Torque and Horsepower

This combustion pressure depends on the volumetric efficiency of the engine, in other words, how good it is at getting in the largest amount of fresh mixture to ignite. This means that you need to get rid of all the burnt gas and completely fill the cylinder with a fresh mixture without losing any out the exhaust before the port closes. However, this can only happen at one particular engine speed because of the fixed port timings (which in any case are a compromise). If the engine is running at a speed below the optimum then there's time for some of the fresh charge to escape out of the exhaust so less pressure will develop at ignition so reducing torque. If running above the optimum then not all the exhaust has time to get out and not all the fresh charge has time to get in which also reduces torque. Keeping that in mind, as the revs increase from below the optimum the combustion pressures begin to rise and so does the torque until it reaches it's maximum efficiency. From there on the efficiency decreases again and the torque begins to fall. This is where we see those torque curves which rise up to a peak then begin to drop off. They're really an indication of volumetric efficiency at various revs.

So much for torque, now what about horsepower? Well as I said earlier, HP is calculated from torque and revs. Twice the torque at the same revs will give twice the HP and twice the revs with the same torque will also give twice the HP (Torque x revs = HP). If you take a graph of the torque curve and multiply by the revs at any point you'll end up plotting a graph for the HP of that engine. But one thing that'll soon be noticed is that the HP keeps rising for a while even after the torque curve begins to fall. The reason is that the revs are rising at a greater rate than the torque is falling off. But there comes a point where the torque begins to fall away faster than the revs are rising and this is the peak HP for that engine.

These are just the basics but hopefully it shows that it's possible to have an engine with quite low torque figures that develops high HP if that torque comes at high revs, not what we'd want for PA work though. It might also be noted that flywheels didn't come into the discussion either

I thought somebody somewhere in another thread said that flywheels increase torque. Now, if "inertial mass" is not "solely responsible" for torque, is "inertial mass" partly responsible for torque?

>Torque times RPM over the constant 5252
>equals Horsepower.

I wonder what the parameters (as in "standards of measurement") are here.

Keith

>
>Thank you a very neat and
>consise explaination. Although if people
>start multipling torque times RPM's
>as in your example Torque
>X RPM=HP. You will have
>some astronomical numbers.
>Nope no FLywheels but I never
>claimed that inertial mass was
>solely responsible, either.

"Inertial mass" not only is not "solely responsible" - it has absolutely nothing to do with it! A flywheel is a convenient mechanism for storing (and delivering) energy, but it never creates power in any manner.

When POWER is measured, it is a RATE: work/time. While a flywheel may smooth the flow of power, it cannot create power. During a period of acceleration, an engine with a smaller flywheel can actually deliver more power to a load. It does so by not having to charge the flywheel.

>Interestingly enough. Relatively low horsepower engines
>like the earlier 2 cylinder
>Harley engines produced Prodigious Torque
>figures, yet were well down
>on comparitive HP. I would
>add that higher torque does
>not necessarily mean higher HP
>either.
>

Interestingly enough, power remains precisely porportional to both torque and speed. Higher torque at the same RPM means higher power.

If the old Harley engine was torquey but down on power, it was because it simply would not rev up. Consequently, torque times speed (power) was reduced.

The point was that given two engines, at the same RPM, the one with double the torque produces double the power. Or that two engines, producing the same torque, the one with double the RPM produces double the power.

>Torque is defined as the force
>at any one point on
>the cicumference of a circle
>in the exact direction of
>the rotation. Times the radius.
> This comes from the
>concept in geometry of a
>"tangent", a line which touches
>exactly one point of the
>circumference of a circle.
>

I never heard anyone try to relate torque to the geometrical concept of tangent before. I believe the origin of the word "torque" has its roots in "twist". Greek or Latin or something..

Torque is the product of a force applied to the end of a moment arm. Nothing more complicated than that.

>Also when discussing such things you
>need to define the standards
>of measurement. HP in what
>units? PHP, BHP? in pound
>feet, Newtons, Watts?
>

Why? It's understood (among people discussing such things) that a particular set of units (e.g. metric or English) are used. But the measurement system used has absolutely nothing to do with the definition of terms.

Whether the horsepower is "peak" or "brake" is irrelevant. (These terms refer to the type of measurement.)

Pound feet is a torque unit. Newton is a force unit. These aren't units of power. Watt is a power unit (metric).

Math and physics are well defined, and need not be muddied up with subjective pronouncements. Spare us.

L.

