# How much thrust is available from the Allison T-56-A-15 engine?

What is the thrust availability per engine in Lockheed C130H? The engines are Allison T-56-A-15 (SHP=4100, SFC=0.5) Propellers = NP2000 eight Bladed(Prop Efficiency if assumed to be 90% constant at all speeds) SHP - Shaft Horse Power

• @mins That answer provides the KW output for the engine, which isn't the same as the thrust it provides which is entirely dependent on the propeller efficiency. The thrust should be measured in newtons, kg-f, or lb-f. – Ron Beyer Mar 9 '16 at 14:49
• @RonBeyer: That's right, it's the power of the turboprop, the thrust developed by the propeller with this input power will depends on the speed, and the propeller efficiency (which is not constant over the speed range ➭ Fn = SHP × 375 × efficiency / speed in MPH). – mins Mar 9 '16 at 16:29
• What is the "speed" in your equation? The speed of the aircraft? The formula breaks down at zero speed (obviously), and speeds approaching zero can't have infinite thrust. Is the "speed" value a cruise speed? At least in another field (marine) we measure thrust using bollard pull techniques, which is akin to chaining the boat to the dock and increasing power until the thrust produced maxes out... – Ron Beyer Mar 9 '16 at 16:36
• @mins The 'speed' in the equation, is it cruise speed? – Evilz Mar 9 '16 at 17:14
• @Evilz: Yes, it is. – mins Mar 9 '16 at 17:19

## 1 Answer

From Raymer's "Conceptual Aircraft Design", page 327, equation 13.15:

$$\eta_p = \frac{TV}{P}$$

Where:

• $\eta_P$ is the propeller efficiency
• $T$ is the Thrust [kN]
• $V$ is the True Airspeed [m/s]
• $P$ is the engine power [kW]

Reverting the formula you get that the Thrust per engine is given by:

$$T = \frac{P \eta_p}{V}$$