Scooter Tow Q and A

by Dave Broyles © 1997

revised 2005

  1. Q. What is scooter tow?

    A. Scooter tow is towing with a stationary winch adapted from a motorscooter with a constantly variable transmission (CVT) and a centrifugal clutch.

     

  2. What is a CVT?

    A. The CVT (constantly variable transmission) is a simple automatic transmission consisting of two variable sized pulleys, one of which gets larger as the vehicle goes faster, and the other is spring loaded to allow it to get smaller as the other one gets larger. The advantage of a CVT is that it tends to keep the RPM constant through a wide speed range and eliminates the need to shift gears.

     

  3. Q. How big a motorscooter is needed?

    A. Motorscooters from 50 to 250 have been tested and work well, but the 250cc scooters have proved best for all around towing.

     

  4. Q. Any particular model or brand?

    A. Yamaha Riva 125, 180 and 200s have been used successfully as have the Honda Elite and Helix 250 water cooled scooters. These are all single cylinder 4-stroke scooters with centrifugal clutches and constantly variable transmissions. I recommend avoiding scooters with manual transmissions.

     

  5. Q. How are they converted?

    A. First, a winch drum is built to replace the rear wheel. Then a guide boxes is built to guide the rope from the winch drum to the glider. A basic setup needs only these items to allow a scooter to be converted on the spot to a winch.

     

  6. Q. How is a winch drum constructed?

    A. Usually an old wheel has flanges welded to it. If the wheel is aluminum, then ¼" aluminum 6061-T6 plate is usually used. For a steel wheel,  3/16" steel plate flanges works well. Reinforcement of the inside of the drum with rings made of 3/16" steel plate is necessary for a 250cc Honda Elite or Helix. A scratch built wheel drum can be made wider and with a flat bottom, and has more capacity than a wheel drum made of a rim.

     

  7. Q. How much rope will a wheel drum hold?

    A. Using 1/8" Samson Alsteel 12 rope, I have gotten about 2500 ft  on a Elite 250 wheel drum 19" in diameter.  The maximum diameter is determined by the clearance between the axle and the engine itself.

     

  8. Q. Is it possible to make the wheel drum wider?

    A. I am currently using a  wheel drum using an Elite hub and a scratch built wheel drum that is 1/2" wider than a wheel built from a rim. This wheel drum has somewhat more capacity than one built from a rim. The ultimate limit is that a rim that is too wide will interfere with the brake arm on the left or the swing arm on the right. Each model scooter has different considerations, except that the Honda Elite 250 and the Honda Helix can use the same size wheel drum if an Elite hub is used.

     

  9. Q. Is the brake on the rear wheel needed .?

    A. The brake is an absolute necessity. When the engine idles or stops, the centrifugal clutch disengages the engine from the wheel, and the wheel will spin wildly and backlash the rope without prompt application of the brake.

     

  10. Q. How can tension be measured during a tow?

    A. There are several different ways. The scooter can be put on wheels and restrained by a tension gauge. The rope can be run through a lever and pulley arrangement with a tension gauge. Currently, the lever and pulley design seems to be the most effective.

     

  11. Q. How high can a glider be towed with a scooter tow system?

    A. This depends on a number of variables such as the amount of rope stretched out, the wind speed, the wing loading, the gross weight of the glider and pilot, the power of the scooter, but typically, with 2000 ft. of rope between the turn-around pulley and the glider, hang gliders to about 600-1000 ft. and paragliders about 25% higher.

     

  12. Q. Can a scooter tow system be used for step towing?

    A. Yes, if several conditions are met. There must be enough rope on the drum to avoid paying it all off on the down wind leg of the step. This probably necessitates using 9/64" Spectra and putting 5000 ft. of rope on the drum. Also, the operator must be very knowledgeable to prevent tangles while the pilot is reversing directions and flying downwind and/or an automatic braking system must be employed. (See the next two questions.)

     

  13. Q. What difficulties are encountered operating a scooter tow system.?

    A. A common characteristic of all scooter tow systems is that they have a centrifugal clutch and what is known as a CVT drive. This is at once their advantage and also their disadvantage. When the throttle is completely let off to idle, the centrifugal clutch disengages, thus letting the drum free wheel. The operator must be aware of this and always apply brake when the engine is throttled down or stops to prevent back lash.

