On Saturday, February 7, 2015 at 9:07:03 PM UTC+13, bumper wrote:
Jim Indrebo (Crazy Creek Soaring) and Rex Mayes (Williams Soaring) have both built tow reels for the Pawnee. I copied some features of their design, and added some features of my own in building three tow reels for SoaringNV.

My reel mounts to the Pawnee tubing just ahead of the pilot. The tow reel uses a #35 chain drive for low maintenance. There are 3 magnets embedded in the reel flange that trigger a hall sensor. This allows a single push of the retract button to retract the full length of rope (pilot does not have to hold button). When the rope fully retracts the reel slows and the hall sensor shuts down the motor (there's a anti-bounce feature that prevents cycling if a magnet should line back up with the sensor).

On reel payout, the line person manually pulls out the rope, connect to glider, and Pawnee taxis forward. The reel motor, is wired to through a resistor to provide a small amount of dynamic braking to the spool so that on taxi forward the reel does not have a tendency to "over spool" (IIRC, resistor is 2 to 4 ohms and is connected across motor leads only when motor is not powered.

Motor is 1/15 hp (from surplus source and designed for robotics I think, cost $20 each) and is sized to allow retraction at any speed up to Pawnee VNE, no need to slow down to retract rope, which on the ground retracts at a rate of about 10 feet per second.

Reel is built "modular" in that electronic box and motor unplugs from reel frame to facilitate swapping out parts.

Note, I have no interest in making more reels!

bumper

So is there no facility to release the rope at the tow plane end?