# Aerodynamic force

I need to find out how to work out the downforce of a flat elevator surface
on my ultralight at certains speeds and deflection. Can someone help with
the formulae.
DIYUL
I'll take a shot at this:
for credible, somewhat accurate values of elevator force, you would instrument the airframe, and conduct flight tests.
For a rough estimate, you could do this. Find the wing area, horizontal tail area, elevator area. Find the gross weight and the design loading, (could be 3.5g, 4.5g, 6g.) Max elevator downforce is design loading X gross weight X (elevator area/wing area) X elevator deflection (degrees)/20 degrees.
Let's see what numbers this turns up for a 1000 lb airplane stressed for 4.5g with 140 sq ft wing area, and 6 sq ft elevator area, in a pull up with 20 degrees elevatior deflection
4.5 X 1000 X 6/140 X 20/20 = 193 lbs.
For what its worth
Brian W

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