Slow, Yamaha RMAX sounds pretty good. I must admit to getting myself a Sabre RC helo with a similar control system (although RPM controlled collective and TR - so no autos). I just wanted to find a way to keep something airborn while i study Quantum Phys (yes seriously). The blades are hingeless, but very far from rigid - fortunately RC blade strike is not serious (relief nut on root).


Dave, the fact that the gyro moments cancel undoes the gyro torque reaction - unless i have missed something. Are the rods changing length to actuate the required moment?

In truth you could just use one gyro for the effect you are after. The gyro mounting would need to have forces in opposition to the blade, but free to gimbol in what would otherwise be the teetering axis (ie 90 degrees out). It still strikes me as overly complex given that the general view is that many weaker tip vortices are better than a few strong ones. Even Prouty was suprisingly vague on the subject of blade number, so i suspect cost and rotor dynamics are a bigger factor.

Mart

Mart,

Yes, you are no doubt correct. The two counter-rotating gyros will probably act the same as if they have no gimbals and are on a common axle.

The problem ~ Assume that the pilot causes the rotor disk to tip down at 180-deg azimuth. Can you come up with a simple linkage arraignment where; 1/ when the two blades are between 45 - 135-deg and 225 - 315-deg, the gyro applies a downward moment to the mast at 180-deg and, 2/ when the two blades are between 135 - 225-deg and 315 - 45-deg, the aerodynamic teetering force of the blades applies a moment to the mast at 180-deg plus restoring the gyro to its 'home' position?

There must be a mechanical way.

Dave

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The following could be a potential application for this idea.

The sketch comes from Intermeshing - Dragonfly - Principal Assembly , which has 3-blade teetering rotors. The objective would be to replace the complexity of 3-blade rotors with 2-blade rotors and a gyro.

• The gyro could be drive at 5,250 RPM from a pinion identical to the pinion on the input shaft, Alternatively, it could be drive by a small seperate crown and pinion with a 6:1 ratio, which would turn the gyro at over 15,000 rpm.
• The moment of the gyro is in the same vicinity as those of the two rotor hubs.
• I think that the two rotorhubs will create a more complex vibration then a single rotorhub but its amplitude might be smaller.

Just ideas.

Dave, in some respects a counterrotating application would simplify the design. The gyro in your picture would not need it's gimbal to rotate with either rotor. The gimble would simply tip as the rotors passed each other with the tip axis at 90 degrees to the rotor crossing line. As long as the gimbal was rigidly linked to the rotor system, to avoid unwanted movement, then the tipping action would not require any significant forces. It would tip one way then at 90 degrees the other way etc - direction would depend on gyro direction.

Could i concieve of a swash/cam mechanism to do this? Probably, but i just find the whole system unecessarily complex. Vibrations are just best cured at source, and since counterotating rotors will not cross above the fuselage this set up doesn't even offer improved hanger usage. Considering that it takes 17mins (i think that was the figure, including 12 bolts for bifilar removal) to fold up the S-92 head for transport, then multiple stowable blades make more sense to me.

IMHO gyros really are better off being used to improve dynamic stability, by forcing roll/pitch velocity control. I admit to understanding where you are coming from with your interleaver design, since this also has natural roll velocity control (horizontal stabiliser and flapback would help pitch to be velocity control). It's just that a combination of more complicated drivetrain and a wider machine would push up outlay and running costs, when a gyro would be just as effective. It also doesn't really help with the retreating blade stall adversely affecting downwash distribution either, but avoids lift imbalance.

Like i say, i suspect we will seldom agree but it does force me to think about rotorcraft design from all perspectives...

Mart

Mart ,

It is looking difficult and it's not only the linkage. The rotor and the gyro actions are out of phase with each other. It just seems that the use of a gyro to eliminate 2-blade vibration might not have been considered before, particularly in respect to twin main rotors.

The interest would be to see if; 1/ it can be done, 2/ the complexity can be reduced, and 3/ it is viable from a practical perspective.

OK Its back on the shelf; for now.
So is Wikinomics. :)

Dave