2 blade rigid rotor
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2 blade rigid rotor
once again I will prove my ignorance of all things Helicopter. Is it theoretically possible to build a 2 blade ridged rotor system. What I am envisioning is the teeter and feather replaced by the same type of plates used on a multi bladed ridged system.
I have been thinking about this for a while and cannot come up with a reason that it would not work. Is the amount of flapping in a 2 bladed system too much? Seems like it would eliminate mast bumping and tail amputations.
Please educate me.
Bill.
I have been thinking about this for a while and cannot come up with a reason that it would not work. Is the amount of flapping in a 2 bladed system too much? Seems like it would eliminate mast bumping and tail amputations.
Please educate me.
Bill.
Feathering will always have to be there, to allow us to change collective pitch, and to get differential cyclic pitch to move the aircraft in the chosen direction. I believe there were a couple of attempts to remove feathering bearings, and just twist the blades to get it, but apparently that was not successful.
2-blade teetering systems exist because they are simple and CHEAP. The CHEAP side of it makes them the accepted starting point for most low-time people, and they are generally the ones to have problems with it.
Next step up is 3-bladed articulated systems, allowing the blades to shuffle around the plane with the lead-lag forces. Then add more blades as desired. Articulated hinges can be replaced with rubber/ plastics as in the AS350 series.
The most rigid is the head of the BO-105 and BK-117, no flapping or lead-lag hinges at all. Flapping is allowed by the flexible blades, not by hinges.
Early experiments with rigid systems caused crashes - the experimenters couldn't see why their models would fly but the real things wouldn't. Then they saw that the models used bamboo blades which allowed flapping - so they devised the teetering head to allow flapping, and away they went.
2-blade teetering systems exist because they are simple and CHEAP. The CHEAP side of it makes them the accepted starting point for most low-time people, and they are generally the ones to have problems with it.
Next step up is 3-bladed articulated systems, allowing the blades to shuffle around the plane with the lead-lag forces. Then add more blades as desired. Articulated hinges can be replaced with rubber/ plastics as in the AS350 series.
The most rigid is the head of the BO-105 and BK-117, no flapping or lead-lag hinges at all. Flapping is allowed by the flexible blades, not by hinges.
Early experiments with rigid systems caused crashes - the experimenters couldn't see why their models would fly but the real things wouldn't. Then they saw that the models used bamboo blades which allowed flapping - so they devised the teetering head to allow flapping, and away they went.
Isn't the 214ST a 2 bladed rigid? Excuse my ignorance, we did operate them, but I never got to fly one. They had air-conditioning so the Nationals had first pick at flying them. The expats got to enjoy 42 degC at 4000' in a 212 with the windows open. Well and truly oven roasted by the time we arrived at the other end.
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From my understanding even the rigid heads all for feathering without a dedicated hinge. So that doesn’t explain why it can’t be done.
Maybe you need hydraulics in order the activate the feathering.
Maybe you need hydraulics in order the activate the feathering.
Excuse my ignorance, we did operate them, but I never got to fly one. They had air-conditioning so the Nationals had first pick at flying them.
Never walked up to one and take a look at it to see what she was made of while you were quaffing cold bottles of water between flights?
Of course you were probably isolated at Tanijiib and never got to where the 214ST's were located.
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The 412 head is basically 2 x 2 bladed hubs bolted one on top of the other, so if you took the second "head" away, and beefed up the remaining blades that could work - but you now lose the offset hinge advantage in the head, so controlling the machine will be quite different.
CHEAP never crossed my mind when I was admiring a Bell 222 at Heliexpo.
By definition, a rigid rotor includes feathering but not flap or lead-lag movement. Could a 2 blade rigid system be built? Sure, but what would you do with it. The ride would be terrible. And with any type of useful load, I would imagine the bending forces at the hub/mast/xsmn would require those components to be pretty substantial in strength/weight/size.
Discap - have a look at this description of the 212 head and see where you could replace the hinges with plates http://www.thecontrols.ca/References...in%20Rotor.pdf as wrench1 says, I don't think it would be very practical
The 135 M/R system is bearingless and hingeless. But feathering and flap (to a limited extent) takes place through a "flex-beam" mounted inside the hollow blade cuff. Lead/lag is handled by elastomerics mounted externally on the blade cuff.
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Now if everyone just stopped goofing off in shop and math class , or on the computer they could of built the Hiller XH -44 in their dads' garage at the age of 19, just like Stanley Hiller. ....or so the story goes.
The "original" Sikorsky ABC concept got its start in Stanley's garage, with a two blade rigid counterrotating head. There are clips on YouTube. Besides the maple seed, It actually probably gots its start with the turn of the century "Wright brothers" types with their steel tube and fabric, hopping contraptions. Scratching their heads , not knowing that without the teetering hinge the rotor will roll to equality vs flapping to equality. Stanley wasn't preoccupied with the two legged birds so he had this all figured out and made a counter rotating head to cancel things out. I can't seem to find the tale of vibration in the story but would guess from the UH12 rotor quickly superseding the xh -44 's enroute to mass production that it lurked not far beyond translation.
Apart from the vibration caused by the inevitable poor bedfellows of coning and flapping without an underslung hingeline ( or multi blade head that is called "rigid" but accommodates some lead lag) I would think the stability and gust response on a single rotor design would make the Boelkow 105 seem a docile beast in comparison. Lockheed anticipated this on a model prototype in the 50's building a rigid two blade that was stabilized by linking it to a gyroscope ring atop the rotorhead. Needless to say they quickly abandoned it due to vibration in favor of 3 and 4 blade heads in the lead up to the Cheyenne project.
I say follow Stanley's lead and build a model RC helicopter refit to a rigid two blade head slowed down to 300 to 500 rotor rpm. I'd advise motorcycle gear and hockey equipment. Happy Tinkering
The "original" Sikorsky ABC concept got its start in Stanley's garage, with a two blade rigid counterrotating head. There are clips on YouTube. Besides the maple seed, It actually probably gots its start with the turn of the century "Wright brothers" types with their steel tube and fabric, hopping contraptions. Scratching their heads , not knowing that without the teetering hinge the rotor will roll to equality vs flapping to equality. Stanley wasn't preoccupied with the two legged birds so he had this all figured out and made a counter rotating head to cancel things out. I can't seem to find the tale of vibration in the story but would guess from the UH12 rotor quickly superseding the xh -44 's enroute to mass production that it lurked not far beyond translation.
Apart from the vibration caused by the inevitable poor bedfellows of coning and flapping without an underslung hingeline ( or multi blade head that is called "rigid" but accommodates some lead lag) I would think the stability and gust response on a single rotor design would make the Boelkow 105 seem a docile beast in comparison. Lockheed anticipated this on a model prototype in the 50's building a rigid two blade that was stabilized by linking it to a gyroscope ring atop the rotorhead. Needless to say they quickly abandoned it due to vibration in favor of 3 and 4 blade heads in the lead up to the Cheyenne project.
I say follow Stanley's lead and build a model RC helicopter refit to a rigid two blade head slowed down to 300 to 500 rotor rpm. I'd advise motorcycle gear and hockey equipment. Happy Tinkering