Larry why not? You wrote >>>A flywheel is a convenient mechanism for storing (and delivering) energy<<< if you can delivery an energy, you can also delivery it quickly or slowly, and power is “speed of energy delivery” -> Power=Energy/Time (sorry for units Fubar ) so the flywheel can deliver and also absorb power. The only trouble is that the energy is limited to its mass inertia and rotation speed, so also time of delivering is limited, but also tank of combustion engine is limited so there is only one difference – the energy in flywheel is mechanical, while fuel has chemical energy.

Yes … just theoretical note … it is clear that the flywheel on engine or even large prop is not worth to speak about “energy storing”

The end result is the engine gets the rpm it needs to deliver all of the power it can make. With all of this power on a gear reduction system this gets the prop going the correct speed. There is no way this motor would have been able to throw this large prop at the needed RPMS to get the flight he was going to need. he was tired of having to use smaller props and figured out a way through gear reduction and excellent machine work to have the best of both worlds. A small motor and a large prop both turning the dseired seperate speeds. I would love to try this in stunt. Get a racing motor on a pipe going 17,000 or 20,000 rpms but getting 10,500 at the prop. This would be cool. The engine would be a such a constant two stroke with no change. Like those Quickie 500 racing motors you hear at the nats all week long. None of this 4-2-4 stuff.

DMoon

Just curious as to why a lower RPM prop would necessarily be assumed to be more efficient than a higher RPM one?

If you want to turn 17-20K, use a very flat prop. No friction loss or additional weight or reliability issue for a prop, versus a gearbox..

Plus, the added advantage of the flatter prop/higher RPM setup.

The issue for stunt is NOT maximum power anyway.

L.

LAST EDITED ON May-06-02 AT 12:19 PM (CST)

>Doug,
>
>Just curious as to why a
>lower RPM prop would necessarily
>be assumed to be more
>efficient than a higher RPM
>one?
>
The faster a prop turns, assuming the aircraft speed doesn't change, the more the more a prop blade tends to run in the turbulence of the blade preceeding it hence the reduced efficiency. Obviously this would vary depending on the type of prop run with flat wide blades being affected more than skinny ones. We use the prop as a gearbox right enough but the range of pitch usability is not enormously wide. Rarely does one see a prop for stunt, regardless of powerplant, out of the range of 3-6 inches of pitch. An FP 40 will turn a 10/3 prop at around 11K R.P.M. and give stunt-like lap times. A honkin' 40 radio motor can do twice that easily with Jetts and Nelsons half again as much, with tons more power, but propping it to run at stunt lap times would be a challenge to say the least. A 25 turning an 8/2 prop at 20K might give a stuntable plane speed but I'll bet it's going to be very "interesting" to trim out. I don't know exactly where the effects of blade turbulence would start to make itself known in the rev range but for a 10" prop moving an airplane at only 55 m.p.h. 20 K revs might be well past that point. That pretty much gets us back to the whole gearbox business which would allow screaming engines and relatively slow turning, more "efficient" props.

Gear reduction would do two things. Let the motor run where it was designed to run. High in the RPM range. The prop would turn in the designed rpm range. The props we use now would apply. There would be no need for a new development of props and all that stuff. The same ones we use now would apply.

There would be no need to sacrifice anything. You would have the motor happy and the prop happy and this means good flying.

A third thing might be that since the motor is in the designed rpm range and really smokin it might run alot more efficient.

Motor going real fast prop going slow. Sounds cool dont it?

Please look up this article it is really cool, even if it wouldnt work for us. It is still cool to see when people figure out something they been trying for along time to get straight. I have always thout it would be too cool to have a transmision of some sort between the prop and the motor to let the motor move up and down in the rpm range and see less effect on the prop or something like that.

DMoon

Lots of friction loss - there's still parasitic drag. The horsepower going into the airplane would be the same as long as you are going the same speed (.35 hp in level flight). But spinning faster makes the parasitic drag HP go up as the cube of the RPM.

Of course, "more efficient" doesn't necessarily mean "better". If you've got power to burn, then you might choose a less efficient prop that had other beneficial characteristics. Like one that runs like it's low gear all the time! That's why we are flying airplane with PA65's pumped up to the max in the same airplanes we used to fly with relatively wimpy ST46's.

We have such a gearbox – it is pitch of prop – less pitch, more rpm, more power. So if your Os Max .25 will twist 10x3 prop twice as much as the 10x6 you will get also twice as much power. We even use such “Gear box” on piped engines: if the .60 engine twist some 12x6 and .40 twist some 12x4 prop, the power is almost same: the torque of .40 is at .40/.60=2/3 while rpm is at 6/4=3/2 than the power of .40 is (2/3) x (3/2) = 1 of .60. So you see piped .40 engine can deliver almost the power of the 4-2-4 type .60.

