Innovation: Helicopter prototype with counter-rotating rotors / Robbe autopilot / Four-stroke gasoline engines

Takashi Hirata, technical director of the company “Kalt,” proudly presents his latest design: a model helicopter with two counter-rotating rotors. According to him, the prototype exhibits excellent flight characteristics; its stability is almost sensational, and no other model helicopter is as easy to control, since there are no torque-related issues. It is still unclear when the model will be released, as there is still a considerable amount of development work to be done before it is ready for mass production.

Above: “Kalt”—prototype of a model helicopter with counter-rotating rotors.

An autopilot from Robbe has been available for about half a year. Its core component is a gyroscope powered by a small electric motor. The movements are “sensed” without physical contact, which explains how it works so precisely. I’ve been a competitive pilot for several years and initially thought it should work just as well without a gyroscope. At a competition in Belgium, Paul Ingold and I were almost the only ones without an autopilot. There’s almost always strong wind in Belgium, and we had a hard time flying clean nose and tail circles. So I decided to buy one of these gyros. After reading the instructions, I installed the gyro in the Star-Ranger. I set the efficiency to 70%, switchable to 30%.

Even the first flight was amazing. The tail was absolutely steady. Now I had to get used to the new control scheme. There’s no more counter-steering or, for example, blocking off during a pirouette. During a turn, I simply tapped the control slightly as usual at the top of the turn; the helicopter now descended sideways and turned only slowly into the direction of flight. Now, for this maneuver, I have to control the tail rotor until the model’s nose is pointing down, then let go, and the autopilot maintains the new flight path.

For flight maneuvers, I set the sensitivity to 30%; for hovering maneuvers, to 70%. It’s best to assign this switch to a separate control channel. If the helicopter responds too weakly to tail rotor deflections, you can slightly increase the tail rotor deflection.

The Robbe gyro comes with a good instruction manual that explains everything about installation, operation, and setup. At first, I recommend setting the sensitivity to no more than 50%; this provides a good balance between automatic stabilization and controllability. Once you’ve gained a bit more practice, you can experiment with varying levels of gyro sensitivity. I’ve already used the Robbe gyro at the Swiss Championship and during several friendly fly-ins, and I’m very satisfied with it. I power it using the Emplänger 1200 mA battery. Anyone who flies more than about five flights without recharging would be wise to ensure the gyro is powered by the auxiliary battery. If that battery runs out, you won’t crash—the gyro will simply stop working.

I’m happy to answer any questions from those interested. Here’s my address:

Rudolf Linder
Eyfeldweg 1, 3400 Burgdorf

sll. The Japanese company “Kalt” sees the future of model internal combustion engines in four-stroke gasoline-powered engines. Our photos from the “Kalt” development workshop in Gotenba, at the foot of Mount Fuji, show an “OS-Gemini” boxer engine converted to gasoline operation, a modified “Kalt FC-1” (7.5 cc) with a mechanical ignition contact (behind the propeller), and—on the test stand—the same engine with a contactless ignition system. Tests with the latest version show that its performance is roughly the same as that of the glow plug version, but it can fly about three times as long on the same amount of fuel. Now that very good mini spark plugs have been developed in collaboration with NRC, nothing stands in the way of mass production of this small four-stroke gasoline engine. The engine is expected to hit the market in mid-1982.