# Calculating Propulsive Efficiency of an Aircraft Propeller

• HansGruber
In summary, the propulsive efficiency of the propeller at this operating point cannot be accurately determined without the power consumed. Intuitively, attempts to calculate it based on the given variables result in an efficiency greater than 1, which is impossible. The necessary variables for calculating power (thrust and velocity) also need to be in compatible units for the efficiency formula to work.
HansGruber
An aircraft is flying straight and level at a speed of 150 mph. Its propeller has a diameter of 8 ft and is generating 300 lbf of thrust at an altitude of 3000 ft. What is the propulsive efficiency of the propeller at this operating point?

no equations given, but from searching around I've found that Propulsive efficiency = (thrust *velocty)/ power

Intuitively, I've tried several ways to calculate power with the given variables, but all of my answers come out to an efficiency much greater than 1, which, of course, is impossible.

You have thrust and velocity, but you don't have consumed power.

You also need to make sure your units match up. For example, thrust*velocity is a power term, and to get that into (ft-lbs/sec) your thrust needs to be in (lbs) and velocity needs to be in (ft/s). Your power term needs to be in (ft-lbs/sec) as well, then your efficiency formula works. But again, you don't have anything that will give you the power consumed.

## 1. What is the definition of propulsive efficiency?

Propulsive efficiency is a measure of the effectiveness of an aircraft propeller in converting engine power into thrust, or forward motion.

## 2. How is propulsive efficiency calculated?

Propulsive efficiency is calculated by dividing the actual thrust produced by the propeller by the ideal thrust that would be produced if the propeller were 100% efficient.

## 3. What factors affect the propulsive efficiency of an aircraft propeller?

The propulsive efficiency of an aircraft propeller is affected by several factors, including the shape and design of the propeller blades, the speed of the propeller, the air density, and the engine power.

## 4. What is considered a good propulsive efficiency for an aircraft propeller?

A good propulsive efficiency for an aircraft propeller is typically in the range of 80-90%. However, this can vary depending on the specific design and operating conditions of the aircraft.

## 5. How can propulsive efficiency be improved?

Propulsive efficiency can be improved by optimizing the design of the propeller blades, reducing the weight and drag of the propeller, and increasing the engine power. Additionally, proper maintenance and regular tune-ups can help improve the efficiency of an aircraft propeller.

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