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We like HP but LOVE torque

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N941WR

N941WR

Legacy Member
Torque is what really makes our planes fly but for some reason we always talk in terms of HP.

Using the formula Torque = (HP*5252)/RPM, I calculated the following for the most popular Lycoming engines:

Engine ....HP.......RPM.......FT-LBS
O-235.....108........2700........210
O-290.....135........2600........273
O-320.....150........2700........292
O-320.....160........2700........311
O-340.....170........2700........331
O-360.....180........2700........350
IO-360....200........2700........389
IO-390....215........2700........418
IO-540....260........2700........506
 
Point?

Technically correct but since RPM was all the same, they will be in exact proportion to HP. Anyhow, it is HP and not torque that makes the airplane go. Torque is a force (foot-pounds) and HP is "the ability to do work" (33,000 foot-pounds per minute). You could have an engine with 1 ft-lb of torque, a really good PSRU and tons of RPM's and you'd still get the HP and thus you could still fly as fast. Conversely, you could have twice the torque and half the revs and get the same result - think monster marine diesels for example. Lastly, a jet engine's torque is not relevant, but its (shaft) HP is very relevant.
 
hevansrv7a said:
Technically correct but since RPM was all the same, they will be in exact proportion to HP. Anyhow, it is HP and not torque that makes the airplane go. Torque is a force (foot-pounds) and HP is "the ability to do work" (33,000 foot-pounds per minute). You could have an engine with 1 ft-lb of torque, a really good PSRU and tons of RPM's and you'd still get the HP and thus you could still fly as fast. Conversely, you could have twice the torque and half the revs and get the same result - think monster marine diesels for example. Lastly, a jet engine's torque is not relevant, but its (shaft) HP is very relevant.
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Exactly. HP is a unit of power, or force applied over a unit of time. Torque is not an independent and elusive property as some people seem to treat it.
 
ericwolf said:
Exactly. HP is a unit of power, or force applied over a unit of time. Torque is not an independent and elusive property as some people seem to treat it.
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Well, fellas this is an interesting discussion about HP and torque that has always been intriguing to me.

I am not an engineer so my concepts/questions are not based on any formal studies of power and motion but I do have some thoughts on all this. Of course anyone who wants to set me straight on any of my thinking that may be in error please feel free to do so.

I have always considered torque as the measure of ability of a spinning object to exert force, or work. In the case of a spinning flywheel on an internal combustion engine (ICE) the torque will be the amount of force the flywheel can produce. So my question is this. If torque is not as important as HP then why should we care whether we load down an engine or not?

I say we have to pay attention to torque because there is a limit to how much force the xxx HP rated engine can produce if the spinning flywheel meets up with an amount of force equal to or greater than the spinning flywheel's ability to "FORCE" movement (torque). If there is enough resistive power against the spinning force (torque) of the engine the engine will no longer be able to produce movement. It will load up and if resistive force continues to exceed the engine's ability to overcome that force the engine will stop completely, sometimes with disastrous results. This "unit of force" is the important part of the HP equation that we have to pay attention to when evaluating our engine's ability to provide "moving force" for our airplanes, or for that matter, anything that we wish to move with that engine.

You can experiment with this principal by using a small house fan. The electric motor has xxx amount of HP that allows it to produce xxx amount of torque (An interesting side note here is that electric motor HP numbers do not equate to the same when compared to ICE HP. One of the primary reasons for this is that electric motors can produce a higher amount of torque with less RPM than can an ICE.). This HP (and subsequent torque) allows the fan to spin the fan blades. With no load on the motor, it will spin away happily at a high RPM. However, if you take your hand and hold one of the fan blades then turn on the motor (Be careful if you actually try this. No need for injuries just to prove a point.) your resistance to the spinning blades will load up the motor. This action is now preventing that electric motor from producing work. The motor does not have enough "POWER" to overcome the resistive force of holding the fan blade. It lacks the proper amount of TORQUE to produce work. Regardless of how fast the motor can rev up, if it does not have enough torque to overcome the resistive force it will no longer produce measurable work.

Now that is my understanding of HP and torque. If I am totally off base feel free to set me straight.
 
