Coaxial rotor question

kolibri282

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The reason is probably that there is, to the best of my knowledge, only one company that uses servo flaps for main rotor control at all. All other manufacturers have no experience with that system so they stick to what they know. From my limited knowledge of the subject it seems that the inherent stability of an intermeshing rotor is slightly better than for a coaxial so Kaman decided that for their K-Max their proven design is the best configuration. Technically there is no reason apparent to me why a coaxial rotor shouldn't be perfectly controllable with servo flaps.

Just my two cents.

Juergen
 
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C. Beaty

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Kaman still uses servo flaps on their intermesher ..... but I think if you look up the coaxial Gyrodyne drones from years back ... they may have used flaps .... I could be wrong ... going by memory.
The Gyrodyne had tip brakes; -vanes that pop out of blade tips to increase the drag on one or the other rotor for yaw control.

Traditionally, yaw control with coaxial rotors was by differential collective; increasing the torque load of one rotor or the other. Unfortunately, yaw control via differential collective reverses upon going into autorotation.

The Gyrodyne didn’t have the reversal problem.

Dick DeGraw had a pedal reversing mechanism linked to collective on his synchopter that reversed the pedals when the collective was lowered.
 

Rotor Rooter

Dave Jackson
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A probable reason why the servo-flaps tend to be unique to the intermeshing is "weaving flutter".

The the downwash from a blade on the upper rotor onto a blade on a lower rotor must momentarily affect the blades angle of attack.

This is a picture of Kaman's first rotor. The first improvement was the removal of the airfoil on the leading edge of the blades.

http://www.Unicopter.com/Temporary/Early Kaman Servo-flap.gif


Kaman's intermeshing helicopters have very low disk loadings compared to the high disk loadings of the Kamov coaxials. This lower disk loading will reduce the aerodynamic interaction between the two rotors.


The table, drawing and graph on Aerodynamics - Rotor Disk - Dual Configurations will provide some more information, if interested.


Dave
 

Stephen Toor

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Thanks for the link, so from the information on the link, best for lower power is two side by side rotor systems and best stability is intermeshing, then coaxial?
 

Rotor Rooter

Dave Jackson
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Thanks for the link, so from the information on the link, best for lower power is two side by side rotor systems and best stability is intermeshing, then coaxial?

That's a difficult question since the rotorcraft has so many variables. and so many end-user requirements.

The best for low power-to-weight ratio will consist of;
  • large disk area(s); for low disk loading
  • few blades
  • slow RPM; for reduced profile drag
  • wide chord
  • optimized blade profile
  • etc.

Of course, excesses in the above will start working to the detriment of the user's requirements, such as;
  • stability
  • controllability
  • price
  • size
  • portability
  • etc.


There isn't a clear answer, but perhaps, the start is to consider what the objective at the end is.



Dave
 

skyguynca

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I looked sometime ago, he just disappeared. Never dug into it. But there's no presence of him for about 4 years or so on the internet
 

Martin W.

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Hey Dave, you still around?
Dave passed away in 2017.... I wish he had arranged to preserve his website .... tons of good info he gathered over many years.

More here
 
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