Talk to a guy with some experience in racing props or just big ol props in general.
there are more theories than Carter has pills -
You start with power available and airframe to be hauled around- then you whittle or layup till you hit the best performance.
when you are close to the hub - throw away the calculator - just eliminate drag -
Q tips/ Scimitars paddles/ -on and on -
On a given plane, the engine and prop COMBO can be killer good - put it on another type plane and it is no better than a popsicle stick and rubber band.
The interaction of the airplane is all important.
The model airplane prop charts are best printed on soft , degradeable paper --

antter,

Yes, you are right. Geometric pitch is relative to the chord angle and has little to do with the airfoil aerodynamics. It's just a geometric reference point. I got a little confused.....hehe
Zero lift angle, as any AoA in a polar is measured between the airflow and the airfoil chord line. So, when we say that a given airfoil has -6 degrees of zero lift AoA, it means that it's chord line makes an angle of -6 degrees with the airflow.

Here's an interesting website that gives an insight into some aspects of propellers.
http://www.apcprop.com/Engineering/e...ng_design.html

I will make a little research and see I can find the major prop brands airfoil section. With them, I can them draw some polars for them and play a little with the results and see if I can come up with a way to calculate thrust by treating the propeller blade as a rotating wing.

I will keep you posted....

APC has great props!
I got some of the very first ones - and ran them against all the current stuff - at the time -
They make many permutations of a given length and diameter and you can really fine tune the performance for a model.
Now they have some super setups for the new high power electric motor setups.
Did you guys know that the best prop for an electric motor is typically different than the prop for a IC engine?

Hey, no advertising
Sorry for being away for so long.
You guys have said that pitch is variable along the whole side of the prop and that the thrust should be calculated for the segments of the prop.
To get ideal results, you would have to divide the prop into an infinite amount of pieces.
Or better yet, find the limit as the amount of pieces goes to infinity. That is, find a function that gives you the thrust for a specific prop with the variable being the number of pieces, and look what the thrust would be as the number of pieces goes to infinity
Sorry for the repetitiveness
TO give you a little background on what I'm going to say
The equation for thrust is
thrust=ct*q*n^2*d^3
ct=coeff. of thrust
q is mass density of air
n= revolutions per second
d=diameter in feet
Output is in pounds
The whole trick in this whole thing is to find the Ct. What I use in the calculator is a regression with the input being angle at 75% of the diameter and the output being the ct. the data was from a trial by NASA, and can be found here. http://naca.larc.nasa.gov/reports/1932/naca-report-378/
I’m wondering if anyone had better methods. I was trying to get some better regressions by collecting data on props and then making a regression for each brand. Anyone have any better answers?
I could make an unloading program, but I’ll have to know how the relative AOA changes compared to speed and rpm. But there is one thing I don’t understand. If the relative AOA is smaller, there is more rpm. But the relative angle is calculated by speed, pitch and rpm. Isn’t this the chicken and the egg thing again
Okay, that’s my very long 2 cents for now.

I would just suggest kind of empirical method for prop, i dont know what you guys think about it.

Take electric engine, not airworthy but just strong one with known efficiency and test different props thrust at different RPM at static condition. With electric engine it must be easy to get the power needed to run a prop at given RPM- just measure current and voltage and substract the power needed to run engine unloaded at same RPM. All setup might be on testbench equipped with dynamometer or kind of weight balance to measure thrust.
It wont take airframe into account but would be a good starting point.

The next would be to get aerodynamic pitch of propeller and estimate the zero thrust speed of prop at given RPM. In such a way we will have two points on the thrust vs airspeed chart- thrust at zero speed and speed at zero thrust for each RPM value (say in steps of 1000 rpm).

Question woud be what to do next- draw a straight line to connect two points? Or fit some function to connect them? To make measurements at non zero speed is propably tricky. Inherent drawback is the stall at static conditions.

I am sure one doesnt need to measure all the props- interpolation should work within similar props.

I would donate few props for such project.


For purely numerical methods one should go for Xfoil and perform calculations for each segment of blade there. But such dedicated soft must exist.

Eagle One- thanks for link, i didnt know that APC have homepage. In my very modest experience i tried APC and props from four other brands with same nominal pitch and diameter and as they say "I feel the difference".

Well - I have done some of this - for small props -again you can NOT tell flight performance , even based on this .
You can tell power/thrust combinations tho.
A common finding is that X power always results in a given thrust-irrespective of propellor design
BUT when flying the aircraft - the results can be very much different .
EXAMPLE: wide blade /low pitch =15 oz thrust
also narrow blade higher pitch - SAME 15 oz thrust - at SAME power input.
In flight --the results are extremely different.
This is from actual experiment and flying.

You can tell power required for thrust at given rpm - BUT the prop is still stationary, that is, not moving thru the air, so the actual perfromance is not same as prop when moving.
The theorizing is interesting but the actual data-even more so.

Yes,
Measuring and comparing the propellers' static thrust won't give reliable results, as the blades of a given prop may stall showing bad static thrust at the test bench, whereas it may show excellent performance in the flight and even outperform other ones that show a better static thrust.