# Lateral tilt

#### Jean Claude

##### Junior Member
We amateurs might settle the question by carefully photographing a gyro, flying s/l against a clear horizon, from another gyro flying a parallel course at the same altitude... not too difficult and no need for special instruments...
So, here's a picture showing 9.5° i.e (L/D)r = 6, not 15 as shows the Dudda's simulation

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#### XXavier

##### Member
So, here's a picture showing 9.5° i.e (L/D)r = 6, not 15 as shows the Dudda's simulation

View attachment 1148068

I don't want to be negative, but a clear horizon is lacking, the blades are 'frozen', and it's difficult to know in what azimuth, and –finally– we don't know the airspeed; the L/D may be 6, but that's the figure predicted by the curve at roughly 80 km/h

#### XXavier

##### Member
Now I've tried Beaty's 'RotorCALC', inserting the values for my ELA at 390 kg and adjusting the lift coefficient until I get the usual 330 rpm:

For 75 mph = 120 km/h if, as it seems, the 'rotor angle of attack' does not include the flapping angle, then the AoA of the disk would be 5,36 + 3,87 = 9,23º

More or less what you say...

On the other hand, and in this paper published in the Journal of the Amer. Helicopter Society in 1965

I find this chart for the Bensen B-8:

Reading some clear values from the chart, and interpolating, I get just 2,35º of rotor AoA for v= 120 km/h

I wonder if that AoA includes the flapping angle...

I feel disconcerted with so many apparently diverging results... After some reflection, I have come to believe that J.C. is right and the book 'Flugphysik der Tragschrauber' is wrong concerning the AoA of the disk. What the book gives as AoA of the disk is probably the angle between the plane perpendicular to the rotor shaft and the relative wind. To get the real AoA, i.e., that between the tip-path plane and the relative wind, one has to add the flapping angle at azimuth 180º of the blade, i.e. the 'blowback angle'.

Thanks to J.C. for enlightening me...

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