     

  14. Q. Is it possible to backlash automatically?

    A. There are two different ways to do this. A constant drag may be applied to the wheel drum, or an automatic brake may be applied when the line goes slack. I have tested the constant drag method, and it works, but adds work to the engine. For training, it isn't necessary, and I don't use it.

     

  15. Q. What is the most common mechanical problem with a scooter tow?

    A. While towing, if the wind increases so that the line stops pulling in while the scooter is at full throttle, all the power of the scooter is dissipated in the centrifugal clutch and it will burn out in about 60 seconds. Idling the scooter and controlling the tension with the brake will protect the clutch.

     

  16. Q. What is the best rope for scooter towing?

    A. I only use spectra, Samson Amsteel 12 18" or 5/64". I find it to be much more cost effective than less expensive ropes.

     

  17. Q. What is a turn around pulley?

    A. To keep the scooter tow system and it's operator close to the pilot launching, one may place a pulley at a distance, and run the rope to the pulley and back to the pilot.

     

  18. Q. What sort of pulley is used?

    A. I used a lineman's pulley cast from aluminum with internal ball bearings.

     

  19. Q. Where may these pulleys be obtained?

    A. Western Power Products, the company that made the lineman's pulley is out of business and I  buy them wholesale and stock them for resale. It is a lineman's pulley, a snatch block made of cast aluminum with ball bearings.

     

  20. Q. What problems are associated with using a pulley?

    A. It must be anchored and maintained properly. The top of the pulley should duct taped to keep the rope from snagging on it.

     

  21. Q. What is the best way to anchor a pulley?

    A. It should be attached to something able to withstand about 1000 lb. of force. I usually anchor it to a mobile home earth anchor screwed 30" inches into the ground, or attach it to the trailer hitch of a parked truck. The anchor should not be able to snag the rope since rope recoil is a substantial problem.

     

  22. Q. What has to be maintained on the pulley?

    A. The bearings are under considerable load.  In the case of the lineman's pulley, the ball bearings should be replaced at least once a year. The bearings should have seals on both sides. If the bearings fail in use, the pulley will heat up and damage the rope, perhaps for several hundred feet and eventually the heat will melt the rope in half.

     

  23. Q. What causes rope recoil?

    A. A sudden release of tow tension will cause an elastic rope to recoil at the pulley for 5 to 10 ft. If it tangles or gets hooked the wrong way on the pulley it will be damaged. Pilots should be trained to signal for the operator to reduce tow tension before releasing.

     

  24. Q. Does the pulley cause extra drag?

    A. The rope from the scooter to the pulley drags on the ground, both causing extra wear and extra drag. If there is turf or other vegetation on the ground, extra care must be exerted to keep the ground rope perfectly straight as the tow force may not serve to straighten it out. On the other hand, tall grasses often cause no particular problem and the rope will straighten right out on the first tow.

     

  25. Q. Is there any way to reduce wear on the rope?

    A. The splices should be tapered, if splices are used. If convenient, the turn-around pulley should be mounted off the ground.

     

  26. Q. What is a retrieval winch?

    A. It is a small winch usually with #18 nylon string on it, that attaches to the towline about 25' from the end. It is used to pull the tow line back after a tow.

     

  27. Q. Why is there a parachute on the end of the line?

    A. The tow line parachute serves two purposes.  The first is to keep the rope from falling to the ground in a pile when released, the second is to cause the end of the rope to drift downwind and reduce the line retrieval distance.

     

  28. Q. Why is there a leader between the tow line parachute and the pilot?

    A. The leader keeps the tow line parachute from inflating near the glider being towed, and eliminates the possibility of the parachute being hung on the glider. It also provides some separation between the retrieval line and the pilot.

     

  29. Why is the retrieval line attached to the top of the tow line parachute?

    A. When the retrieval line starts pulling the tow line back, it collapses the tow line parachute, and pulls it back top first to keep it from dragging in the air and on the ground.

     

     

     

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