SuperCobra Video Camera Helicopter

Project Summary

In 1994, the main goal of the project is having a wireless video link to to my website while the heli is in the air. The website is done and the heli is done. I only have to evaluate a wireless video system. I used my ex-roommates ATV gear for testing and it worked fine. For now, I have a vendor picked out, I just need to see if anyone else has used their equipment with success. I also wanted to take video at altitude and digitize it for use on my website. As a side note, the JR equipment outperformed the Futaba equipment by a huge margin. The 8 watt transmitter we were using would interfere with the Futaba. The JR PCM equipment did not even notice it!

With a large enough heli, I would be able to get it back down safely, just in case the engine quit. So autorotation capability was very important. I purchased an old GMP Cobra. The first thing I did was find inexpensive blades that were long enough to produce good lift and could auto well. I found some wood symetrical 864mm blades for scale ships. I extended the boom 12 inches in anticipation of someday either making or finding 1000mm long blades. The head speed was lower because of their extra length. But at 1350 rpm, the blades only needed one degree of pitch to hover. This demonstrated that the blades were fairly efficient at high tip speeds. Maximum pitch was something like 6 or 8 degrees. Weight came out to 220 grams. CG is at 35%. A little tail heavy for such a long blade. The first set of blades tracked perfectly. The 2nd and 3rd sets refuse to cooperate. I went to an Xcell type rotor head and it helped some, but tracking still wanders 1/2". So I think the CG of blades should be 30% or less. I removed the 1/8" lead and installed 3/16" lead. Chordwise CG went from 37% to 32%. Weight is 220 grams. Now the blades track perfectly.

For a couple years the Cobra had a .093" diameter wire drive system. It failed eventually and I went to a carbon torque tube. The difference was incredible. The tail is much more steady and responsive now. It still has a mechanical gyro. It also has much less drag over the wire drive. I had to use 3 bearing supports because of the extra long boom. I also added carbon boom supports. The tail rotor servo is mounted to the vertical fin. It gives great tail rotor authority and is very stable.

The engine is an OS 61 rear exhaust long stroke. It has a new piston and liner that I had to port for extra power. The engine has a Supertigre carb on it, and a long tuned quiet pipe.

Gross weight with batteries and camcorder was around 18 lbs. The Cobra flew just fine. It accelerated and handled well. Empty weight is 11.5 lbs. Fuel capacity is about 17 ounces.

Updates

June 5, 2000: After seeing the improvement in the Shuttle by installing a new dual ball bearing swashplate, it was time to put one in the Cobra to see if that would iron out the shaking. It actually seemed to help. I continued to spin the rotor head at a faster and faster RPM, trying to reach the 1350 RPM from before the shaking problem. The shaking still existed, but was much better. On the third lap of the the first flight, the Cobra threw a main rotor blade. It was a rotor blade root failure. The bolt just pulled right through the wooden root. Destruction of the Cobra was nearly total. I think the swashplate survived. The parts were as far away as 100 feet. The parts were aligned in two straight lines on the ground. This is the pattern I have seen twice before with helicopters throwing a blade. Since the Cobra is so old and parts are very hard to find, I think it would be smart to buy a brand new machine. The Cobra was a very quiet ship.! It had a very distinct blade noise that sounded very cool. It was easy and fun to fly. It was a great Research and Development tool for many experiments....

October 2,3 1999: The SuperCobra got a new piezo gyro. It proved that the old mechanical one was in bad shape. The tail drifting was gone. It was fun to take it for slow laps at the Sacramento OctoberFly on Oct. 2,3, 1999. Close inspection of the drivetrain, should turn up the tail shaking problem.