HP and Torque

My real world example is the modification I made to my little 50cc Honda C110 motorcycle in 1963. I had the Honda dealer install a 1/2" stroker kit, which was essentially an offset crank pin.

The result was a little Honda that would accelerate rapidly with lots of low RPM torque, especially when pulling hills, but the downside was that it didn't rev as high. Top speed suffered even with different drive sprocket combinations. I became unhappy with the stroked engine and actually had the Honda dealer put it back to stock configuration.

What does this have to do with our Lycomings? They are designed with long strokes compared to the cylinder bores and thus respond very well to RPM changes. They've often been called Tractor Engines, but the engineers who designed Lycomings and Continental aircraft engines chose the bore and stroke for much the same reasons as the engineers who designed tractor engines. (As an aside, I believe Lycoming in the early years provided air cooled engines to the tractor manufacturers but I don't have a source to quote here.) Aircraft engines are designed for a narrow RPM range within which they are expected to respond to load changes. That's why both the Torque and HP curves are important when considering any engine's performance.

That's my real-life experience and my paradigm based on it. You may disagree, but "that's the way I see it."
 
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The physics definitions

Power = work / time and work = force * distance. An amusing thing about the definition is if there is no movement there is no work and therefore no power. Torque = force * distance (sound familiar?) What really comes into play is the horsepower and torque "curves". No engine has a flat horsepower or torque output. I should add that power is approximately (torque * rpm)/5252
Nice thread, it let me get back to my physics roots.
Paul
 
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RVbySDI said:
If torque is not as important as HP then why should we care whether we load down an engine or not?
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I guess that it depends on what you mean by loading down an engine. As you apply more load to an engine at full throttle, the RPM will decrease and you will not be able to produce as much power. An example being in too high of a gear in a car or a cruise fixed pitch prop during takeoff.

The IO-360 on my -8A produced 180HP at 2700RPM, which means that the torque at this condition is 350 ft-lbs. It is not an independent property. There is no way that the torque could be anything other than that in this condition. My car is rated at 170HP at ~5500 RPM (don't remember exact RPM). The torque produced at this condition is 162 ft-lbs. Notice that to get to the same horsepower, my car engine had to spin up to twice the RPM as my IO-360. Why? It only has 153 cubic inches of displacement vs. the 360 ci of the IO-360 (and some other design factors).
 
I knew this was going to get interesting!!

So now I'll jump in.

Without torque there is no horsepower.

HP = rpm x T(torque)/5252(constant)


Torque is a raw power measurement and horsepower is how far you can carry that power.

Horsepower is what most people want to hear. Really in aircraft I agree that torque is a better indicator.

OK now I'll really step out here! This is why most of your auto conversions don't match the power of standard aircraft engines and need to run a reduction unit to get their rated horsepower at a propeller speed. Once this is done the typically are burning more fuel.

As to the Honda 50 post. If you increased the stroke by .500 inch you probably ran out of volumetric efficiancy of the cylinder head. The engine couldn't achieve the same high RPM it was capable of before the increased stroke. It no longer had the breathing capacity for the increased displacement. This was probably a good thing as your piston speed was so high from that much of a stroke increase. The engine would have self distructed before you reached your old rev limit when it was a 50cc.

Let the flogging begin.

Ted
 
Horsepower is what really makes our planes fly but for some reason we always get wound up about torque. :D

If you want 200hp at 2700RPM, at the prop shaft, the torque is the same, at the prop shaft, regardless of the engine.

When you talk about horsepower, you talk about the ability to do work. When you talk about torque, the time related portion of the equation is missing. You have no idea what sort of work you can do.

A Pratt & Whitney PT6 doesn't have much torque, about 131 lb/ft at rated rpm (30000). But no one questions the ability of 750shp to power an airplane. :D
 
Torque is a raw power measurement...
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NO! This is why most people get confused about this stuff. Terms like power are used in a colloquial manner.

For best happiness, stick with the standard scientific definitions of terms. Power (i.e. horsepower) is the rate at which work is done. Torque is simply a type of force vector.
 
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Equilibrium

Really, if you consider this at equilibrium (constant airspeed), then its meaningless since torque is proportional to hp.

The reason we like torque (primarily in the car environment) is because that's the important quantity for ACCELERATION. Power is really only an issue (cars, airplanes, hoses, whatever) in determining how fast we will eventually go. To push a vehicle at speed takes POWER (work over time).

