Thread: Discussion snap flaps
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Old Nov 20, 2012, 05:09 PM
Kiesling is offline
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The reason for using elevator to camber mixing is to minimize the drag for a given Cl. Cl is a function of the angle of attack and camber. For a given Cl, the airfoil has a camber setting that provides the lowest drag. So, by using elevator to camber mix correctly, you ensure that the wing is generating the desired lift as efficiently as possible (lowest drag). Fortunately, it works out that the correct ratio of elevator to camber is fairly linear for most modern airfoils so it is relatively easy to set up. For a typical F3B model, for every mm of elevator movement there should be around 1 mm of camber movement. This goes for both up and down (positive camber for up elevator and negative camber for down elevator). The ratio for camber/elevator is actually a little less than 1, but when you include compliance of the linkages, the 1 to 1 ratio works out to be about right.

Note that when you start using elevator to camber, you don't need as much elevator throw to get the desired result (as the OP suggests). I think this is why some people write elevator to camber mixing off - they use the same throw and pull the same and the model turns tighter for the same input creating a higher Cl and the model slows down more than it did for the same elevator deflection without the mix. If you compare the same turn radius with and without the mix, you should find the turn with the mix to be cleaner.

I use elevator to camber mix for all flight modes (except launch and landing) and it is on all the time.
FWIW
Tom
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