Effect of prerotation on takeoff distance

The minute he pulls the stick back, releases brakes, and begins forward movement then that is no longer the case for the remainder of the flight.
Not exactly.
The anti-rotational state of the pre-launch still continues during the run up to about 20 mph
The stronger the pre-launch, the longer the anti-rotation state continues.
This is what causes the initial rpm supplement to lose almost all of its benefit.
 
PS: I might be able to submit it to the EE students at USD. Their classes won't start until the end of September as it does need electronic sensors on the rotors, and the lift and the airspeed at least. They may pick it up this semester. So better write it up now.
Then I can test whatever you gys want with blades stop and at any air speed you wish.
 
Not exactly.
The anti-rotational state of the pre-launch still continues during the run up to about 20 mph
The stronger the pre-launch, the longer the anti-rotation state continues.
This is what causes the initial rpm supplement to lose almost all of its benefit.

...And being it so, it's for me a mystery why a rotor-powered takeoff is shorter... The evolution of the rotor flow of a gyro in the course of the takeoff is probably very complex, and hasn't received much attention from aeronautical research...
 
Not exactly.
The anti-rotational state of the pre-launch still continues during the run up to about 20 mph
The stronger the pre-launch, the longer the anti-rotation state continues.
This is what causes the initial rpm supplement to lose almost all of its benefit.
In your opinion, how much does total rotor mass (and thus momentum) affect this?
 
Not exactly.
The anti-rotational state of the pre-launch still continues during the run up to about 20 mph
The stronger the pre-launch, the longer the anti-rotation state continues.
This is what causes the initial rpm supplement to lose almost all of its benefit.
And a good example why a pre spinner that is independent from the engine and can be left on during the roll until that magic airspeed where auto-rotation takes over will always provide the best performance, by maintaining rrpm.

wolfy
 
Jean mi your translator had taken a turn “potato masher” :) I run my prerotator to 140/150rrpm static commence the roll and release the prerotator at 200rrpm after which the rrpm accelerates very quickly
 
Then I can test whatever you gys want with blades stop and at any air speed you wish.
That's very nice, John.
Unfortunately, a reduced scale model will not be representative. Due to the low Reynolds Number, autorotation is only possible for a blades pitch setting almost nul. In this case the down blast during static pre-rotation does anot exist.
 
It's probably a very complex thing, with many variables...
I will have to say that I have always felt, and found, rotor aerodynamics to be extremely complex, far more so than the traditional fixed wing sort.
 
Xavier, wolfy, Tiger,
A crucial point is the rotational inertia of the rotor. Without it, prespinner is useless, because the rpm immediately drops to 0 when it is released.
With a very high inertia, launching at 200 rpm will require a very long run, before getting the takeoff rpm.
My simulations have confirmed the takeoff distances under a wide range of inertia conditions and pre-launch rates:
For the Cierva C30 140 hp and the procedure of the time (forward stick up to about 45 km/h):
145 m calculated, instead of 140 m measured when the pre-launch rate is 90% and 865 kg.
90 m calculated instead of 90 m measured when the pre-launch rate is 110% and 765 kg

Pre-launch rate is the ratio Prelaunching rpm / Flight steady Rpm
Mesureds read in Aeronautical Research Committee report n° 1859

Reducing the inertia of our seesaw rotors would be very beneficial, but the increased coning would certainly worsen the vibrations 2/rev in the control stick.
Hence the interest in looking for ways to reduce these tremors.
 
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Interesting... IIRC, some small, RC autogyro models have even negative pitch... When I learned of it, I didn't understand the reason, until someone pointed out the Reynolds number...

The Wells turbine, used in some wave-power electric generators work in autorotation and have zero pitch, very convenient for the reversing flow of air that they work with...

717398.fig.002.jpg
 
Wolfy, I could add a sensor on the front wheel suspension to cut my electric potatoe masher when the front wheel lifts
I guess you could, but thats over complicating things.
The torque on the air frame that is felt in the initial pre spin has less effect once power is added and the roll is started. (the rudder gets more effective).
Just gradually work up to leaving the spinner on more and more into the roll, so long as you can let off the spinner instantly any time you choose.

wolfy
 
I will have to say that I have always felt, and found, rotor aerodynamics to be extremely complex, far more so than the traditional fixed wing sort.

I find a certain charm in that complication. It gives the rotating wing an attractive shade of mystery...
 
That's very nice, John.
Unfortunately, a reduced scale model will not be representative. Due to the low Reynolds Number, autorotation is only possible for a blades pitch setting almost nul. In this case the down blast during static pre-rotation does anot exist.

In a pressurized wind tunnel, a model could autorotate at the same Reynolds number that a full-sized autogyro under normal conditions. It would be interesting to know if this has been observed in one of the few pressurized wind tunnels...

Now that I'm writing this, I remember that Cierva tested the reality of autorotation in a wind tunnel at Cuatro Vientos (IIRC). Sure it was a normal-pressure wind tunnel and probably not large, so he must have used small rotor models...
 
Yes, that's the big (3m width), closed-circuit wind tunnel at Cuatro Vientos. But it was completed in 1924, well after the first successful flight of Cierva's invention...

P.S.: I've just discovered that the first tests of the rotor were made in late 1923 in the 'big' wind tunnel with a 1/10 scale rotor. The best biographer of Cierva (Warleta) writes that the inventor perhaps tried a small model with his car, but it that wasn't so, the first experimental confirmation of the auto-rotation was with his first full-size prototype, the C.1, at the Getafe airfield (October 1920).

From 'Autogiro - Juan de la Cierva y su obra'. José Warleta, 1977

mf07yjj.jpeg
 
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At reduced scale the friction losses on the blades are relatively higher and autorotation will require a lower blade pitch setting. Perhaps 0 degree instead 3 degrees.
Because that, larger disk A.o.A is required to give the same deflection.
 
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At reduced scale the friction losses on the blades are relatively higher and autorotation will require a lower pitch setting.
Because that, larger disk A.o.A is required to give the same deflection.
Thank you, JC.
If we reduce the pitch setting to scale then will the smoke trail be accurate repersontation in the video?
 
Yes, the smoke will a accurate representation of scale 1 if the Cl is the same, but it will required of reduce the blade pitch setting for obtain the autorotation, and then ajust the A.o.A disk for obtain le same cL
 
Yes, the smoke will a accurate representation of scale 1 if the Cl is the same, but it will required of reduce the blade pitch setting for obtain the autorotation, and then ajust the A.o.A disk for obtain le same cL
Hi Jean, thanks so much.
However, I'm much dumber than I appear. What does the term cL stand for? Need to know the terms to do the math.
 
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