But the torque curve, and where we are operating on it, determines our acceleration profile.

Frankly, in airplanes this is usually just not an issue. But in cars we experience it much more directly. We almost never get to drive a car at max power for any length of time, but we can experience max torque for a while (like in to race to the next stop light :D )
 
its like carrying water, if you can carry gallons instead of cups you will get the job done sooner or you will have to make more trips (rpms/horsepower) with your cup.
 
Torque is Just Rotational Force

pczar3 said:
Power = work / time and work = force * distance. An amusing thing about the definition is if there is no movement there is no work and therefore no power. Torque = force * distance (sound familiar?) What really comes into play is the horsepower and torque "curves". No engine has a flat horsepower or torque output. I should add that power is approximately (torque * rpm)/5252
Nice thread, it let me get back to my physics roots.
Paul
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Not quite right on Torque Paul. Torque is just rotational force. Nothing to do with distance.

If you push down on a stuck bolt with a 100 pound force on a five foot cheater pipe you have a torque (force) of 500 foot-pounds. If that bolt does not turn you have no "distance" and no work is done. But the Torque remains the same.

HP is what makes your plane go.

When I took High School Physics it was an elective. Reading this thread, I think we need to make it mandatory.

Hans
 
power = work / time
work = force * distance
force = mass * acceleration

I've always visioned torque as an engine's ability to get up to its horsepower peak. In other words, plotting an engine's torque output at various engine speeds (the torque curve) describes its ability to change RPM. The term "good low-end torque" is an expression of the desire to get away from the low end.

We indeed love torque because that is what we feel in the seat of our pants. All horsepower does is tell us how long the trip is gonna take.
 
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The reason we like torque (primarily in the car environment) is because that's the important quantity for ACCELERATION.
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Ugh. Acceleration is caused by horsepower, as it is very definitely a time (rate of change) based concept. I could accept "torque over an rpm range", but this includes the concept of time and essentially describes the hp curve.

As acceleration is a rate of change concept (e.g. feet per second per second), it is obvious that what really matters is the ability to do work over time (hp * time). Thus, what really matters is the area under the hp curve, or average hp during the timed event.

I'm leaning on my desk right now, applying torque to the pedestal leg. I'm sure not getting anywhere fast though. :rolleyes:


When I took High School Physics it was an elective. Reading this thread, I think we need to make it mandatory.
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Amen. :)
 
Ted RV8 said:
Without torque there is no horsepower.
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To the point this is what I was saying. So in our airplanes, or for that matter in our cars, the amount of spinning force we can apply to the propeller or to the rear wheels is what we want to know about. How much force can I apply to my propeller at 2700 rpm? This force will be transferred to movement by the propeller. Of course now we are going to have to get into the pitch characteristics of the propeller. Without the proper pitch of the prop blades we will lose all of that torque and not be able to transfer it into forward motion.
 
As has been said torque and power are not independent of each other. Horsepower moves the airplane, car, truck, boat whatever, but without torque you can not have power.

Horsepower has never broken a shaft yet, however torque has broken many things. The engine that turns 6000 rpm to produce 200 HP can and likely requires much smaller shafts to transmit the torque. If it is geared down through a transmission of some sort than at the output end, the shafting has to be bigger to handle the torque, although the power is the same.

Producing more than 1 lb-ft of torque per cubic inch of displacement is doing pretty well. The IO-360 does this through its rather narrow operating range and suits it purpose very well as the aircraft it powers do not need a large RPM range. If an engine is producing over 1 lb-ft per cu in you know the design is very good, the greater the RPM band that it can produce this over the better the design.

Modern auto engines with turbos and / or fancy manifold and camshaft designs can produce this kind of torque over a very wide range. My pickup truck engine of 340 cu in (5.6 liters) produces 385 lb-ft at 3200 RPM but also produces 90% or greater (340 lb-ft) from 2000 to 4500 RPM. This means it pulls a trailer like a train.

