Piston engine torque?

[RipCurl]

So last night I was thinking about how crappy it is to get only 235 hp out of a 520 cubic inch engine, when the auto industry can get 500hp out of a normally aspirated, production 505. Then I realized that the design lends itself to torque output more than anything else. Big bore, long stroke, and low hp - sounds like a diesel to me. Curious, I did a little searching on google, but couldn't find any numbers. So, I ask, are these airplane engines torque monsters, or are they just built with really old technology so they can't make much power?

 

[A Squared]

You can't find any numbers because it's a totally useless number unless you're a magazine writer. The only meaningful measure is power. Torque, by itself is pretty much meaningless. It is common for automotive magaziner writers to talk about Torque at XXXX RPM, the thing is, thy don't have the basic physics to realize that when they say torque at a certain RPM they are in fact talking about power, not torque. There was a thread on this a little while ago. Someone computed the torque for some aircraft engine.

Link: http://forums.flightinfo.com/showthread.php?t=38846

 

[Uncle Sparky]

More of it has to do with longevity. Of course an auto manufacturer can take the same displacement engine(different configuration mind you) and get 265 more hp out of it, because when it blows up(even though they rarely do)you can just pull over to the side of the road. In contrast, aircraft engines are not tuned to squeeze out every last pony.

The fact that the aviation industry (esp. GA) has an aversion to change, is a huge factor as well. That 0-520 is, very basically, the same thing that's been around since the 40's. It's an air-cooled, push-rod, two-valve, opposed layout, just like the Cub motor. If it works, why fix it?

The latest diesels are producing much less crankshaft hp than the gasoline engines that they are replacing but making up for it with a PSRU just as you eluded to. I can't find torque numbers either but I'm sure you ARE correct as far as the engines possibly being built with emphasis on torque.

One more factor might be to consider WHERE the auto guys obtain their torque info. It's not uncommon for manufacturers in any industry to fluff their numbers. The bike guys,for example, will list CRANKSHAFT hp instead of rear wheel hp because the number is always a good bit higher, even though rear wheel hp is what the guy on the street really needs to know. In a reverse twist of the same theme, maybe these guys are getting the high TORQUE numbers after the power has been chanelled through the drivetrain.

 

[Uncle Sparky]

There was a thread on this a little while ago. Someone computed the torque for some aircraft engine.

I hope that........

it's a totally useless number unless you're a magazine writer.

.....isn't the conclusion you came to.

I'm guessing that you're not a motorcycle rider.

Here's a quick example of torque vs horsepower. You're in your Cessna 172, in position. You apply full power. The RPM goes to a peak that is short of Redline. After you level off in cruise you have to, now, pull back the power lever because you will NOW exceed redline.
This engine's peak HORSEPOWER is produced somewhere near redline and then falls off shortly after it is exceeded. Why won't this engine achieve redline and more importantly, peak horespower, while sitting static on the runway?

I think you may find that TORQUE may be somewhere in the answer to this question.

 

[Headwind]

When an auto engine gets 500 H.P. from 500 cu. in. it is usually above 8000 RPM.
You can't turn the prop over 2700 RPM. If you geared the engine to turn 3 times faster than the prop your TBO would probably be about 75 hours.
The GTSIO 520 puts out about 50 H.P. more than the TIO 520. It turns appr. 1.5 RPM's per RPM of the prop and the TBO is much shorter. Big piston engines that turn slow last much longer.
If you would like to compare the H.P. on a piston engine to the torque on a turbo prop here is the formula: torque X RPM divide by 5250 = H.P.

HEADWIND

 

[A Squared]

Why won't this engine achieve redline and more importantly, peak horespower, while sitting static on the runway?

Very simple, because it does not have the power to turn the propeller at redline, And it's rated pwer is based on maximum RPM, so it won't develop it's full rated power.

This engine's peak HORSEPOWER is produced somewhere near redline and then falls off shortly after it is exceeded.

No, this is not true. it's maximum RATED power is produced at redline. if you turn it faster at wide open throttle, it will develop more power. How much faster and how much more varies with the engine. The Continental 0-200's in the formula one racers turn at around 4000 rpm and develop considerably more horsepower than the max rated 100 hp that you get in a C-150.

