Assumption: All helicopters are quite similar in physical layout, therefore the ratio of moment-of-inertia between different helicopters should be quite close to the ratio of gross-weight between different helicopters.

If the above is true then is possible to evaluate comparative yaw rates between helicopters by comparing their Coefficients of Yaw.

Calculate the desired helicopter's values at maximum vertical lift.

Take the average of the Coefficient of Lift from the Blade element calculations.

Divide it by the average of the Coefficient of Drag from the Blade element calculations.

Multiply the rotor thrust by the above figure and this should give the rotor torque that must be overcome by the tail rotor.

Tail rotor: Airfoil - Profile 0012, Chord 4" to 3" (tapered), 18.5" span with 2.5" cutout.

Arm (mast to tail rotor) = 8 feet approx.

Tail rotor PTO is before 3.6:1 gearbox there for if rotor is turning at 500 rpm then the tail rotor is turning at 1800 rpm.

Tail rotor thrust = 15.7 lbs (this has been calculated using main rotor disk program)

Torque = 125.6 ft-lbs

If about 20-25% more power has been included to his tail rotor to give yaw.

Before building his tail rotor assembly, Fred applied full lift and torque to his helicopter, as if it was lifting off. He hooked a scale to a cord which was attached to the tail boom 12 feet back from the mast, where he planned to put the tail rotor. He said that the pull was 25 pound. This is a torque of 300 ft-lbs. He added about 20-25% more power to his tail rotor to give yaw. His helicopter's gross weight is about 750 pounds. This gives a excess-torque to weight ratio of (25% *300)/750 = 0.1 

The SynchroLite rotor disks alone should give about 58 ft-lb of torque (see calculations and large type note below)

58/550 = .105. This may be OK.

Blade pitch (theta) for hover out of ground effect and maximum yaw (in degrees)

See [Rotor - LAYOUT - Blade/Blade Clearance; Item 0199]

Sin(6) * 550lbs = 57.5lbs

Rotor hub to helicopter centerline = 1.125'

Torque = 57.5 * 1.125 = 64 lb-ft.

[Note: The maximum negative longitudinal cyclic is -9 degrees. This means that the maximum yaw available from the rotors, even with the disks tipped outward more than the 25 degree mast angle, is Sin(9). Sin(9) * 550lbs = 86.0 lbs. Rotor hub to helicopter centerline = 1.125'. Torque = 86.0 * 1.125 = 97 lb-ft.] This means about 11 lb-ft of torque for every degree.

Ruddervator axles point down at 45 degrees from the horizontal.

At maximum yaw left ruddervator is pitched down 30 degrees.

At maximum yaw right ruddervator is pitched up 30 degrees.

Disk loading is 1.6251 lb/ft-sq.

Ruddervator dimensions are mid chord = 11"

Span = 21"

Area of both ruddervators, in plan view = ((11 * 21) / 144) * 2 fins = 3.2 ft-sq.

1.6251 * 3.2 = 5.2

sin(45) * 5.2 = 3.68

sin (30)* 3.68 = 1.84

(for ref. only) Masts centerline to ruddervator centerline = 6'

Ruddervator centerline to tail boom centerline = 0.875'

Torque = 1.84 * 0.875' = 1.61 lb-ft