Re: [RCSE] Contests, Landings, etc.

[Chuck Anderson]

My club, the Coffee Airfoilers. developed a tension limiter winch about 30 
years ago.  It was published in the Jan/Feb  1977 issue of Sailplane and a 
number of clubs built the winch.  We set the tension at the tow ring at 25 
pounds and was able to launch sailplanes up to 11 pounds without 
problems.  We used 110 pound test line and never had problems with broken 
lines unless the contestant elected to launch without the tension 
limiter.  The tension limiter could be be bypassed, but if the contestant 
launched without the tension limiter, he got no reflights for broken 
towlines.  Most flyers with larger models found that they could get better 
launches by standing on the winch petal and let the winch do the 
pulsing.  The only disadvantages to using the tension limiter winch was the 
extra work required to maintain and setup the winch.  It was also necessary 
to periodically adjust the tension for variations in line ground drag as 
the day went on and the wet grass dried out.  The remains of the original 
tension limiter winch base is still in the woods behind my storage shed.

Chuck Anderson
At 10:54 AM 10/1/2004, you wrote:
----- Original Message -----
From: "Michael Lachowski" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Friday, October 01, 2004 7:28 AM
Subject: Re: [RCSE] Contests, Landings, etc.
> The correct way to limit launches is on the motor side, not on the
> line side.   Broken lines just slow down contests and make everyone
> unhappy.
>
I agree with Michael.  The motor side is the place to limit pull on the
winch line, if that is what is desired.
There is a simple technique that I have heard has been tried with some
success in the past. It involves mounting the winch on a spring loaded
pivoting device that electrically limits the force on the line.  A
microswitch interrupts the circuit between the foot switch and solenoid when
the pull on the winch line moves the winch on the pivot against the pull of
the spring (the weight of the winch itself is also involved). This cuts
power to the winch motor until the line tension lightens enough to allow the
spring to pull the winch off of the switch.  The spring is adjusted against
the pull on the line using a simple spring scale such as is used to set up
highstarts to set the trip point.  If you just stand on the pedal, the
result is a near constant force  pulsing of the winch line throughout the
launch. Actually the pull slightly declines as the diameter of the stack of
line on the drum increases with line taken in. This scheme works without
breaking of the line or releasing the model early.
This is 1920's technology, but effective.  A more expensive technique using
strain gauges and electronic motor speed controls could be devised. 8^)
I am sure that with proper launch technique, towering launches can still be
achieved with such a system set at 80 pounds pull launching 4 pound models.
I suspect that experimentation will show that 20 to 30 pounds will be more
than adequate.
Tim

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