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vissarion.eu
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How calculate propeller efficiency if I know propeller trust ant motor power and motor efficienty?
How conwert thrust to watts?twasnow said:convert thrust to watts (or any standardized unit of energy)...
vissarion.eu said:How conwert thrust to watts?
Cyrus said:You can't covert thrust to watts. Thrust is not power.
twasnow said:Thrust is power and it is expressed as either Jules / Second, horsepower, Foot-pounds / Second, or of course Watts.
all of these are easily convertible.
Please point us to ANY reference that lists thrust as a measure of power.twasnow said:Thrust is power and it is expressed as either Jules / Second, horsepower, Foot-pounds / Second, or of course Watts.
all of these are easily convertible.
FredGarvin said:Please point us to ANY reference that lists thrust as a measure of power.
To answer the OP you need to know the aircraft speed to calculate the efficiency:
[tex]\eta_p = \frac{T*u}{P_{shaft}}[/tex]
where:
[tex]\eta_p[/tex] = propeller efficiency
[tex]T[/tex] = thrust
[tex]u[/tex] = aircraft speed
[tex]P_{shaft}[/tex] = shaft horsepower provided by the engine to the propeller
FredGarvin said:Please point us to ANY reference that lists thrust as a measure of power.
To answer the OP you need to know the aircraft speed to calculate the efficiency:
[tex]\eta_p = \frac{T*u}{P_{shaft}}[/tex]
where:
[tex]\eta_p[/tex] = propeller efficiency
[tex]T[/tex] = thrust
[tex]u[/tex] = aircraft speed
[tex]P_{shaft}[/tex] = shaft horsepower provided by the engine to the propeller
Care to try again? I have 4 or so propulsion references on my desk right now plus a handful of places on line I can cite for the definition of propulsive/propeller efficiency. You are flat out wrong on all accounts.twasnow said:Oh and one other thing Mr. perfect, your calculation there provides the efficiency of a plane getting from point A to point B, Not the propeller efficiency.
FredGarvin said:Care to try again? I have 4 or so propulsion references on my desk right now plus a handful of places on line I can cite for the definition of propulsive/propeller efficiency. You are flat out wrong on all accounts.
Because you don't use the word "thrust" to describe what a propeller is doing when it is powering a desk fan. "Thrust" means propelling an object.twasnow said:How is your equation not about plane efficiency it is using aircraft speed
what if the propeller he is talking about is in a fan, or say a pump...
FredGarvin said:Please point us to ANY reference that lists thrust as a measure of power.
To answer the OP you need to know the aircraft speed to calculate the efficiency:
[tex]\eta_p = \frac{T*u}{P_{shaft}}[/tex]
where:
[tex]\eta_p[/tex] = propeller efficiency
[tex]T[/tex] = thrust
[tex]u[/tex] = aircraft speed
[tex]P_{shaft}[/tex] = shaft horsepower provided by the engine to the propeller
twasnow said:Oh and one other thing Mr. perfect, your calculation there provides the efficiency of a plane getting from point A to point B, Not the propeller efficiency.
vissarion.eu said:Be and not bad calculate propeller efficienty with following effect...:Then air created by propeller push plane to opposite direction than fly plane...
Cyrus said:You have way, way, too many significant digits.
1 HP = 745.7W
Also, why did you use metric units, and then throw in HP? The denominator should be in watts.
Side: It's spelled percent. (No o, or s)
I not think that. Car with proppeller waste more fuel whan car driven with wheels.xxChrisxx said:1. Why on Earth do you think at 30km/h a prop would give better fuel efficiency than driveshafts and wheels?
vissarion.eu said:I not think that. Car with proppeller waste more fuel whan car driven with wheels.
xxChrisxx said:It's early and my brain hurts from a night of drinking.
Even in my lowered state of mental agility I can tell something about the above just doesn't seem quite right.
1. Why on Earth do you think at 30km/h a prop would give better fuel efficiency than driveshafts and wheels?
Run it with numbers the bother way around.
100 l for car and 70 l for prop.
Using the same equations you have, just flipped.
You get 142% efficiency. Wow.
2. Why do you think this is calculating the propellor efficiency?
3. What do you think the propellor efficiency acutally is, as you seem to be using a different definition to every textbook I've ever read on the subject?
Look at what variables you have included in your 'calculation'.
Vehicle speed working axially to the prop.
Power output, from getting fom A to B to measure fuel useage.
Trust required to remain at set speed of 30km/h.
Compare the above to the equation that we know that works for prop efficiecnt that you dismissed.
You not good me understand. I not say 100 l for car and 70 l for prop. I say 100 l for propeller powered car and 70 l for normal car.100 l for car and 70 l for prop.
Why do you think this is calculating the propellor efficiency?
Car powered propeller must be like normal car.3. What do you think the propellor efficiency acutally is, as you seem to be using a different definition to every textbook I've ever read on the subject?
xxChrisxx said:Fair enough, I read it wrong (told you, my brain wasnt up to speed). The method you specified is still crap though.
I think there is little more to say on this, multiple textbooks disagree with you. Others have explained prop efficiency sufficiently well. Either you are dismissing it because you are stubborn or becuase you have a non standard definition of propellor efficiency.
xxChrisxx said:Your calculation is crap. The above post is similarly pointless to furthering your argument.
Fred showed you how to calculate prop efficiency.
/Thread.
I say motor output power. This mean not motor power, but output power, power, that motors gives. So power is not 18000 W, but 20000 W. Little mistake you make.xxChrisxx said:... Shaft HP = Rated motor output * mechanical efficiecny (assumre 90%)
For a car this value could be much much lower.
Power(shaft) = 18000 W
I from Lithuania. I not wery good understand english language.Is there some sort of language barrier here? Where are you from vissarion?
Motor output power is power in watts for example, that makes shaft motor. For example motor input power 100 W (10 V, 10 A), motor output power 70 W. This mean, that motor eficienty is 70 %. I don't known how exactly measure motor output power. Input power value taken from volts * ampers (V * A) in electric motor.xxChrisxx said:What do you mean by 'motor output power'? Where was the power value taken from? (Compare to list above).