#### n3puppy

##### Well-Known Member

- Joined
- Jun 25, 2019

- Messages
- 215

Static Thrust Calculator - STRC

This is a common format I see when results are tabulated

3300 rpm with 72" Prop = 988.7 lbs of Static Thrust at 77 Degrees with a (3) blade prop at .9 CF

72" x 10 = 988.7 lbs Static Thrust. Needs 82.671 hp

72" x 5 = 988.7 lbs Static Thrust. Needs 41.335 hp

72" x 2= 988.7 lbs Static Thrust. Needs 16.534 hp

72" x 1 = 988.7 lbs Static Thrust. Needs. 8.267 hp

72" x 0.5 = 988.7 lbs Static Thrust. Needs 4.133 hp

Instinct tells me that the same 988lbs thrust for any pitch is not plausible.

Every formula (not calculator) I have seen always has pitch as a variable when calculating thrust. Change the pitch - thrust changes. Example formula below. (Set Vo to zero for static thrust)

If I am to believe the output of this calculator.....

I could build VTOL ultralight with a 500lb MTOW

Hang it from a 72in 3 blade prop with a virtually flat pitch (0.5inch)

Prop makes 988 lbs thrust according to calculator

Climb vertically at almost 2G (Thrust/Weight ratio 1.98 to 1)

All while using a $120 Harbor Freight 6.5hp motor (only need 4.133 hp)

Am I interpreting the results wrong?

Or is the calculator wrong?