Lift balancing on the Gyrhino

Aviator168

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Hi forks,

It has been a long while since I last post. How is everyone? I am getting back to gyroplanes from a long side track. I am curious how the Gyrhino balance the lifts between the advancing and retreating blades. Since it has three blades and does not seem to be doing the flapping like other gyros. Does the pilot have to actively use the collective to balance the lift or it use some other automatic mechanizms to do the job? Anyone know? Thanks.
 

Vance

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The flapping hinges take care of the dissymmetry of lift of the three blade rotor without the pilot’s intervention.
 

Aviator168

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I don't quite understand. Are you saying the hings of the individual blades or the entire hub assembly can flap?
 

XXavier

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The individual blades are free to flap. So, the tip-path plane tilts back, the AoA of the advancing blade is reduced and the AoA of the retreating blade is increased.

That's probably the way Gyrrhinos's rotor works. There are other ways to solve the problem of the dissymmetry of lift, but that one is the most usual.
 

Aviator168

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What I am having problem is that since the advancing blade and the retreating blade are not tied together, how is the dissymmetry of lift cost the blades to flap? Unless the blades are tied together through the hub.
 

XXavier

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What I am having problem is that since the advancing blade and the retreating blade are not tied together, how is the dissymmetry of lift cost the blades to flap? Unless the blades are tied together through the hub.
No need of that. Cierva used individually flapping blades in his first successful autogyro prototype, almost 100 years ago, and that became the standard solution to the dissymmetry of lift both for gyros and for helicopters.
 

Aviator168

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Are you saying when an independently hinged blade generates more lift will automatically cause another independently hinged blade to flag down even without linkage of any kind? This is why I ask the original question and I still don't understand. I do understand how the two blade teetering work and just need some good explaination and hopefully some good diagrams to get this through to me.

Edit. Another thought. Maybe just by tilting back the rotational axis will automatically balance the lifts.
 

XXavier

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Are you saying when an independently hinged blade generates more lift will automatically cause another independently hinged blade to flag down even without linkage of any kind? This is why I ask the original question and I still don't understand. I do understand how the two blade teetering work and just need some good explaination and hopefully some good diagrams to get this through to me.

Edit. Another thought. Maybe just by tilting back the rotational axis will automatically balance the lifts.
The individually hinged blade responds in an individual way to the forces (aerodynamical or other) that act upon it. It does of course ignore what the other blades are doing...
And it makes no difference if the number of blades are two, three, four... (or even one...). The first rotor to work in this way was Cierva's (in his C4 prototype, four-bladed, if I remember correctly... In 1923.)
 

Aviator168

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OK. That might explain the advancing blade flapping up, but the retreating blade is not going to flap down. So the balancing of lift is by reducing the AoA of the advancing blade without simultaneously increasing the AoA of the retreating blade.

Edit: Take that back. The advancing blade is at its most tilt when it is aligned with the aircraft and at this point the centripetal force forces it to flap down so the AoA is increase. Now I totally understand how it works. The forces involved and their interaction is different from the two bladed seesaw setup. Thanks XXavier for keeping this conversation going to the end.
 
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XXavier

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OK. That might explain the advancing blade flapping up, but the retreating blade is not going to flap down. So the balancing of lift is by reducing the AoA of the advancing blade without simultaneously increasing the AoA of the retreating blade.

Edit: Take that back. The advancing blade is at its most tilt when it is aligned with the aircraft and at this point the centripetal force forces it to flap down so the AoA is increase. Now I totally understand how it works. The forces involved and their interaction is different from the two bladed seesaw setup. Thanks XXavier for keeping this conversation going to the end.
It may be different, but not much, I think. If you take one of our usual teetering hub bars, and put a flapping articulation in the middle, I believe that the flapping motion of the individual blades will not be exactly the opposite, so the blades will not keep exactly aligned, but the difference will not be large...
 

Aviator168

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I think they are different. If you look at the gyroplanes with blades hinged, the cone is more apparent than the one using the seesaw scheme. Also, when the blade at the back position, its rotation plain is always normal with the rotation axis, not so with the seesaw blades. I do think the seesaw bladed rotors are more efficient.
 

XXavier

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I think they are different. If you look at the gyroplanes with blades hinged, the cone is more apparent than the one using the seesaw scheme. Also, when the blade at the back position, its rotation plain is always normal with the rotation axis, not so with the seesaw blades. I do think the seesaw bladed rotors are more efficient.
Yes, you're right, since independently hinged blades are free to form the angles determined by the forces involved...
 

Jean Claude

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Even with seesaw rotor, the descent is almost not forced by the rise of other blade. Each blade rises and falls individually above or below the average cone. Just the centrifugation forces the descent, and increases the A.o.A. So, asymmetric lift desapears.

The low coning of the seesaw rotors is simply due to the choice of heavy blades reducing the stick vibrations
 
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WaspAir

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I think they are different. If you look at the gyroplanes with blades hinged, the cone is more apparent than the one using the seesaw scheme. Also, when the blade at the back position, its rotation plain is always normal with the rotation axis, not so with the seesaw blades. I do think the seesaw bladed rotors are more efficient.
Teetering systems are simpler, in that they don't need lead-lag or individual flapping hinges, and can be easier to fit in a small hangar space, but they are not inherently more efficient. Airfoil shape, twist, aspect ratio, and other parameters that might make one blade more or less efficient than another are separate issues from articulation at the hub. Articulated systems can have their own advantages, such as greater low-g tolerance, bigger c.g. range, lower vibration (smoother in flight), jump capability, etc.

P.S. individual blade flapping is in response to the airspeed each blade sees at each point in the rotation (it's an aerodynamic force, not a centripetal reaction). Lower airspeed coupled with higher angle of attack (from downward flapping) on the retreating side balances higher airspeed with decreased angle of attack (from upward flapping) on the advancing side.
 
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Aviator168

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P.S. individual blade flapping is in response to the airspeed each blade sees at each point in the rotation (it's an aerodynamic force, not a centripetal reaction). Lower airspeed coupled with higher angle of attack (from downward flapping) on the retreating side balances higher airspeed with decreased angle of attack (from upward flapping) on the advancing side.
Cannot agree with this. How do you explain that in an articulated rotor system, during pre-rotation when rpm is low, the blades do not flap down.
 

Vance

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Cannot agree with this. How do you explain that in an articulated rotor system, during pre-rotation when rpm is low, the blades do not flap down.
In the multi blade systems I have seen stops keep the rotor blades from going down too far.

In my opinion the coning angle is a balance between weight of the aircraft and rotor rpm and weight of the blades unrelated to the method of attachment or how many blades there are.
 
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Vance

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Vance, the stops for the blades not to hang too low on the ground for the pre-rotation.
The stops are to keep the blades from hanging too low for lots of reasons.

Helicopters have them too.
 

Jean Claude

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Wyne,
Because of the lift, the blades always remain above the plane of the hub and browses a coning.
With the forward speed, the browsed cone is tilted backwards relative to the plane of the hub. It is due to the blade rises from 6 o clock. until 12 o clock when it is on the advancing side, then it descends from 12 o clock until 6 o clock when it is on the retreating side. By doing this, its A.o.A is smaller when it is fast, and larger when it is slow so as to automatically keep the same lift (The plane of the cone is now just more nose up than the plane of the hub)
Sans titre.png
From the book "Autogyros" of Franklin Harris
 
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