The aircraft should be as small and light and as simple as possible, subject to the following constraints:
| Characteristic | AN | Spirit of St. Louis |
| Nominal* still air range (st. mi) | 4000 | 4040 |
| Max. stall speed (mph, start flight) | 60 | 71 mph |
| Max. T.O. speed | 60/70 | 80+ mph |
| Max. T.O. field length | 1000/2000 | 2250 ft |
| Min. initial climb rate | 500/300 | 334 fpm |
| Min. initial climb angle | 10 deg / 3 deg | 2.56 deg |
| Cruise / stall speed | 1.3 | 1.33 |
| Mission duration (3610 st. mi) | 48 hrs | 42 (no wind), 33.5 (actual) |
*Nominal component values are shown below. We should also achieve xx% certainty of 3150 n mi range with the following degraded performance assumptions:
| Component | Nominal Value | Degraded Value |
| Prop efficiency | .75 | - 0.1 |
| Full power bsfc | .6 | + 0.05 |
| Cruise L/D | ? | - 0.5 |
| Zero Fuel Weight | ? | + 5 lbs |
Computed climb rate and gradient computed at 1.3 Vs = 92 mph for Spirit. Lindbergh actually flew at 95 mph to start, but took off at 5250 lbs which would have required 2500 ft for take-off. End cruise speed = 75 mph
Lindbergh's data shows level flight at 85mph and 155 bhp.
At the same speed, if we have (220-155)*eta extra horsepower, we expect an available climb rate of RC = 65 hp * eta / 5135 lbs = 5.57 ft/sec (with eta = .8) or 334 fpm.