Tycho 400 (oz9000)

About this Plan

Tycho 400. Radio control trainer. Wingspan 60in, for .45 engines.

Includes ingenoius altimeter cut-out, to limit flight ceiling to 400 feet.

Quote: "A standard aircraft altimeter is an expensive and weighty instrument. And even accepting the physical cost and size, it delivers only a dial reading meaningful to a pilot's eyes. Within the instrument is a sealed pressure can which expands and contracts to air pressure and records changes of elevation as slight as two feet. Why wouldn't a toy balloon do the same thing? Certainly second best to a real pressure can, but cheap! 10c. That appealed to me. I lashed one across a drinking glass and took it up in my Cessna. At 400 feet, the balloon expanded 3/32in with considerable pressure, enough to actuate a switch. At 1,000 feet 1/4in of expansion, at 2,000 feet, almost 1/2in of travel. Dropping back down toward the field the membrane returned to status quo. With this simple rig, the glass container limits expansion in all but one direction, to create a measurable change in the balloon membrane.
Now if a large plastic fuel tank was opened on the end, a 10c balloon could be contained within. A piece of fueline tubing to inflate the balloon leading out the filler neck of the tank, to the exterior of the aircraft. You blow up the balloon until the balloon starts to swell and reaches an adjustable stop. Clamp off the tubing. The balloon is now full of air, set for today's barometric pressure. Now screw home an adjustable trigger, a 3/32in space away from the balloon protruding through the opened end of the tank. All this can be seen visually through a little window or through an open hatch.
As the model reaches a 400 foot altitude, the balloon will have expanded considerably, coming in contact with a flat smooth trigger plate. This can be linked in any number of ways to retard your throttle ...this is a simple rig which would not recycle. If you exceed your altitude, you go to idle rpm and have to come in and land to reset. All of which will make you judge your ceiling a little better. At the time of this writing, it is anything but fully tested, but in the interest of keeping friendly with the FAA, it is important that we start doing something constructive immediately. Consider this altimeter to be just the germ of an idea and open for further experimentation..."

Tycho 400, Flying Models, December 1972.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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