Power vs Thrust??
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Power vs Thrust??
If anyone can give me a laymans answer to the following, I would be very happy. With respect to Max RATE climb and max ANGLE climb, the books say that max RATE is acheived with excess POWER, whereas max ANGLE is with excess THRUST.
What is the differance between THRUST and POWER?
What is the differance between THRUST and POWER?
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Time.
Thrust is an applied force. Power is an applied force over a given time.
For a jet aircraft, "thrust horsepower" is a function of static (0 airspeed) thrust and airspeed. I forget the equation...
Thrust is an applied force. Power is an applied force over a given time.
For a jet aircraft, "thrust horsepower" is a function of static (0 airspeed) thrust and airspeed. I forget the equation...
Okay, try this.
Say one aircraft climbs at 600 kt and can produce a thrust of 10000 lb at that speed. Another aircraft (same weight) can produce 20000 lb but only at 100 kt.
So with twice the thrust the slower aircraft can climb at a steeper angle-- but the faster one is moving so much faster along its shallower angle that it gains altitude faster. Power is defined as force times speed, and in this case the fast aircraft has thrice the power of the slow one. So it gains altitude faster.
Say one aircraft climbs at 600 kt and can produce a thrust of 10000 lb at that speed. Another aircraft (same weight) can produce 20000 lb but only at 100 kt.
So with twice the thrust the slower aircraft can climb at a steeper angle-- but the faster one is moving so much faster along its shallower angle that it gains altitude faster. Power is defined as force times speed, and in this case the fast aircraft has thrice the power of the slow one. So it gains altitude faster.
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Orion1
At the risk of over simplifying,
Power is generally produced by an engine that turns a propeller ie not a jet engine. The power produced by the engine is of no use to you until you slap a propeller onto it - the propeller/engine combination then produce thrust.
The thrust required to fly an aircraft exactly matches the total drag curve(the bucket graph), so thrust is a fairly simple concept.
The power required to achieve the above is not so simple - it varies with the thrust required to fly(bucket graph), as well as with the speed at which you are flying.
In order to determine a power requirement at a given speed, you go to the bucket graph and extract the thrust requirement and then multiply it by the TAS. This will give you the power required to fly at that speed. Note : this is a hypothetical exercise. It is not intended for you to actually calculate.
In terms of climb performance, it is generally accepted that best ROC will be where the most excess power is. I am sure that there are ways to mathematically prove that best AOC will occur at a certain point on the power required/available curve(I think it generally co-incides with V for min power), but I think the boffins in the white coats thought it simpler to explain AOC to us in terms of thrust rather.
Anyway hope it helps.
At the risk of over simplifying,
Power is generally produced by an engine that turns a propeller ie not a jet engine. The power produced by the engine is of no use to you until you slap a propeller onto it - the propeller/engine combination then produce thrust.
The thrust required to fly an aircraft exactly matches the total drag curve(the bucket graph), so thrust is a fairly simple concept.
The power required to achieve the above is not so simple - it varies with the thrust required to fly(bucket graph), as well as with the speed at which you are flying.
In order to determine a power requirement at a given speed, you go to the bucket graph and extract the thrust requirement and then multiply it by the TAS. This will give you the power required to fly at that speed. Note : this is a hypothetical exercise. It is not intended for you to actually calculate.
In terms of climb performance, it is generally accepted that best ROC will be where the most excess power is. I am sure that there are ways to mathematically prove that best AOC will occur at a certain point on the power required/available curve(I think it generally co-incides with V for min power), but I think the boffins in the white coats thought it simpler to explain AOC to us in terms of thrust rather.
Anyway hope it helps.
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Thrust is the (usually) forward acting force produced by an aircraft's propulsion system.
(I say usually because in the case of thrust vectoring or reverse thrust systems, thrust can act in various directions.
In the case of jet aircraft, thrust is produced directly by the engine. In the case of piston/props and turboprops, the engine produces rotational power (called brake horsepower and shaft horsepower respectively)which the propeller then converts into thrust and thrust horsepower.
Work is done when a force moves its point of application in the direction of the force. If a force of one pound moves its point of application through a distance of one foot it carries out one foot pound of work.
Power is the rate at which work is done. It is the product of the force causing the motion, multiplied by the velocity at which the point of application moves. If a force of one pound moves its point of application at one foot per minute it expends one foot pound per minute of power.
In the case of an aircraft the thrust power is equal to the thrust multiplied by the true airspeed.
(I say usually because in the case of thrust vectoring or reverse thrust systems, thrust can act in various directions.
In the case of jet aircraft, thrust is produced directly by the engine. In the case of piston/props and turboprops, the engine produces rotational power (called brake horsepower and shaft horsepower respectively)which the propeller then converts into thrust and thrust horsepower.
Work is done when a force moves its point of application in the direction of the force. If a force of one pound moves its point of application through a distance of one foot it carries out one foot pound of work.
Power is the rate at which work is done. It is the product of the force causing the motion, multiplied by the velocity at which the point of application moves. If a force of one pound moves its point of application at one foot per minute it expends one foot pound per minute of power.
In the case of an aircraft the thrust power is equal to the thrust multiplied by the true airspeed.
