# DONG090909 Conjecture when the rotor has forward speed

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#### dong090909

##### Well-Known Member
1. First guess
The conditions for the lift balance of the coaxial anti-propeller rigid double rotors are: the upper and lower rotors are in the same phase
Proof method:
Junior high school mathematics and physics: vector analysis of forces
2. Second conjecture (an extreme case of the first conjecture)
If the number of blades can be infinite , the lift balance of the upper and lower rotors can be achieved at every moment. a flying saucer

3. Background:
A. When I first saw the Sikorsky ABC rotor concept, I remembered: the differential compensation theory commonly used in electronics, I think its biggest benefit should be to reduce lift fluctuations.
B. I'm curious: why the great companies don't mention: Conditions for rotor lift balance. At least I can't search it. And it affect the direction in which humans resolve lift fluctuations
C. I estimate:
---Flexible rotor, it really doesn't make sense.
---The rigid rotor is subject to the influence of the few blades of the mainstream helicopter, which does not reflect the value (more blades, low flight efficiency)
D. I tried simple communication with aviation professionals on the mainland, at least they did not overturn my point of view.
E. Unfortunately: these two conjectures are an important aerodynamic basis for the aircraft I designed.

4. Therefore, I hope you can review my conjecture.

Thanks

#### TFF

##### Well-Known Member
Is this what you are looking for?

#### dong090909

##### Well-Known Member
Is this what you are looking for?

Sorry, I must admit that my English is very poor and I need time to digest it.

#### Martin W

##### Well-Known Member
.

You need to understand why helicopters cannot fly fast

---- the tips of helicopter blades are moving at 300 mph air speed
---- but when the helicopter is flying forward at 100 mph the advancing blade now experiences 400 mph airspeed and the retreating blade sees only 200 mph
--- - it is called dissymmetry of lift ... and the high speed advancing blade flies higher than the retreating blade (the rotor system becomes tilted sideways)

Sikorsky ABC uses counter-rotating blades to mainly use the advancing blades for lift and speed ..... cost millions of dollars to gain a bit of speed . Not practical .

You are not alone.
Some of the smartest engineers in the world work on advanced rotor systems and they hit brick walls all the time

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#### Martin W

##### Well-Known Member
.

TFF ... looks like were were typing the same things at the same time.
Good post ... thanks.

#### dong090909

##### Well-Known Member
Is this what you are looking for?

The document is the compensation method of a single rotor, and my plan is a compensation method of two rotors up and down, working together.
Anyway, many thanks for sharing the information.
thanks.

#### dong090909

##### Well-Known Member
.

You need to understand why helicopters cannot fly fast

---- the tips of helicopter blades are moving at 300 mph air speed
---- but when the helicopter is flying forward at 100 mph the advancing blade now experiences 400 mph airspeed and the retreating blade sees only 200 mph
--- - it is called dissymmetry of lift ... and the high speed advancing blade flies higher than the retreating blade (the rotor system becomes tilted sideways)

Sikorsky ABC uses counter-rotating blades to mainly use the advancing blades for lift and speed ..... cost millions of dollars to gain a bit of speed . Not practical .

You are not alone.
Some of the smartest engineers in the world work on advanced rotor systems and they hit brick walls all the time

.
My main idea is that the rotor is only used for lifting and landing, while the fixed wing is used for flight

#### Dan Thomas

##### Well-Known Member
--- - it is called dissymmetry of lift ... and the high speed advancing blade flies higher than the retreating blade (the rotor system becomes tilted sideways)
And the cyclic, in forward flight, also has the retreating blade at a higher AOA as well. To tilt the rotor forward, the max blade pitch must be at 90° before it reaches aft side due to gyroscopic precession, and at minimum pitch 90° after, making the advancing blade at a lower AoA. A happy coincidence of physics that makes the helicopter's limited forward speed possible at all.

Nothing else works.

So much more going on there than what meets the eye. So much to trip up the young inventors just like it tripped up the old guys 100 years ago. Physics, as far as I know, hasn't changed its laws one bit....

#### Jay Kempf

##### Curmudgeon in Training (CIT)
Gyroscopic precession is a real monkey wrench in understanding all this. However is you are past that you then need to understand this thing called Mu.
"The ratio of the forward speed of a helicopter to the tip speed of its rotor is expressed as µ (Mu)."

The best and brightest like the people involved in the: AH56, X-2, ABC, Carter Copter, etc.. ; have (had) been dancing on this variable using slowed rotor and crazy stiff and CG tailored coaxial rotor blade designs.

Doing a little research on those that have gone before you might shed some light on how the problem has been dissected in the past.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
Oh and BTW, the Boeing/Sikorsky current Blackhawk replacement under development is a coaxial, pusher prop, heavy, complicated new take on this category.

