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Old Jan 07, 2015, 11:09 AM
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RickC_RCAV8R's Avatar
Canada, BC, Castlegar
Joined May 2014
530 Posts
Coaxial Operation

Gentlemen :

I am trying to understand the theory of the coaxials and am having problems wrapping my head around this concept. As I understand it , one set of blades does not have the pitch changing / levelling flybarattached while a second set does . As such , if one uses the fixed pitch set as a reference , only the difference of RPMs of the shafts with relation to each other would change the YAW . If both sets are at the same RPM , you would get a straight UP / DOWN lift . if one set is faster than the other , the overall syysem response would yield a yaw in the one direction due to angular momentum . Am I correct in this theory ?

My idea is to strip down a pair of these little machines to the point where I could bolt the whole frame onto a rotation shaft for a V22 Osprey test platform . Use the little heli;s as the engine nacelles and use another micro servo to do the TILT rotor function .

Is this too far out there ?
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Old Jan 07, 2015, 02:40 PM
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Letchworth, Great Britain (UK)
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You're right about the principles of how the coaxials work. In an Osprey you'll presumably want to keep both props at the same rpm, and you won't need the flybar or the variable pitch. So I think you'll need some way to fix the top rotor instead of letting it float. With fixed blades and no flybar you should be able to cut down the shaft to the top rotor so that the rotors run much closer together than they do in a coaxial heli. If you've got the helis lying around, it's a nice cheap way to get yourself two contra-rotating prop sets
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Old Jan 08, 2015, 06:30 AM
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spykez's Avatar
Joined Jul 2011
1,088 Posts
It's going to be difficult to get a tilt rotor built.

But there are kits.


Now to your question about coaxial main rotors. The idea is to have the torque from both (acting on the fuse) cancelled out. Since torque here would be a function of pitch and rpm, varying either will vary torque.

Mall heli's generally do this in a very simplistic manner by just varying rpm. I think there is at least one tilt rotor somewhere with fixed pitch, but function wise, I don't know. I don't think it'll give you the level of finesse of a cp model. ... As I suspect one probably gets better control when the dominant variable would be pitch as I would think the response would be faster. I expect that's what happens in that scale v22 and other cp coaxes and real 1:1 birds. But I don't know for certain.

Edit: here's a link for a mall heli tilt rotor
And, on yeah, remember the walkera avatar gunship. That doesn't fully tilt but it does tilt the rotors.. A bit. Iirc.
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Last edited by spykez; Jan 08, 2015 at 06:38 AM. Reason: Edit link added
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