underside of the wing.which reduces lift, and that results in a flightpath that tends to reduce towards a ballistic path. case is odd, the lift being reduced. The pitch trim case mitigates the pitch change to an extent but the nose still lowers unless AoA is increased to recover CL. The Cp doesn't move much, the moment reduces but the flightpath degrades, lift is greatly reduced for a given AoA. Increasing pitch gets towards buffet boundary, but increase in AoA reduces the lower normal shock.. If you are closed loop, the crew notice an increase in backforce to maintain level flight, but if you are open loop or at a control limit, then the nose will drop until MACH number starts to reduce with increasing temperature. Both of these cases however did not get into compressibility issues, these effects occur well beyond MMO, but are noticeable before Md.
If the above doesn't gel with AP3456A, or AFNA etc, I was surprised by the hi res DES/LES 3D study of the wing. I expected to see a Cp shift rearwards, was not expecting a collapse of CL. Where stab and elevator maintain the authority to increase AoA, the effect is not overly dramatic. If you are open loop, it is much more eventful.
Enough of that.