At 01:18 PM 12/23/2007, you wrote:
So Chuck, Tell us how the tension limiter worked and how well it worked. What were the good points and problems? Could such a scheme be used effectively today?
The Jam/Feb 1977 issue of Sailplane contained an article by Chet Tuthill describing the winch system developed by Jim Robinson and other members of the Coffee Airfoilers model airplane club. The tension limiter was a major part of that article. The tension limiter was a separate base for the standard winch. For normal flying, the winch was removed from the base and used like any other winch.
The base for the winch had a pivot just ahead of the CG of the winch and battery and had a microswitch at the rear of the platform. The tension limiter switch was wired in series with the foot peddle. A spring held the platform against the switch until line tension caused the platform to rock forward opening the tension limiter switch. When line tension decreased, the spring forced the platform aft closing the switch. The inertia of the winch and battery gave a very smooth pulsing when launching larger models if the contestant held the foot peddle down and let the winch do the pulsing.
The tension limiter proved to be very reliable and we used if for many years. As usual, there ain't no free lunch. The tension limiter winch took a few minutes longer to set up but the considerable reduction in broken lines made it worth while. The tension limiter was set by attaching a 25 pound spring scale to the tow ring and the bolt compressing the spring was screwed down until the desired pull was reached with the foot peddle held down. We checked the tension limiter between rounds and adjusted as necessary to maintain a contestant pull. The winch and turnaround were both mounted on the ground so the tension usually changed as the dew on the grass evaporated. Mounting the winch and turnaround off the ground would reduce this problem.
After a few years, we began receiving complaints about not being able to zoom so in order to satisfy those who came to zoom instead of thermal, we added a bypass switch. If the contestant chose to bypass the tension limiter, NO RELAUNCHES were permitted for broken tow lines. A few people had trouble taping the peddle while the tension limiter was cycling. These fliers could usually get better launches by putting the metal to the metal and letting the tension limiter do the tapping. Fliers with Oly II's and similar models didn't notice any difference from normal winches.
We finally got tired of listening to complaints about not being able to get good zooms so discontinued using the tension limiter and went to heavier towlines. The original tension limiter base is still rusting in the weeds behind my shed in the woods behind my house.
Chuck Anderson RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
