Hello Folks

Ummm, no. Everything does not relate to line of flight where angle of attack is concerned. it does if you refer to fixed wing but when it comes to autogyros you can throw most of the aerodynamics for fixed wing in the trash <-- practicing my American

It would appear that this thread on precession has been hijacked

Sorry Hal, I didnt mean to be confusing. I think the big stumbling block here is what the definitions really are.

Using a rotor blade as an example :

Angle of incidence- This is mechanically fixed as you stated, it doesn’t change regardless of how much flapping or how fast it spins except for delta hinging which we will ignore for the sake of this description. Angle of incidence is the difference in angle between the chordline of the airfoil and the longitudinal axis, because this is a gyro the longitudinal axis must be at 90 degrees to the rotor mast.

Angle of attack- This is a constantly changing angle especially for an autogyro. The precise definition for angle of attack is 'the difference in angle between the chordline of the airfoil and the relative airflow'

I have made additions to the drawing to make things a little more clear.

An easier way to explain it is this, take yourself down to the lovely warm seas you have in Florida ( remembering to take plenty of sunblock) and wade out up to your shoulders in the sea.

Hold out your arm straight with your palm facing the seabed and spin round ! You will feel the water flowing equally over the top and bottom of your hand. Now as you spin move your arm up and
down and you will feel an increase in pressure on the top and bottom of your hand depending whether you are flapping up or down. This is because the relative waterflow is changing and therefore the angle of attack of your hand to the oncoming flow of water is also changing. Notice that your hands incidence did not change, only your hands angle to the flow of water changed due to the up and down movement of your arm.

If you stand still and simply move your arm up and down you would feel the flow as a pressure increase on the top and bottom of your hand respectively. Remember this flow is still there if you also spin round. You will see that angle of attack is a combination of values of both the vertical and horizontal flow.

Oh and Phil, I will have you know that it hasn’t rained here for over 3 hours !!! This weekend its going to be in the eighties with horrible humidity..........of course it will have to rain for 3 weeks after as payback

Much respect to you Hal

Sean