1/ Low pitch versus high pitch. If you will use calculator and make some numbers about it you will easily find that both props have the same response to slowing down or up. It means there is no difference in pull ability or braking. It means if you slow down the flat prop has half of angle of attack difference on blade airfoil compared to high pitched prop. But airspeed is twice higher, so the final lift will be more or less same. The only difference is that lover angle of attack is able to make more pull if the model is slowed even more or more static pull.

2/ Gearbox versus direct prop (at same engine RPM): Engine delivers same power; just prop has more diameter and more pitch on geared version. The benefit of larger props is fact that more prop disc area is out of fuselage crossection (better efficiency) and fact that larger prop can have lower absolute angle of attack on tips (better pulling at low speed). Question what it does on our more or less constant speed flying. The load of prop grows up with growing diameter much quicker than with RPM. So if you will use 2:3 gearbox, you will need say 10x4 direct prop or 11x6 geared prop. The pitch must be in ratio of gear to keep same speed at same RPM and diameter must be matched to 3:2 higher torque. The diameter 11” is only eyeballed but it is not too far from true. I can state exact number if anybody wants, but it is certainly much less than in ratio 3:2 thanx fact that load grows much more with radius than with rpm. However as you see the second advantage of larger prop does not happen because it looks it will be even more than on 4” pitched prop on our model. The first advantage is clear, but I am asking do not we have problem with too large props on our models? The first advantage is really helping on applications like hi rev electric engines or on scale models. And now comes the question: why not to use 3 blade prop, which loads the engine in same ratio 2:3 like a gearbox? And we are where we are – don’t we?

I saw a note that gear box does not carry load from prop 1:1 if we go up hill. It is true the load is transferred only in gearbox ratio, but THE PROP makes also load in ratio – unfortunately inverted. So if you have gear box 2:3, the load comes back from prop only by 2:3 but prop makes load 3:2 as the diameter is larger, so there is also nothing to win – yes it really means that gear box does not convert power or conducted energy – it converts just its form, nothing else – like electric transformator does not change power, just relation voltage:current. Such transformation helps if you run out from numbers – you can not have 12V powered engine giving 50KW, because your fuses will burn thanx too much current, you can not power your model at 100 000rpm with 0,5KW engine because your prop will be too small out of the spinner.

If gearbox should be an advantage it must be a really hi rew engine designed for say 25 000 rpm.

I think first of all we need to speak about engine itself, and than to find proper prop or may be also gearbox so:

1/ regular 4-2-4 engine: It flies rich and its torque curve is falling down unloaded. It makes a stability we know from this type of power plant. The prop load matches “happy point” and its pitch gives wanted speed. Such power plant works well even it does not deliver its best power – the disadvantage is more weight for same power.

2/ full power hi-rev like we see on low rew engines like FP or LA Os max or 4 cycles or diesels: Those engines have decreasing torque curve somewhere at ~12 000 rpm. If you match some 3.5” pitched prop, you will also see useful setup. It is not so well working like 1/ but extra power on similar model will help keep speed also and you have advantage of lightweight FP/LA.

3/ the 2/ can be improved by tricky under cambered prop: The trick is in its airfoil which does not unload engine if does not make pull. The unloaded prop airfoil has up to –2 AoA. If you will look to polar of such airfoil, you will see that its drag does not vary from –2 to 2 AoA too much – or even better – grows unloaded. It is typical property of airfoils designed for free flight – they are optimized for CY=1 and they produce drag at CX=0,02. If you unload such airfoil, so it makes no lift CY=0 the drag grows to CX=0,05. There are similar tricks with props pitched at 3” at tip and at 6” at root. If the prop is unloaded, the tip falls to negative angle of attack and thus does not allow overspeeding. It is typically used here in Europe on 4 cycles. I saw it described somewhere on interned in short notes by Beringer about his models with Saito.

4/ pipes can make 2/ much better: The reflected negative pressure wave followed by positive supercharges engine if slowed down and brakes if unloaded. If you stick UCT prop from 3/ and you will use another trick – more baffles in pipe, you can also have very well defined 4-2-4 run from 1/. Can we have anything better?

Yes, I am thinking of device controlling regular R/C carb to keep constant rpm by feedback from rpm sensor. It can be very simple and with actual R/C equipment also very small and light. It will give constant rpm, but it is still not constant speed. I hope there could be installed clever positive feedback in term of – if rpm falling down add more throttle than necessary – it means loaded engine runs little more than unloaded – it same effect like nose up lean and nose down rich. But it is just my hope and I would like to try such a thing.

Did I forget something ?

