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AERO 309 – Module 6 Homework

1. Say that you have an engine that is rated at 1300 hp and a propeller with a diameter of 7

ft. Use momentum theory to calculate the maximum thrust possible (in lb) from your

engine at sea level. Explain why a real engine and propeller produce less thrust than the

value you calculated.

2. Use the attached propeller charts for this problem. The propeller diameter is 10 ft and

assume that the rotational speed of the propeller is constant at 1200 rpm. Assume that

you are at standard sea level conditions.

a. For each of the seven pitch angles, what is the maximum propeller efficiency?

What is the advance ratio and velocity for each of the maximum propeller

efficiencies?

b. For each pitch angle, what is the thrust coefficient and thrust produced (in lb) at

maximum propeller efficiency?

c. For each pitch angle, what is the power coefficient and power needed (in ft*lb/s

and hp) at maximum propeller efficiency?

d. What is the velocity and Mach number at the tip of the propeller? The velocity at

the tip will include both the forward velocity and rotational velocity.

3. A propeller-engine combination produces 600 hp of power. If the total displacement is

20,000 cm3, the engine efficiency is 0.93, the propeller efficiency is 0.84, and the

rotational speed is 2600 rpm, calculate the mean effective pressure of the engine.

4. A turbojet is at an altitude of 33,000 ft traveling at a Mach number of 0.64. It has an inlet

area of 8 ft2 and an exit area of 5 ft2. The exit velocity is 1700 ft/s and the exit pressure is

700 lb/ft2. The fuel-to-air ratio (by mass) is 0.05.

a. Ignoring the mass of the fuel, calculate the thrust produced by the turbojet.

b. Recalculate the thrust of the turbojet but do not ignore the mass of the fuel.

c. What is the percent error in ignoring the mass of the fuel when calculating the

thrust?

d. The turbojet has a diffuser after the engine inlet. At the end of the diffuser, the

Mach number is 0.2. Calculate the pressure at the end of the diffuser. (Hint: the

flow is isentropic so the total pressure will be constant)

e. Estimate the thrust of this turbojet engine at sea level.

5. A turbofan has a static thrust at sea level of 60,000 lb. Estimate the thrust available at

the conditions in question 4.