On Wed 01 Sep, Frank & Lori Koegler wrote: > What's "washout"? Ah, yes, should have explained that. A wing without washout is a wing where the reference line of the airfoil(s) used are perfectly aligned, no twist at all. As one wants to keep the wing tips maintaining lift as long as possible (as otherwise the flying becomes pretty much like balancing a ball on your head - pretty unstable and quite difficult). This affects the placing of an aircraft's airbrakes, for instance, so they normally go inside the ailerons. In short, a good aircraft should have aileron control at all speeds - if possible. If the aircraft is a polyhedral you should still aim for that the tips stalls after the inner portion of the wing. So if the wing has some taper, or the profile towards the tip stalls earlier (at a lower angle) than the root profile (this is often, but not always, the case), due to different thickness, or various other reasons, the normal solution is to twist the wing, so that the inner section has a greater angle than the tips. For instance, if you use Eppler profiles the twist should generally be very little 0-2.5 degrees, depending on which taper and profiles you use, while swept wings can have as much as 9-10 degrees (Miachev bombers)! The problem with washout is that while it can be used to tailor the lift distribution of a wing perfectly (an elliptical lift distribution is perfect on everything but flying wings), the washout will only work perfectly for one speed! And aircraft with a lot of washout tend to have a very fixed maximum speed, as the wingtips on a very twisted wing will produce downforce at high speed, eventually breaking itself up if you pass maximum allowed speed. So designers try to use as little as possible and instead play with different airfoils, or making small changes to the basic airfoil towards the wing tip (often added droop towards the tip - a classic addition to later models of certain buizjets, as with such a relatively easy modification they can lower the minium speed on approach and take off, or increase gross weight, or both, with little cost. 'Droop' in this context is a minute change to the nose of the airfoil, often by bonding a section to the basic wing. Even the mighty Avro Vulcan flew badly until quite a lot of droop was added on the outer wing panels! Hope this helped? Tord, Sweden *'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.* -- If reply difficulties - use [EMAIL PROTECTED] Tord S. Eriksson, Ovralidsg.25:5, S-422 47 Hisings Backa, Sweden RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
