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#21
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How does this explain the behaviour of non-radio-controlled model
gloiders that return to level flight anytime? They are built perfectly symmetrical, have a smooth polar and no controls at all... They have a lot more dihedral or polyhedral to help them return to level flight. Interestingly, a well trimmed hand launch free flight glider will climb almost straight up, "flop" into a glide without stalling, and then start turning in a stable, constant circle. Great fun! Jim Vincent CFIG N483SZ illspam |
#22
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At 12:18 24 April 2004, Andreas Maurer wrote:
On Fri, 23 Apr 2004 20:14:02 GMT, 'Bill Daniels' wrote: A perfectly symmetrical glider with a perfectly smooth polar and frictionless controls SHOULD develop a spiral dive from a hands off turn. How does this explain the behaviour of non-radio-controlled model gloiders that return to level flight anytime? They are built perfectly symmetrical, have a smooth polar and no controls at all... Bye Andreas My hand-launced gliders are built with crossed controls, which produces this effect. A slight amount of rudder into the turn keeps it going. A slight amount of opposite aileron keeps it from overbanking. A slight amount of up elevator lifts the nose. Just enough weight on the nose keeps it from making phugoids. Just enough dihedral helps it right itself. It is not the most effective climbing setup possible, but it produces stability much like a sailboat with the tiller down, the main sheet slack, and the jib tied across to the opposite side. It requires experimentation to get it right and they have to be built for a left-handed or right-handed person. It must turn to the left for a right-hander and vice versa. |
#23
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"Bill Daniels" wrote in message news:eOeic.21511$GR.2890579@attbi_s01...
The aerodynamics of this are interesting. I was taught (and that was long enough ago for it to have passed from fashion, apparently) that shallow, medium, and steeply banked turns were defined by the control inputs required to maintain them, to which the actual angles of bank are merely incidental. Shallow turns require pro-turn aileron to maintain the angle of bank. Steep turns require anti-turn aileron to preclude over-banking. As in level flight, medium turns balance the converging lift vectors of wing dihedral and require no control displacement whatever to maintain angle of bank. This isn't to say that medium turns are stable, only that at some particular angle of bank all lateral forces produced by a wing with dihedral will balance about the c.g.. From an instructional standpoint, it's easy to demonstrate and serves as a graphic intro to the subjects of stability and control. One caution: Dont add this to the student's plate before he's in the habit of (I mean "really learned") to manuever by applying whatever force, rate and displacement of controls may be necessary to achieve the desired result. This is one of those things that can get a student to thinking too much and (except possibly for spin recoverier) I've never seen anybody's flying improved by watching their hands and feet while maneuvering. Cheers, Eric |
#24
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On Sat, 24 Apr 2004 14:04:11 +0200, Andreas Maurer
wrote: On Fri, 23 Apr 2004 20:14:02 GMT, "Bill Daniels" wrote: A perfectly symmetrical glider with a perfectly smooth polar and frictionless controls SHOULD develop a spiral dive from a hands off turn. How does this explain the behaviour of non-radio-controlled model gloiders that return to level flight anytime? They are built perfectly symmetrical, have a smooth polar and no controls at all... Free Flight gliders - at least in the F1A class, which I fly - are not aerodynamically symmetrical: There is always more wash in on the inner wing in the turn and the rudder is set into the turn, giving a crossed-controls effect. Without the differential wash-in most designs will have nasty spiralling tendencies. The flight regime is somewhat different, too. The model is trimmed at min. sink (about 8-10 kts) and is flying in a still air circle that requires 40 - 60 seconds to complete. That's a 30 - 40 m diameter circle being made by a 2.5 m span model, which is a relatively much larger circle than we tend to use in our sailplanes and yet is small enough to fit easily inside a thermal column. -- martin@ : Martin Gregorie gregorie : Harlow, UK demon : co : Zappa fan & glider pilot uk : |
#25
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Also, adding stab tilt helps the free flight glider turn towards the high side.
All these are tweaked in until the glider performs as desired. I also fly Jet-X gliders, little free flight gliders with a small rocket engine attached that burn for about 10 seconds. If done right, a thing of beauty. If not, they loop like mad or auger in dramatically. Always fun. My hand-launced gliders are built with crossed controls, which produces this effect. A slight amount of rudder into the turn keeps it going. A slight amount of opposite aileron keeps it from overbanking. A slight amount of up elevator lifts the nose. Just enough weight on the nose keeps it from making phugoids. Just enough dihedral helps it right itself. Jim Vincent CFIG N483SZ illspam |
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