I estimated the force on the flap as the dynamic pressure times projected area.
press,d = 1/2 x dens x velocity^2 in psf
dens = .07/32.2 slug/ft^3
vel in fps
For 90deg flaps projected area is simply the flap area. Use flap area in ft^2 . get force in lbs.
Torque is force times half the flap chord times sine of the flap angle. Sine 90deg = 1. If you use the chord in inches and convert the force to ounces you wind up with torque in inch-ounces.
At 30 mph, v = 44 fps.
Press,d = 1/2 x .07/32.2 x 44^2 = 2.1 psf
Force = 2.1 x 40/144 = .58 lbs 16 x .58 = 9.4 oz
I guessed the flap chord is 3".
Torque = 3/2 x 9.4 = 14 oz-in
If the flaps are deflected 30 deg I multiply the 90deg torque by the sine of 30 deg. That is rough but provides a method for sizing servos.