In general, a recip engine will develop more power the faster it turns. There are 3 practical limits to this: structural failure, valve float and volumetric efficiency. Structural failure is obvious, if you turn an engine too fast, it comes apart. Valve float is when you are turning so fast that the springs don't have time to fully close the valves during the cycle so you lose power. That is why some very high revving engines use desmodromic valves, which are closed by positive mechanical action rather than by a spring. Volumetric efficency refers to the engines eficiency in moving a volume of a gas. As an engine turns faster, it reaches a point where it can no longer move a full fuel/air charge into the cylinder, and move the exhaust gasses out in the small time the valves are open. Headers, tuned exhausts, tuned manifolds and such are all for one purpose, to improve the volumetric efficinecy of an engine.
Anyway, the point is that peak horsepower in an airplane engine is not developed at the maximum rated RPM, which is a fairly arbitrary number selected by the manufacturer. Power increases with RPM, up to the point that the valves start to float, the engine comes apart, or it can't breathe fast enough.

I'm sure you ARE correct as far as the engines possibly being built with emphasis on torque.

No, the aircraft engine designers do not design for "torque", they design them for power. The reason they have large bores and long strokes is simple: A direct drive aircraft engine has a practical RPM limit of somewher around 2700-2800 rpm. The Beechcraft Duke engines turn at 2900 on takeoff, and I think that is hte highest revving direct drive aircraft engine (certificated anyway) That's because the prop loses a lot of efficency at those speeds, so there's just no point in making an engine that can turn faster (remember we're talking direct drive here) So, if you're limited to 2700 RPM, the simplest way to get more power is to increase displacement, which means increasing bore or stroke or both.

 

[GravityHater]

If you geared the engine to turn 3 times faster than the prop your TBO would probably be about 75 hours.

Can we extrapolate this to say that I would be better running my IO520 at 2300rpm (in cruise with full throttle above 5000'), than I would at 2450rpm as some pilots do, with regard to longevity only?

 

[Uncle Sparky]

That sure is a long winded way to not answer my question.
Very simply, what attribute keeps the engine from exceeding redline as it does in the air?

That is why some very high revving engines use desmodromic valves, which are closed by positive mechanical action rather than by a spring.

As luck would have it, I used to build Ducati(desmo valvetrain motorcycles) street and race engines for Action Sport Cycles in Fort Lauderdale. The Ducati does NOT turn the same high RPM as it's Japanese, Four Cylinder, Spring Valve counterparts.
What Desmo valves DID allow us to do was use larger valves and "square lobe'd cams", to the point of literally allowing paper thin tolerances in transient stroke clearance.

the simplest way to get more power is to increase displacement, which means increasing bore or stroke or both.

We also had a very nice Dyno at Action. I know from reading the curves on the computer that if we added a Big Bore kit to a bike, Torque(if you believe in such things)would increase and if we installed High Compression Pistons, Peak Horsepower would increase. Maybe Motorcycle, Internal Combustion engines follow different rules of Physics than every other engine on the Planet?!

 

[RipCurl]

Sorry guys, didn't mean to open up this whole can of worms here. On the plus side, I have learned quite a bit between this thread and the linked one...

 

[A Squared]

Uhhh, sparkey, I did answer your question. read my post.

"because it does not have the power to turn the propeller at redline"

Perhaps you missed that?

I probably shouldn't have tossed in the comment about desmodromic valves, but I think that you'll agree that the faster an engine turns, the more important it is to have fast springs? regardless, the discussion of valve float and valve trains is off the subject.


" if we added a Big Bore kit to a bike, Torque(if you believe in such things)would increase and if we installed High Compression Pistons, Peak Horsepower would increase."

Unnnhhuuuhhh, you increase displacement, you increase power, and if you increase compression you increase power, albeit at different points in the rpm range. That really doesn't contradict anything I've said, unless you want to quibble about me characterizing increasing displacement as "the simplest" way to increase power, yes there are other ways, and increasing compression is one, but in the context of aircraft engines, the manufacturers tend to fairly consevative with compression because of detonation.

So tell me, what's the torquiest engine you ever built? the biggest, baddest one? The Dyno king? how much torque did it put out?

 

[Uncle Sparky]

Sorry guys, didn't mean to open up this whole can of worms here. On the plus side, I have learned quite a bit between this thread and the linked one...

