Disclaimer: my degree is in computer science, I only walk through the aerospace engineering department on they way to my driving simulator lab. :-)
Jon S. Berndt wrote: >> Also note that if your left wing is dropping due to being on the edge of >> a stall and you try to compensate with right aileron, >> > > "Right aileron" as in trying to roll to the right? > Yes, that's what I meant. > Left aileron TED follows from right aileron TEU. The pilot causes the left > aileron TED movement. I'm not sure what you mean. > TED = trailing edge down? By "right aileron" I mean turning the wheel to the right and commanding the aircraft to roll right. >> This effectively increases the angle of attack a bit >> > > Why? I'm trying to picture the mechanics of that and can't quite. Seems to > me like deflecting the left aileron down would cause the airflow to deflect > down and reduce the angle of attack - all other things remaining constant. > The hinge moment might also tend to reduce the angle of incidence of the > outer length of the wing, thus reducing alpha. > I'm probably mixing up my terms here. Imagine some cross section of the wing (ie. airfoil.) This could be some complex shape, especially if it includes the aileron in a deflected state. To compute wing incidence at that cross section, you need to come up with some sort of "average" zero incidence line fit through the airfoil shape. There's probably a name for that and an official way to determine this zero incidence line. If you look at the cross section of the wing (through a point that includes the aileron) when you deflect the aileron down (TED), you are increasing the angle of that "average" zero incidence line relative to the wind stream. If you deflect the aileron up (TEU) you are reducing the average incidence of that section of the wing. So now, take an airplane that is flying at a high angle of attack where the wing is struggling to stay ahead of a stall. Now deflect one aileron down (TED). You have just slightly (or perhaps more than slightly) increased the incidence of the wing across the area covered by the aileron. All other things remaining equal which it will be in the short term, you have just increased the aoa on a portion of your wing, and if you are riding the edge already, it might be just enough to push you over into a snap roll. Maybe said a different way, imagine your wing is riding on the edge of the amount of air it can push down without stalling. Now you deflect the aileron down and try to push the air down even more. For what it's worth, I experienced this first hand in my Piper Cub (R/C) model (so I was safely on the ground.) I was attempting to do a loop, but in retrospect I started too low and too slow. I got really slow over the top and due to my low altitude, I tried to tighten up the backside of the loop on the way down by feeding in some additional elevator. But the cub snapped hard on me. I released the elevator and got some speed and then pulled back again to avoid the ground and she started to snap again. But I somehow managed to find some sort of middle ground with the elevator to keep pulling out of the dive while maintaining just enough aileron authority to somehow save it. Both wing tips were literally inches from the ground at various points in the manuever and I was still flying right on the ragged edge of the stall. I was one tremble short of another full snap roll. The spectators claimed that ground effect saved me. :-) Somehow in the end I was back flying with no vegetation in the gear or wing tips. WHEW! BUT! Had I known then what I know now and steered with the rudder rather than the ailerons, it probably wouldn't have been nearly such a close call. Curt. -- Curtis Olson http://www.flightgear.org/~curt HumanFIRST Program http://www.humanfirst.umn.edu/ FlightGear Project http://www.flightgear.org Unique text: 2f585eeea02e2c79d7b1d8c4963bae2d _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
