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Harry,

We've been down this road before,with the ''downwind turn myth'' thread. You saying it's all nonsense,is nonsense. Your statement ''Wind has no effect on airspeed in a turn, and changes in groundspeed have no effect on handling'',while tehnically true,is overly simplistic,and misleading.

The intent is to make the newbie aware that visually perceived speed will change significantly,at a constant airspeed,when changing course in a strong wind.That is a huge point. If he flies the airplane at a comfortable buffer above stall speed into a 20 kt headwind,then turns downwind,the groundspeed,and more importantly perceived speed, will be 40 kts faster,if he doesn't change pitch/power. An inexperienced pilot may incorrectly perceive that the airspeed is increasing,and make the improper input of decreasing power/increasing pitch,leading to a stall,and departure from controlled flight.I have seen it happen more than once.

You,and others have argued the semantics of this,yet it continues to be a problem for newer pilots.It may not be explained exactly correctly on the JPO sight,but at least the attempt is being made to enlighten newbies that there are extra considerations when operating in stronger winds.I applaud that effort.

Erik


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The effect is even worse in very gusty or variable winds. Le'ts say your model jet stalls at 30kts. You are on final approach into a 15 knot wind. You are flying to maintain what appears to be 35kts across the ground. Your actual airspeed at that point is 20kts. If the wind suddenly quits or makes a drastic change in direction, your airspeed, at that split second, is now 20kts and you stall. Full size airliners always add a buffer on the Vref speed precisely for this reason. On the Airbus, the computers do it automatically. On the 757, you add 1/2 the steady state wind and all the gust factor to your Vref (approach speed). With model airplanes we have to do all this by eye.

With model airplanes, because we are not sitting in the pointy end with airspeed indicators, this problem can be insidious. Let's say you are flying your model jet on downwind and the wind at that altitude is 20kts on the tail. You are flying the model at what appears to be the proper speed, yet in reality the true airspeed is 20kts less. You turn base and final, and for a brief moment, until the momentum of the airplane catches up, you are flying at your actual airspeed, which may very possibly be below stall speed! Since we usually start a descent at that point, I suspect many a stall has been averted for that reason.