No need to apologize, it's the nature of ANY strong willed, god ferin', F*CK the masses pilot to argue his point until his face turns blue and his eyes pop out! It's the "fight in us" that gets us where we are.

I think if you weed through all of the B.S.(I'm not pointing fingers and not claiming innocence), as I think you've done already, I think your answer is reliablility, above all else. Yes, these engines can make as much HP(or Torque ) as their automotive counterparts. As ASquared pointed out, racing engines, using the same engine with internal mod's, can produce quite a bit more horsepower. Racing engines aren't intended to fly for thousand's of hours though and car engines don't posess the ultimate burden that aircraft engines do. Getting your A$$ back to Terra Firma!

So tell me, what's the torquiest engine you ever built? the biggest, baddest one? The Dyno king? how much torque did it put out?

I know that your patronizing me BUT one bike does come to mind. It was a plain Jane 900ss with the Kitchen sink. The bike was dual plugged(not common in bikes like it is in aircraft), had a Falicon Crankshaft(cut and welded), porting was done by our Guru Chuck House(look up Chuck House Performance on the internet), lumpy cams from Vee-two, out of Australia, 41mm Keihin flatslide carbs and I installed a Gia-Ca-Moto big bore/high comp piston kit. When I finished with the kit and took it for a test ride, I just about gave myself a coronary. I tried to wheelie it in first gear like a normal mortal motorcyle and it wanted to instantly rotate about it's rear axle! I tried the same thing in second with the same results. Third gear wheelies were a little more manageable, so I took it by the Jap-bike shop and did a couple third gear power wheelies up and down the Boulevard in front of their shop while they were trying to sell bikes to customers.

 

[A Squared]

yeah, but how much torque did it put out? That was the question.

 

[gfvalvo]

First, an aircraft engine spends almost its entire life running at 60 to 75% of its rated output power. Try that with you typical high horsepower / small displacement rice-rocket motorcycle engine and see how long it lasts.



On the subject of HP vs torque vs RPM …..Arrrrrrrgh. It’s obvious a lot of people slept through high school physics. Since I can’t stand the sloppy application of basic science, let me try a few ideas from introductory physics:



Question: what pushes an airplane along?

Answer: THRUST



Now, a piston plane generates thrust by taking a mass of air, accelerating it with the prop, and moving it backwards. This action causes a re-action that we call thrust (Newton’s 2nd law). In order to accelerate and move this air we must do WORK, which is defined as the application of a force over a distance. Want more thrust? Then we must do this work faster. Now we’ve added a time element. The RATE at which work is done is called POWER. Thus, more thrust requires more power. The coupling by the prop of the power generated by the engine to the air is what makes the plane fly. A_Squared is right!!!



The power generated by the motor is proportional to the product of its RPM and Torque. Borrowing again from A_Squared, think of torque as a “twisting force”. Trouble is, above a certain RPM (say 2700), the prop just can’t move the air efficiently. So you just can’t increase power by continuing to increase RPM. Connecting a bigger engine to the same prop doesn’t help either. If a given prop requires 100 HP to turn at 2700 RPM, then using a 500 HP engine does you no good. At 2700 RPM it will still be developing 100 HP. Push up the throttle and it will exceed 2700 RPM and the prop will loose efficiency. The engine may now be developing more than 100 HP, but it’s not being coupled to the air. No extra thrust, just a lot more noise.



Well, if RPM is fixed how do we get more HP? If we increase the pitch (bite) of the prop, it will accelerate and move more air on every revolution. Same thing if we use a bigger prop. So at 2700 RPM we’ll be moving more air per unit time and therefore generating more thrust. But wait; now the prop is A LOT harder to turn at this speed. That means we need more TORQUE! Now the bigger engine will help. It can continue to turn at 2700 RPM but supply a larger twisting force (torque) to the shaft and prop. More horsepower!!



Bottom line: Power makes the airplane fly. But you have to be clever in order efficiently couple that power to the air and generate thrust.

 

[UnstableAviator]

Link me up

Here's a link to an Avweb article that addresses just how good aircraft engines are at their jobs.

http://www.avweb.com/news/columns/187683-1.html



BTW, the formula for hp is:

Torque x RPM/5252 = HP

Using basic algebra, a 285hp IO-520 will make 554 lb.-ft. of torque at 2700rpm.

