Aerodynamics Question

[Timebuilder]

Profile, since you, Avbug, and skiddriver have much more experience and understanding than I do, let me comment from the position of a relative layman.

Perhaps the nose-up attitude mentioned by profile isn't being addressed. Is this attitude considered to be during the pitching moment, before a stable pitch attitude has been reestablished, and thus in a state of constant change? If not, if the pitch angle is stable, how does this affect a rate of roll, or the ascent or descent of a wing which is holding a constant bank angle?

Aside from the peculiarities of different examples of "same model" airplanes as mentioned by Avbug, I was taught that other things being equal (rigging, repairs, fuel tanks) the coordination of the airplane is the major factor that effects a differing critical angle of attack, and determines which wing will drop in a stall while in turning or straight and level flight.

I welcome all of the insights of threads like this. I like to learn, especially if I have believed something that is just plain wrong!!

 

[avbug]

I'm certainly not going to argue with Pete Reynolds, who probably knows more about Lear fringe charactaristics than anyone else alive. However, I will state without question that dutch roll can be stopped with aileron alone, rudder alone, or a combination of the two, including high altitude cruise.

Very often, applying very light rudder control crossed with very light aileron control will steady the airplane, and then gently releasing the control inputs will return the airplane to steady flight.

I had some simulator scientist a few days ago tell me that the airplane is uncontrollable at high altitude cruise without the yaw damper, because a flight safety instructor had shown this to him in the sim. Hogwash. He told me about the dutch roll that takes over and becomes uncontrollable. Perhaps this can be replicated in the sim, but it doesn't duplicate the airplane in flight. The airplane is eminently controllable.

Think about it...following a yaw damper failure, you can let the airplane fly you, or you can fly the airplane. You can do this by applying basic control inputs to make the airplane do what you want. If you want to be a bonehead, you can let yourself get behind the airplane. I have been in the airplane, and watched an individual roll it right over after entering a pilot induced series of divergent osciallations in dutch roll that resulted in his complete loss of control. It can happen. The individual who did that was an idiot, however.

All that aside, I have a good idea of whence I speak, because I maintain currency in the airplane. How about you?

 

[ksu_aviator]

I'm going to agree with AVBUG on this one. He explained it perfectly, I'm just going to offer another view.

The college I went to had a former Royal Air Force, Tornado Pilot as the department head. I remember very specifically him describing stalls as a manuever they used. They would roll into a 90 deg AOB and pull back until the aircraft stalled, if it was cordinated the aircraft would stall parallel to the ground in the exact same manner as an aircraft that was doing a normal straight ahead stall. Neither wing would "dip" or "break" first. He went on to explain that no matter what attitude the aircraft was in that you could recover simply by "pushing forward" or decreasing the angle of attack. Cordinated flight is the key to whether or not a wing stalls first. Also, remember that airspeed has nothing to do with whether or not you are stalled. The AoA is the only factor. Indicated stall speed will vary with weight, etc.

Ok, not as eligant as AVBUG's post, but maybe it will shed some light.

 

[profile]

Actually I find that I agree with most of that last Avbug post.

As for the stall, yes, if your nose in on the horizon at 90 degrees you won't have it break off to one side. The issue is that when the nose is up at at some angle to the horizon the nature of the turn becomes a roll. Take a model airplane and pitch it up, then make it turn, you will see that it is actually rolling as well, the more the nose is up (or down) the more pronounced the effect, until when you get into a vertical climb you are only rolling.

 

[Mickey]

Keep in mind that a lot of trainers are so stable that you need to keep in a lot of aileron to maintain a bank would would cause the raised wing to have a higher AOA due to the lowered aileron at that section of the wing. My $0.02 Have fun.