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Rotor Head Design


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#1 LJS1993

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Posted 01 June 2018 - 11:46

Okay guys without getting too general or in fear of asking a question that contains no clear answer; here I go.  What is in your opinion the "best" rotor head design?  Is there a design that clearly possesses an advantage over the others?  Is there a design that is inherently inferior to other designs?  Shoot!!


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#2 SBuzzkill

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Posted 01 June 2018 - 13:00

Any vehicle design is going to have compromises in one area to boost another.  What is your definition of the best?  Performance?  Comfort?  Maintenance?  Cost?  Safety?


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#3 r22butters

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Posted 01 June 2018 - 13:03

Well from the amatur perspective, I've flown seven different models, four fully-articulated and three semi-ridged, and from my experience I'd have to say,...

Semi-ridged, hands down my favorite!

What can I say, two blades is the way to go! It looks better, easier to park, and well, I just prefer the "feel" better,...fully-articulated feel kinda, I don't know,...weird!?

,...but hey, I'm just a sea level joy rider, although taking a 206 up to Mt. Saint Helens was pretty cool too,...as long as it was covered in snow:)

R22 and Bell 222 all time favorite choppers.,...guess why? :D
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#4 LJS1993

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Posted 01 June 2018 - 15:26

Any vehicle design is going to have compromises in one area to boost another.  What is your definition of the best?  Performance?  Comfort?  Maintenance?  Cost?  Safety?

 

How about safety?



#5 Eric Hunt

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Posted 01 June 2018 - 17:28

Safest? 

Fully rigid, like BK117. 'G' limits +3.5 to -1, turbulence means little to this bird. Amazingly agile, but every movement of the disc is passed on to the cabin. A smooth ride is best obtained if CSAS and autopilot are fitted.

 

Next?

Articulated. Plus smooth ride.

 

Least safe?

Teetering. Possible to get mast bump and separation. 'G' limits +2.7 to +1. Get a smooth ride, but not particularly responsive, as the disc has to move first and then drag the cabin along with it.


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#6 chris pochari

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Posted 01 June 2018 - 19:26

Being interested in rotor heads myself I figured I'd pop in with a question. What are you guys' opinion on Rigid bearingless flexbeam type rotor heads, i,e EC135, UH 1Z, MD 902, UH 1Y, Kawasaki OH 1.


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#7 Eric Hunt

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Posted 02 June 2018 - 00:13

Flown the 412 with that head, it was smooth and responsive, as fast as any Huey would be, but without the delays of the teetering head. Always had SAS running, as against the BK I flew which didn't have any stab aug at all, and in the hands of a vigorous pilot would cause some crewmen's breakfast to re-appear.


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#8 DizzyD

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Posted 02 June 2018 - 13:40

Underslung teetering is my least favorite design (still loved my R44 tho)


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#9 Wally

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Posted 02 June 2018 - 16:46

As asked before in this thread- what is 'best'?

Speed and maneuverability? As many blades as possible, rigid, articulated and/or whatever you call the StarFlex and its ilk. One sacrifices a hover efficiency, at least theoretically.

You want power in the hover versus speed? The fewer blades, the better. Two blades don't do 'fast' well, generally. There are exceptions- the 222 and 214 were fairly rapid.

Yes, the underslung/teetering has issues with low-G. Lots of 'classic' (old) helicopters with two blades still around. And nothing auto-rotates like a Huey or even a 206.

I kinda liked the on-condition aspect of the Starflex. No cracks, no separation, no worms? You could expect the bearings in the control linkages wore out quicker than the head.
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Just a pilot (retired, so I have a LOT of time)...


#10 overtorque

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Posted 03 June 2018 - 16:12

How does the robinson design get away without lead lag hinges?. The way I understand it as the blade flaps up it will want to increase in speed due to the coriolis effect. The lead-lag hinges would then absorb this, but what about that semi-rigid underslung robinson?


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#11 Eric Hunt

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Posted 03 June 2018 - 16:27

A 2-blade (teetering) system cannot allow lead/lag, or both blades would be on the same side of the disc at the same time, creating a massive destructive imbalance. So, the blade grips and the head have to be strong to absorb the stresses.


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#12 r22butters

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Posted 03 June 2018 - 16:46

How does the robinson design get away without lead lag hinges?. The way I understand it as the blade flaps up it will want to increase in speed due to the coriolis effect. The lead-lag hinges would then absorb this, but what about that semi-rigid underslung robinson?


"Because of the underslung rotor, the center of mass remains approximately the same distance from the mast after the rotor is tilted". Therefore we Robby dudes don't experience the Coriolis Effect to the same degree as our fully-articulated counterparts. Thus sayeth the good old Rotorcraft Flying Handbook.

The newer Helicopter Flying Handbook on the other hand,...well lets just say, some things don't need to be "updated". :)
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#13 overtorque

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Posted 03 June 2018 - 16:49

I'm getting deeper down the rabbit hole here:

 

With a lead-lag hinge system, what's absorbing the slight dis-balances caused by the leading and the lagging of each blade?


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#14 Eric Hunt

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Posted 03 June 2018 - 20:47

Blade dampers, like shock absorbers, are on the back of each articulated blade. When the blade wants to move from its position due to multiple forces, the springs inside the damper resist it, and work to push the blade back to position, and the damping controls the rate that this re-positioning takes place.

 

A faulty damper can cause big imbalances, leading to ground resonance.


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#15 chris pochari

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Posted 03 June 2018 - 21:04

Schweizer 300/Hughes 269s seem to be prone to ground resonance, have a look at the NTSB database! Could there be something about its rotor head design that's causing the high incidence of ground resonance? 


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#16 Eric Hunt

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Posted 03 June 2018 - 22:38

More likely the oleos in the skid gear getting worn. It's all a combination of blade balance, oleos, dampers. Also with wheeled birds, tire inflation can be a factor.


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#17 LJS1993

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Posted 04 June 2018 - 00:05

Okay if you guys could design a helicopter to your own personal specifications what type of rotor head would you go with?



#18 Whistlerpilot

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Posted 05 June 2018 - 05:16

Hands down the AS350 series now H125 starflex. Simple effective low maintenance reliable and responsive. Combined with probably the best in class gearbox it makes for the best heart of any helicopter in my opinion.
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When life's path is steep keep your mind even.


#19 chris pochari

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Posted 05 June 2018 - 19:06

http://www.helico-fa...-genie-a-l.html



#20 Whistlerpilot

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Posted 05 June 2018 - 21:43

Merci Chris, René Mouille est certainment Monsieur Helicoptere!
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