robertl
WellKnown Member
What about a jet engine?
======================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?
View attachment 98739View attachment 98740View attachment 98741
==========================
Rotax 277UL 2.0 to 1 Ratio Pitched 3025rpm 
54" X 18  

Exactly.Most props within the normal realm of pitch and diameters on fixed wing aircraft produce 4 to 4.5 pounds of thrust per hp, according to actual pull testing with scales.
100hp will give you around 400450 pounds of thrust. Static thrust figures are not that useful in reality on fixed wing aircraft.
===========================Published formulas indicate prop static thrust varies with changes in pitch.
Examples of questionable Static Thrust from calculator  using correct data.
Calculator produces static thrust numbers that do not change with pitch or HP.
3150rpm, Pitched 100rpm for 3050rpm with a 58" Prop = 282.26 lbs of Static Thrust at 77 Degrees with a (2) blade prop.
58" x 21 = 45.808 hp needed. 282.26 lbs Static Thrust.
58" x 20 = 43.627 hp needed. 282.26 lbs Static Thrust.
58" x 19 = 41.445 hp needed. 282.26 lbs Static Thrust.
58" x 18 = 39.264 hp needed. 282.26 lbs Static Thrust.
58" x 17 = 37.082 hp needed. 282.26 lbs Static Thrust.
58" x 16 = 34.901 hp needed. 282.26 lbs Static Thrust.
58" x 15 = 32.720 hp needed. 282.26 lbs Static Thrust.
60" x 21 = 52.461 hp needed. 323.25 lbs Static Thrust.
60" x 20 = 49.963 hp needed. 323.25 lbs Static Thrust.
60" x 19 = 47.464 hp needed. 323.25 lbs Static Thrust.
60" x 14 = 34.974 hp needed. 323.25 lbs Static Thrust.
62" x 21 = 59.813 hp needed. 368.55 lbs Static Thrust
62" x 20 = 56.965 hp needed. 368.55 lbs Static Thrust.
62" x 19 = 54.117 hp needed. 368.55 lbs Static Thrust.
62" x 12 = 34.179 hp needed. 368.55 lbs Static Thrust.