Truck drivers talk mostly about torque and something called torque rise. It took me awhile to figure this one out. On-road trucks operate in a different part of the torque speed curve than our cars or the Lycoming engines do. The trucks peak torque occurs about 1200 RPM however the trucks are normally operated in the 1500 to 2000 RPM range. More HP but less Torque. The advantage to this is when the truck starts to climb a hill and the engine starts to slow the torque INCREASES resulting in less shifting. Very neat, very smart.

So I guess you talk about what is important to your application. Aircraft it is HP, trucks it is Torque. For aircraft you can determine the power that the engine is producing and from there deduce torque but power is the easier thing to measure from the cockpit.

Bob Parry
 
Torque is what we actually measure on a brake type dyno. Hp is a consequence of that torque at a given rpm.

Hp is really what is important in accelerating any vehicle and keeping it moving. As stated before, it is the area under the curve which is important and what race engine builders strive to increase, not peak values.

All things being equal, an engine with half the displacement turning twice the rpm will produce about the same hp. It will have about half the torque but regains that at the prop flange through a 2 to 1 gearbox (minus losses).

Modern turbo diesel engines produce high torque by applying high manifold pressures (120 inches is not uncommon) but since they are relatively low rpm devices, they still don't produce that much hp. They make this up with considerable gearing. Turbos pump up power and torque tremendously on any engine. Witness the approximately 1400 lb./ ft. developed by the race Continental 550 twin turbos at Reno running 75 inches.

A diesel truck climbing a steep hill would probably have gear down a bit but the manifold pressure would go from perhaps 50 inches in level road cruise to 100+ inches going up the hill.

On the small end of the scale my 36 cubic inch sport bike produces about the same hp as a 235 cubic inch Lycoming. You wouldn't want that bike engine in your RV9 any more than you'd want to straddle the Lycoming in the Suzuki however. I can't say I'd like to listen to the Suzuki running at 14,000 rpm through a 5 to 1 gearbox in cruise for too long!
 
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question

Ok, this is for the physics professors.

If we accept, for the sake of simplicity of discussion, that we are ignoring the effect of prop pitch on the following situation, is it the amount of HP or is it the amount of torque the engine is putting out that is producing the forward thrust of the airplane as the pilot shoves the throttle wide open?
 
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Physics 101

RVbySDI said:
To the point this is what I was saying. So in our airplanes, or for that matter in our cars, the amount of spinning force we can apply to the propeller or to the rear wheels is what we want to know about. How much force can I apply to my propeller at 2700 rpm? (snip)
Click to expand...

You just defined POWER. How much Force (Torque) times Distance (how many Revolutions, in this case 2700) divided by Time (Per Minute).

Notice that you did not define Torque. Torque is meaningless to moving an airplane unless you know how much over what amount of time, aka RPM. So you say how much Force at a certain RPM you are really talking POWER.

Here it is in algebra:

Since Power = Work/Time and Work = Force * Distance, therefore:

Power = (Force * Distance)/Time

Converting to our example units it looks like this:

Horsepower = (Torque * Revolutions)/Minute

Hans
 
The Answer is...

RVbySDI said:
Ok, this is for the physics professors.

If we accept, for the sake of simplicity of discussion, that we are ignoring the effect of prop pitch on the following situation, is it the amount of HP or is it the amount of torque the engine is putting out that is producing the forward thrust of the airplane as the pilot shoves the throttle wide open?
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Horsepower!

Imagine an electric airplane. Electric motors produce peak torque at zero RPM. You push the power lever forward on your 1000 ft-pound electric motor. But today you screwed up your walk around and left your super-duper propellor lock on which prevents your propellor and motor from turning.

You have 1000 foot pounds of Torque, but you aren't going anywhere, are you?

If it was torque that moved you then all of our RV's would be faster and quicker than those 750 HP PT-6 Turboprops with their measly 131 foot-pounds of Torque...

Hans
 
Guys, I will gladly plant a great big bulls eye on my chest for you to take pot shots at. If it allows me to understand something that I did not previously understand, I will gladly take every shot.

I am here to learn something I did not know before. If that means being made fun of for not knowing it already then so be it. BRING IT ON!!

Inquiring minds want to know and I, for one, have an inquiring mind!
 
RVbySDI said:
Ok, this is for the physics professors.

