Calculating Tip-Speed with Velocity

[Zipper730]

I know you can determine tip-speed in feet per second (without velocity) by calculating
Diameter * 3.1416 * RPS, so with an 11 foot propeller, an RPM of 1431 (23.85 R/S), you end up with 824.2 fps.

How do you calculate the effects of RPM *WITH* Speed? I've been getting different formulas to calculate the speed?

drgondog S Shortround6 W wuzak X XBe02Drvr

 

[gumbyk]

It's essentially the hypotenuse (diagonal) of a right triangle made by the forward speed of the aircraft, and the tip speed of the prop.
so total tip speed = sqrt(tip speed ^2 + aircraft speed^2)

 

[pbehn]

Do the different formulas give different results? There are several ways to consider the problem, as a triangle or a helix. The result must obviously be the same but the way to achieve that result are different.

 

[gumbyk]

Do the different formulas give different results? There are several ways to consider the problem, as a triangle or a helix. The result must obviously be the same but the way to achieve that result are different.

A helix is just a triangle wrapped around a cylinder.

 

[pbehn]

A helix is just a triangle wrapped around a cylinder.

I know, so you can calculate it as a triangle or as a line drawn around a cylinder, which was why I asked the question, the calculations look different but are essentially the same and obviously give the same result.

 

[gumbyk]

I know, so you can calculate it as a triangle or as a line drawn around a cylinder, which was why I asked the question, the calculations look different but are essentially the same and obviously give the same result.

There is one assumption with this, and that's that the centreline of the helix is the same as the direction of travel. i.e. the offset of the engine would alter the calculations.

 

[pbehn]

There is one assumption with this, and that's that the centreline of the helix is the same as the direction of travel. i.e. the offset of the engine would alter the calculations.

I am sure there are all sorts of considerations, I was only speaking in general term about Zippers post. There are many ways to present the formula, they look different but are basically the same, like the many ways to calculate the hypotenuse on a triangle.

 

[Zipper730]

Wait, so the hypoteneuse is like the track that the propeller would trace as it spins while moving forward? Speed and rotation become two of the legs and the velocity becomes the hypoteneuse? Don't ask me why I can come up with that connection, I'm not in tip top shape.

 

[pbehn]

Wait, so the hypoteneuse is like the track that the propeller would trace as it spins while moving forward? Speed and rotation become two of the legs and the velocity becomes the hypoteneuse? Don't ask me why I can come up with that connection, I'm not in tip top shape.

Basically yes. If you take the tip of the prop at any point, then after one revolution of that tip as the plane goes forward the distance covered by the plane is the vertical leg of a triangle, the distance covered in a circle is the other leg of the triangle and the hypotenuse is the total distance travelled, in one revolution by that particular tip, to turn it into a speed you need the RPM of the propeller to give a time value. There are many ways to express it.

 

[Aquadraco]

... Or you could simply go here, punch in the numbers, and let the website calculate it - Warp Drive Propellers Tip Speed Calculator