I’ve spent most of today getting the autogyro ready for its third test flight tomorrow. Firstly, I now understand what the shim under the blades does. As the blades are fixed to a flat disk that spins, if the blades were at zero degrees incidence, then all the lift produced would be upwards. The shim gives the blades negative incidence, so there is a small component of the lift in the forward blade direction. Now, with the blade fixed to a spinning disk, this forward component of the lift makes the blade spin. The more negative incidence you add, the more force there is to spin the blades. There must be an optimum amount of incidence which causes the blades to spin at the correct speed to produce enough lift for flight, but I haven’t worked it out yet. I’ve just added a bit more to my blades for tomorrow’s test flight. It’s easily removed if it doesn’t work, though.
The next thing I did was to correct the tracking by bending the left u/c leg back into position. I can’t think how it got bent… Now it looks nice and straight, so I’ve moved on to looking at the control movements. There isn’t much I can do here, except make it all nice and square and get the head back to 90 degrees to the mast, which is the suggested neutral trim position.
Then I had a look at the videos of last week again. It’s all very consistent when you watch. As soon as it gets to a certain speed something kicks in and it yaws abruptly to the right. After wracking my brains about P effect and gyroscopics, I realised that I was missing the obvious. It’s almost certainly the reaction force as the the rotor head spins anti-clockwise. The yaw force is clockwise, so that great big triple rotor on the top is the most likely culprit. I took the head apart, I oiled the bearings and I put it back together again, which is about all I can do with it.
That’s all there is to it really, so I’m hoping for some wind tomorrow so I can do a hand launch. We’ll just have to see how it goes.