If we accept, for the sake of simplicity of discussion, that we are ignoring the effect of prop pitch on the following situation, is it the amount of HP or is it the amount of torque the engine is putting out that is producing the forward thrust of the airplane as the pilot shoves the throttle wide open?
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Not a physics professor, but I've got a healthy appreciation for Sir Isaac. On the shoulders of giants and all that.

The effect of prop pitch is irrelevant, it's the amount of HP that is producing the forward thrust.

The term HP includes the concept of torque, and convolves it with distance and time. It's the combination of torque, distance and time that provide a complete description of the ability to do a job.

In this respect, it's as meaningless to talk about torque in isolation as it would be to talk about time or distance in isolation. If you want to talk about all of them at once, the word horsepower is convenient. :)

To offer a crude analogy, what element is more important, or what element "makes" 2024 aluminum alloy? Is it copper, or is it aluminum? Well, without both elements it's not 2024, so the question is kind of silly, right?
 
Trying it Again: It's the HP

RVbySDI said:
Ok, this is for the physics professors.

If we accept, for the sake of simplicity of discussion, that we are ignoring the effect of prop pitch on the following situation, is it the amount of HP or is it the amount of torque the engine is putting out that is producing the forward thrust of the airplane as the pilot shoves the throttle wide open?
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It is the HP. In this situation, the relevant math is:
HP = TAS x Drag.
Translation: Foot-Pounds-Per-Minute = Feet-Per-Minute times Pounds. Torque which is merely a force, is not necessary to the equation. The formula requires units conversion; I made it simple. As Bill pointed out in the beginning (quite correctly) HP is the product of torque and rotational speed. You need both to get HP from a recip engine. Then you need a transmission to get that power to the prop - except that most of us just bolt the prop onto the crankshaft.

If you don't want to ignore prop efficiency, then you have to say: Thrust HP which is abbreviated as THP = TAS x Drag and BHP = THP / PropEfficiency where propeller efficiency is a decimal less than 1.0 (like 75% for example). So this means that a 100 hp engine gives you 75 THP with a 75% efficient prop. Again, highly simplified.

The fact that our engines are mostly direct-drive and not speed-reduced for the prop may cause some confusion. I'll repeat the analysis that I and others offered above. A small amount of torque with a huge amount of revolutions per minute will still produce power that will move you and/or lift you.

Prop pitch is not relevant here except that it measures either a geometric feature of the prop or in the case of "effective pitch" the relationship between revolutions and distance advanced with each revolution. None of this says anything about force or power.

This is high-school or even junior high physics, not professor level.
 
N941WR said:
I always love to start a good fight! :D
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Good...........

Because today, my 180 HP RV6A got better fuel milage than the 50 lb. lighter 160 HP RV9A that we always fly with. Not only that............it climbs and fly's faster too! About 20 mph faster. Both have C/S props; and I'm not sure whether it's just horsepower, or that torque I always feel on the last third of throttle on takeoff. :D

Bottom line.............put a bigger engine ( 0320) in this time. Your plane will love it! :)

L.Adamson

P.S. --- It doesn't always do better fuel wise. I just have to brag when it does.. :)
 
I still do not believe that the formula is correct regardless of what the internet says.

Take the engine spec from this page:
http://www.stealthtdi.com/Jetta-Intro.html

1.9L (1896cc / 116 cu/in); 90 bhp @ 4000; Torque 149 lb/ft @ 1900

The formula Torque = (HP*5252)/RPM does not work.

Take the Spec for a GMC 4.3L V6 and it also does not work.

moz-screenshot.png
http://www.motortrend.com/cars/2005/gmc/safari/specifications/index.html
190 HP SAE @ 4,400 rpm; 250 ft lb @ 2,800 rpm

or

http://en.wikipedia.org/wiki/GM_Vortec_engine#V6
180 hp (130 kW) to 200 hp (150 kW) and 245 lb?ft (332 N?m) to 260 lb?ft (353 N?m)

My little 1.9L VW TDI has 1/2 the HP of my 4.3L V6 GMC Sonoma but 60% of the torque.

Can someone explain this?

Yes peak torque occurs at a different RPM than peak HP but doing the math, the formula given in the first post of this thread does not work.
 
RVbySDI said:
Ok, this is for the physics professors.

