Thread: Discussion A non-aerodynamic proof that a lifting wing pushes down on the earth View Single Post
Dec 31, 2012, 06:35 AM
Registered User
Germany, BW, Stuttgart
Joined Mar 2012
1,081 Posts
Sparky,

I was inspired by your effort and decided to give it a try. Rather than try to hold a helicopter in place, I fixed a prop vertically to blow down on a scale covered by a large plastic plate. I put another plate over the top of this and supported it so that I could adjust its height above the rotor. The pitch of the prop is far from ideal for this setup, but it's what I had on hand.

Prop diameter: 9.5"
Prop height above lower plate: fixed at 3.5"
Prop height below upper plate: adjusted from 1" to 5"
Scale reading with rotor stopped: 0-10 g
Scale reading with rotor turning and no upper plate: 1,000 - 1,020 g

The first two attachments below are crude pictures of the setup. The next shows the definition of the parameters I used. The last attachment shows the results.

On the results graph:
-The triangles show the ratio of F_scale (the force measured by the scale with the upper plate at a given height) to F_no-plate (the force measured by the scale with the upper plate removed).
-The squares show the ratio of T_rotor (the upward rotor thrust with the upper plate at a given height) to T_no-plate (the rotor thrust with the upper plate removed).

The force measured by the scale drops off very rapidly as the upper plate is moved closer to the prop from above. With 1" of separation, the force measured by the scale dropped to 115 g (just over 10% of what it showed with no plate).

Although my method for measuring the thrust of the rotor was crude, it's good enough to show that the rotor's thrust isn't changing by much.

This setup could certainly be improved in a number of ways, but the variation of the force measured by the scale was very repeatable.

EDIT: I came up with a much improved method for measuring the thrust of the rotor (accurate to about 5% of the total thrust). This method showed no discernable difference in the thrust due to the presence of the upper plate (at all upper plate heights).