Scratch built autogyro with electric prerotator

An autogyro is a combination of an airplane and a helicopter. It has a rotor generating lift like a helicopter, but the rotor is not powered in flight. The vehicle is driven forward to remain in the air, this is done by a normal propeller, just like an airplane. The vehicle is controlled the same way as an airplane, but it is a totally different experience to fly.

This is a presentation of my home built autogyro. This design has evolved from a few different prototypes. I built it four years ago, and it still flies gait today.

The takeoff can be very tricky with an RC autogyro. The difficult part is getting the rotor to spin fast enough, especially when there is no wind. Therefore I have made an electric start mechanism for the main rotor. It is a friction drive system with a brushed speed 280 motor that is engaged when the rotor is tilted fully backwards.

I have programmed a microprocessor the measures the signals the the rotor servos, it senses how the rotor is tilted and starts the motor when the rotor is tilted fully backwards. The microprocessor can be seen in the image below.

To control my autogyro I can tilt the rotor forward and backward, as well as left and right. The is a rudder on the tail to help with turning, but there is no elevator. I used the following setup:

• Axi 2212/26 (Gold Line)
• 10x4.7 propeller cut down to 225mm diameter
• JETI Model 19A ESC
• Old Hitec 5CH, 35Mhz radio system
• JR NES-537 servos for tilting the main rotor
• HTX 900 servo for the rudder
• 4 Cell, 13.2V, 1200mAh, A123 LiFePO4 battery
• Brushed 6V Speed 280 motor for the rotor start mechanism

Other data:

• Rotor diameter: 980 millimeters
• Length: 690 millimeters
• Weight: 870 grams
• Flight time: 5 to 8 minutes

The most critical part of an autogyro is the rotor head. The rotor blades are mounted to the rotor head using hinges that are angled in a way that makes the blades decrease their angle of attack when they are bent upwards by their own lifting force. This reduces the difference in lifting force of the blades going backward opposite to the direction of flight and the blades that go forward against the direction of flight. If the blades where mounted solidly to the hub, the rotor would need to be tilted a lot to compensate for that.

The fuselage is built of 10mm thick blue foam, reinforced with fiberglas and carbon fibre strings soaked in epoxy. Since the have been some people asking for plans of my autogyro, I have made a document with detailed high resolution pictures with annotations.

The pdf is available for download on my website:

http://axelsdiy.brinkeby.se/airplanes/autogyro/autogyro.html