If we accept, for the sake of simplicity of discussion, that we are ignoring the effect of prop pitch on the following situation, is it the amount of HP or is it the amount of torque the engine is putting out that is producing the forward thrust of the airplane as the pilot shoves the throttle wide open?
Click to expand...

Power is DEFINED as the ability to do work over time. Moving an airplane forward a given distance in a specific amount of time requires power (by definition). That's all there is to it.
 
N941WR said:
Torque is what really makes our planes fly but for some reason we always talk in terms of HP.
Click to expand...

My spindly arms have applied over 450 foot-pounds of torque to various bolts, but there is no way those same arms could produce enough of anything to get an airplane off the ground. Torque is worthless unless it can be applied quickly and continuously (power).
 
RV6_flyer said:
I still do not believe that the formula is correct regardless of what the internet says.

Take the engine spec from this page:
http://www.stealthtdi.com/Jetta-Intro.html

1.9L (1896cc / 116 cu/in); 90 bhp @ 4000; Torque 149 lb/ft @ 1900

The formula Torque = (HP*5252)/RPM does not work.

Take the Spec for a GMC 4.3L V6 and it also does not work.

moz-screenshot.png
http://www.motortrend.com/cars/2005/gmc/safari/specifications/index.html
190 HP SAE @ 4,400 rpm; 250 ft lb @ 2,800 rpm

or

http://en.wikipedia.org/wiki/GM_Vortec_engine#V6
180 hp (130 kW) to 200 hp (150 kW) and 245 lb·ft (332 N·m) to 260 lb·ft (353 N·m)

My little 1.9L VW TDI has 1/2 the HP of my 4.3L V6 GMC Sonoma but 60% of the torque.

Can someone explain this?

Yes peak torque occurs at a different RPM than peak HP but doing the math, the formula given in the first post of this thread does not work.
Click to expand...

Works fine. Your VW TDI makes 54hp at 1900rpm and 118 lb/ft at 4000. Hard to compare turbocharged engines directly to atmo engines. Very few engines have torque and power peaks at the same rpm.
 
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RV6_flyer said:
I still do not believe that the formula is correct regardless of what the internet says.

Take the engine spec from this page:
http://www.stealthtdi.com/Jetta-Intro.html

1.9L (1896cc / 116 cu/in); 90 bhp @ 4000; Torque 149 lb/ft @ 1900

The formula Torque = (HP*5252)/RPM does not work.
Click to expand...

Gary, the formula is correct... it relates torque to hp, at a given rpm.

Taking that Jetta engine example:

90 bhp @ 4000 rpm means it is making 118 lb-ft of torque at that rpm.
149 lb-ft of torque @ 1900 rpm means it is making 54 bhp at that rpm.

If you look at the complete torque and hp curves vs. rpm for an engine, you can see the relationship holds at every rpm. In fact, you only need one of the curves... you can compute the other one using the formula. And again in fact, that's the way it is done in practice; a dynamometer just measures torque at different rpms, and bhp is computed from that using the formula.

--Paul
 
I still do not believe that the formula is correct regardless of what the internet says.

1.9L (1896cc / 116 cu/in); 90 bhp @ 4000; Torque 149 lb/ft @ 1900

The formula Torque = (HP*5252)/RPM does not work.
Click to expand...

With apologies to the Bard, "There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy. :D

To produce 90hp @ 4000rpm the engine is producing about 118 lb/ft of torque, @ 4000rpm. That is a very believable value, given that the engine is operating twice as fast as it's torque peak. It is typical for an IC engine's torque to fall off in the upper rpm range of the engine.

You didn't think that the 149 lb/ft of torque was maintained forever, did you? :rolleyes:

A major goal of IC engine design is to have the torque peak as early as possible in the rpm band, and maintain that torque as late as possible. For several reasons related to simple physics, this is a difficult task.
 
L.Adamson said:
Good...........

Because today, my 180 HP RV6A got better fuel milage than the 50 lb. lighter 160 HP RV9A that we always fly with. Not only that............it climbs and fly's faster too! About 20 mph faster. Both have C/S props; and I'm not sure whether it's just horsepower, or that torque I always feel on the last third of throttle on takeoff. :D

Bottom line.............put a bigger engine ( 0320) in this time. Your plane will love it! :)

L.Adamson

P.S. --- It doesn't always do better fuel wise. I just have to brag when it does.. :)
Click to expand...

