Originally posted by Pooface
HT, could you possibly explain what the buffet does? if i was flying flaps out just over the buffet speed and AoA, and then crossed the envelope, and went full stick back, which would turn me tighter/faster? would be very useful to know i think
I'm not sure if HT will respond, but I can explain that for you, and my apologies if this is a bit lengthy.
You have basically asked two questions, what the buffet does, and what would happen if you were just above the stall/buffet speed, and then used aft stick to increase the angle of attack into post stall flight.
Before I answer those questions, I should say a few words about the stall, just to make sure we are on the same page. Normally, the amount of lift generated by a wing is directly proportional to the angle of attack, that is they vary linearly with respect to each other. That means that if you were to plot lift against angle of attack, the graph would be a straight line. However, as the angle of attack increases, there is a point where the lift begins to fall off and that is known as stalling. That corresponds to the point where the angle of attack has increased to the point that the air flow around the wing can no longer follow the shape of the wing and begins to separate from it, forming a turbulent wake that starts near the trailing edge of the wing. It can happen gradually, or sharply depending on the profile and geometry of the wing. For examples of wing geometry, with a rectangular wing the air begins to separate near the trailing edge at the root first, so the aircraft suffers root stall, which is desirable because if the wing stalls near the root first the ailerons remain effective longer. With an elliptical wing the air separates more evenly along the trailing edge of the whole wing so there is only little advance warning of a complete stall. Most WWII aircraft have a wing taper approximately equivalent to that of elliptical wings. Wings with more taper than that tend to stall near the tips first and that is very undesirable because it promotes lateral instability. These affects can be modified with twist, washout, camber and the use of different wing sections along the span. The profile of the wing is also important, and sharper leading edges tend to result in abrupt stalls, while larger more rounded leading edges stall less abruptly. That is why trainer aircraft have fairly round leading edges, and that often causes problems when pilots convert to real fighters, because they are often surprised when their aircraft stalls with much less warning than they are used to.
The reason for the loss of lift, and stall is due to the separation I mentioned earlier. Normally it starts near the trailing edge of the wing and moves forward as the stall becomes deeper creating a turbulent wake. It is that turbulent flow impinging on the aft portions of the fuselage and on the empennage that cause the buffet and the sound that pilots in WWII called the burble. The turbulent wake is significant because not only is lift lost in stalling, but the turbulent flow over the control surfaces at the wing and tail reduce the control effectiveness/power, which is one of the reasons for a high rudder at the tail, to ensure lateral control at high angles of attack.
Now to answer your first question. The buffet and associated noise are both characteristics that are symptomatic of the stall, they don't do anything themselves, other than make gunnery a little more erratic. If you had asked what does the stall do, the answer would be that stalling reduces lift, increases drag and causes buffeting and noise due to the turbulent wake.
The point is that while the buffeting is new, the stall has always been there, and the buffeting doesn't add anything new other than the movement and sound you hear on the screen, the aerodynamics of the stall are the same as they always were, it is just that now you have a much better indication of when the stall occurs.
To answer your second question, if you continue to pull aft stick once you reach the stall, you will lose lift and gain drag, and that means that you lose the ability to turn as well, and when you are outside the envelope, you risk departure from controlled flight. But those effects are caused by the stall not by the buffet, and that has not changed, the buffet just warns you when it is about to happen.
i think the reason it makes such a difference is because it is so instant. im sure it would be better if it faded in just a little, so we had a little warning.
You do get a warning, the volume of the stall horn increases gradually up to the stall when the aircraft begins to buffet, or burble, as they called it in WWII. Ideally, you should approach the stall gently, so that you don't overshoot and lose lift. In the past, the stall horn did exactly the same job as it does now, but you had no clear indication of when you had stalled until you noticed the lateral instability, that is the tendency to drop a wing and enter a spin, or the loss of lift and nose down pitch stability and by then it was already too late.
That's why some folk complained, because their aircraft was dropping a wing, or spinning with out any warning, now the warning is there, as HT always intended it would be. I already notice that the buffet and associated sound are already helping folk to avoid that and flying aircraft that had a tendency towards lateral instability is now easier.
Lastly, I just want to add, that all this is not directly related to other changes we are noticing in the flight model, the differences in the P-38 with full flaps, for example. Those things are being caused by changes in the flap and thrust modelling that have had an influence on the excess power available in the low speed region of the envelope. So if you notice that the spitfire behaves differently at low speed, it isn't because the buffet is doing anything that wasn't happening before, it is because the flap and thrust modelling has changed.
I will be producing EM diagrams for the new flight model and overlaying them to discover what impact the changes have had on dissimilar air combat, particularly for the aircraft where there is an obvious difference, and I'll pass on the diagrams and conclusions as I produce them.
Hope that helps...
Badboy
