Prony brake calculation help (for determining engine horsepower)

In summary, the person is seeking help in determining the horsepower at the axle of their engine using the numbers they have obtained from their Prony brake. They mention getting a reading of six pounds of torque, 4 inches off the center line of the axle, and at a rate of 30 rpm. They are also considering using a calculator to help with the calculations. The conversation also includes a discussion about the correct spelling of "Prony brake" and the potential use of a pony to calibrate it. The expert then provides a summary of the calculations used to determine the horsepower, including conversions from pounds to newtons and inches to meters.
  • #1
Pinon1977
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TL;DR Summary
I need some help here. I'm trying to determine how to use the numbers I'm getting for my pony break to determine horsepower at the axle of my engine. Right now I'm getting a reading of six pounds of torque, 4 in off of the center line of the axle at a rate of 30 rpms. Can someone help me determine what the horsepower is here?
I need some help here. I'm trying to determine how to use the numbers I'm getting for my pony break to determine horsepower at the axle of my engine. Right now I'm getting a reading of six pounds of torque, 4 in off of the center line of the axle at a rate of 30 rpms. Can someone help me determine what the horsepower is here?
 
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  • #4
HP = Torque x RPM / 5,252

Torque is in foot pounds.
 
  • #5
6 pounds of torque, 4 in from the center line of the axle, at 30 rpm.
Let us know your setup and how you measure 6 pounds.

6 pounds = 2.721 kg. If pounds are a weight, then
convert to force 2.721 * 9.8 = 26.7 newton.
4 inch = 0.102 metre. Torque = 26.7 * 0.102 = 2.723 Nm.
30 RPM = 0.5 rev/sec. Angular velocity = 3.1416 rad/sec.
Power = 2.723 * 3.1416 = 8.555 W.
HP = 8.555 / 745.7 = 0.0115 HP.
 
  • #6
Baluncore said:
I assume by "pony break" you mean "Prony brake".
https://en.wikipedia.org/wiki/Prony_brake

I used to think it was a pony brake. I mean, it does make sense that you would measure horsepower on a pony brake.

Edit: Maybe use a pony to calibrate it?
 
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  • #7
Yes you would assume correctly. Proney. Stupid voice to text misspelled it for me. That's what I get for not proofreading. Haha. Anyhow thanks for the feedback. Much appreciate itQUOTE="Baluncore, post: 6893999, member: 447632"]
I assume by "pony break" you mean "Prony brake".
https://en.wikipedia.org/wiki/Prony_brake
[/QUOTE]
 
  • #8
Baluncore said:
6 pounds of torque, 4 in from the center line of the axle, at 30 rpm.
Let us know your setup and how you measure 6 pounds.

6 pounds = 2.721 kg. If pounds are a weight, then
convert to force 2.721 * 9.8 = 26.7 newton.
4 inch = 0.102 metre. Torque = 26.7 * 0.102 = 2.723 Nm.
30 RPM = 0.5 rev/sec. Angular velocity = 3.1416 rad/sec.
Power = 2.723 * 3.1416 = 8.555 W.
HP = 8.555 / 745.7 = 0.0115 HP.
Hello there. This is the feedback I was looking for. Thank you!
 
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1. What is a Prony brake and how does it work?

A Prony brake is a device used to measure the power output of an engine. It consists of a belt or strap wrapped around a pulley attached to the engine's output shaft. The brake applies a load to the engine, causing it to slow down. By measuring the force required to keep the engine at a constant speed, the power output can be calculated using the formula P = 2πNT/60, where P is power, N is the speed in revolutions per minute (RPM), and T is the torque in pound-feet (lb-ft).

2. What are the steps for calculating engine horsepower using a Prony brake?

The steps for calculating engine horsepower using a Prony brake are as follows:

  1. Attach the Prony brake to the engine's output shaft.
  2. Adjust the brake load until the engine is running at a constant speed.
  3. Measure the speed of the engine in RPM using a tachometer.
  4. Measure the force required to keep the engine at a constant speed using a dynamometer.
  5. Calculate the torque by multiplying the force by the distance between the force and the center of the pulley.
  6. Plug the values for speed and torque into the formula P = 2πNT/60 to calculate the engine's horsepower.

3. What factors can affect the accuracy of a Prony brake calculation?

There are several factors that can affect the accuracy of a Prony brake calculation, including:

  • Friction between the brake and the engine's output shaft
  • Inaccuracies in measuring the force and distance
  • Variations in engine speed during the test
  • Wear and tear on the engine's components

4. Can a Prony brake be used to measure the power output of any type of engine?

No, a Prony brake is only suitable for measuring the power output of engines with a rotating output shaft, such as internal combustion engines and electric motors. It cannot be used for engines without a rotating output, such as jet engines or rocket engines.

5. Are there any alternatives to using a Prony brake for calculating engine horsepower?

Yes, there are other methods for calculating engine horsepower, such as using a dynamometer or measuring fuel consumption. However, a Prony brake is a simple and cost-effective method that can be used in a variety of settings, making it a popular choice for many scientists and engineers.

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