No, I'm either going to rebuild the O-290 or put in a 506 ft-lb IO-540 with a four bladed fixed pitch Catto.

Back to the cat fight...
 
Good grief...

I've never seen so many folks argue half of the problem before :D

Its not power or torque, they're coupled! You don't have one without the other (if the engine is spinning)

You know this whole mess really started be the car makers SELLING the max horsepower rating. Funny thing is, we never really operate the engine there.

So the relevant point becomes how much torque (aka power) does it produce at what point on the curve. In other words, where are we operating the engine. The nice shove in the back comes from the force the engine makes for us, and we can easily calculate that from the torque curve and therefore also calculate the instantaneous power being produced.

This is why a lower rated power engine may accelerate better than a higher rated power one. Because we're operating it at a better spot on the curve, not because it takes less power to accelerate us (or torque!).

Good, now can we discuss primer! or may tailwheels!! :D
 
Not trying to be a smart @#%, but...

Riddle me this Batman...

After landing your "A" model on the grass the nose gear tucks under putting around 1 G of energy into the gear leg as it bends back. When the forward motion of the plane begins to slow up and the gear begins to unload, up and over you go.

With that said, is it torque or the power in the gear leg that puts you on your back? :confused:
 
Well

An engineer generally thinks of a SPRING as operating as force = K*deflection, so since the force is operation with a moment arm then I guess it would be TORQUE now wouldn't it ROBIN! :D:D
 
Hi Nucleus...

We are in violent agreement! The distance in the case of torque is the distance over which the force is applied. As you said, 100 lbs at 5 feet (thats the distance factor I was talking about for the torque). I agree they should make physics mandatory, it was when I was in school.
Paul
 
pczar3 said:
We are in violent agreement! The distance in the case of torque is the distance over which the force is applied.
Click to expand...

Paul, keep in mind though that while work and torque have the same dimensions (force times distance) the role of distance in the two is different. In torque, it is the distance from the rotational axis that the force is applied. In work, it is the distance traveled while the force is applied. So work requires movement but torque, by itself, doesn't. In the formula relating torque and horsepower, motion (rotational motion) enters the equation via the rpm term; torque by itself won't do it.

I agree they should make physics mandatory, it was when I was in school.
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Unfortunately requiring taking it and requiring learning it are not at all the same. Google "force concept inventory" for some of the sad story about that: "nearly 80% of the students could state Newton?s Third Law of at the beginning of the course ? but less than 15% of them fully understood it at the end?.

--Paul
 
Bryan Wood said:
Riddle me this Batman...

After landing your "A" model on the grass the nose gear tucks under putting around 1 G of energy into the gear leg as it bends back. When the forward motion of the plane begins to slow up and the gear begins to unload, up and over you go.

With that said, is it torque or the power in the gear leg that puts you on your back? :confused:
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Neither - it's poor pilot technique.

Speaking purely from a physics standpoint, it's torque. The wheel drag and the momentum vector are 180 degrees out of phase in the vertical plane, but they are offset vertically and this offset distance becomes the lever arm about which the mass of the aircraft will rotate.
 
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trade off

so if i have alot alot of horsepower and little torque i underdrive my prop, alowing me to deliver the lesser torque at a faster rate.
or if i have high torque and less horsepower i directdrive it because i can deliver my same amount of torque at a slower rate ???? wouldnt a higher torque engine turn a higher pitch prop? doesnt torque then turn the prop?
 
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Attempt at a layman model

After reading the many messages in this thread, I decided to offer a couple of physical examples that may help differentiate torque vs power (horsepower) for the laymen in this group.

Most, if not all of us, have used a bmf wrench or breaker bar for a large fastener. Imagine the situation where you trying to break a fastener loose. The situation is such that you can stand on the end of the wrench. You are exerting considerable torque on the fastener due to your weight on the end of the wrench but you have not even broken a sweat because the wrench is not moving. In this case, zero power has been expended. Now let's assume the fastener suddenly breaks loose and you come crashing to the ground, get back up and spin off the nut with your fingers. In this case, only a very small amount of power was used because even though the wrench did move, the torque dropped to zero in a hurry.

