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American Eaglet
Does somebody know, how works its spoiler roll controll? Is this machine
suitable for a low time pilot? George |
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"George Vranek" wrote in message ... Does somebody know, how works its spoiler roll controll? Is this machine suitable for a low time pilot? George I haven't flown the American Eaglet but I have flown another glider with spoiler roll control. I also had the opportunity to discuss the AE's handling with a pilot who had flown one. I wouldn't recommend it. Spoilers, as roll control devices, have several problems when applied to gliders. First the basics. Ailerons produce roll and adverse yaw. (Note, "adverse" used in this context doesn't mean "bad", just opposite). Roll spoilers produce roll and "proverse" yaw meaning "in the same direction". One would think that roll spoilers with their proverse yaw would be perfect in that no rudder coordination would be required. However, the perfect ratio between the roll produced and the yaw produced only happens at one, fairly low airspeed called the auto-coordination speed. Spoilers produce roll by spoiling lift on one wing but not the other. However, the lift available to be spoiled is essentially constant over the full speed range i.e. lift equals weight which is constant. The result is that the roll authority is essentially constant over the full speed range. On the other hand, the drag produced by a spoiler increases with the square of the airspeed. The result is that above the perfect auto-coordination airspeed, spoilers produce a skidding turn. At high speeds, the skid is extreme and full out-of-turn rudder may not be enough to keep the yaw string centered - not good. In fact, it's really scary. Further, in a thermalling turn roll spoilers make it difficult to hold off overbanking. A bit of top aileron will just hold the bank where you want it and the "adverse" provides yaw into the turn - meaning little rudder is needed to fly perfectly coordinated circles. To hold off overbanking with spoilers, the top spoiler has to be kept deployed which creates an out of turn yaw, which in turn, requires into-the-turn rudder, which produces still more overbanking, which requires still more top spoiler... Trying to thermal with one spoiler open is not a good thing. So, substituting spoilers for ailerons is an all-around bad thing. But, thinking about this a bit more, what differential spoilers really do is replicate the rudder, not the ailerons. In fact, differential spoilers connected to the pedals work like a MONSTER rudder which would be VERY useful on a big flying wing. I've been trying to convince my friend Jim Marske of this for 35 years. Note that one thing I didn't say is that differential spoilers produce more overall drag than aileron with rudder used to oppose adverse yaw. In fact, it's about a wash with a slight edge to the spoilers. The drag of deflected ailerons + deflected rudder used to oppose adverse yaw while rolling into a thermalling turn is quite high. Roll spoilers actually produce slightly less drag in the same situation. Bill Daniels |
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Earlier, George Vranek wrote:
Does somebody know, how works its spoiler roll controll? Is this machine suitable for a low time pilot? It's a compelling package, but I think the execution does not do it justice. Here's what Derek Piggott thought about it: http://www.glidingmagazine.com/Featu...cle.asp?id=178 Thanks, and best regards Bob K. |
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Very good report, Bill
The Nimbus 3 and the Genesis 2 have very small *tip spoilers*, in addition to normal differential ailerons. They seem to work by add a bit of drag, way out near the tip and help counter the adverse yaw. They are about 4" X 18" and move up twice as fast as the aileron, so that full aileron gives a spoiler standing up at 90 degrees. The early Genesis 2 had these tip spoilers actuated by the rudder pedals, but later models used the stick to actuate them. The return spring used on the tip spoilars gives just enough input to keep the stick centered. I like that because I know the stick is perfectly centered, by just relaxing my grip, a tad. JJ Sinclair |
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"JJ Sinclair" wrote in message ... Very good report, Bill The Nimbus 3 and the Genesis 2 have very small *tip spoilers*, in addition to normal differential ailerons. They seem to work by add a bit of drag, way out near the tip and help counter the adverse yaw. They are about 4" X 18" and move up twice as fast as the aileron, so that full aileron gives a spoiler standing up at 90 degrees. The early Genesis 2 had these tip spoilers actuated by the rudder pedals, but later models used the stick to actuate them. The return spring used on the tip spoilars gives just enough input to keep the stick centered. I like that because I know the stick is perfectly centered, by just relaxing my grip, a tad. JJ Sinclair I was told that the original system on the Genesis was much superior to the final version but that the "production costs" were higher given the long control cable routing and the need to deal with differential thermal expansion effects on the control system. I didn't quite buy the argument. That said, the later Genesis that I flew handled pretty well. Bill Daniels |
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