Last edited 3/9/2006 by Raymond Wagner
Our Problem is that we need to investigate a family of props in order to determine the best one for our airplane. This means we will need a map for each different prop.
Lets take a look at 2 data sets for 2 different props.
15 deg pitch, Von Mises, pg 390. I think this is probably a good prop data set to start with.
efficiency is hard to curve fit so lets convert it to thrust coefficient:
This section plots the data and shows a typical spline curve fit of it. We will not be using the curve fit of this section, it is just to show how it is done.
Cubic spline fit thrust and power coefficient:
calculates second derivatives
interpolates for any J:
now lets calculate efficiency:
Thrust Power / Shaft Power Absorbed
Shaft Power Produced / Drag Power (windmill)
This section plots the data and shows a typical spline curve fit of it. We will not be using the curve fit of this section, it is just to show how it is done.
from: Theory of Flight, Von Mises, pg 302-309
blade pitch at 3/4 radius of prop
(usually measured from bottom of airfoil)
difference between measured alpha and zero lift alpha
representative blade pitch, measured from zero lift:
Average 2Dairfoil lift slope:
Approximate cl
stall angle:
controls thrust break at low speed
Lift coefficient:
cd
Propeller aspect ratio:
from: Theory of Flight, Von Mises, pg 302-309
blade pitch at 3/4 radius of prop
(usually measured from bottom of airfoil)
difference between measured alpha and zero lift alpha
representative blade pitch, measured from zero lift:
controls J operating range of prop
Solidity:
proportional to blade to disk area,
similar to activity factor
controls high speed slope of both C
representative blade is a the 3/4 of the radius of the prop
pg 306
or
Ref Von Mises pg 303
Thrust Power / Shaft Power Absorbed
Shaft Power Produced / Drag Power (windmill)
Helical zero thrust relationships:
In order to convert the independent variable from
15 x 8 Propeller