Rotor Head Design

[LJS1993]

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!!

[SBuzzkill]

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?

[r22butters]

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?

[LJS1993]

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?

[Eric Hunt]

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.

[chris pochari]

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.

[Eric Hunt]

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.

[DizzyD]

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

[Wally]

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.

[overtorque]

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?

[Eric Hunt]

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.

[r22butters]

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".

[overtorque]

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?

[Eric Hunt]

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.

[chris pochari]

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?

[Eric Hunt]

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.

[LJS1993]

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

[Whistlerpilot]

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.

[chris pochari]

http://www.helico-fascination.com/recits/daniel-liron/272-rene-mouille-du-genie-a-l.html

[Whistlerpilot]

Merci Chris, René Mouille est certainment Monsieur Helicoptere!

[Whistlerpilot]

Merci Chris, René Mouille est certainment Monsieur Helicoptere!

[Rupert]

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.

[Eric Hunt]

 

 

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.

[r22butters]

Played golf yesterday up near the Cache Creek casino while a fire raged in the surrounding hills. Plenty of tankers and choppers flying about, including a Skycrane that meandered by a few times.

 

Then a huge thumping sound came over the 17th green, so I looked up (knowing exactly what I'd see) as the fire service Huey, with its massive-ass blades, came over the hill!

 

No other helicopter makes an impressive an entrace as the Huey!

 

TWO BLADES RULES!!!

[mike0331]

Hueys do sound sweet. When I was in pendleton the USMC is still flying twin-rotor cobras and we were right by the airfield. The crack from those things was impressive.... allllll night.