Since little to no power was expended, neither of the above examples apply to a continuously running engine and prop situation, but are valuable for comparison.

Now lets assume a different situation where the nut is corroded or galled onto the bolt such that with all your effort, you can just get the wrench to move by using all the armstrength you can muster but the nut does not get any looser with successive turns. You are putting killer torque on this thing to get it to move and you are sweating up a storm because of the effort of each turn to get this darned nut off. The sweat is a result of continuously expending power. This is the crux of the difference between the torque and power conversation. Force and motion together equal power.

Power is required to CONTINUOUSLY exert torque on a spinning object. If it is not spinning, no power is expended. The example of the nut breaking completely loose could be compared to suddenly feathering a prop. No thrust, no torque, no power expended. Our props can be compared to the galled nut example where the effort required to turn them never goes away as they continue to bite the air and provide thrust.

I hope this helps.
 
rzbill said:
Power is required to CONTINUOUSLY exert torque on a spinning object. If it is not spinning, no power is expended. The example of the nut breaking completely loose could be compared to suddenly feathering a prop. No thrust, no torque, no power expended. Our props can be compared to the galled nut example where the effort required to turn them never goes away as they continue to bite the air and provide thrust.I hope this helps.
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I appreciate this discussion. It really allows me to use my brain.

Ok, Bill, your statement above does confuse me some. You say that "If it is not spinning, no power is expended." This statement is very confusing to me. Here is the crux of my confusion:

If the spinning flywheel on an IC engine is held in place and not allowed to spin but the engine continues to run there will be fuel being expended. That fuel is being converted from chemical energy to some mechanical energy. There will be some measure of "power" being transmitted regardless of whether the flywheel spins. That "power" may very well be displayed as an explosive catastrophic failure of a rod, bearing, gasket or something. It may not be represented by the "spinning" of a flywheel, or prop, but there will still be power being exerted.

So I really have a hard time equating power with only the spinning of a flywheel on an internal engine. If there is no movement of any kind but there is still force being exerted onto anything there is still "power" there. The power may show itself in some other form than we anticipate but it is still there.
 
rzbill said:
You are exerting considerable torque on the fastener due to your weight on the end of the wrench but you have not even broken a sweat because the wrench is not moving. In this case, zero power has been expended.
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It's a small thing, but actually you have done work in lifting your body up onto the wrench. the amount of power used depends on how quickly you climbed up there.
 
RVbySDI said:
So I really have a hard time equating power with only the spinning of a flywheel on an internal engine. If there is no movement of any kind but there is still force being exerted onto anything there is still "power" there. The power may show itself in some other form than we anticipate but it is still there.
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The confusion is one of definitions. Everyday folks have an intuitive idea about what power is, but to an engineer/physicist it is defined as work/time, and work is defined as force x distance. So, by definition, power must involve movement.

For example, suppose you're huffing and puffing trying unsuccessfully to open a stuck pickle jar. No matter how red in the face you get, no work has been done on the jar, and hence no power was used (in opening the jar). However, there was a great deal of work done in moving all that extra blood around your body and so power was used by your body.
 
szicree said:
The confusion is one of definitions. Everyday folks have an intuitive idea about what power is, but to an engineer/physicist it is defined as work/time, and work is defined as force x distance. So, by definition, power must involve movement.

For example, suppose you're huffing and puffing trying unsuccessfully to open a stuck pickle jar. No matter how red in the face you get, no work has been done on the jar, and hence no power was used (in opening the jar). However, there was a great deal of work done in moving all that extra blood around your body and so power was used by your body.
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Thanks Steve for the analogy. I do understand the equation of power and its relationship to movement. I think what trips me up is the narrow definitions we use to define POWER. I think there is a lot of "movement" going on with IC engines even when there is no spinning of the flywheel going on. The movement may come in the form of a rod blasting through a crank case or a valve stem shooting through the exhaust. Even if the motor is not producing spinning action at the flywheel there is still going to be a great amount of force that is producing power that is moving something somewhere.
 
Good grief!

Perhaps it would be a good idea if the curious simply studied the commonly accepted account of how James Watt developed the term "horsepower".

If nothing else you'll be amused to learn horsepower has nothing to do with thundering horseflesh. It's the power of an old nag walking in a circle <g>.
 
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