285 x 5252/2700 = torque

Assuming ISA conditions of course. I'll still get 2700rpm taking off at a 5000' DA airport just as I'll get 2700 taking off from sea level on a 0*F day. Sure doesn't mean I'm getting 285 horsepower or all 554 lb-ft of torque....and the resultant thrust. Now, I'm off the my secret underground laboratory to finish developing my tuned intake runners that add no weight or other detriments but significant torque and efficiency to an aircraft engine that operates in a 300rpm range.

 

[sstearns2]

I'm glad that so many people seem to understand that horsepower is all that matters in determining performance.



I'll add that horsepower per displacement is a useless number. There are only two ratios that really matter in airplane engines: weight per horsepower, cost per horsepower-hour (takes into account purchase price, fuel burn, MX, and longevity).


Scott

 

[enigma]

So last night I was thinking about how crappy it is to get only 235 hp out of a 520 cubic inch engine,

Rip, the 520 ci aero engine to which you refer is hooked up to a propeller and that propeller can only turn somewhere around 2700 revs per minute before said propeller loses efficiency (tips go supersonic and it quits making lift/thrust). If you took the same engine and allowed to turn more rpm (up to the point of it's ability to breath efficiently, and assuming that it it physically strong enough to turn those revs without turning into a hand grenade) it would make more horsepower.

In truth, building power is easy, first you improve the ability of a recip engine to move air/fuel into the combustion chamber, then improve the engines ability to exhaust the burned gasses from out of the chamber. Horsepower will be determined by how many pounds of fuel that your engine can efficiently burn in an hour. The more fuel you can burn, the more power you make.

It's a little harder to make your engine last at the revs you must turn in order to make more power. Force on a component goes up with the square of the speed increase, so a component such as a connecting rod must be four times as strong in order to turn only twice as fast.

Since safety is the paramount goal with an aero engine, keeping the revs down is of great importance.

In essence your 520 ci engine is limited by the prop and by the need for safety. As such it's rated power is limited by outside factors. It's not the engines fault

.....when the auto industry can get 500hp out of a normally aspirated, production 505.

Fortunately for them, the auto industry is not significantly limited by litigation. The aero industry could make slight improvements (within the constraints of the issues I addressed in the above soliloquy) in power, but doing so might show that the previous design could be somewhat lacking; a fact that some pond scum lawyer would most certainly use against the manufacturer the first time some Dr. ran his Bonanza out of gas and crashed.

Then I realized that the design lends itself to torque output more than anything else. Big bore, long stroke, and low hp - sounds like a diesel to me. Curious, I did a little searching on google, but couldn't find any numbers. So, I ask, are these airplane engines torque monsters, or are they just built with really old technology so they can't make much power?

Torque production is a function of cylinder pressure (peak and average) and engine geometry. The reason that a long stroke engine is more torquey than a short stroke is not the long stroke, but the angle the rod makes to the crank. In other words, as you increase the distance between the crankshaft rotational centerline and the rod end, you end up with a longer lever which allows more turning force. It's sort of like slipping a piece of pipe over the handle of a wrench in order to help break loose a stuck bolt.

Aero recip engines tend to be torquey because they are built for low rpm ops, that's all.

BTW, a diesel makes a lot more torque than the average gasoline because of the higher cylinder pressure that those engines produce during the power stroke. They utilize heavy reciprocating components in order to safely deal with those higher cylinder pressures, and in turn they tend to turn slow because of the mass of those components. A gasoline engine is limited in cylinder pressure by numerous factors. The first being that the air/fuel mix must be close to stoichemetric in order to produce an efficient flame. In other words, you can't just add more gas to the cylinder. You just have to use the cylinder more often (more revs per minute) It's sort of like drinking beer. You can't add more beer to your bottle, so you are forced to drink more bottles in a given sitting. again a

In modern auto engines the need for emission compliance also limits their output because too rich a mixture will increase hydro carbon emissions, while a lean mixture will increase NOx emissions.

