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  #16  
Old 04-17-2012, 11:00 PM
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Dave Jackson
 
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Juergen,

Quote:
The two rear rotors work in the induced velocity field of the front rotors, which means they have to be inclined backwards to be able to develop the same lift as the front rotors.
I have always assumed that 'induced velocity' is in reference to situations where the rotor, or propeller, disk is physically (mechanically) increasing the freestream velocity. This results in the streamtube having a small diameter.

Here is a movie of Helicopter Rotor in Axial Descent Transitioning into Autorotation Through VRS. Interestingly, it shows the diameter of the airflow beyond the disk as being increased; after autorotation is reached. In this situation gravity is driving the rotor.

I suspect that with a quad gyrocopter the rear rotors might be operating in an mild 'ground cushion' type of effect due to the front rotors resisting the upward flow of air.

The following sketch (with exaggeration) is a attempt to portray a situation where the craft is climbing. The pilot has pushed forward on the overhead sticks. This has shifted his weight back about the gimbal above his head. His push has also tipped the four individual disks back by their control rods, which provide different degrees of tip.


The 'coning' within each rotor and between the four rotors is only to provide speed stability. Their cone could be reduced.


Dave
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  #17  
Old 04-17-2012, 11:14 PM
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Juergen,

I just read your post #15.

IMHO the 'induced flow' vortices at the tip and just behind the trailing edge of the blades are downward, but they are very quickly carried up and through the plane of the disk.


Dave
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  #18  
Old 04-17-2012, 11:59 PM
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I think that to move away from the standard gyro rotorblade system is a move away from what makes a gyroplane unique .... long rotating wings and the inherent (gyroscopic) stability it produces .... if we are going to deviate from that .... we might as well just install a fixed wing above .... and end up with a weight shift trike or kite. My thinking anyway.

I do think it would be interesting to test a system using "4 small rotors" like you propose ... just to see how it compares to a long blade system.

Dave .... we need to buy you a wind tunnel for Christmas .... you come up with some interesting concepts that need further testing ....
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  #19  
Old 04-18-2012, 12:12 AM
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Quote:
Originally Posted by Rotor Rooter View Post
Another idea is thanks to Stan. He brought up the subject of root loss a couple of days ago. The idea is to fill the diamond area between the four rotors and reduce the tip loss on 25-percent of the circumference of all four rotors. In addition it could act as a lifting body.
Dave
Dave .... back to the subject of "root loss" (on a two blade system) ..... I recall a couple of years ago a picture of a secondary (smaller) rotor centered in the main rotor to make up for root losses .... not sure if it was a gyro or helicopter .... I am sure it was on this forum.

Anyone remember ?
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  #20  
Old 04-18-2012, 01:02 AM
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Arnie, interesting idea. Perhaps if it was bigger and had a large pitch it might also offset some of the torque caused by pre-rotation.

Dave
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  #21  
Old 04-18-2012, 01:37 AM
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Quote:
Originally Posted by Rotor Rooter View Post
Arnie, interesting idea. Perhaps if it was bigger and had a large pitch it might also offset some of the torque caused by pre-rotation.

Dave
That may even be the case .... (If I recall) it was a counter-rotating (propeller) centered under or above the rotor , and was for supplemental engine cooling as well (high mounted engine) .

That makes me think it was a helicopter (the requirement for supplemental cooling) ... the designer decided to incorporate the powered cooling fan (prop) to counter some of the torque as well .

I thought I had saved the photo ... but unable to locate it right now..
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  #22  
Old 04-18-2012, 01:22 PM
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Arnie,

Here is a model that Hans built a year ago. He was not happy with the thrust, but that is due to having one motor drive both 'rotors'.



Dave.
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