![]() You can see the bottom of the wing at the root but disappearing at the tip. Here are the results on the first two wings: On future builds I will get the twist established while gluing the spar, probably using a long tapered wood block along the trailing edge set to the right amount of twist. Here I am holding pressure with my thumb forward and fingers back to hold the twist as the glue dries:īoth hands are required for this but someone had to take the picture. It has built about 16 planes to date and no end in sight.) I resharpen it frequently with a dry wet stone. (This is a $.50 break away knifi from the special bin a the local Chevy dealer. The blade is extended to about 2" so it can "feel" the gap between the foam boards as I go. Here I am using a long thin knife to cut the original glue joint: I think that will be enough in combimation with the undercambered tips that are common to the Flite Test designs. I am going back and cutting the glue joints at tha backs of the flat bottom panel and then twisting as I reglue them. My flying wings were all built holding the flat wing bottom against the building board, so no wash-out. The rule-of thumb value I have heard most often is 3 or 4 degrees. In the real world of modeling science where only our egos and a small investment of time and coin are at risk rule-of -thumb engineering and trial and error will do. If we were putting Mom and the kids in these things that would all be justified. The amount required can be calculated precisely if you have all of the design data, an aeronautical engineering degree, a math degree, a wind tunnel and several weeks of spare time. If you need two degrees to compensate for tip vortex and two degrees for tip stall avoidance asside from the vortex effect then you need 4 degrees total. So there are two components contributing to the requirement for wash-out and they are addative. There is not time to recover if this happens on a landing. Immediately that wing loses lift and a sharp roll can occur. If the tip stalls first it usually happens on one wing first. Second: It is desirable to have an actual lower effetive angle of attack at the tip so that the wing root stalls first. The vortex disturbance has the effect of the air near the tip striking at a slight upward angle as compared to at the wing root resulting in an effective higher angle of attack if the wing is made flat. Tip vortex has an effect on the air pattern near the wing tip. The main reason for using wash-out is to avoid wingtip stalls which usually happen on landings with disasterous results.įirst, airflow is not unifrom over the full length of the wing. Wash-Out is a twist built into the wing so that the wing tip is at a lower angle of attack than the wing root. The one exception is still hanging on my garage wall in pieces, the victim or tip stall on landing. I always used it on my conventional planes when I was doing nitro. ![]() I have read from several sources that wash-out is almost universally required for stability in flying wings. This article is about some of the finer details needed for setting up a flying wing for stable flight. ![]()
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