My '74 helicopter

C. Beaty

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I stumbled across a good photo of the helicopter I built in ’74. There was never any intent to sell anything so doll up was not an issue.

Power was by a Canadian Kohler 440 cc snowmobile engine of ~30 hp without the exhaust system.

Empty weight was ~300 lb. using 3 cutdown Hughes OH-6 rotor blades.

It was a floating hub system without flap or drag hinges; the blade feathering bearings were connected to the apices of a triangular aluminum plate, laminated from 4 layers of structurally bonded 0.093 sheet that was in turn connected to the rotorhead via rubber bushings. This permitted the hub to self-align with the rotor tip plane, eliminating the need for individual flap and drag hinges.

The rod that can be seen sticking through the rotorhead was tilted for cyclic and raised and lowered for collective. It pivoted on a ball bushing at the hub center.

The tail rotor shaft can be seen to be curved; that’s to permit it to operate above critical speed. A small diameter straight shaft will encounter whip if operated above the critical speed which is determined by stiffness and unsupported length for a given shaft weight.

This thing was built over a period of 3 months, already having the rotor system left over from another project.

The most time consuming part was development of the tail rotor. I made up a test stand driven by a 10 hp electric motor with the tail rotor gearbox mounted on trunnions arranged so that torque could be measured. I had overlooked the loss due to centrifugal air pumping; at the intended speed of 2400 rpm, zero thrust consumed 2 hp. Plugged the blades and power dropped to ½ hp as it should have been.

In this hovering shot, the left skid is low; that’s because the rotor must be tilted to counter sideways push from the tail rotor and the tight coupling between rotor and airframe causes the tilt.

Tight coupling between rotor and airframe requires that the CG be as near to the rotor center as possible to minimize gyroscopic effects.
 

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C. Beaty

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I didn't forget.

The forum won't let me post a picture larger than 50 KB so I had to go back and reduce resolution.I expect it's because I'm on a slow connection and something times out.
 

CLS447

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Chuck , I believe it is 150 KB.

But now I am adding pics that are waaaayyy over that.....It seems to be sizing them for me.

It just takes a little while for them to download. But it doesn't say TOO LARGE anymore !

Did you try it yet ?
 

Aviomania

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Nicely done!!!! especially if it was designed and built in 3 months!!!

was 30 hp enough to brake ground effect?
 

C. Beaty

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As you know, Nicolas, the “secret” to flying with limited power is low weight, low disc loading and low blade loading. Blade loading sets rotor tip speed.

Yes, it was able to fly out of ground effect but not exactly like greased lightning.
 

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C. Beaty

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I don’t have much documentation, Nick. I had a twin lens reflex camera at the time but didn’t use it very much because it was such a hassle to develop film and make enlargements. Photography has traveled a long way over the past 35 years. Light years as compared to rotorcraft.

Most of the photos of this helicopter were given to me by others.
 

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StanFoster

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Chuck- I must say that you are very high on my list of people that impress me. I am going to hang around you a little bit to see if genius is contagious! Stan
 

C. Beaty

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The old saying Stan is; “90% perspiration and 10% inspiration.”

The poerspiration is liable to rub off if you get too close.
 

Jens

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C-74

C-74

74 helicopter -what a great machine.
Sort of a new reference for how small a 1 man helicopter can get.

How about using hydraulik for the tail rotor?
Can not work? And no one have done that - or?

Nick,
Look how high the engine is - no main shaft at 5000 rpm to worri about..
 

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Aviomania

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As you know, Nicolas, the “secret” to flying with limited power is low weight, low disc loading and low blade loading. Blade loading sets rotor tip speed.

Yes, it was able to fly out of ground effect but not exactly like greased lightning.
That were Grate times!!!!! ( i always say i was born in the wrong time.... i love to experiment with flying machines.... ). Life Pace is so fast now days that it takes grate effort to devote time where you love to...... unless you have tones of money :)

I hope soon i will be able to visit a major rotor-craft fly-in in the US and hear stories and ideas in person!!!

:first:
 

brett s

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How about using hydraulik for the tail rotor?
Can not work? And no one have done that - or?
That would be a lot heavier than what he's got there. There's a reason plain old shafts are used for tail rotors :)
 

Jens

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Yes, the shaft solution have less weight, better eficiency, less noise - a lot or a little.
But hyd is mechanical simpler. And more important, control of thrust could be MUCH simpler - because you could use a prop and just vary the rpm.

Some one must have tried this? For a prototype heli, a homebuild heli or something.
 

brett s

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No, you can't just vary the rpm of a prop - you need thrust in both directions.

I fail to see where a hydraulic motor + pump + tank + fittings & long lines (and you might need a cooler too) is any simpler than a shaft running on a few bearings with a 90 degree gearbox on one end.
 

gyromike

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Yeah but Brett, hydraulics would be so much more 'cool'.
You could say, "I have a hydraulically powered variable speed tail rotor", and impress all of the newbies.

Say it with me...Hydraaaauuuuulic...
:rolleyes:
 

Jens

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Thrust in one direction should be enough. If you let go of thrust, the frame will for sure rotate.

Probably variable pitch is faster, more precise etc.

The hydraulic, for a hydraulically powered variable speed tail rotor, that is needed for a C-74 or similar should be quite similar to a powerfull hyd prerotator - I guess.
 
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brett s

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Thrust in one direction should be enough. If you let go of thrust, the frame will for sure rotate.
Not if you aren't using much or any power, as in an autorotation or when descending at a low power setting.
 

Al_Hammer

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A hydraulic tail rotor was tried on the Masquito prototype. This heli had several unusual features, such as a hiller servo controlled main rotor and a very short , fast turning main rotor.

A couple of snips from pprune:

The Masquito boys in Belgium tried a hydraulic tail rotor drive gearbox but changed it to a cable drive because if I remember correctly they either could not get it to hold oil for long enough , or maybe the whole thing got too hot.


Hydraulic driven tail rotor was tried on the second prototype Masquito heli
from Belgium. Now they are back to flexible shaft (as used in Wunderlich prerotator) driven tail rotor.

http://www.aviastar.org/helicopters_eng/masquito.php
 

C. Beaty

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There are many ways of transmitting power over a distance of 10-12 feet.

As a general rule, cost, weight, reliability and durability point to a drive shaft and gear box.

The main loss in a gearbox comes from churning lubricating oil. This loss is dissipated as heat so the operating temperature of a gearbox is a good measure of its efficiency.

Should I be tempted to do a repeat today, I’d take a good look at what’s available in Gates Polychain belts. Gates must make long skinny ones.
 
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