Contra-Rotating Propellers

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sanman

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What is the best way to do contra-rotating propellers? Are there any off-the-shelf kits that can be used to modify an existing propeller-hub-shaft assembly?
 

jedi

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I do not know of any but Henryk is the CR hero of HBA. You might PM him or just wait for him to find this.

What engine or power output/rpm do you have in mind? Any particular airframe/engine combination.
 

Martin W

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What is the best way to do contra-rotating propellers? Are there any off-the-shelf kits that can be used to modify an existing propeller-hub-shaft assembly?
Probably difficult to find something off-the-shelf that would be suitable for aviation because industrial units are typically heavy.

They require sophisticated components ... a differential gearset to reverse one shaft ... plus one shaft turns inside the other so at 3000 prop rpm the internal support bearings are seeing 6000 rpm .... not stuff easily found at your local bearing supply store.

Good luck with your experiments.
 

PMD

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=yes,CR, but NOT differential...
Now I am confused. The leading prop seems to be solid drive from the hub/gearbox but the trailing prop only driven from an open set of bevel gears (open diff). The only torque it could transmit would be from frictional losses in the spider gears and their bearings (clearly demonstrated in the video).
 

henryk

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The only torque it could transmit would be from frictional losses in the spider gears and their bearings
=loses are very small =at 70 HP (G13) temperature of litle gear <50 deg.Celsi...

=thrust 230 kG with 3+2 blades 1.7 m propellers !


RPMs are in opposite proportion to the reactional momentum...
 

PMD

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All I am seeing is a second propeller spinning due to the airstream of the first. The main body seems to be driven by the gearbox, and the bevel gear on that side seems to be rigidly attached - or is it the spider that is being driven with the props free to react and transmit torque one to the other? BUt, on second though THAT would no work either. What is being driven and what is driving what?
 

Geraldc

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What is being driven and what is driving what?
If A rotates and C is fixed then B will rotate in opposite direction.
If A rotates and B is fixed then unit C will rotate in opposite direction to input. ===EDITED===
If you drive through B and attach a prop to C and another prop to A
then if the load on each is equal prop C will turn the same way as input and prop A will turn the other way.
1638909956560.png
I have shown the gears on Henryk's drawing here.
1638911312679.png
 
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henryk

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If you drive through A and attach a prop to C and another prop to B
then if the load on each is equal prop C will turn the same way as input and prop B will turn the other way.
=coloures and indexes are right,
but =

INPUT (crancshaft) on "B", f.e. 6000 RPM,

AUTPUT "C" (propeller "A")=2000 RPM (the same direction),
AUTPUT "A" (propeller "B") =2000 RPM (opposite direction).

"
If A rotates and C is fixed then B will rotate in opposite direction."
1: -1

"If A rotates and B is fixed then unit C will rotate in opposite direction to input. "
1:-0.5

=on video "hand propeller breaking"=

"A"(propeller "B") stopped, propeller "A" rotate 3000 RPM !
 

PMD

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The way I see it the only way this could work is that "B" is the drive from gearbox. Shaft and gears "C" must drive the inner prop flange (but I can see no structure connecting that shaft to anything - appears to be floating in space) and gear "A" will then drive the outer prop in opposite direction. This is the only arrangement I can see that would allow stopping the outer prop and holding it, thus speeding up cross shaft and gears "C". This is actually how Gerald's coloured note of Henry's drawing shows (drive of inner prop from cross shaft. However, the structure to take the drive from the shaft to the inner prop flange is nowhere to be seen.

If you go back to Henry's first post the third picture showing two props has the inner prop bolted to some sort of can that COULD be mounted to the cross shaft. The outer prop that would be stuck on such a long shaft and connected to the outer gear "A" would have to have a truly magical bearing to handle the thrust and bending loads from that prop.

There is a lot of critical information missing here.
 
Last edited:

Geraldc

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=coloures and indexes are right,
but =

INPUT (crancshaft) on "B", f.e. 6000 RPM,

AUTPUT "C" (propeller "A")=2000 RPM (the same direction),
AUTPUT "A" (propeller "B") =2000 RPM (opposite direction).

"
If A rotates and C is fixed then B will rotate in opposite direction."
1: -1

"If A rotates and B is fixed then unit C will rotate in opposite direction to input. "
1:-0.5

=on video "hand propeller breaking"=

"A"(propeller "B") stopped, propeller "A" rotate 3000 RPM !
Thanks Henryk I have edited my post.
 

PMD

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From the airboat world, a company called Rotator used to sell them. Don't know if they still do.
 
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henryk

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I can see that would allow stopping the outer prop and holding it,
=I was "hand breaking" inner propeller too,but not so easy (asymmetrical !)

BTW=auter propeller blades have greater "step" (input stream velocity is bigger)...

PS="gearless" CRDifferential on the electric motor...
 

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Riggerrob

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Probably difficult to find something off-the-shelf that would be suitable for aviation because industrial units are typically heavy.

They require sophisticated components ... a differential gearset to reverse one shaft ... plus one shaft turns inside the other so at 3000 prop rpm the internal support bearings are seeing 6000 rpm .... not stuff easily found at your local bearing supply store.

Good luck with your experiments.
6,000 rpm is common in automobile and motorcycle engines.
 
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