Sidious
Well-Known Member
I thought the whole purpose of decreasing the RPM and increasing the pitch at cruise speed was to achieve the most efficiency of the propeller for a given forward velocity BUT the effect of decreasing RPM seems like it would cancel out the effect of an increase in pitch....
When we are talking about the Rotational Velocity, Forward Velocity and Resultant Velocity it seems to me it becomes counter intuitive when we decrease the RPM on a constant speed prop when we get to our cruise speed.
After climbing we usually decrease the RPM to about 2400 in an Arrow at training cruise. By decreasing the RPM aren't we decreasing the Rotational Velocity as well? By decreasing the Rotational Velocity we are also giving the forward velocity the ability to decrease the angle of attack. In my mind this cancels out the effect of increasing the pitch.
Here are some rough pictures of what I am talking about. In picture 1 we have a section of a blade with a given forward velocity (FV) at cruise.
We then increase the pitch by decreasing the RPM and I believe we will then have the same AOA because of the decrease in rotational velocity.
Anyone that has read this far, thank you and if you have any comments it would be appreciated.
When we are talking about the Rotational Velocity, Forward Velocity and Resultant Velocity it seems to me it becomes counter intuitive when we decrease the RPM on a constant speed prop when we get to our cruise speed.
After climbing we usually decrease the RPM to about 2400 in an Arrow at training cruise. By decreasing the RPM aren't we decreasing the Rotational Velocity as well? By decreasing the Rotational Velocity we are also giving the forward velocity the ability to decrease the angle of attack. In my mind this cancels out the effect of increasing the pitch.
Here are some rough pictures of what I am talking about. In picture 1 we have a section of a blade with a given forward velocity (FV) at cruise.
We then increase the pitch by decreasing the RPM and I believe we will then have the same AOA because of the decrease in rotational velocity.
Anyone that has read this far, thank you and if you have any comments it would be appreciated.