The Two-Speed Ignition Control was an early development of Jim Walker to control the speed of Ignition Engines

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Jim Walker's Two-Speed Ignition
Control System for U-Control

Diagram of the Two-Speed Ignition System for control line model airplanes by Jim Walker

Wood U-Reely with speed control that Jim Walker used with his U-Control system of Control Line flying
Wooden U-Reely with two speed ignition control

Jim Walker's attempts at speed control started before World War II when Jim used a third line in the Fireball to regulate the Ignition Timer (spark advance/retard) on the engine in the Fireball. This way you could take off and land realistically with the Fireball. Additional details can be found on the U‑Control patent page.

This is the system of early ignition engine speed control developed by Jim Walker. The instructions and diagrams (illustrations) were included in the pre-war Fireball kits. So motor (engine) speed control for U-Control flying goes back to those early years. This system allowed him to accomplish his famous Sabre Dance. A solenoid in the plane is operated by a voltage ariving through insulated lines coming from the U-Reely hand control. The relay allows for two positions of "on" or "off" and this is used to advance and retard the spark of the ignition engine. This system predates carburator controlled systems.


The high speed point makes contact at all times, and slow speed is obtained by delaying the firing time through the slow speed point. Notice in the drawing that the slow speed point is normaly connected to the high speed point, and high speed is obtained by energizing the relay, which in turn disconnects the slow speed point.

The pigtail leads from the bell crank to the relay should be of indoor radio aerial wire or similar type. Since flying wires average one ohm per foot, the relay should be 1,000 ohms, or more. Here is a table of relays and voltages recommended:

Internal wiring of Jim Walker's U-Reely with speed control for control line flying
Early photo of wiring for ignition speed control
  1. Leach Relay 1.280 ohms. 22-1/2 or 30 volts.

  2. Price Relay (shown in diagram) 1,800 ohm.

  3. Sigma and other type sensitive relays:

    • 2.000 ohms, 22-1/2 to 43 volts
    • 5,000 ohms, 45 volts
    • 8,000 ohms, 45 to 67-1/2 volts

Note that 4-1/2 volt boosters are specified. You will find tliat most of your ignition troubles disappear, if you use 4-1/2 volts for boosters, and that the life of your flight batteries will be increased 5 to 8 times.

The batteries arc mounted in two Austin pen cell type boxes with one end of each removed and fastened to 1/8" plywood. Also shown is a photograph of the newest U-Reely Control handle with two-speed relay control switch button. Follow these specifications for greater pleasure in control line flying.




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