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#1
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What happens if a sailplane has no horiz stabilizer or elevator?
There are some designs which have no horizontal stab: flying wings
for example. There are also canard setups (the speed canard, for example). For a sailplane, I was thinking about how one might design away the typical T-tail stabilizer and elevator. First of all, how much dynamic stability does the horiz. stab contribute? If it were eliminated by design, would it be absolutely necessary to compensate by using a swept wing (either forward or backward)? When deflected, how much torque does an elevator provide? I'm considering these factors, because eliminating the elevator and stab would reduce drag. From there, one could potentially design a ducted surface, or use moveable weights in the tail to change C.G and therefore pitch. In the first case (ducting), there are commonly used NACA ducts (they look like little triangles on power planes) that are commonly used as air vents on power planes. They have the advantage of producing minimal drag when the vent is closed. On a glider, they could be used in the tail to direct airflow and produce pitching moments. There is a tail-rotor free turbine helicopter which uses ducted bleed-air, I believe, to control yaw this way. The other option, which is more elegant, is to use a moveable weight in the tail for pitch. Move the weight forward to pitch down, backward to pitch up. One difficulty is if the weight must be quite heavy, or the stick movement needed to move it is too heavy. I suppose this in some part is a function of the length of the tailboom. Another complication is that a regular elevator is more effective at high airspeed, and less effective at low airspeed (more deflection is required for the same torque). This isn't necessarily true with a weight-shift pitch control. Hmmm...anyone have data about forces provided by the elevator is flight? Drag caused by the elevator/ vert. stabilizer in level flight? How about torque produced by weight shift near the arm of the elevator? I suppose the best way to experiment with this is in a model glider first, then in a full scale glider with BOTH pitch systems (elev/stab, AND weight shift). Then finally with the elev/stab removed. |
#2
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Nature gave birds the horizontal stabilizer, I'll stick with the birds.
"Mark James Boyd" wrote in message news:4001c97d$1@darkstar... There are some designs which have no horizontal stab: flying wings for example. There are also canard setups (the speed canard, for example). For a sailplane, I was thinking about how one might design away the typical T-tail stabilizer and elevator. First of all, how much dynamic stability does the horiz. stab contribute? If it were eliminated by design, would it be absolutely necessary to compensate by using a swept wing (either forward or backward)? When deflected, how much torque does an elevator provide? I'm considering these factors, because eliminating the elevator and stab would reduce drag. From there, one could potentially design a ducted surface, or use moveable weights in the tail to change C.G and therefore pitch. In the first case (ducting), there are commonly used NACA ducts (they look like little triangles on power planes) that are commonly used as air vents on power planes. They have the advantage of producing minimal drag when the vent is closed. On a glider, they could be used in the tail to direct airflow and produce pitching moments. There is a tail-rotor free turbine helicopter which uses ducted bleed-air, I believe, to control yaw this way. The other option, which is more elegant, is to use a moveable weight in the tail for pitch. Move the weight forward to pitch down, backward to pitch up. One difficulty is if the weight must be quite heavy, or the stick movement needed to move it is too heavy. I suppose this in some part is a function of the length of the tailboom. Another complication is that a regular elevator is more effective at high airspeed, and less effective at low airspeed (more deflection is required for the same torque). This isn't necessarily true with a weight-shift pitch control. Hmmm...anyone have data about forces provided by the elevator is flight? Drag caused by the elevator/ vert. stabilizer in level flight? How about torque produced by weight shift near the arm of the elevator? I suppose the best way to experiment with this is in a model glider first, then in a full scale glider with BOTH pitch systems (elev/stab, AND weight shift). Then finally with the elev/stab removed. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#3
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At first glance I would want some reassurance about
the the spinning characteristics and recoverability of a weight shift pitch control glider with a conventional wing section! Also I wouldn't fancy flying it inverted. I think you are proposing a highly unstable and unworkable configuration i.e. a deathtrap. The longitudinal control would work differently at different pitch angles. In a vertical climb or dive there would be no 'elevator' control. In a steep dive spin recovery the conventional wing section would bunt uncontrollably past the vertical. The weight in the tail would then reverse its effect and increase the negative g loads. I think it would be so violent that the glider wings would depart immediately but even if they didn't you would be in a non recoverable position just waiting to exceed VNE sufficiently for the wings to come off a second or two later. In fact even trying to fly in a fairly level attitude would be extremely difficult as any forward pitching would diminish the effect of the weight 'elevator/tailplane' so that you would then have to send it back past the postion of stable level flight just to stop the nose