Often when you get a speaker with PhD after their name you get lots of hot air that is difficult to comprehend. Such was not the case when Harvey Wichman visited PVPA at the February meeting. The title of his talk, in true PhD style, was "The Right Instrument in the Wrong Place: Revisiting the Stall/Spin Problem." The instrument to which he referred was the lowly slip indicator. Now gliders don't have to many stall/spin accidents, not that it couldn't happen, because they tape a string right in front of the pilot's nose where he can see it. As long as the string is pointing at the pilot all is well and if the glider gets into a slip, off the string goes to the side and the pilot sees it and corrects. But try hanging a prop on the front of your airplane and the string is useless. This is where "the ball" comes in. It's a slip indicator that works inside the airplane and out of the relative wind. More about that later.

Harvey went on to explain in detail how adverse yaw comes about when one aileron rises into the more rarified air and the other drops into the denser air producing more drag that the other one. This creates a yaw in opposition to the direction of the turn and we must correct with rudder. Now this happens with all airplanes but then when you put a spinning propeller up front a new wrinkle known as P-factor is introduced.

P-factor refers to the fact that on American airplanes the right, down moving, propeller blade pulls harder than the up going left propeller blade whenever the aircraft is flying at a high angle of attack. Thus in slow flight or a climb propeller airplanes yaw to the left and we compensate with right rudder. Pilots tend to do a lot of skidding, which is not too much of a problem as long as the airplane is well above stall speed.

Harvey went on with his classic illustration of a bad situation. Our pilot is descending, flying slowly, turning to final for landing. Even though the nose of the airplane is pointing downward the wing is at a high angle of attack because it still needs to generate lift equal to the weight of the airplane. Now our pilot finds he needs to tighten his left turn to final to line up with the runway.

This is where it can begin to get dicey. Our pilot makes his turn, left wheel (or stick) and left rudder. Pull back for more angle of attack because in the steep
1 1/2 g turn his 2,000-pound airplane now weighs 3,000 pounds and now a larger proportion of the lift is the lift is being used to turn the airplane instead of supporting it. We have a high drag situation and the airplane will stall if the pilot doesn't add power. Our pilot adds power, lots of power, while holding the bank and pulling back on the controls. High angle of attack, plus low speed, plus high power equals classic high P-factor, which together with left rudder means excessive left yaw and a skid.

The airplane is now in a skidding left turn. The pilot lowers the left aileron to raise the wing and that increases the shallower angle of attack of the wingtip and the entire wing stalls. The drag of the down aileron yaws the wing backward even further and with one wing stalled and the other flying, one moving forward and the other backward.SPIN. At this altitude.well let's just say this is why we practice these things with lots of air between the ground and us.

All this could have been prevented had our pilot glanced down and checked the ball in his slip indicator. But he was too busy watching the ground coming up to meet him and this would have meant putting his head inside the cockpit to find the instrument and read it.

This is where we come to the right instrument in the wrong place. Harvey suggests we move the slip indicator right on top of the glare shield. This would put it in the pilot's line of sight. Now before you go ripping your panel out, we have done a little research for you. Did you know small slip indicators might be had for under $30.00 at places like Aircraft Spruce?