Stalling: How to Ruin a Perfectly Good Day!

[from the AMA national newsletter, November 2001]

by Michael Heer
(Portions of this article have been modified by AMA Technical Editor Ed McCollough)

This article is for the novice flier because I have been seeing a rash of “beginner mistakes” involving stalls that result in crashed airplanes. This is with club members and with the powered fliers in Lodi as well. The problem is that too many are learning about stalls by destroying or damaging airplanes. They don’t see the stall coming and don’t react until it is too late to correct. So you experts can skip to something else, as this article will be so basic it may even seem insulting to the novice, but we need to think about these things in advance of our flights to spot and avoid the stalls that kill close to the ground.

A stall is caused when your airplane loses forward airspeed to the point where it is no longer enjoying the benefit of lift. This is the point at which the wing stops flying. This most often occurs when the critical angle of attack for that airplane is reached and the lift stops and the wing stalls.

Fortunately many of our gliders have rather mild stall characteristics. If we slowly stall, the nose of the airplane drops and the glider picks up speed and lift returns with little loss of altitude. If it continues to stall, drop and correct, stall, drop and correct, we call that “porpoising” because it resembles a porpoise jumping out of the water repeatedly. We learn that when the glider starts the climb we can hit with a little burst of down-elevator and avoid the stall and return to level flight.

With a more radical angle of attack the stall is worse and the drop is greater. When the stall occurs with the airplane or glider pointing straight up or close to that, the airplane falls backward and we have no control initially. Then the airplane drops until it flips over to obtain a nose first position, we get air flowing over the wing and the control surfaces, and we once again obtain control of our airplane. That is, if we had enough height for all that to take place. If we were too low, our airplane has crashed and is destroyed or in need of repair.

Most of the problems I have witnessed of late have been with powered airplanes (gas and electric) with novice pilots treating the elevator control as the source of lift and giving lots of up signal while the airplane is still slow and near the ground—crash! Speed is what is converted to lift with slight use of the elevator. The more speed you have the more elevator you can use, but as the airplane slows you have to ease off the elevator or you will stall. For example, with the Sky Scooter it needs to be flown level after it is tossed to build up speed and then slowly given some up elevator and let it climb a bit and then ease off, build up speed and slowly climb. If I feed in up-elevator right after I toss the airplane, the airplane would climb very briefly, stall and then crash as it would lack any air flowing over the surfaces and it would be uncontrollable and would fall.

To avoid stalls right after a launch you want to 1) launch into the wind, 2) fly level until the airplane picks up speed, 3) climb slowly until you get to cruising speed and altitude and then have fun. Go easy on the elevator and life will be a whole lot better. Those crashes seconds after tossing or lifting off are no fun, I know! I am so used to my Zagi climbing even with a little tail wind that I tried to fly the Sky Scooter launching with the wind rather then taking a short walk ... two seconds later, crash and a $2.50 prop is gone.

from Thermal Topics
Modesto RC Club
Michael Heer, editor
Modesto CA