Just another post on Horsepower, Torque, and Other

Horsepower, Torque, and Other RPM Numbers

Horsepower (Hp) is the power output of an engine or a motor. Most model engine manufacturers give the maximum, or peak, horsepower rating of their engines as one of their selling points. Horsepower is a calculated number. This number is calculated from the engine's torque and the RPM (revolutions per minute--also note that RPM is already a plural. RPM's is incorrect) at that torque. Torque is the actual twisting force on a shaft, and can be measured with a dynamometer, or "dyno".

When an engine is put into a dyno for testing, a calibrated load is put on the engine. This is usually some kind of weight. The engine is run at full throttle, and the RPM is measured. Different loads are put upon the engine, and the RPM is measured each time. With enough measurements, a torque versus RPM curve can be plotted.
At each point, the horsepower can be calculated. The formula is:
Hp = (Torque x RPM) / 5252
This is when torque is measured in foot-pounds. If the torque is measured in inch-pounds, then the formula is:
Hp = (Torque x RPM) / 63,025
(Fractions and some rounding are ignored in the above formulas.)
A curve with horsepower plotted against RPM will then show where the peak horsepower happens. Unfortunately, this can be misleading. The only time peak horsepower is needed, or desired, is in a racing installation, where every bit of power you can squeeze out of the engine is needed. For most applications, peak torque is needed. After all, it's torque that is the force that turns the propeller. Peak torque almost always occurs at a much lower RPM than the peak horsepower.

For example, a typical .46-size engine will develop its peak horsepower at about 16,000 RPM, but it will develop its peak torque around 12,500-13,000 RPM. For almost all uses, then, the engine should be set up so that it will turn 12,500-13,000 RPM at full throttle.

Another set of engine RPM is what some manufacturers term, "practical RPM". This is the RPM range in which the manufacturer has run the engine. One .46-size engine has that range listed as 2,000-17,000 RPM. Unfortunately, you will never be able to run the engine through the full range with one setup.

The low end of the range is the slowest speed the manufacturer could get the engine to run with one particular setup. The high end of the range was found with another setup, and was as high as was dared before the engine started to have a very significantly shortened life. Much faster, and the engine will not hold together. Consider the top end of the range the "redline" speed of the engine.

If you can get the engine to run very well at low speeds, the top speed will be sacrificed, and the same is with the top end. You won't get a particularly low idle if you set your engine up for maximum RPM.
The actual operating range is somewhat towards the middle. The same .46-size engine with the 2,000-17,000 RPM practical range really winds up with an RPM range of about 2,700-13,000, when set up in most models. This RPM range will give an excellent throttle response along with a very good idle and long engine life (assuming proper operation and care). For a .46-size engine, this means a 10x7, 10x8, 11x6, or 11x7 propeller.

Nowadays, many engines have larger propellers listed than have typically been used in the past. This aren't necessarily the best propellers, but are suggested because the engine manufacturer is trying to help with noise reduction. Many places around the world have very stringent noise restrictions, so the propeller suggestion is to help reduce noise. A larger propeller will turn at lower RPM than a smaller one, so engine and propeller noise are reduced. Most engines won't develop their best torque or power at those RPM levels.

In the U.S., most noise restrictions aren't as severe as in Europe or some places in Asia, so the engine can be run at more efficient settings, allowing more power to be developed.

SCOTT

idle and long engine life (assuming proper operation
>and care). For a .46-size engine, this means a 10x7, 10x8,
>11x6, or 11x7 propeller.
>
>
>SCOTT

Scott, looks like this came from an R/C board somewhere?

>
>
>idle and long engine life (assuming proper operation
>>and care). For a .46-size engine, this means a 10x7, 10x8,
>>11x6, or 11x7 propeller.
>>
>>
>>SCOTT
>
>Scott, looks like this came from an R/C board somewhere?
>
>Jim Pollock

Jim. It was sent to me and I thought I would share it.
Some good stuff.
Scott(An engine is an engine...in the box) Riese

LAST EDITED ON Dec-11-03 AT 04:44 PM (CST)
 
>For example, a typical .46-size engine will develop its peak
>horsepower at about 16,000 RPM, but it will develop its peak
>torque around 12,500-13,000 RPM. For almost all uses, then,
>the engine should be set up so that it will turn
>12,500-13,000 RPM at full throttle.

How would this be best be accomplished? Optimum fuel setting and change the loading by changing props until this condition is met or select a prop and tweak the needle? I think it would depend on the design of the engine. Porting configurations, compression, timing, etc. etc all play a part. I'm not sure I agree with this as a carte blanc statement.

Like most things in this world...... it depends.

PS While I was writing the above I was thinking about an old ringed Super Tigre and a new .46 LA. Real differences in these two engines.

