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#11
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Scott wrote:
Nature gave birds the horizontal stabilizer, I'll stick with the birds. Nature also gave them flapping wings. Did you fly an aircraft that uses that principle? André |
#12
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Nature didn't invent the weel, I suppose you don't have legs under your car
? "Scott" schreef in bericht ... 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! =----- |
#13
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Mark,
I've been hitting the books lately. I've just read Aerodynamics for Naval Aviators (ASA). An excellent treatment of aerodynamics for the aviator without the oversimplification one typcially sees in most "learn to fly" books. It has sections on static and dynamic stability that will help give you a better grounding for exploring the questions you've asked. And frankly, it's not bad reading. I was very surprised. Not nearly as dessicated as I feared. A good addition to any pilot's personal library. BTW, it's easy to do the math to figure out what kind of loads you'll need to produce on the tail to maintain pitch control. Use your weight and balance calculations to exptrapolate approximations of the moment arm between cg and center of lift, then match torques with the tail's moment arm. Repeat this process for a load factor of two or three (steep turns) and you'll find that you'll need to move a lot of mass quickly and quite a distance to stay in trim. Just not very practical. But interesting thoughts. OC |
#14
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Neal Pfeiffer wrote in message om...
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. ************************************************** ***************************** Moveable weights for pitch control aren't as responsive in the negative pitch airfoils used in conventional gliders because increasing speed increases the downward pitching moment which the wing produces. Moving the weight forward to drop the nose and increase speed leads to the requirement for back stick to increase downward pressure on the horizontal stab and keep the nose from continuing to drop. If you tried to do this only with weight shift, you would need to move the weights forward to increase speed and then progressively move the weight backward as the speed builds up just to maintain stability. Computerized fuel shifting on airlines does this but they still use all-flying-tails for the fine corrections. Weight shifting for pitch control is very workable in flying-wing type gliders as they are very responsive to changes in cg; and the inherent stability of the reflex wing keeps the glider very close to the weight shifted pitch.(and speed) Several Genesis owners use rudimentary forms of weight shift on a regular basis. One has mentioned putting ankle weights on the rudder pedals and moving them back and forth, someone else has stated in the GenesisFlyers Yahoo Groups site that inflating the lumbar support adds 4 knots to the trimmed speed. There have been discussions about using nose and tail water tanks and shifting from one to the other to trim for best thermalling or high speed. This is a very workable improvement for Genesis 2 and Marske Pioneer type gliders. Weight shifting on the Pioneer may work even better as it may be possible to fly with a very aft cg which keeps the nose high and then use forward stick to deflect the elevators down increasing the lift coeffecient of the wing. Moving the weight forward would then allow it to fly fast with the elevators slightly raised the way flapped gliders fly with negative flaps.(reflex) 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. ************************************************** ****************************** It's hard to argue against correctly-sized tails, although I suspect that what you call "correctly-sized" is what I spitefully and maliciously call a boomsnapper. Boomsnappers interfere with low energy landings as your pitch at flair is limited by your willingness to slam down tail first and damage the boom. Some boomsnappers (G 102) are speed limited because, oops!, the elevator isn't as strong as we thought and it is prone to flutter. The G103 Acro is acro no more because that big heavy extremely strong tail boom isn't as strong as it should be. Need to slap on a few more layers of carbon so's it don't come off. So, how strong and durable are those tiny, light weight tail booms on newer high performance gliders? Are they at least as strong as the wing spars on Shemp-Hirth gliders? How strong will they be when they are as old as Grobs? Got to keep that tape on tight, too, cause lifting of the front edge of tape near the elevator causes an almost total loss of elevator authority. Genesis 2 and Pioneer owners all seem to really like the handling characteristics of their flying-wing gliders and as a group they don't seem to miss or wish they had longer tail booms. Long tailed aircraft are certainly easier to make and they satisfy an esthetic which sees ships, trains and trucks as boxes or tubes which carry cargo, so an aircraft should be a box or tube with wings. The more it looks like a truck the safer it "feels". |
#15
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In article ,
Chris OCallaghan wrote: Mark, I've been hitting the books lately. I've just read Aerodynamics for Naval Aviators (ASA). An excellent treatment of aerodynamics for the aviator without the oversimplification one typcially sees in most "learn to fly" books. An excellent book. The only place I found the equation for the relationship between weight and stall speed. Good stuff about the different effects of different types of flaps. Too bad it's buried in the "abyss" (my garage) due to new space needs (bassinet, changing table, laundry basket, mom's cozy chair...) New pilots aren't hard to train, but they sure take a long time to GROW! |
#16
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#18
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Mark James Boyd wrote:
I'm considering these factors, because eliminating the elevator and stab would reduce drag. That's right. You should also consider eliminating the wings, that would reduce even more drag. I suppose the best way to experiment with this is in a model glider first, Well... I suppose too... if you want to experiment this with a full scale glider, it will be difficult to find a pilot to put in ;-) -- Denis R. Parce que ça rompt le cours normal de la conversation !!! Q. Pourquoi ne faut-il pas répondre au-dessus de la question ? |
#19
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In article ,
Denis Flament wrote: Mark James Boyd wrote: I'm considering these factors, because eliminating the elevator and stab would reduce drag. That's right. You should also consider eliminating the wings, that would reduce even more drag. An interesting, but more challenging, idea... An aerodyne without wings...hmmm... I suppose the best way to experiment with this is in a model glider first, Well... I suppose too... if you want to experiment this with a full scale glider, it will be difficult to find a pilot to put in ;-) Denis Hmmm...methinks some sort of pully system in a plain old glider might do it. Get a weight of the right size so that if it lodges in the tail, you are still within safe CG, and if it lodges in the nose, you are still within safe CG. Maybe this is only a 1 pound weight. Then have an additional control which moves this weight. Go up to altitude and see if moving this weight gives sufficient control. The biggest safety feature would be ensuring the weight didn't come loose during a critical phase of flight (near the ground) and your supplementary "weight" cables don't hinder the original controls in any way... A weight right in the tail which moves maybe 3 feet forward when the auxiliary stick is moved might do it. Hmmm... |
#20
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Denis, you should read up on the French designer Charles Fauvell and his
flying wings. They flew pretty well although I think Jim Marske's designs are showing higher performance. Tailless designs fly quite well and the performance really doesn't suffer. They would be perfect for small jet engine self launchers. Bill Daniels "Denis Flament" wrote in message ... Mark James Boyd wrote: I'm considering these factors, because eliminating the elevator and stab would reduce drag. That's right. You should also consider eliminating the wings, that would reduce even more drag. I suppose the best way to experiment with this is in a model glider first, Well... I suppose too... if you want to experiment this with a full scale glider, it will be difficult to find a pilot to put in ;-) -- Denis R. Parce que ça rompt le cours normal de la conversation !!! Q. Pourquoi ne faut-il pas répondre au-dessus de la question ? |
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