A diesel (like a turbine) always has an excess of oxygen in the cylinder because diesels are throttled by fuel delivery, not by air delivery. As such, in a diesel one must only pump in more fuel to gain an increase in cylinder pressure and the attendent increase in torque and obviously an increase in power. Back to our beer example, in a diesel the stein is always oversized and the amount you can drink is related by how much beer you load into that stein.

regards,
enigma

 

[sstearns2]

The reason why most airplane engines run at low RPM is purely to avoid needing a gear reduction system to lower the prop RPM to useful levels. There are airplane engines that run a 5-6000 RPM all day long that don't have any more longevity problems than the large displacement/low RPM engines. Rotax is the most common.

Scott

 

[Uncle Sparky]

yeah, but how much torque did it put out? That was the question.

Sorry, I had to go to work. I dug through my jetting notes and the numbers are:64ft/lb of Torque and 89 Horsepower. By comparison, my 2003 GSXR-750 produced 125 rear-wheel H.P. and didnt posess anywhere NEAR the bottom end performance of the previously mentioned Ducati. Gfvalvo, I'm glad to see that you're a big fan of Asquared and that you feel compassionate about you're mechanical beliefs(as misguided as they may be), but you're not exactly correct! You might want to check out this site:
http://vettenet.org/torquehp.html

I especially like the part that says......

"Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower. "

I guess this guy is another one of us losers that didn't "pay attention in High School!" Dang!, There just GIVIN' those PhD's away these days!

Thank you Enigma! For giving me hope that I'm not the Omega Man of engine physics 101. "Soilent Green is made of TORQUE, IT'S........MADE OF TORQUE....D*mn YOU!!!!!!"

 

[A Squared]

Sparkey,

I checked out the site. More of the same "torque makes a car accelerate" from somone who probably didn't escape high school physics with a passing grade. Doesn't prove a thing other than that an enthusiasm for mototorized sports doesn't confer an understanding of physics.

Yes I know how a dynamometer works, that doesn't change the physics one bit.

Now, Your king killer torque monster of all time put out 64 foot-pounds of torque. OK, what would you say if I told you I could give you a power plant that put out *triple* that torque, was smaller, lighter, burned less fuel than your engine, and I could build it for around 500 bucks. Would you be interested?
Of course you would, hell with that much torque, you could flip the ol' Duke right over on it's back in fourth gear, maybe even fifth. Wouldn't the chicks be impressed by that?

OK here it is: 5 hp Briggs and Stratton lawn mower with a 1:23 gear reduction. Gives you about 200 ft-lb of torque at the output shaft. There you go, triple torque plus.

I see you shaking your head, you don't look happy, I'm not sure why not, you got triple the torque, and torque (according to you) is the only thing that matters ... so you should be delighted..... maybe it's because you think the girls will laugh at the little pull start handle?

No, you're dissapointed because there's not enough *power* to make the bike do squat. You have torque up the wazoo, but there's no *power*.

 

[Wang Chung]

That thing got a Hemi?

This is WAY better than the presidential debate that's on right now! I'm actually learning something. Or am I?

Maybe I'm just weird, but these scientific theory cat-fight threads are very entertaining to me. Keep up the good work, gentlemen, and don't let things degenerate into bitter name-calling. But sarcasm is definitely OK.

 

[Uncle Sparky]

Geee-Zuzz man??.get a grip! I'm not a very religious person but now I'm convinced of it??..there IS, in fact, such a thing as reincarnation and I am now completely sold on the fact that you were a Poodle or Chihuahua or some other ankle stature breed.

I'm not really sure of the guy's credentials but he does put the issue at hand into very simple terms and figures that I assumed even YOU could comprehend.



"If you have a one pound weight bolted to the floor, and try to lift it with one pound of force???."

"Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar???.."

Now, I may be alone here and anyone who has been paying attention strike me down if I am ???Please, Please Strike me with a large, blunt, lead fortified, object and put me out of my misery??..BUT the simple terms like "A block" "A Lever" and "A Fulcrum"
..just as the, apparently, cranially deficient Mr. Augenstein has used to express Torque(represented by the arm from the fulcrum to the weight) and Horsepower(represented by the RATE at which the weight moves)..tend, just a wee bit, towards the layman(myself self inadequately included)comprehending the definitions of Torque and Horsepower and their relationships than....

