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#41
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On 19 Aug 2005 14:33:29 -0700, "5Z" wrote: Once it starts moving, even slowly, the wing is producing lift. The more lift is produced, the more difficult it is to cause a wing to drop, as this lift distributed over the whole wingspan damps a tendency to roll. Eliminate this damping by opening the spoilers and now the feeble aileron is able to cause a roll. ... text deleted ... -Tom This topic of why opened spoilers assists low speed roll control really is one of those questions that comes up again and again. From a post 5 years ago on r.a.s. Bob ==============================*=================== =========== From: Bob Gibbons ) Subject: Dropping a wing on takeoff Newsgroups: rec.aviation.soaring View: Complete Thread (63 articles) | Original Format Date: 2000-11-02 21:18:53 PST This topic, that is, why deploying spoilers seems to help roll control at low speeds, has come up often in RAS during the years. Unfortunately, we seldom seem to get responses from knowledgeable aeronautical engineers as to the real cause for what is generally acknowledged as a real effect. Earlier today I asked Dick Johnson the cause of this effect. I will try to summarize his reply, but I may miss some of the finer details, so any aerodynamicists, feel free to correct me. BTW, for those who are not familiar with Dick credentials, in addition to his long history of contest successes, Dick is a professional aerodyamicist with 50+ years of experience. Dick's response was that the effect of increased roll effectivness with spoiler deployment is real, and is caused by a 3-dimensional flow effect initiated by the spoiler deployment disturbing the normal low pressure area over the top of the wing in the area of the spoilers. The breakup of the normal low pressure in the spoiler area results in a lateral spanwise flow in the airfoil forward of the ailerons. This lateral flow modifies the normal pressure distribution on the airfoil forward of the ailerons and allows the airfoil in the aileron section to operate at a higher angle of attack (without flow separation, i.e., stalling) than would otherwise be possible, thus allowing greater aileron effectivness during the takeoff roll. The effect is more pronounced in standard class gliders since without the benefit of flaps to modify the airfoil camber, standard class airfoils are often set on the fuselage at a higher angle of attack than the corresponding airfoil on a 15m flapped ship. Furthermore, 15m ships, with interconnected ailerons, can decamber their airfoil (select negative flap) and generate increased resistance to flow seperation at the ailerons during the early ground roll. Hope this helps, and, as I said, this is an restatement by a non-professional, corrections by practicing aerodynamicists welcome. Bob ================================================== ============ |
#42
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In article ,
dav wrote: 3.I fly a Hornet often, an aircraft with I believe the same fuselage as the Mosquito, and it also shows the wing drop on ground run tendency, due to high AOA in the two point position. I've observed that the Club Libelle (similar to the Hornet) suffers from wing drop, while the Std Libelle doesn't. -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O---------- |
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