MMAC Contest & Model Trim

Why do some planes fly pretty consistent day after day while others seem to vary? I thought using a covering that changes a great deal with humidity was the major part of it but it seems there is more to it than that. I have to believe the aerodynamics of some planes results in a plane that has greater stability and the plane is a little more tolerant in slight variations in the trim. I know wood changes with weather conditions and I would assume plastic does to a smaller extent. Many years ago when I first started flying radio control glow planes I remember people warning about the plastic pushrods and how they would change with temperature. The speed of the aircraft multiplies the trim issues. 

Streak Landed on Sandy Road

As I build new planes I go to the extra effort to build in screw adjustments for rudder and stabilizer. I find that I am making small adjustments on different days; it is not just get one trim adjustment and leave it forever. Sometimes it seems the trim changes throughout the day. 

My goal with my competition free flight models has been just to get consistent flights so I can get as much experience as possible without breaking it. After three years I am starting to think more about the performance. Recently I have been working with ½ A Streak glow model. Throughout the first several flying sessions I worked getting a consistent climb and transition. Some of the short first flights were rather nerve racking, on a couple of occasions the plane did a loop after launch, one time it pulled out just as it hit the ground.

Dave B at North Branch

With a washin wedge on inside right panel and tiny amount of right rudder some of the time, the power pattern is good and the plane transitions well. The issue now is it comes down too darn fast, at first I thought I was just launching into bad air but that cannot be the case on every flight. My theory now is the plane is just too heavy; it weighs 6 ounces while other people have built the plane to slightly less than 5 ounces. My Basic Yeller Pee Wee 30 model which has slightly less wing area weighs much less than 4 ounces; a big difference. 

Wilbur Folded Wing

At the last contest I attended near North Branch Minnesota on my second official flight of my Wilbur rubber model the wing folded right after launch. Between the test flight, the first official flight I had added a larger number of turns to the rubber but less than I have used in the past. The wing structure is minimal so I will try to strengthen it without adding too much weight. Even with a big boxy fuselage this model glides pretty well.

More Dramatic Wing Folding

Flew discus launch glider and catapult in the contest as well, with the discus I was getting good altitude compare to others but just couldn’t seem to get the glider in a thermal it could stay with. My catapult glider that I struggled with and broke so many times is now flying consistent.

For a small contest there were several people flying towline glider, as it had gotten windy I did not attempt to fly my Jetstream towline. If you had a good flight there was a good chance it could land in a tree.

Bill Kuhl