In general, a recip engine will develop more power the faster it turns. There are 3 practical limits to this: structural failure, valve float and volumetric efficiency. Structural failure is obvious, if you turn an engine too fast, it comes apart. Valve float is when you are turning so fast that the springs don't have time to fully close the valves during the cycle so you lose p

(don't put yourself through the agony of actually reading all of this again, it's just there for effect?Get to the end of the story
)
ower. That is why some very high revving engines use desmodromic valves, which are closed by positive mechanical action rather than by a spring. Volumetric efficency refers to the engines eficiency in moving a volume of a gas. As an engine turns faster, it reaches a point where it can no longer move a full fuel/air charge into the cylinder, and move the exhaust gasses out in the small time the valves are open. Headers, tuned exhausts, tuned manifolds and such are all for one purpose, to improve the volumetric efficinecy of an engine.
Anyway, the point is that peak horsepower in an airplane engine is not developed at the maximum rated RPM, which is a fairly arbitrary number selected by the manufacturer. Power increases with RPM, up to the point that the valves start to float, the engine comes apart, or it can't breathe fast enough.

No, the aircraft engine designers do not design for "torque", they design them for power. The reason they have large bores and long strokes is simple: A direct drive aircraft engine has a practical RPM limit of somewher around 2700-2800 rpm. The Beechcraft Duke engines turn at 2900 on takeoff, and I think that is hte highest revving direct drive aircraft engine (certificated anyway) That's because the prop loses a lot of efficency at those speeds, so there's just no point in making an engine that can turn faster (remember we're talking direct drive here) So, if you're limited to 2700 RPM, the simplest way to get more power is to increase displacement, which means increasing bore or stroke or both.

Now, a piston plane generates thrust by taking a mass of air, accelerating it with the prop, and moving it backwards. This action causes a re-action that we call thrust (Newton?s 2nd law). In order to accelerate and move this air we must do WORK, which is defined as the application of a force over a distance. Want more thrust? Then we must do this work faster. Now we?ve added a time element. The RATE at which work is done is called POWER. Thus, more thrust requires more power. The coupling by the prop of the power generated by the engine to the air is what makes the plane fly. A_Squared is right!!!



The power generated by the motor is proportional to the product of its RPM and Torque. Borrowing again from A_Squared, think of torque as a ?twisting force?. Trouble is, above a certain RPM (say 2700), the prop just can?t move the air efficiently. So you just can?t increase power by continuing to increase RPM. Connecting a bigger engine to the same prop doesn?t help either. If a given prop requires 100 HP to turn at 2700 RPM, then using a 500 HP engine does you no good. At 2700 RPM it will still be developing 100 HP. Push up the throttle and it will exceed 2700 RPM and the prop will loose efficiency. The engine may now be developing more than 100 HP, but it?s not being coupled to the air. No extra thrust, just a lot more noise.



Well, if RPM is fixed how do we get more HP? If we increase the pitch (bite) of the prop, it will accelerate and move more air on every revolution. Same thing if we use a bigger prop. So at 2700 RPM we?ll be moving more air per unit time and therefore generating more thrust. But wait; now the prop is A LOT harder to turn at this speed. That means we need more TORQUE! Now the bigger engine will help. It can continue to turn at 2700 RPM but supply


zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz?zzzzzzzzzzzzzz?zzzzzzzzz
On second thought, you ARE right. Torque is just a Fairy Tail term that ill-informed MotoJournalists use to mask their utter lack of knowledge of anything remotely mechanical.

....and Lift is just a fancy term that Bernoulli used to score with the chicks!!.they thought it sounded really cool when he said it with an American accent!

....and Gravity??..wu'll shoot that's easy! It's some fantasy phenomenon that Newton came up with when he was hanging out underneath the apple tree. It's a known fact that guys that hang out underneath stuff? (awnings, overpasses, woodsheds..)are usually up to some kind of wrongdoing. In fact the planet "sucks" you to the surface. That's right, it's not just a bumper sticker, it is now a known fact , THE EARTH SUCKS!

 

[bigD]

This thread kinda reminds me of the "Pitch for airspeed, power for altitude" arguments.

Anyone arguing 100% one way or the other isn't seeing the forest from the trees.

 

[TonyC]

Aww, this sounds like fun. Can I play? Let me put on my thinking cap . . . hmmmm . . . Physics . . . oh, yeah, I remember that - - my daughter's taking it in 11th grade now, perhaps I should ask her . . .