continuing to drop. Then there's the difference in control forces that would be needed to shift the weight up and down the tailboom at different pitch attitudes. Then there's high speed cruising which would increase the pitching effect of the wing so that the weight would have to go further and further back as the speed increased (even neglecting pitch change effects as above) so the faster you go the futher back the stick. Conventional glider wing sections are unstable in pitch and the advantage of an aerodynamic pitch trim and control device is that it increases its effect with airspeed and works in all attitudes. If you want to get rid of the tail you need to use a flying wing chord section or to use thrust vectoring (maybe that could be a use for the jet on the other thread but it wouldn't be a glider) John Galloway At 22:24 11 January 2004, Mark James Boyd wrote: There are some designs which have no horizontal stab: flying wings for example. There are also canard setups (the speed canard, for example). For a sailplane, I was thinking about how one might design away the typical T-tail stabilizer and elevator. First of all, how much dynamic stability does the horiz. stab contribute? If it were eliminated by design, would it be absolutely necessary to compensate by using a swept wing (either forward or backward)? When deflected, how much torque does an elevator provide? I'm considering these factors, because eliminating the elevator and stab would reduce drag. From there, one could potentially design a ducted surface, or use moveable weights in the tail to change C.G and therefore pitch. In the first case (ducting), there are commonly used NACA ducts (they look like little triangles on power planes) that are commonly used as air vents on power planes. They have the advantage of producing minimal drag when the vent is closed. On a glider, they could be used in the tail to direct airflow and produce pitching moments. There is a tail-rotor free turbine helicopter which uses ducted bleed-air, I believe, to control yaw this way. The other option, which is more elegant, is to use a moveable weight in the tail for pitch. Move the weight forward to pitch down, backward to pitch up. One difficulty is if the weight must be quite heavy, or the stick movement needed to move it is too heavy. I suppose this in some part is a function of the length of the tailboom. Another complication is that a regular elevator is more effective at high airspeed, and less effective at low airspeed (more deflection is required for the same torque). This isn't necessarily true with a weight-shift pitch control. Hmmm...anyone have data about forces provided by the elevator is flight? Drag caused by the elevator/ vert. stabilizer in level flight? How about torque produced by weight shift near the arm of the elevator? I suppose the best way to experiment with this is in a model glider first, then in a full scale glider with BOTH pitch systems (elev/stab, AND weight shift). Then finally with the elev/stab removed. |
#4
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In article ,
John Galloway wrote: At first glance I would want some reassurance about the the spinning characteristics and recoverability of a weight shift pitch control glider with a conventional wing section! Also I wouldn't fancy flying it inverted. I think you are proposing a highly unstable and unworkable configuration i.e. a deathtrap. The longitudinal control would work differently at different pitch angles. In a vertical climb or dive there would be no 'elevator' control. In a steep dive spin recovery the conventional wing section would bunt uncontrollably past the vertical. The weight in the tail would then reverse its effect and increase the negative g loads. I think it would be so violent that the glider wings would depart immediately but even if they didn't you would be in a non recoverable position just waiting to exceed VNE sufficiently for the wings to come off a second or two later. Hmmm...excellent points. I can see that both weight shift and ducting have problems in spin recovery (a very important area). So two more ideas for getting around having a tail in the way of turbine temps.: 1. Mount the turbine slightly "cockeyed" a few degrees so the blast isn't right at the tail. Needs some rudder for powered flight, and doesn't look elegant, but it's a simple solution to implement. 2. Use a canard. Has anyone ever made a glider with a canard for control before? I'm guessing maybe not since there are some obvious disadvantages in a glider (landouts, aerotow, turbulence caused by a canard)... |
#5
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V tail or twin rudders on the ends of the horizontal stabilizer makes the
most sense to me. "Mark James Boyd" wrote in message news:4001c97d$1@darkstar... There are some designs which have no horizontal stab: flying wings for example. There are also canard setups (the speed canard, for example). For a sailplane, I was thinking about how one might design away the typical T-tail stabilizer and elevator. First of all, how much dynamic stability does the horiz. stab contribute? If it were eliminated by design, would it be absolutely necessary to compensate by using a swept wing (either forward or backward)? When deflected, how much torque does an elevator provide? I'm considering these factors, because eliminating the elevator and stab would reduce drag. From there, one could potentially design a ducted surface, or use moveable weights in the tail to change C.G and therefore pitch. In the first case (ducting), there are commonly used NACA ducts (they look like little triangles on power planes) that are commonly used as air vents on power planes. They have the advantage of producing minimal drag when the vent is closed. On a glider, they could be used in the tail to direct airflow and produce pitching moments. There is a tail-rotor free