Too long? Too pure English? Too stupid?

Thanks. Great post! You have clarified some issues for me.

SK

The graphs look surprisingly familiar! Actually, Scott's paper has nothing about instantaneous torque. It has plots from a pressure tap in the head describing more-or-less instantanous cylinder pressure. To create the plots on your website, I took this data, digitzed it, then derived the torque from the pressure, the area of the piston (giving me piston force), the stroke, and the crank angle (giving me lever arm at each point). RPM was derived from the prop dimensions, {Rg coming from Pete Soule's approximation, and the mass coming from a Rev-Up 12-5 I happened to have in my extensive prop collection} and integrating the torque over time.

There are a bunch of caveats on these plots, all listed when I posted it here originally (under the thread about 4-strokes "turning easier" by the inestimable Brad "Godzilla" Walker.)

>By comparing the two graphs
>it's easy to see what
>affect increased torque has on
>prop speed. Unfortunately (and for
>FUBAR's benefit) it doesn't state
>what prop is used. Not
>so much the actual size
>(on this engine probably a
>12x6) but the weight. If
>it was a light wood
>prop then fitting a heavier
>APC (possibly doubling the moment
>of inertia) would have given
>less variation in prop speed
>but instantaneous torque would have
>remained unchanged.

According to Scott's paper, it was a 12-5 (presumably Rev-Up) on Duke's Fuel.

Not hundreds of revolutions in one rev, but a rate equivalent to hundreds of revolutions per minute. Theta dot, not theta!

The torque graph, scaled by 1/prop inertia, is the instantaneous angular acceleration (omega dot, or theta double dot) Integrate this, and you get the RPM.

It's pretty well mandatory to understand this to have a chance of understanding how flywheels effect torque and rpm.

I am at a loss.

Some of us haven't learned to take advantage of the fact that the internet allows us to receive information, as well as transmit.

You might want to consider that having a narrow power band, while making motorcycles hard to ride, is in fact a boon to model airplane engine stability.

>I was speaking as possibly using
>gear reduction as a reglulating
>mechanism for RPM stability, That
>would be present when gear
>reduction is used and the
>engine is more lightly loaded,
>as opposed to a direct
>coupled prop of similar size
>and relying on a tuned
>pipe to help torque and
>stability.

So you're suggesting that you use a flywheel large enough to minimize the RPM change to a few tens of RPM over a period of maybe tens of seconds. Let me know how that works out for you.

Somewhere, Howard is having a meltdown!

I think I'll stick with my little slide whistle.

If I understand FUBAR correctly (and I'm starting to get the knack), due to the torque reduction looking back at the engine, you will need to go to a 3x11 prop.

Length and pitch will necessarily be (approximately) transposed.

L.

BUT...if you have your needle valve set correctly,
when the nose of the plane goes up, the fuel mixture
becomes leaner, and RPM's increase. When the nose
goes down, the mixture goes richer & RPM's decrease.

So...why...would...you...need...a...gearbox?

They are used on electrics, like the Speed 400,
because there is no fuel mixture change to take into
account. And to get longer flight times from the
batteries.

Yeh, that's it! A worm drive!

L.

"I keep tryin' to think, but nothin' happens.." - Curly Howard

>...Take a gear box with say
>a 2 to one reduction ratio.
>If you spin it one way it is
>very easy to move a resistance
>at the other end.

That would be the reduction in output speed

>When you turn it from the
>other end it takes twice
>the effort to turn a
>similar resistance.

That would be the increase in speed.

>Hence torque multiplication and torque reduction.

Because of the increase or decrease in output rpm

>Of course this also effects RPM.
>But put RPM aside for a moment.
>
>Air loads the propeller, it applies
>a resistance, add to this
>the additional load placed on
>the propellor when the airplane
>climbs during a vertical. All
>of this load tries to
>reduce engine RPM. And when
>the airplane dives the load
>is lightened and the engine
>then wants to pick up
>RPM and over speed.
>
>But if a gear reduction is
>applied, these loads are not
>as impacting upon the engine...
>
>Only Dangerous when Bored!

Here is where I got lost. Why aren't they? If the load on the prop shaft is increased, the load is increased on the engine. If the load on the prop shaft is decreased, the load is decreased on the engine. This would hold true with or without a gear box.

Leonard Neumann

"In other words the engine can sit and make it's max power with less interference by load."

That is exactly what I am talking about right there with the gear reduction thought. The load is applied differently to the motor. We could probably run alot smaller motors and tanks and make the planes alot lighter.

The motor runs where it is designed and the prop turns the rpm it needs to give us the correct speed.

The motor sure would last alot longer.