I use a Torque Reaction Dynamometer or Fan Break. This uses a predetermined amount of weight set on the propeller centerline at a given distance. The torque is calculated by how far the engine is able to move the weight in a circle. With this number Torque can be calculated. Horse Power is a simple calculation of Torque (inch ounces) X RPM / 1,008,000.

Remember the standard in corrected Horsepower you are assuming Temperature of 60 Deg F, Barometric Pressure of 29.92 inches of mercury (14.7 Pisa) and no humidity.

This system is available threw Aero Products for around $130.00

Larry Foster

LARRY...I asked on this fourm about two years ago about DYNO'S?
and now You say the Randy has them?? Went to his web sight and I can't find them. PLEASE POINT ME THE RIGHT WAY.

Yes I'll call Randy

Scott( dollar short and ...)Riese

LAST EDITED ON Dec-11-03 AT 09:19 PM (CST)
 
It shouldn't be too difficult to build a dyno (or dynamic torque meter). You'd need to mount the engine on a platform that rotates, and you put something in there to resist the rotation (maybe you twist a piece of large music wire). Put some kind of stop in the system so that if something breaks, the whole platform doesn't twist around and around. You'd probably only want it to move 10-15 degrees at the most. And you'd want some kind of damper (so you can actually get readings that aren't constantly flunctuating) and some sort of dial to measure the rotation. Then you can calibrate it using a torque wrench. Now, all you need is to mount the engine, use a range of props, and use a tach to measure RPM.

LAST EDITED ON Dec-11-03 AT 09:43 PM (CST)
 
See, for instance, http://www.clcombat.info/dyno.html
There are pictures and the address for ordering your own.
I thought everyone knew about these people;
they've advertised in the magazines for several years.

WOW...Thanks. Looks like the combat people have there act together.

Scott(still like stunt)Riese

LAST EDITED ON Dec-11-03 AT 11:28 PM (CST)
 

If anyone buy's one spend the time using a good polyurethane to protect it. It's a lot of work but well worth it.

Larry

>If anyone buys one, spend the time using a good
>polyurethane to protect it.

The one in the photos is well varnished, though not well photographed.

>LARRY...I asked on this fourm about two years ago about
>DYNO'S?
>and now You say the Randy has them?? Went to his web sight
>and I can't find them. PLEASE POINT ME THE RIGHT WAY.
>
>Yes I'll call Randy
>
>Scott( dollar short and ...)Riese

Scott:
Randy's web site doesn't cover a lot of the items he carries, unfortunately I don't have Randy’s Catalog because every time I get one I end up giving it away.

It's made by American Hobby Products, 12 West Hill Circle, Reading Mass. 01867 (781) 944-8316

Larry

>I use a Torque Reaction Dynamometer or Fan Break. This uses
>a predetermined amount of weight set on the propeller
>centerline at a given distance. The torque is calculated by
>how far the engine is able to move the weight in a circle.
>With this number Torque can be calculated. Horse Power is a
>simple calculation of Torque (inch ounces) X RPM /
>1,008,000.
>
>Remember the standard in corrected Horsepower you are
>assuming Temperature of 60 Deg F, Barometric Pressure of
>29.92 inches of mercury (14.7 Pisa) and no humidity.

What about the load from the prop that is on the engine? Wouldn't you have to add the torque required to spin the prop to the reading found on the dyno?

LAST EDITED ON Dec-12-03 AT 11:21 AM (CST)
 
>What about the load from the prop that is on the engine?
>Wouldn't you have to add the torque required to spin the
>prop to the reading found on the dyno?

We're measuring the prop load; it's the whole point of the thing.

>A curve with horsepower plotted against RPM will then show
>where the peak horsepower happens. Unfortunately, this can
>be misleading. The only time peak horsepower is needed, or
>desired, is in a racing installation, where every bit of
>power you can squeeze out of the engine is needed. For most
>applications, peak torque is needed. After all, it's torque
>that is the force that turns the propeller. Peak torque
>almost always occurs at a much lower RPM than the peak
>horsepower.
>
>For example, a typical .46-size engine will develop its peak
>horsepower at about 16,000 RPM, but it will develop its peak
>torque around 12,500-13,000 RPM. For almost all uses, then,
>the engine should be set up so that it will turn
>12,500-13,000 RPM at full throttle.

For almost all uses, huh? Oy vey!

Kewl post.

That's the basics, everyone should read it.

Thanks Zilla.

I also thought it was kool.

What about the load from the prop that is on the engine? Wouldn't you have to add the torque required to spin the prop to the reading found on the dyno?

The City Smasher

Excuse me for pointing it out, but above statement is representative of some of the things said about dynos and dyno testing which just drive me up a wall and make further discussions quite frustrating.

You don't add the load required to spin the prop to anything. Instead, you are measuring the torque required to spin a specific prop at a specific rpm.

There could be no prop at all. Blow air over the motor to cool it, let the unit being tested drive an electric motor.

