RCU Forums - View Single Post - J3 cub, crash on take off nearly every time.
Old 10-11-2008, 04:30 PM
Join Date: May 2004
Location: Oklahoma City, OK
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Default RE: J3 cub, crash on take off nearly every time.

Naww, the airplane couldn't care less what direction the wind is blowing or how fast it's going. The only time this comes into play is when transitioning to/from the ground, or trying to keep the plane oriented to a ground object (like when we try to keep our models within a certain distance from us). If you maintain the same throttle setting, your plane will have exactly the same airspeed going upwind as it does downwind. Flying objects have no concept of "upwind" or "downwind" or "crosswind" or any kind of wind other than relative wind.

The problem occurs when you try to maintain the same GROUND TRACK flying downwind as when you're flying upwind/calm conditions, and is also where you may get the impression that flying with the wind, slowly, can give you problems. For instance, say you're on the downwind leg of your landing pattern and are about to turn base. Since the plane is in an air mass that is moving relative to the ground (and you), you will need to start your base turn earlier than usual to end up at the same distance on the base leg. If you don't consider this, you will start your turn at the usual point in the pattern and get blown further away from the field.......or (more likely), you will involuntarily make a steeper-than-normal turn and pull back more on the elevator to keep the plane from drifting out. And this is where the danger lies and your wing loading goes up. This is harder for us RC'ers than for flying full-scale, because at least in a full-scale you have a better view of bank angle and also can refer to your instruments to maintain a more consistent airspeed....so even if you make your turn too late, you can discipline yourself to keep the airspeed up, stick/yoke pressure down, and stick with approximately the same bank angle that you typically use. For RC, all we really have to go on is what we can tell of bank angle, and amount of back-stick. The latter, actually, is a pretty good gauge of how close you are to stalling, assuming you have a fair amount of stick-time with the aircraft in question (and haven't dialed in a bunch of trim).

Try it some time. Force yourself to fly the plane the same way in a strong downwind leg as you typically do in calm conditions. Same throttle setting, bank angle, back-pressure, etc. Your descent gradient will be shallower, and the plane will drift with the wind, but it won't handle any differently, and you won't run into any stalling issues (assuming there are no gusts/wind shear).