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Old 10-20-2008, 11:04 PM
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qldviking
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Default RE: J3 cub, crash on take off nearly every time.


ORIGINAL: dabigboy

No, wind speed makes no difference whatsoever as far as the plane is concerned. If your Cub was getting slow enough to stall it's because you were slowing it down involuntarily in order to keep it at a familiar speed relative to you: groundspeed. Now, there is a danger in flying slowly in GUSTY conditions, and that is that as gust intensity increases, so must airspeed, for safety. An example would be flying stable at 20kts and suddenly getting nailed with a 5kt gust in the direction the plane is flying: airspeed drops to 15kts and then rises back to 20 as the plane seeks its original (stable) 20kt condition where all forces are balanced.

It definitely looks misleading from the ground, when your plane is hauling booty downwind and yet you have very little elevator control and are near a stall. But it's because you are deliberately throttling back and pulling the elevator back to make the plane look "normal" from the ground. The thing with RC models is we have no speed reference other than groundspeed, so we must consciously consider what the wind is doing and factor that in. Consider this example: a plane is flying normally in a stationary mass of air. Now imagine the ground is zooming by beneath it at 20kts. How does that affect the plane? It doesn't.


Finally got it together to test your last line where you statements regarding moving air mass etc.
conditions were 15kn S/E breeze that was fairly constant, we had a good windspeed monitor and a radar speed detector and crew to work it all and take notes. Air plane was another embers 144" cub running a saito 300 twin
Our airfield lies on the coast, no hills etc for miles around us
The throttle was touched at all once airborne

We did a few runs cross wind to try to get a reference speed to work with and found at our chosen setting we had a groundspeed of 32 mph.
we then proceeded to fly 15 circuits directly with the wind and then directly into the wind
average winspeed 18mph
Groundspeed differences flying into the wind were an average of 8 1/2 mph slower
groundspeed differences flying with the wind were an average of 7 1/4 mph faster
each leg was recorded for both wind speed and ground speed and the variations over all the runs was minimal within 5%

But it confirms my thoughts that our aircraft are NOT locked in a cell of moving air mass, and tail wind will rob you of airflow velocity over your wings and control surfaces if flying slow like I enjoyed doing.