1. Place a 12 x 12 x 3/4" piece of plywood across two bathroom scales.

2. Record no load scale settings.

3. Place sailplane main wheel in center of plywood and block fore and aft to prevent ship from rolling off scales.

4. Place 3rd scale on box 16" high and place under tail wheel.

5. Record sum of both front scales minus no load readings.

6. Record weight on tail wheel scale.

7. Hold stick vertically against nose of ship and mark line on floor corresponding to tip of nose.

8. Measure distances to contact point of main wheel and tail wheel.

9. Check horizontal distance from nose to vertical center of main spar shear web.

10. Record distances from nose to the center of gravity of all other items to be carried in the ship that are not included in the sailplane when weighed empty.

11. Compute total gross weight.

12. Multiply all items times their distance from the nose to get index units.

13. Add all index units and divide by gross weight to got horizontal e.g. location distance from nose.

14. Subtract the e.g. distance from the centerline of spar distance. Permissible range is minus 3/4" (aft of centerline ) to plus 4 1/4" (ahead of centerline.)

15. C.G. location in terms of mean aerodynamic chord = 1/24 (e.g. distance - spar centerline distance -6.9") All distances are in inches from nose reference.

16. Maximum forward e.g. is 23.3% MAC or 4 1/4's ahead of spar centerline. Locations farther forward would require flight with excessive up elevator, complete stalls would be more difficult and difficulty would be experienced getting the nose up sufficiently for low-speed landings.

17. Maximum aft c.g. is 44.2% MAC or 3/4" aft of spar centerline. Locations further aft would result in negative stability and possibly poor spin recovery.

The following sample weight and balance calculation on the original HP-11 will help you in setting up your own calculation.

In this example, the 0 moment arm center is located at the nose. It could, of course, be any other point without changing the results.

Your dimensions and weights could vary so it is suggested that you measure and weigh your own ship and make corrections accordingly. Level the plane of the fuselage steel tube assembly aft of the seat before weighing and measuring.

Maximum allowable gross weight is 720 lbs.

Allowable c.g. range is 23.3 - 44.2 MAC (4.25' ahead to 0.75" behind center of main spar.)

Center of Gravity = (Total Index Units)/(Total Weight)

MAC = (Wing Area)/(Wing Span) in the case of the HP-11, MAC = 104sq.ft/52 ft = 2 feet = 24 inches

MAC% = (C.G - Leading Edge MAC)/MAC