#### dong090909

##### Well-Known Member
I still feel that you have not answered my question directly.
Also, you cite the idea of a flexible rotor
No here: swashplate, no tilt, no pitch adjustment, no change in angle of attack
Do not pursue the ratio of forward speed to wingtip speed
Gyroscopic precession is also known as the gyroscopic effect, and this aircraft does have a use

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#### Dan Thomas

##### Well-Known Member
No here: swashplate, no tilt, no pitch adjustment, no change in angle of attack
No control, either. It's been tried many times. The articulated rotor is necessary for controllability. The early helicopter experiments never had any success until Sikorsky developed the fully articulated rotor.

"Rigid rotor" does not mean that the rotor is not articulated. It means that it uses elastomeric or flexible metal pivots instead of hinges and bearings. Some make the blade itself flex in all three axes to do the same thing. It's not like an airplane's fixed-pitch propeller at all.

Youtube used to have a video of some Eastern European fellow trying to fly his machine that had two propellers, one on each side and driven off a singe engine. Weight-shift control. As soon as it was off the ground, or even light on its casters, it had a mind of its own. There was a crosswind, which meant the the blades advancing into the wind had more lift, picking up that side, and gyroscopic precession would cause it to tilt 90 degrees to that and it was instantly in trouble. Totally unflyable.

Like I said on a thread somewhere recently, the stuff we see is the stuff that works. The stuff we don't see has usually been tried many times and doesn't work. Aviation history is packed full of failures. The whole field has been thoroughly explored.

What aviation needs is not more attempts of the same things that failed. It needs revolutionary stuff like:

-new, strong, lighter, cheaper structural materials

-new, lighter, cheaper, safer and more powerful motor systems or engines, and that includes batteries

Those two things alone would revolutionize VTOL flight. The airplane and the car appeared shortly after practical internal combustion engines were designed. Faster, bigger and safer aircraft, and more capable helicopters, appeared when the turbine engine became worthwhile. They were revolutionary technologies.

#### BBerson

##### Light Plane Philosopher
No here: swashplate, no tilt, no pitch adjustment, no change in angle of attack
That's standard for the 200 or so new evtol designs.
Looks like the four corner props are variable speed control props that tilt for forward thrust.
The fixed central large rotors are lift rotors that stop after wing borne flight.
The concept might work.

#### TFF

##### Well-Known Member
Retreating blade efficiency applies no matter if you have controls or not. You might not go fast enough for retreating blade stall, but the effect is still there.

#### BBerson

##### Light Plane Philosopher
He doesn’t have any retreating blades with his tilt props and stopped main rotors.
I don’t think his design is understood here. Go back and look at the paper model.

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#### TFF

##### Well-Known Member
They got to be spinning sometime, even if he stops them.

Then you get into a torque issue spinning them up or down. Want folding helicopter blades? Fly them below a certain rpm and they fold like a book. To spin them back up from a stop in the air has to be slow. If his top and bottom blades are coupled the torque will be canceled, but if they are variable it will wrap itself into a ball, assuming the blades don’t fold. It’s what makes rotor blade stalls scary. The chance of the blades folding is competing with them being out of control and chopping the tail off.

If it is only going to fly 60kts, the wings need to be a lot bigger. 0-60 is a great helicopter speed range. 25-60 is the meat of the 103 flying range. At such a slow speed everything is fighting it’s self and nothing is dominant. It’s not a good airplane nor helicopter.

In this design he needs to separate the factions. Make a helicopter and make an airplane. At some point in the flight profile it has to convert to one or the other, so it is expected to be able to do either. Then add them together once the individuals are sorted. The plan might be together but they have to work separately.

#### BBerson

##### Light Plane Philosopher
It isn’t a helicopter. The new generation are almost all rigid fixed pitch blade “ multi-rotor”

#### Dan Thomas

##### Well-Known Member
It isn’t a helicopter. The new generation are almost all rigid fixed pitch blade “ multi-rotor”
Yeah, but they're not coaxial. Coaxial propellers won't give any control. The multirotor things have rotors on arms well spaced out, and use RPM control for aircraft pitch and roll and vertical flight. For yaw, they would increase RPM on the ones turning one direction, and slow the ones turning the opposite direction. The big problem with all of that is the potential for failure of ANY part of the system. It won't autorotate. Parachutes are no good at the typical operating altitudes. Things happen fast with such failures, and it would have to be flown by computers with several backups, and all the motors and props would need to be big enough to carry the machine if a certain percentage of them were disabled.

Like so many machines, a hybrid using wings and rotors is a compromise of numerous concepts, and you end up with an unhappy machine whose utility is minimal. Where is the Moller Skycar? Where is the Fairey Rotodyne? Where are the Cierva and Pitcairn and McCullough and Air & Space autogyros? How affordable and practical is the V-22 Osprey?