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Rotor Head Design


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#21 Whistlerpilot

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Posted 05 June 2018 - 21:43

Merci Chris, René Mouille est certainment Monsieur Helicoptere!

When life's path is steep keep your mind even.


#22 Rupert

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Posted 15 June 2018 - 17:26

Compromise, compromise, compromise.

 

Do you want it smooth and vibration free? Quiet? Fast? Efficient heavy lift? Rugged? Easy to maintain? Cost-effective to build? Fuel-efficient? Each rotor system has its strengths and weaknesses.

 

All things considered, in this atmosphere and gravity, a cruise speed of 135 knots and below, and a gross weight less than 17,000 pounds, the two-bladed under-slung rotor system wins hands down.

 

If you want to cruise faster than 135 knots with reasonable smoothness and practicality, or cost-effectively transport a gross weight greater than 17,000 pounds, then you need to go to a fully-articulated system with three or more blades.

 

The best turbulence machine I've ever flown, a Bell 222 with an elastomeric, flat-in-plane semi-rigid, underslung, pre-coned rotor system. In a 222 I've flown in turbulence that would rip the wings off a fly.

 

Rigid rotor systems bring their own set of problems. I flew the EC-145 for five years. Loved it. Big improvement over the BK-117. Passengers don't like it in turbulence, and, even with active-dampening, alarming to passengers while going through translational lift.

 

I've flown both the 212 and the 412 on the same contract . Greatly prefer the 212 for its lift and good manners, not to mention ice-tolerance.

 

If I won the lottery, I'd go for a two-bladed Bell product with an under-slung teetering rotor system. Maybe a Long Ranger...an L3 or L4. Though, I could really go for an MD530F. What a machine.

 

About the under-slung thing, as the advancing blade goes up, the entire disk pivots under teetering hinge and moves to the right (viewed from behind) towards the rising blade. Very low stress.

 

All the Jet Rangers and Long Rangers, all the metal-bladed tip-weighted 47's, and all the 205's and the 212 fly exactly the same. Magnificently. Best autorotation going, with the exception of the Sikorsky S55T.

 

We have forgotten that the 205 set the absolute helicopter speed record of more than 200 mph back in the early 1960's. They took the horizontal stabilizers off and flew it so nose low it looked like a flying propeller. I understand they condemned the airframe after the record flight.

 

They also condemned the airframe on the first Marine Corps CH-53 that they used to demonstrate the aerobatic abilities of the CH-53. A person involved in the filming of the flight said the G's pulled during the rolls and loops bent the radio shelves and otherwise twisted the air frame. Some time later Sikorsky and the Marine Corps filmed the same maneuvers, again, but with a specially lightened air frame. Worked great the second time.

 

I consider the MD500 series of helicopters the most aerobatic of helicopters, even over the Messerschmitt-Bolkow-Blohm (fun to say) 105. A late and respected fellow pilot regularly rolled and looped both 105's and 500's. He preferred the 500. Got killed in a 500 while doing aerobatics, but not because the machine failed him.

 

During the Vietnam War, Army Cobra pilots did things in Cobras that one would consider aerobatic. Return to target wing-overs and such. During that time I flew Ch-46's, and we would tail chase with Cobras. The Ch-46 (lightly-loaded) will out fly a Cobra in everything except dive speed. Great fun for young pilots.


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#23 Eric Hunt

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Posted 15 June 2018 - 17:53

 

 

About the under-slung thing, as the advancing blade goes up, the entire disk pivots under teetering hinge and moves to the right (viewed from behind) towards the rising blade. Very low stress.

 

Ummm... the advancing blade is going DOWN, the retreating blade going up, and that is how the disc is tilted forward when going forward. The underslung bit makes the high part (the back, not the right side) poke out a little further to increase the apparent length of the blade, and decrease the front part.

 

Funny how people hang onto the concept of "flapping to equality", when that concept disappears as soon as the cyclic is poked forward to stop it from happening.






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