The hard part would be getting people to learn to rethink their approach to the "Stunt Run" The 4 stroking 2s motor would not be needed. All the 4-2-4 stuff would be pretty much gone from the equation.

DMoon

PS Howard as long as your gear reduction is correct you can run your 11.3. It will be ok dont worry the 11.3 will still work.

Look at it this way.

I had a 454 with 11.5:1 compression(525 hp give or take few). My standard large starter would not trun the motor over very well at all. It would wear the starter out in about a week! Ouch!!!$$$$!!!

I got a GEAR REDUCTION starter. The starter motor is half the size uses half the energy needed to run a standard starter and weighs half as much yet through GEAR REDUCTION delivers TWICE the cranking power. That is right TWICE the cranking power. Needless to say starting the monster was never a problem again. The battery lasted alot longer too. These type starters are standard on corvettes now. I know I am talking about an electric motor. I was simply using it as an example that can show how much you could gain from smaller high reving motors through gear reduction.

The advantages of gear reduction can be endless. Dont clutter it up with other variables until you actually get out there and hook it up on a motor and see what happens.

DMoon

Don't confuse power with mechanical advantage (gearing).

The output of the geared motor has more torque. It also turns slower for the equivalent RPM of the motor. In reality, the gearing mechanism actually absorbs a little power from the motor.

What you are talking about, with gearing, is equivalent to getting a 2-liter race engine to develop 600 horsepower by having it rev to 27,000 RPM. Such motors are good for about one race.

I still say, the proof is in the pudding. Someone needs to show up with a .25 engine running reduction gearing and a big prop at a contest and clean everyone's clock. That pudding would prove the concept.

L.

LAST EDITED ON May-07-02 AT 10:36 AM (CST)

You are missing my point completely(I think) I want to use the machanical advantage to get max power out of the motor. I know full well that machanical advantage doesnt = power. A 40 size Jett racing motor going full bore is making a serious amount of power. Probably more than what the choked down 61 is making. That is what I want to get at. I am so sick and tired of having to constantly fight speed up at the beginning of the year with pipe length and prop pitch. Always trying to govern it and limit the engine. Around here is different every year. The wheather is never the same. What worked great last year aint doing squat right now. Maybe tap into the HP range of a motor the high end revs that it really wants to run and the game could be changed. Let the motor limit itself by running it at its MAX power then ruducing the shaft speed to a usable prop speed.

You see in my illustration about the starters it is obvious that you need less motor to acheive the same result using gear ruduction. In the case of the starters the smaller motor was actully able to deliver more force using gear reduction because it could spin up to its desired rpm level to generate the power needed to torque the 454 over. The straight ahead starter is a much stronger bigger beefier motor yet since it cant get spinning the speed it needs to create the power to roll over the 454 it is actually less powerful of a device.

In F1 it was a normal thing for motors SMALLER than 2 litres(1.5) to get a 1300 hp on turbo chargers and now they get an easy 900 with no turbo. Sure they dont last long. This is not what I am talking about though.

There are many over the counter motors designed for major RPMs in the 20K range. If they didnt last people wouldnt by them would they? JETT has any number of motors that can do it all day long. OPS OS also. They are made to do this regularly and for sustained periods of time. If you dont think so please do some reading up on RC stuff. Technology of today just keeps yeilding better and stronger engines for tomorow. We just get the smallest and lightest ones we can find and rework the sleeve. I guess you could say we scavange around until we find a suitable case and then someone gets the insides to work correctly for our application. What if we didnt have to do that. Just hook up some gears and go. The motor counter at the LHS would all of sudden be very interesting to look at. Where as now you have to just walk by and wish PA 65s and the likes were available over the counter.

DMoon

And, again, the proof is in the pudding. Some convincing pudding would be for someone to show us all how it is done with a high revving .25 using a reduction gear, pulling a big stunt ship around in a winning fashion, and lasting a real long time because it was operating in the RPM range it was designed to..

With no puddin', we are just speculating. Wouldn't you agree?

Personally, I have strong doubts. I need to be convinced.

L.

But if this little .25 turning a large prop through gear reduction (in a superior manner) is such a great idea, I think it is time for someone to actually do it.

Here's your chance to revolutionize CL stunt!

L.

http://www.vettenet.org/torquehp.html

Bill Mitchell
Apex, NC
District 4
AMA540930

On this we all agree - there's plenty of room for new ideas. The article is quite readable and makes the points.

And if this new idea does work well, I'd be a fool not to try to use it myself. If you read some of the other threads, apparently the hardware already exists to try it in a practical application.

It will be interesting to see such a rig in operation.

L.