How to calculate propeller tip speed

My good friend F. Grindlay, preparing to calculate propeller tip speed.

A recurring question is how to calculate propeller tip speed. I have never needed to do this in all my years as a pilot, but it may be necessary if you build your own plane, or maybe it just shows up on the exam.

Let’s take an example.

  • Propeller RPM = 2400 rpm
  • Propeller blade length = 6 feet

If you want the answer in km / h, you have to convert 6 feet to Km, or maybe instead to meters first.

1 foot = 0.3048 meters and 6 feet = 1.8288 meters.

But you must have the radius to use the formula, so then it will be 3 feet = 0.9144 meters.

And then you probably remember that the sign π (pi) is 3.14

The formula you use is:

Vtip = 2πrRPM

Vtip = 2 x 3.14 x 0.9144 x 2400

Vtip = 13 781.8 meters / minute

Multiply by 60 to get meters per hour

Vtip = 13 781.8 x 60 = 826 910.9 meters / hour

And finally divide by 1000 to get km / h

Vtip = 826 km / h

If you do not remember how many feet there are in a meter, you can use the calculator. Set feet on the outer scale above meters on the inner scale, and then read 0.91 on the inner scale under 3 on the outer scale.

Using the flight computer to convert between feet and meters

Here are some questions for ya:

Blade angle ___ from the hub to the tip of a propeller blade in order to maintain an optimal ___ from hub to tip.

  • Increases, Angle of Attack.
  • Decreases, Angle of Attack.
  • Decreases, Geometric Pitch.
  • Increases, Effective Pitch.

As an aircraft with a variable-pitch, constant-speed propeller accelerates along the runway:

  • The blade pitch angle increases, maintaining a constant angle of attack and R.P.M.
  • The angle of attack will remain constant and the engine R.P.M. will increase.
  • The linear velocity of the propeller tip will gradually decrease.
  • The angle of attack will decrease and the engine R.P.M. remain constant.

Which of the following will increase the angle of attack of a fixed pitch propeller blade?

  • Decreased TAS and decreased RPM.
  • Decreased TAS and increased RPM.
  • Increased TAS and decreased RPM.
  • Increased TAS and increased RPM.

Here is a website for those who want to go in depth. https://aerotoolbox.com/propeller/#Tip_Speed_and_Helical_Motion

And a video

https://youtu.be/yldLbCuEQwo

have a good day