Positive control Check

Friends- If you haven’t heard, Quebec Delta was grounded a little while ago when one of our members had flown it and found that it was badly out of trim. The adjustment was so far out that the glider ballooned up unexpectedly on takeoff, and required full forward trim and forward stick pressure for the entire flight. When Jack disassembled the glider to investigate, he found that the pushrod that controls the elevator trim had been badly bent. Fortunately Jack was able to straighten the pushrod and reassemble the glider. If the pushrod had been bent any more, we would have had to order a new one from Germany, and the glider would probably have been grounded for months. So how did this happen? The only thing we can imaging is that someone was overly aggressive when they did a positive control check. So let’s have a quick review: Why do we do a positive control check?- Gliding is a unique sport. Our gliders can fly cross country without an engine. We use the lift that nature provides us, and we challenge gravity. Occasionally gravity wins, and we have to land away from our home airfield. Our gliders are designed so that we can disassemble them, bring them back to the field in a trailer, and reassemble them. The FAA gives glider pilots the privilege of doing this. With that freedom comes the responsibility of making sure we have correctly hooked the controls up. The goal of the positive control check is to confirm just that. How do we do a positive control check?- I’ve heard a lot of people passionately describing the perfect positive control check, but the goal is very simple. With one person holding the control stick, and another person out at the control surface (aileron, spoiler, elevator or rudder) we want to make sure that the control stick moves the control surface smoothly through its full range of motion, and that the two are positively connected. That means that the control is being both pushed AND pulled by the control stick. If the controls are not hooked up correctly, it might be possible for the control stick to push the control, but not pull it back the other way. So the member standing at the control surface puts one hand on each side, and provides GENTLE resistance to the motion, while the member at the control stick moves the control to both ends of the travel. The member at the control surface should feel an equal amount of force in each direction. How strong are the controls?- Our gliders have controls that are designed to move AIR. When we push the control stick to the left, the left aileron rises and the right aileron goes down. They push on the wind, which pushes back to bank the wing. There isn’t a lot of force involved, and our controls are only designed to be strong enough to resist that force. Stronger control systems would weigh more, cost more, and degrade our performance. That means that the control systems are not build to be stronger than we are. If one glider pilot tries to hold the control surface from moving, and the glider member tries to push the stick hard enough, something is going to bend or break. Usually, the pushrods fail in compression, and buckle. So how hard should we push the control stick when we are doing a positive control check? No harder than we push the control stick when we are flying. How about the trim?- The trim is a secondary control surface. It is designed to produce even less force that the primary control surfaces. As a result, it is not very strong at all. We should NOT try to do a positive control check on the trim. It is enough to move the trim control in the cockpit and see that the trim responds correctly. Thanks folks. Let’s take care of our gliders. Without them we are nothing more than a lawn mowing club. Phil Klauder Phil.klauder@verizon.net