n3puppy
Well-Known Member
- Joined
- Jun 25, 2019
- Messages
- 339
Can someone help me understand how to use the Static thrust calculator that is often quoted when discussing engine hp numbers?
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?
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?