FORCE: strength or energy exerted or brought to bear

WORK: the transference of energy that is produced by the motion of the point of application of a force and is measured by multiplying the force and the displacement of its point of application in the line of action (FORCE x DISTANCE)

POWER: the time rate at which work is done or energy emitted or transferred (WORK / TIME)


If I want a car that can maintain a certain speed, I want a car that can produce a certain power. If it's speed that I'm concerned with, I want to measure that power at the drive wheels. If I substitute halfsize wheels on the car with the same engine producing the same power, I can haul a heavier load up a hill, but I can't go as fast. If I substitute oversize wheels on the drive wheels, I can go faster but I better lighten the load or find a downslope.

Now, if I want to keep the wheel size constant and supply the same power to the road from different motors operating at different speeds, it's easy to lose track. Not only do I need to consider the output of the motor, but also the gearing to the wheels. I could use an engine that supplies the power via a direct drive, or I could use an engine turning 10 times as many RPM's and transmit it through a gearbox. Ultimately, though, what COUNTS is how fast will the tires turn.


TORQUE: a force that produces or tends to produce rotation or torsion <an automobile engine delivers torque to the drive shaft>; also : a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation (FORCE x DISTANCE)

HEY, that sounds like WORK ! It's work in a circle, ain't it?!?!?

And, if we consider how much WORK it can do in a given amount of time, that would be power, right???


Complicated in the above auto examples, but what if we could set some constants to simplify the analysis.

Whaddya say we assume a direct drive prop? Since direct drive props are most common, we'll go with that. One variable down, one to go.

Why don't we assume the same prop for this analysis? Since different shapes and sizes of props require different forces to push them through the air, all examples use the same prop, OK?

SO, what's left? Force... Distance... Time...

Can't we say that TORQUE and POWER are directly proportional here? Aren't they linearly related? An increase in TORQUE results in a proportional increase in POWER, and a decrease in TORQUE results in a like decrease in POWER, right?



So I've got me thinking. The physics-student daughter is fast asleep, as should I be, and the brain's a bit fuzzy now.

Consider 2 bicyclists with identical bicycles, both with 12-speed gearing. Both Cyclists are travelling the same speed along the same course. Both cyclists are identical in abilities -- strength, endurance, maximum pedaling speed, everything. In fact, they are side by side as they travel this hypothetical course. Cyclist A is pedaling in 1st gear - - feet are spinning furiously, but with little force. Cyclist B is pedaling in 12th gear - - feet are pushing against the pedals mightily hard, but they're moving quite slowly.

Which cyclist is imparting more torque to the rear wheel?

When you think of a car or truck with high torque, which cyclist do you think of?

Low-end torque? Ever heard that term? Which cyclist has that?

As the cyclists approach a steep incline, which would you prefer to be? Is that torque?

High-end torque - - ever heard that one? Which cyclist has high-end torque?

As the cyclists approach a gradual downslope, which would you prefer to be?

As long as the bicyces are traveling at the same speed, they must be receiving the same work, so the legs must be imparting the same work, right? One (A) is imparting little force over a long distance, and one (B) is imparting a large force over a short distance. The product in both cases is equal. The torque is the same. The POWER is the same.

And yet, we tend to think of there being different torques, right?


The cyclists decide to test their individual maximum speed on the downslope - - Cyclist A soon reaches his maximum pedaling speed - - his legs can move no faster. Cyclist B moves ahead. Which is producing more torque now?

Is torque a real force? Yes.

How meaningful is it in practical application? Well, it depends on the application, maybe.

What REALLY matters in an aviation motor? Power, which is directly proportional to torque.


I like pitch for airspeed in cruise.







.

 

[Uncle Sparky]

I retract and apologize for my previous "Tommy" comment. Very nicely and more importantly, SIMPLY, explained.

and No disrespect meant towards Mr. Enigma.......a very accurate and PERTINENT breakdown as well......

Uncle "Sparkles" is now chuckling his pretty little head to sleep..................zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz LMAO! zzzz
zzzzzzzzzzzzzzzzzzzzzzzz

 

[TonyC]

5 hours sleep wasn't quite enough - - what was the "Tommy" comment?





.

