I am not sure if your problem is related to prop pitch, but
maybe I can contribute a little to how one might make that measurement. When I
first got my Ercoupe, I spent a good bit of time checking things to see if it
conformed
to various specifications. As part of
that drill, I wanted to check if my propeller was pitched as stamped on the
hub. For what it’s worth, here is how I did it:
Propeller pitch is defined as the distance in inches that a
propeller will move forward in one revolution.
This is based on the propeller blade angle at the 75% blade station. The
relationship between propeller pitch and blade angle can be expressed as:
Propeller pitch in inches) = (2 Pi) (75% radius
in inches) (tangent of blade angle at given radius in degrees).
As an example, if we have a 7148 prop we can first calculate
the 75% radius point as ½ x 71 inches x 0.75 = 26.6 inches. To calculate blade
angle we have 48 inches =
(2 pi) (26.6 inches) (Tangent of blade angle in degrees). Solving this
equation for blade angle yields
16 degrees.
To measure blade angle on the airplane, we first measure out
from the center and mark the 75% radius station on both blades. A propeller
protractor is then typically
used to measure the blade angle at these points referenced to the hub. The
ones I’m most familiar with are very
expensive but there is an inexpensive pl
astic one available that I bought from
Warp Drive inc. I have also experimented using a digital level to measure blade
angle. If you have the type that allows you to zero in any
position, it simplifies the measurement.
References:
The definition of propeller pitch cited above was taken word
for word from “Aircraft Propellers and Controls” by Jeppesen. The formula that
relates propeller pitch to blade angle can be derived using trigonometry along
with the knowledge of what propeller pitch means. I have also seen it written
down in at least
one publication. Issue number 54 (page
11) of “Contact” magazine contains an article entitled “Understanding and
Applying
Propeller Pitch Factors” which includes this formula. “Contact” is a fairly
obscure publication that caters to a bunch of hooligans that experiment with
auto converted engines on homebuilt airframes (smile)
I would encourage anyone to hire a pro to do this or at least research these
things for yourself, but maybe this could serve as a starting point. If there
are propeller specialists out there, please let us
know if any of what I just said bears any resemblance to truth.
Cheers,
Bill
415 CD
Kostas
said: Next step is to check prop pitch.
Ed said: Can anyone point all of us to a reference
that tells how to check propeller pitch in the field?
