# C-4 "Centenario" Autogiro project

#### Jean Claude

##### Junior Member
Here are the results of my calculations for this four bladed rotor 8.5 x 0.225 m, assuming a total mass of 350 kg,
For 312 rpm pitch setting = -1.2° And at 20 m/s a1=0.3° b1 = 0.5° A.o.A shaft = 22° Rotor drag =1380 N

Such a high rrpm produces very high losses due to friction which requires a large angle of attack of the disc, and a negative pitch setting in compensation.
If you want to use 4 commercial blades of pitch setting suitable for an acceptable efficiency (i.e. about 3°), then each pair carrying only half the load, the rrpm will be about: 315/1.41 = 220 rpm which will not pose any safety problem as long as Mu does not exceed 0.35 (ie here about 125 km/h)

For example, with for bladed 8.5 x 0.225 when the pitch setting is +3°, my calculation gives:
223 rpm at 20 m/s a1=2.2° b1 = 0.7° A.o.A shaft = 9.5° Rotor drag =715 N
But in order for such unstayed blades to maintain their usual coning, it will be necessary to accept an 80 kg rotor and to allow for a few degrees of freedom between the two pairs, otherwise cracks will appear very quickly at the roots

#### Arco

##### Junior Member
Thanks Jean Claude

#### Mayfield

##### Gold Supporter
allow for a few degrees of freedom between the two pairs, otherwise cracks will appear very quickly at the roots
Jean Claude,

Could you please expound a little on this. Chuck and others repeatedly warned against paired teetering rotors because of rapid fatigue cracks at the root. If I have read your work correctly, in this thread, stays between the pairs, at some specific radius, helps structurally.

Thanks Jean Claude,

Jim

#### Mayfield

##### Gold Supporter
Jean Claude,

I re-read your posts 51, 53, 54, and 56. It seems to make sense to me now. Thank you.

If it is convenient, could you expound on the "stays" a little. Structure, material, any possibility of a modern interpretation to this type rotor?

Jim

#### Jean Claude

##### Junior Member
Equi-distribution cables can only remove stresses in the roots if the below shrouds keep the blades with no coning.
But in this case, the additional drag is penalizing to high Rrpm. This becomes unacceptable when we aim for Vne above 55 mph.

Cable diameter required for 1000 lbs: at least 8 mm diameter. This is acceptable compared to a 0.7 m chord of blade, but not compared to a 0.22 m rope blade

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#### Arco

##### Junior Member
Elapsed time 243 days/ Pending time 115 days
We have already started the fabric covering.
The stabilizers and the wings are already finished.
The best of all is that we have had young people who want to help us.
Each day less time left!!

To meet us and collaborate https://centenarioautogiro.com

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#### raghu

##### Senior Member
The first trial will be using the conventional rotor that we know to minimize the risk, but we can do the four-blade rotor when the autogiro will be tested and the new way to fly tested and safe.

In any case, if we do the 4 blade rotor head, will be always a fix rotor, no cyclic input.

Our main concern is how to control the autogiro in the take-off and landing, as you know the autogiro will be controlled by the ailerons, and tail surfaces.

In a gyro the control is done by the cyclic so even we have cero airspeed we have control, but in our case, we need a minimum FW airspeed to control the autogiro.

From the other side, the current airstrips are runways, (longitudinal lines) with no possibility to align the take-off and landing path with the wind. In the old times were circular strips facing the wind.

This is our main concern.

How to control the autogiro in the case of cross wind?

We need a minimum speed to have “control” by the ailerons like a FW, but in a FW you can reduce the incidence angle of the wing after take-off to kill the lift. In our case the rotor will be turning, and our “wing” will have the chance to tip over the ship even when our forward speed will be cero.
There was of course an early of version of the C4 in which Cierva controlled roll directly (tilt head) rather than by ailerons and pitch by elevator. He did not pursue with this set up (and direct control for a while) as he found the loads and vibration to be very bad. He solved the vibration and load problem much later when he perfected direct control.

You could use this configuration (direct roll and elevators for pitch), it would be historically accurate and give you much more control in roll and alleviate your concern with crosswinds.

#### Arco

##### Junior Member
There was of course an early of version of the C4 in which Cierva controlled roll directly (tilt head) rather than by ailerons and pitch by elevator. He did not pursue with this set up (and direct control for a while) as he found the loads and vibration to be very bad. He solved the vibration and load problem much later when he perfected direct control.

You could use this configuration (direct roll and elevators for pitch), it would be historically accurate and give you much more control in roll and alleviate your concern with crosswinds.
Thanks Raghu, yes, we thought about that configuration. This was the first configuration used by de la Cierva, but he had so many problems that he changed to a fix rotor. This second configuration was the one that flew.
Yes, could be possible, but we are running out of time, few weeks left before January so now we are focused to do the idea we had at the beginning of the project, no time for changes.
We are at the limit to achieve the date, ………let see if we could do it.
After January 17 we would like to do some improvements because now we are doing the minimal work to have a “flying” ship.

#### Aerofoam

##### Active Member
The first radio control autogyro I built had a teeter bar with a delta 3 pivot angle, but it was fixed. The tractor gyro had wings with polyhedral tiplets at a 45deg. angle. (it looked like a Cierva with a lower aspect ratio wing) It had rudder and elevator control and the roll imparted by the tiplets worked very well, you could fly this gyro aerobatically.
I was able to do rolls and loops easily, but the power to weight ratio was ridiculous.....

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