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The behaviour described in a previous message as an "insipient spin" with
the ASH-25 seems to be a very simple early part of a stall. If ailerons are used close to the Stall AOA, they might seem to work in reverse, which is consistent with the description given in that message. This is due to the fact that in the pre-stall, you're already close to the Stall AOA. The lowering Aileron (to pick up the low wing) will produce an increase in the AOA in that part of the low wing, thus exceeding the Stall AOA and essencially stalling that part (where the aileron is) of the low wing. In other words : Pre-stall, left wing is low (for instance), right aileron will stall the left wing tip thus increasing the bank angle and going to a spiral, an apparent control reversal, easily corrected by : The correct control input, which is to apply right rudder to pick it up, and move the stick forward enough the reduce AOA. This is the reason why instructors teach all students to pick up a low wing during pre-stall by using Rudder (opposite rudder, for that matter), and not by using coordinated controls as it is suggested, because the aileron will work against the intended recovery. Even if the glider wing was designed with some twist to lower the AOI at the wingtips, they will still suffer from this reverse effect when in a pre-stall condition. All existing airplane and glider literature clearly recomends picking up a low wing with opposite rudder during pre-stall, along with lowering the nose. I have never seen a manual suggesting to pick up a low wing at the pre-stall with "coordinated controls", it would surprise me very much if the ASH-25 suggested something like that. What it may be suggesting is that you always use coordinated controls (the correct use) while thermalling, and if you sense the glider in a pre-stall condition, lower the nose slightly and use coordinated controls to continue the turn. I wrote about this before : While thermalling, if you feel an inpending stall, it may not be necessary to "dive like mad" to recover. It may be a simple case of lowering the nose only slightly and maybe applying some opposite rudder for a few seconds. If you do it calmly, other gliders in the same thermal won't even notice that you were about to stall. Again, any experienced instructor can demonstrate this. Happy flying. "Chris OCallaghan" wrote in message om... I've noted that many 25s have wing extended wing tips, some factory, some home built. The vertical stab was designed to some theoritical maximum... This would be yet another aggrevating factor. What fascinates me about these reports is the effect in the real world of the designer's tradeoff between stability and controlability. Bigger vertical stabs would reduce the likelihood of a spin, but at the cost of much drag. Less drag is better, but you don't want a sailplane so unstable that moderate turbulence can flick it into a spin from a low speed turn. So if you want to give it a good low speed roll rate, you have to depend on the pilot's proper use of the powerful rudder he'll need to counteract adverse yaw. But pilots are people, and we all make mistakes. So the conscientious designer must needs put enough surface area back there to prevent autorotation so long as the pilot neutralizes the controls at the first indication of an insipient stall. Even if the stall progesses, so long as the controls aren't crossed, it shouldn't lead to a spin. Little modern gliders seem to reflect this philosophy. As bigger gliders become more popular among lower time pilots, shouldn't we be examining their characteristics more carefully? While manuals give very precise instructions on how to recover from a fully developed spin, they recommend coordinated use of ailerons and rudder (accompanied by a forward motion of the stick) to pick up a dropping wing during the initial phase of a stall, straight ahead or turning. In other words, the designer is recommending picking up the low wing so long as it is accompanied by a "firm easing of the control stick forward." This procedure is recommended because it results in the minimum loss of height. We were all taught, thouigh, that if the wing begins drop during a stall, we neutralize the ailerons, ease the stick forward, and kick opposite rudder. Given the number (I counted 4) of over the top spin entries noted in another thread, I wonder if we haven't been to aggressive in preventing the "insipient spin" with spin recovery control motions. And as a result, misinterpret any yawing of the nose during a stall to be the preamble to a spin. I'm splitting hairs. And it's certainly not the stuff for students to be pondering. They need a one size fits all recovery. But I'm genuinely interested in just what is going on at the stall and immediately after, and if our perceptions haven't been altered by the necessity of the shortcuts we take during training to get us quickly to the point where we can go teach urselves. Robert Ehrlich wrote in message ... Chris OCallaghan wrote: This is an interesting case. I haven't really thought this through since stalling is difficult in most properly balanced sailplanes at high angles of bank. A long wingspan adds yet another aggrevator. But your speed is higher in a steep turn, thus the vertical stabilizer is more efficient. And right off hand I can think of several outcomes that would look like spins, but are, in fact, something else. Think of a wing over, for example. If you shot the initial 90 degrees of turn after apex, it would look very much like a spin entry. Nonetheless, I haven't tried a stall from a coordinated steep turn, with controls crossed and the yaw string straight. And I won't have a chance for another month or so... Perhaps, for the time being, I need to ammend my position to say that a spin is unlikely in most sailplanes if the ailerons and rudder are neutralized. In the meantime, if you have a chance to repeat, see if the instructor will let the "spin" develop. I'm interested to see if it is really a spin (I think the chances are good, though, if the controls stay crossed). Try it again, but at entry, center the ailerons and rudder, but leave the stick back. That is, add no further aggrevation after the stall break and see what it does. By the way, how rapid was the autorotation at stall break? How much change in direction did you experience before rolling back to level? How much altitude did you lose, if you took notice? And was there anything unusual about this particular 25? There was nothing unusual about this 25, only about myself. It was my first flight in the ship, I had a very low experience at this time ( 100 hours) and had only flown ASK21 and ASK23. This happened twice in the day at a low bank angle. There was almost no autorotation or change in direction. It was rather the feeling that increasing outside stick could no more counter the overbanking tendancy, but rather increased it, that made me realize that the inner wing was stalled and the I had to quickly release back pressure to avoid some mess, so nothing wrong happened before immediate recovery. My propension to low speed flight came from my familiarity with the ASK23 whose wing loading is much lower, and from the fact that it was a weak day where low speed rather than high bank angles helps to remain close to the core of thermals, at least in the ASK23 I was usually flying. It was my first attempt to make a flight longer than 5 hours, I felt it was better to try it first with an instructor behind me and in a glider in which this may be achieved even in unfavorable weather. This last point turned out to be true, all other gliders were in the hangars when we landed at the end of the day and the duration was effectively over 5 hours. However I had to wait another season before getting my silver duration, but this is another story. BTW I cannot try what you suggest since this 25 is no more in my club, nor any other club 25 (but 2 private ones) and the instructor in such a repeat attempt would probably be myself as I got this rating during last September. |
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