Aces High Bulletin Board

General Forums => Aircraft and Vehicles => Topic started by: niklas on July 23, 2002, 07:04:58 AM

Title: prop pitch angle
Post by: niklas on July 23, 2002, 07:04:58 AM

Hello

Does anyone know where the prop pitch angle is measured? Is it the AoA of the prop tip, or 0.5 of the radius? I mean due to the twist the Blade has many AoA (standing aircraft).

The problem is that some aircraft have a angle bandwith of +15 - +90°. But with +15° the prop is stalled for takeoff right? Btw, is the prop of a Cessna with fixed prop stalled for takeoff?

On the other hand, when +15° refer to 0.5 of the radius, the outer section could produce lift. That´s why i ask


Thank you
nik

Title: prop pitch angle
Post by: Razzor on July 23, 2002, 08:10:45 AM

Don't confuse the Angle Of Attack of the prop with the Pitch of the prop.

I'm sorry to say that I don't have an answer for you. I would imagine that it's some place along the length of the prop where the pitch is an average between the root, and the tip. I don't have a clue.

The pitch of the prop of a Cessna (fixed pitch) is not "stalled" at take off, or at any other time it's in flight. I think you might be confusing AOA with the actual Pitch of the prop, they are two completely different things.

Title: prop pitch angle
Post by: funkedup on July 23, 2002, 04:50:42 PM

Niklas that is a very good question that I don't know the answer to.

I know Wells was digging into this a couple of years ago, maybe he can help.  I started to get into modeling props once but it became a pain in the bellybutton and I got bored with it.  :)

It would be convenient to measure pitch so that zero pitch gave zero thrust.  But I doubt they did it that way because I don't think most props can be adjusted to that point.

Title: Re: prop pitch angle
Post by: Badboy on July 23, 2002, 05:38:24 PM

Quote

Originally posted by niklas
Hello

Does anyone know where the prop pitch angle is measured? Is it the AoA of the prop tip, or 0.5 of the radius? I mean due to the twist the Blade has many AoA (standing aircraft).

Thank you
nik

Yes, the blade angle of a propeller is variable from root to tip, however, for comparison of various propellers, the blade angle at the three-quarter radius is normally used as a reference.

So, when you use the propeller curves for performance calculations, the family of curves for each propeller are also marked with the blade angles at the three-quarter radius. The same convention is used for propellers with manual pitch settings. The blade angle is defined as the acute angle between the chord of the propeller section and the plane of rotation. In the very rare cases where that convention has not been adopted, the station at which the blade angles have been measured has always been given. However, 0.75r appears to be standard practice for every document I've seen dating back to the early thirties.

Hope that helps

Badboy