Hi Bob,

Recently, I reviewed the book, finding a new question that I asked several days before. It is the theory that abrupt up-elevator input can cause the stalling angle to be exceeded at almost any speed. I have tried in a simulator that is X-plane. I know that someone said this was just entertainment simulator, but in my option it is quite 'serious' simulator because it has received certification from FAA for use in logging hours towards flight experience and ratings as long as you get the corresponding hardware and access to pro software level.

Anyway, return to the subject. For proving that theory, I tried in C152 in this simulator, but no matter how to perform, either high speed or low speed, I could not make the stall happen when aircraft was diving, input abrupt pull-up. The only result was making a loop like aerobatics.

After that, I was thinking to try different aircraft to see how it goes. If still not happen, I might just give up on this simulator. I tried on C172. It happened, just like what is said in the book.

So now I am rethinking this theory. Wanna ask you if this theory could happen in all aircrafts? I mean, for example, C172 is much heavier than C152(I checked both manuals); maybe it only happen on heavy aircrafts; it is less possible to happen on light aircrafts? I also found this in Wikipedia, "A dive bomber dives at a steep angle, normally between 45 and 90 degrees, and thus requires an abrupt pull-up after dropping its bombs. This puts great strains on both pilot and aircraft. It demands an aircraft of strong construction, with some means to slow its dive. This limited the class to light bomber designs with ordnance loads in the range of 1,000 lb (450 kg) although there were larger examples."

So could you explain little bit to me, please?

Appreciate

Chao

There's really quite a lot that can be said about this. Firstly, I'm not surprised that you find it difficult or impossible to produce the effect in a simulator. The most important element at play is inertia. The fact that the aircraft tends to keep moving along its original flight path after the abrupt pitch-up occurs. This inertia effect would not be a high priority in the software design. Also it is not only the weight of the aircraft that contributes, it is also wing design and in particular the wing area. Aircraft with small wings compared to their weight (high wing loading) are much more prone to high speed stalls. For example it is very difficult to observe the effect in a Tiger Moth because the biplane configuration results in a very large wing area compared to weight (low wing loading).

Many aerobatic aircraft such as the old Victa Air Tourer, the CT4 ex-military trainer, the Cessna 152 Aerobat and almost all advanced aerobatic aircraft, will readily stall in response to abrupt up-elevator input. In fact that is a desirable characteristic since some more advanced aerobatic manoeuvres such as snap rolls, require the pilot to induce a high speed stall prior to entry. The degree of elevator deflection and therefore the rate of pitch varies from aircraft to aircraft as well. So it depends on just where the designer as placed the elevator control stops. For structural reasons, high speed stalls should only be attempted at speeds below Va (see the aircraft's flight manual).

I suggest you find an aerobatic instructor, go for a flight and have him/her demonstrate some snap rolls. It's a fun way to learn.

Another reminder is that when an aircraft is in a stalled condition, it is "still flying" and may produce enough lift to recover from the dive. If your aircraft was in a co-ordinated balanced condition (it isn't sideslipping and doesn't have any major rolling effect) with a symmetrical aerodynamic body, it shouldn't spin.

To test this out, try moving the rudder a bit to the side when you do that test, if you put enough it should have a wingdrop which may result in a spin.

"Stick and Rudder" (the 1945-ish book) actually makes a reference to this behaviour, in the fact you should be able to stall and float the plane down without spinning out by applying just enough rudder to oppose any turbulence that may shift your aircraft off balance, and correct that balance, resulting in a leaf-like descent.

.. but keep in mind that the real Va for the day and the design load factors come into play. If you are significantly above Va, and pull a heap of positive g, you will rip the wings (or possibly the tailplane) off prior to stalling. Below Va you should stall prior to doing any structural harm .. one of the definition aspects of Va

Another reminder is that when an aircraft is in a stalled condition, it is "still flying" and may produce enough lift to recover from the dive Do you have an authoritative reference for that one ? I think not.