Focke Achgelis FA-61 (oz3396)

About this Plan

Focke Achgelis FA-61. Scale autogyro model.

Quote: "A real breakthrough in model aircraft design, this R/C autogyro is easier to fly than many so-called 'trainers.' It's also great for modelers who hate to build wings! Be the first in your block.

This twin-rotor, semi-scale helicopter can be flown by anyone capable of flying a 3-channel trainer. The reason, of course, is that the helicopter is not really a helicopter at all, but an autogyro! However, before I confuse everyone, let me give a short history of the real FOCKE-ACHGELIS 61.

The F-A 61 was one of the first truly practical helicopters, and was the brain-child of Doktor Heinrich Karl Johann Focke_ The machine made its first flight, lasting 28 seconds, on June 26, 1936. The first craft was built using the fuse-lage and engine of a FOCKE-WULF 44 basic trainer, with the tailplane mounted on top of the fin and the propeller cut down to the diameter of the engine cylinders to serve purely as a cooling fan. It gave no assistance in forward flight, although it probably fooled many authorities into believing that the machine, like the model, was actually an autogyro. The twin rotors, mounted on steel-tube outriggers on both sides of the fuselage, were fully articulated 3-blade assemblies with a blade angle that could be increased or decreased so as to provide lateral movement of the craft by creating a lift differential between rotors.

In May of 1937, the F-A 61 made its first autorotational landing. In 1938, the controlability was demonstrated by Germany's celebrated aviatrix, Hanna Reitsch, who flew the machine inside the Deutschlandhalle Sports Stadium in Berlin. These feats were all accomplished by the first prototype which was given the registration D-EBVU. Meanwhile, a second prototype, D-EKRA, from which my model has been copied, was completed and from 1937 onward established many records including the following:

1. Distance: 143 miles on June 20, 1938.
2. Altitude: 11,243 ft on Jan 29, 1939.

You may be interested to know that this particular configuration is still in use today in several Russian helicopters, one of which I believe is gigantic, with two 114 ft diameter rotors.

The model, of course, is actually an entirely different sort of craft. I have been experimenting with R/C autogyros for several years, and have never really had success until now. All the previous models were of single rotor configuration and all exhibited the same sensitivity to one thing, torque from the engine. To overcome this, I had to install small ailerons, and though the machines did fly, they were very erratic and not too stable.

The idea of the twin rotor design came from an old Roy Clough article in a late 1940's AIR TRAILS. I thought that possibly, a stable craft could result from this configuration. Not being an engineer, I had to rely on my experience with free-flight gyros for blade angles, sizes, and rotor angles. For other dimensions, it was all hit and miss - fortunately for me, more hit than miss.

The first model I built using this configuration was nothing more than a highly modified FALCON 56. To my amazement, and everyone else's the model flew after only a couple of changes in center of gravity location and blade angles. A short time later, I came across a picture of the F-A 61 in an old Air Progress magazine, and thought it would make an ideal subject because of its configuration. Since no accurate 3-views were available, and to keep the model simple, I built it from photographs, using as basic a construction technique as possible.

The model itself has a simple box fuselage with spruce rotor booms, and a T-tail. The rotors themselves are also simple. They consist of 3/16 sheet balsa blades bolted to hubs made from 3/32 aluminum. No complicated hinges or flapping mechanisms, just light simple rigid rotors. The rotor bearings should also prove to be no problem..."

Direct submission to Outerzone.

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