Hey Chuck, and all you helicopter / gyronuats (spelling deficiency)

skyguynca

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The infamous prop copter, there are pictures of it but they're knockoffs of Benson's design
People were selling drawings, infact Vortech still sells the plans, they have a few pictures but nobody's flown one.

It's like the propane powered tip Jet Helicopter. Ramjet tip jet helicopters actually flew but none of the propane ones fly they don't develop enough thrust.

David
 

WaspAir

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Ramjets (tip combustion) like the Hiller Hornet tended to really gulp fuel and make noise (and the Hornet autorotation descent rate was rumored to be 3000 fpm). The Djinn with compressor driven cold tips worked much better. I suppose you could rIg up a propane fueled compressor if one wished, but I haven't seen one. I have plenty of propane powered flight hours but all LTA.
 

C. Beaty

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A former Sikorsky engineer, a Russian I think, started a company selling plans for tip jet helicopters using valveless pulse jets. One of his designs had a one blade rotor system.

I, fat dumb and happy, tried a one blade, counterweighted rotor on my gyro. They don’t work. The single blade goes whichever way the cyclic control says to go but the counterweight doesn’t.
 

Doug Riley

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It did have a cycle of sorts and a pulsing exhaust sound, Chuck.

Someone who, I think, was trying to sell Gluhareff propane engines showed up at one of our ultralight flyins perhaps 15 years ago. He had an engine on static display. I was expecting something resembling a large Bernz-o-Matic torch -- a tool you might use for heat to shrink-wrap a boat.

It was a couple orders of magnitude scarier than that.

All the way across the field, the thing was deafening when he throttled it up. Certain parts of the engine glowed orange when running. It sounded like a Vulcan-Gatling gun off an A-10 Warthog.

Yet, for all that, IIR these engines created only a few dozen lb. of thrust. The laws of slipstream/free stream ratio and disk loading are a b---ch. Of course, direct-lift gadgets like Bensen's two-McCullochs-on-a-sawhorse suffer from the same problems. Horribly inefficient, and dangerous in the way they put petroleum-fueled mayhem so near the pilot.
 

C. Beaty

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When I started out to build my helicopter in the 1970s, I decided to try a 1-blade tail rotor despite my disappointing experience with a one blade main rotor. I had heard the old timers talk about how great a one blade propeller was from the 1930s (the Tidd propeller?) and I was also aware that the Hiller Hornet ram jet helicopter had a one blade tail rotor.

But before getting too involved, I decided on a minimum effort experiment to check it out. I cobbled together a 2’ diameter teetering rotor with pitch set manually by loosening a set screw and run by a ½ HP 1750 rpm electric motor. (synchronous speed for a 4-pole induction motor is 1800 rpm with US 60 Hz power.)

The thing vibrated violently whatever the collective setting but the reason was immediately obvious; the drag of the rotor blade was higher than that of the streamlined counterweight. That causes the blade to want to remain stationary and let the drive shaft rotate in a circle.

Such a rotor can be balanced by an additional counterweight at 90 degrees but the counterweight would have to slide in accordance with collective pitch setting.

It finally dawned on me that a conventional 2-blade tail rotor made more sense.
 

okikuma

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Here's a video of a homebuilt co-axial helicopter in Japan. By the valve covers, the motor looks to be a Subaru EA-82.

After watching the video several times, I believe there is no collective pitch on this helo, therefore the blades are set at a fixed pitch. The "collective stick" on the left side is really just a large throttle lever. When the pilot lands, one can clearly see his left hand doesn't move a traditional roll on/roll off throttle (lack there of) under his grip, and when the "collective" is bottomed out, one can hear the engine RPM reduce in unison.

If this is a one off co-axial design, I admire his simplicity, even with the Gates type of wide belt and 90 degree transmission. Yaw control looks soley by changing the angle of the vertical stabilizers under the down wash of ths rotors. The subaru motor is very adequate in horsepower and with four stroke reliability.

This little helo would be easy to fly for a beginner.

Wayne

 
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