Is this a good or a bad propeller?

Question

I want to see if a propeller is bad or good for generating static thrust. This is what I know about the propeller and the engine used to turn it during a test:

Engine shaft power, $P$ = 0.58 hp

Propeller diameter, $D$ = 8.5 ft

Revolutions per minute, $RPM$ = 245

Static thrust, $T$ = 18.75 lbf

Can I calculate the efficiency of the propeller? What is the maximum achievable efficiency?

Additional explanations

The formula I was suggested to use could be exactly what I need. However, using it, I do not get some reported experimental results like:

Engine shaft power, $P$ = 6 hp

Propeller diameter, $D$ = 8.5 ft

Static thrust, $T$ = 66 lbf

Propeller efficiency, $\eta_{prop} \geq 66\%$

Gear efficiency, $\eta_{gears} \geq 85\%$

Doing the calculations: $\eta_{prop} = \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \eta_{gears} \cdot \frac{D^2}{2} \cdot \rho )}} = 37.2\%$ which is well below 66%.

@Ralph Looks like another question about the Wright brothers. — , Oct 25 '15 at 13:00
Why the downvotes with no comments? Seems like a perfectly reasonable aviation question to me. +1 to help restore CAVOK. — Simon, Oct 25 '15 at 15:34
Possible duplicate of Is there any equation to bind velocity, thrust and power? — , Oct 25 '15 at 22:12
There is no requirement to provide an explanation for voting, nor should there be. — CGCampbell, Oct 26 '15 at 13:59
I do not believe that qualifying a propeller as bad or good is just an opinion. "A well-designed propeller typically has an efficiency of around 80%", (Wikipedia). So, an eff = 37.2% is quite bad. — Robert Werner, Oct 28 '15 at 03:54
Honestly, the second propeller (T = 66 lbf) is exactly the one used by the Wright brothers in December 1903. They utilized a 12 hp engine, 2 propellers of diameter D = 8.5 ft and they got a total static thrust T = 132 lbf. According to the brothers the efficiency of both propellers was 66%, a figure nobody had reached before. In reality it appears that the 1903 propellers were below 40% efficient which means the two brothers used in fact bad aerial screws even by the standard of the time. — Robert Werner, Oct 28 '15 at 03:59

score 2 · Answer 1 · edited Apr 13 '17 at 12:59

2

Engine shaft power: P = 0.58 hp, Propeller diameter: D = 8.5 ft, RPM = 245, Static thrust: T = 18.75 lbf

$\eta_{prop} = \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \frac{D^2}{2} \cdot \rho )}} = 49.5\%$

where $\rho=1.2 \frac{kg}{m^3}$

So at an efficiency of 49.5% that propeller is rather poor.

Note: I used the formula that relates static thrust to efficiency, power and propeller diameter from here.

edited Apr 13 '17 at 12:59

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answered Oct 25 '15 at 14:17

Robert Werner

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It is known that the efficiency of a plane propeller is low at small forward velocities, so just because eff_prop =~50%, when the plane does not move, it does not mean the propeller efficiency will remain the same as the plane speeds up. – Robert Werner Oct 28 '15 at 17:05

Is this a good or a bad propeller?

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