 

[Uncle Sparky]

Say Good Bye Tommy.......

..the "beheading" thread........It would seem that I posess a talent for stirring up she-ite!

 

[TonyC]

..It would seem that I posess a talent for stirring up she-ite!

Well, if a penchant qualifies as a talent, I suppose so.





.

 

[enigma]

The reason why most airplane engines run at low RPM is purely to avoid needing a gear reduction system to lower the prop RPM to useful levels. There are airplane engines that run a 5-6000 RPM all day long that don't have any more longevity problems than the large displacement/low RPM engines. Rotax is the most common.

Scott

Scott, You're correct when you say that the slow speed is related to the need to avoid a reduction unit. I'll admit that it has been a while since I checked; but the last time I looked, a Rotax (either two or four stroke) has a TBO of less than five hundred hours. To me, that is a longevity problem!

In fact, high reving recip engines do suffer longevity problems when compared to low rpm engines. A F1 engine turns somewhere around 19K RPM, and makes a bunch of power, but I wouldn't want to hang one on a Kingaire even though it makes enough power to pull said Kingaire.

regards,
enigma

 

[A Squared]

Sparky,


I think you need to actually read what I've posted, I never claimed I didn't believe in Torque, or that it didn't exist. On the contrary, torque is very real, it is measure of a very real quantity. What I said is, in the context of engine output: "Torque, by itself is pretty much meaningless.", which is true, without a "RPM" atatched to it, torque tells you virtually nothing about the output of a powerplant. That's the point of the silly example with the lawnmower engine. You get all kinds of torque, but if you put it in your bike, you're going to have junior high kids passing you on their mini-bikes, flipping you the bird, and stealing your girlfriend.

So your duccati engine developed 65 ft-lb of torque, so what? I can develop 65 ft-lb of torque with a 3 foot wrench and a good strong yank, does that mean I can make a Ducati do third gear wheelies using just a wrench? Obviously, no. 65 foot-lb is a completely meaningless number, until you add RPM. Then it means something. Specifically it means power. You may think you're talking about torque, but really when you say XX torque at YYY RPM you are speaking of power. The words "350 foot pounds of torque at 2500 revolutions per minute" is really just an unnecessarily convoluted way of saying "166 horsepower."

Torque is a force, and force does not imply any motion Your house exerts a force on its foundation.

Work is Force and Motion, exerting the force over a distance.

Power is Force, Motion, and Time, exerting the force over a distance at a certain speed.

Now which of those is more descriptive of vehicle performance (airplane, motorcycle, car... whatever) Force? Force and Motion? or Force, Motion and Time? Kinda sounds to me like power is more a little more relevant to performance than force alone (torque).


OK, let's try this. Let's compute performance using our respective favorite performance indicators.

I've got a 2500 lb car with a 150 hp engine.

you have a 450 lb Ducati with a 65 Ft-lb engine.

Using only the given information (don't try to sneak RPM in there) we'll compute the acceleration of our respective vehicles (neglecting friction and drag losses)

Ready set ...... go !!!!!

OK, I'm done. In 5 seconds, my car will accelerate to just a hair over 70 mph.
(I can show you the math, or you can trust me)

How's your calculations coming? Not done yet?

waiting.....




waiting......



waiting.... Still working on it?


waiting......


waiting......




OK, I'll help you out here. You can't do it. Its mathematically impossible to compute acceleration from Torque. You can't do it, you don't have enough information.


Which is why I say that torque by itself is pretty much meaningless for performance. You can rail and bluster all you want, and make all your little snide and irrelevant comments about dogs, but at the end of the day, you still can't predict performance using torque alone. It's just simple (really really simple) high school level (no I take that back, junior high school level) physics.

Gotta go, my owner just put out a fresh bowl of kibble.

 

[Uncle Sparky]

..........can't...........look...........at computer screen!

........must........NOT..........touch...........KEYBOARD!!

I CAN'T DO IT! I-JUST-CAN'T-DO IT!
Like some kind of bug to the zapper, I can't stop myself!!!!!
Where does it end?

Oh the humanity of it all!!!

Hhhho-KAY! The man asked if the engine in question produced much torque and his question was answered by someone else(see posts by TonyC and Enigma)......Let's try and move on little fella. .........make sure master gives you DeCaf kibbles....