Project Sunrise
Los Angeles California 1974
Flight of the Worlds First Solar Powered Aircraft
by
Roland Boucher
The power required to fly an aircraft can be calculated from the few simple equations shown at the right where:
1) P power is in foot-lbs/sec
2) T thrust in pounds
3) V velocity in feet /sec
4) Q wing loading in pounds/sq ft.
5) Ar aspect ratio of the wing
6) Cd the coefficient of drag of the aircraft
7) Cl the coefficient of lift of the selected airfoil.
The Factor in the bracket is essentially a figure of merit for the aircraft. Table 1 shows the results of these calculations for a wing with an Eppler 387 airfoil operating at a Reynolds number of 100,000. Sunrise is essentially a powered sailplane with a thin fuselage and small tail. The Drag (other) from the fuselage and tail and was assumed to be 20% of the wing at a lift coefficient of 1.0.
Drag due to lift is assumed to be CL2/πAr.
An Efficiency Factor of 0.19 was assumed.
6 Minimum Power = 5.5 W3/2 / b ft lbs /sec
7 Minimum Power = 7.5 W3/2 / b watts
The bracket amount on line 5 is a square root.
Table 1 Values for the figure of merit for an Eppler 387 Airfoil operating at a reynolds number of 100,000 with the drag of Tail & Fuselage assumed only 20% that of the wing
P 3P 3