Ultra-light Coaxial--NO GEARBOXE!

[quadrirotor]

What do you think of this set-up?
Preclude the contact of the two rotors!
Enable autorotation!
The main rotor is attached to the engine and is turning by reaction when the above propeller is turning. The precession of the prop is balanced by the precession of the engine.

A smaller version could be a good prerotator for a gyro and could help, in flight, not to lose rrpm...


Schema of principle.
MZ engine 25 hp.
Radcam engine. 60 hp.

[Bob]

I see no reason it wouldn't work provided you give it proper care while constructing it to get the ballance and rudder placement proper.
in the event of engine out your autorotation would be minimal however yes it would still have rotor spin but much less than optimum because of the drag of the upper prop I sujest longer rotors as the longer blades would help over come the drag of the center prop due to an engine out sinerio.
but all in all it looks like a great idea.... Build it and see !
<grin>
Bob.......

[quadrirotor]

I thought the prop would help, the autorotation, in case the engine stops!

[Adam H]

Just a few months ago our club went through a cox helicopter fad when a bunch of us bought them from this website. http://www.coxmodels.com/prodinfo.asp?number=004421
It seems like this idea is using the same principle, except on the model the little .049 engine and little fuel tank spin with the main rotor.

[Al_Hammer]

The prop will absorb most of the power, leaving very little for the rotor.
Basic physics says that power(hp) is torque(ft-lb) X rpm/5252
If the engine is 100 hp, then torque works out to be 210 ft-lb, (assuming a prop rpm of 2500.)
If the rotor turns at 400 rpm, the power to the rotor is 210 * 400/5252= 16 hp.
The prop is using more than 6 times the power.
I agree that the prop won't do much to help autorotation unless it has pitch or feathering control.

[quadrirotor]

You are right AL, this is what is called a false good idea!!! The prop and the rotor "have" the same torque but not the same power (1/2 engine)!!
:peace: :first: :clap:

[quadrirotor]

Can this work?

[Al_Hammer]

This arrangement also has unequal power to each rotor, but it looks like it would work, in principle.
The faster rotor (500 rpm) uses 1.42 times the power of the slower rotor(350 rpm), so it is not as efficient as two rotors working at optimum speed, yet it is less complex than a typical coaxial.
Throttle changes will affect the rotors unequally, so I wonder what problems there might be trying to govern the rotor speed against load changes.

[gyromike]

This arrangement seems to work pretty well.

http://avia.russian.ee/foto/robinson-22.gif

[GyroRon]

And Mike..... thats why I love ya man!

[quadrirotor]

Thanks Al, that's only for the exercice...I don't like Coaxial helo...The Touringcopter is my favorite, and i had not your advice on it!

[Bob]

Hay ! thanks Al !
been looking for the HP formula for a long time now ! <GRIN>
for some reason I couldn't find it anywhere in any of my books !
strange !
thanks
Bob........

[quadrirotor]

This set up could be compared to this one... :D


Bensen little zipster 1958:

http://avia.russian.ee/helicopters_eng/bensen_zipster-r.html

[quadrirotor]

Just for info, the set up of the "little Zipster":

[Rotor Rooter]

Alternatively, how about a GEARBOX, but NO ENGINE? :)

Drive identical rotors with this and compressed air. (http://www.unicopter.com/1311.html) http://www.unicopter.com/Think.gif

[quadrirotor]

Alternatively, how about a GEARBOX, but NO ENGINE? :)

Drive identical rotors with this and compressed air. (http://www.unicopter.com/1311.html) http://www.unicopter.com/Think.gif

Too many small peaces, for me!

Related thread:

http://www.rotaryforum.com/forum/showthread.php?t=18431