turbine helicopter which uses ducted bleed-air, I believe, to control yaw this way. The other option, which is more elegant, is to use a moveable weight in the tail for pitch. Move the weight forward to pitch down, backward to pitch up. One difficulty is if the weight must be quite heavy, or the stick movement needed to move it is too heavy. I suppose this in some part is a function of the length of the tailboom. Another complication is that a regular elevator is more effective at high airspeed, and less effective at low airspeed (more deflection is required for the same torque). This isn't necessarily true with a weight-shift pitch control. Hmmm...anyone have data about forces provided by the elevator is flight? Drag caused by the elevator/ vert. stabilizer in level flight? How about torque produced by weight shift near the arm of the elevator? I suppose the best way to experiment with this is in a model glider first, then in a full scale glider with BOTH pitch systems (elev/stab, AND weight shift). Then finally with the elev/stab removed. |
#6
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One of the guys at the forefront of tailless sailplane
design is Jim Marske. He's been experimenting with most of the ideas you bring up, including the movable trim weight. He regularly offers seminars on tailless sailplane design. Bob K. http://www.hpaircraft.com |
#7
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On Sun, 11 Jan 2004 17:11:11 -0800, "Gary Boggs"
wrote: V tail or twin rudders on the ends of the horizontal stabilizer makes the most sense to me. Interference drag is pretty bad in both cases. Bye Andreas |
#8
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Check out the German Horten's from WWII. They test flew flying wings
as gliders and were planning jet versions. Very interesting piece discussing them on the History Channel this evening. Chip Fitzpatrick |
#9
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"Mark James Boyd" wrote in message news:4001f9e3$1@darkstar... 2. Use a canard. Has anyone ever made a glider with a canard for control before? I'm guessing maybe not since there are some obvious disadvantages in a glider (landouts, aerotow, turbulence caused by a canard)... Yep, Burt Rutan. The Solitaire. Good designer, but this effort was not covered with glory. Gliders need to fly right at the edge of a stall. http://www.sailplanedirectory.com/zwfmot.htm Larry Pardue 2I |
#10
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The Horten flying wings utilized a non-optimal spanload distribution
(wingtips loaded downward) in order to be stable, effectively a tail at the wingtips. Because of this, their performance was not particularly good. The Swift (see reference below) is a more modern flying wing that addresses some of the shortcomings of the earlier ones. http://aero.stanford.edu/Reports/SWIFTArticle1991.html Other tailess glider variations were done by Al Backstrom (the Flying Plank) and Jim Marske (Pioneer & Monarch). http://www.nurflugel.com/Nurflugel/F..._backstrom.htm http://www.flyingacesclub.net/alamo/...gwingstuff.htm http://www.continuo.com/marske/ or for the committed flying-wing person: http://www.nurflugel.com/nurflugel/nurflugel.html - - - - - - - Moving of weights within a fuselage (or other part of the aircraft) is not a viable solution. Response needs to be quick and reliable, even for unusual attitudes. - - - - - - - Based on the vast majority of the gliders in existance, however, using a correctly-sized tail is not a bad way to go. Remember, if you don't truly enjoy what you're flying, you probably won't fly it long. Tailed aircraft are probably easier to make fly good. ...... Neal Mark James Boyd wrote: There are some designs which have no horizontal stab: flying wings for example. There are also canard setups (the speed canard, for example). For a sailplane, I was thinking about how one might design away the typical T-tail stabilizer and elevator. First of all, how much dynamic stability does the horiz. stab contribute? If it were eliminated by design, would it be absolutely necessary to compensate by using a swept wing (either forward or backward)? When deflected, how much torque does an elevator provide? I'm considering these factors, because eliminating the elevator and stab would reduce drag. From there, one could potentially design a ducted surface, or use moveable weights in the tail to change C.G and therefore pitch. In the first case (ducting), there are commonly used NACA ducts (they look like little triangles on power planes) that are commonly used as air vents on power planes. They have the advantage of producing minimal drag when the vent is closed. On a glider, they could be used in the tail to direct airflow and produce pitching moments. There is a tail-rotor free turbine helicopter which uses ducted bleed-air, I believe, to control yaw this way. The other option, which is more elegant, is to use a moveable weight in the tail for pitch. Move the weight forward to pitch down, backward to pitch up. One difficulty is if the weight must be quite heavy, or the stick movement needed to move it is too heavy. I suppose this in some part is a function of the length of the tailboom. Another complication is that a regular elevator is more effective at high airspeed, and less effective at low airspeed (more deflection is required for the same torque). This isn't necessarily true with a weight-shift pitch control. Hmmm...anyone have data about forces provided by the elevator is flight? Drag caused by the elevator/ vert. stabilizer in level flight? How about torque produced by weight shift near the arm of the elevator? I suppose the best way to experiment with this is in a model glider first, then in a full scale glider with BOTH pitch systems (elev/stab, AND weight shift). Then finally with the elev/stab removed. |
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