The *only* reason we tend to test with props is they are handy and cheap. Unfortunately, they are not as consistent as desired, which is why the cautious tester will have a set just for testing and they will *not* be wood props. Another alternative is a set of bhp props. They are no doubt pretty crummy for flying, but I remember Graupner or some other Euro-trash company offering them for sale and at one time they were available here in the U.S. from an importer.

>What about the load from the prop that is on the engine?
>Wouldn't you have to add the torque required to spin the
>prop to the reading found on the dyno?
>
>The City Smasher
>
>
>Excuse me for pointing it out, but above statement is
>representative of some of the things said about dynos and
>dyno testing which just drive me up a wall and make further
>discussions quite frustrating.
>
>You don't add the load required to spin the prop to
>anything. Instead, you are measuring the torque required to
>spin a specific prop at a specific rpm.

So really all you did was dyno the prop.

>There could be no prop at all. Blow air over the motor to
>cool it, let the unit being tested drive an electric motor.

Or let an electric motor drive a prop.

>The *only* reason we tend to test with props is they are
>handy and cheap. Unfortunately, they are not as consistent
>as desired, which is why the cautious tester will have a set
>just for testing and they will *not* be wood props. Another
>alternative is a set of bhp props. They are no doubt pretty
>crummy for flying, but I remember Graupner or some other
>Euro-trash company offering them for sale and at one time
>they were available here in the U.S. from an importer.

Frank already has them.

Look Dirt, I think you should understand exactly where my statement came from.

Frank used several props all cut to different lengths (Master Airscrew nylon). He then "calibrated" the props by driving each by an electric motor of given horsepower. In effect, he had "dyno'd" the props and found the torque required to spin each one. Then each prop is connected to the engine and spun up to max RPM. From this value and the accompanying chart created from the curves generated by the props, you can back figure HP and torque.

The load of the prop is the reacting torque that the engine is reacting against to rotate. All you are doing by using the dyno shown in the picture is measuring the torque required to SPIN A GIVEN PROP A GIVEN RPM. You really only have data gathering capability about props not engines. You could accomplish the same thing with any motor that would spin the same prop the same RPM. Right?

Godzilla,

Sigh...

You must make up your mind. Is the goal to test props or engines? Pick one.

Dan:
I use mine to see if changes I make improve or degrade the motor. Apples to Apples. I use a set of props for this purpose only. Take the Fox 35. I use a 10X6APC for all baselines, and then I go to an 11X5 APC and then an 11x6 APC. When I test them in a four cycle it becomes an ear thing then I go to peak RPM. After all of this I fly the engine because that's where we truly see it. I've made changes to the OS LA's that improved performance on the bench but didn't in the air. Only reason I do it is because it's fun for me to do. I've tried posting results here and everything comes under fire, so I stopped doing that.

Larry Foster

Sure. Once you've got a set of calibrated props
(or other calibrated load), you don't need a dyno.
You can just run through your set of props with a tach,
do a little math, and plot the results.

>Sure. Once you've got a set of calibrated props
>(or other calibrated load), you don't need a dyno.
>You can just run through your set of props with a tach,
>do a little math, and plot the results.
>
>Preston

Thank you Preston!!!!!

Geez...

Thank you Preston, indeed. Called last night, you didn't have the foresight to be home at the time.

Will you be at the Swap Meet, John Hall's place, tomorrow?

"Wouldn't you have to add the torque required to spin the prop to the reading found on the dyno?"

Well, yes. It's, as the British say-- Oops, we can't say here what the British say. It's zero.

Dan:
I use mine to see if changes I make improve or degrade the motor. Apples to Apples. I use a set of props for this purpose only. Take the Fox 35. I use a 10X6APC for all baselines, and then I go to an 11X5 APC and then an 11x6 APC. When I test them in a four cycle it becomes an ear thing then I go to peak RPM. After all of this I fly the engine because that's where we truly see it. I've made changes to the OS LA's that improved performance on the bench but didn't in the air. Only reason I do it is because it's fun for me to do. I've tried posting results here and everything comes under fire, so I stopped doing that.

Larry Foster

One would think a custom tuner of engines such as yourself would have by now developed a much thicker skin.

Would it help if each time one of us gained a piece of information from your more technical postings we drooled all over the screen in thanking you from the bottoms of our hearts?

Larry, I want to thank you so very much, drool, for the dyno tests, drool, prop suggestions, drool, fuel mixes, drool, engine setup, drool, drool, etc., my beard is soaking wet and I am getting dehydrated.

C'mon, Larry. Sometimes ya just gotta whiff some of these guys off. Godzilla and I do it all the time. And we *like* each other.

LAST EDITED ON Dec-13-03 AT 02:33 AM (CST)
 
Guess I'm thinned skinned lately, must be all the pain killers I'm on. I'll keep my suck shut on this one and let it go.

Dang just can't keep my suck shut, and Dan I look up to you your my most favorite Stunt Guy (well next to Bart Klapinski) I wana be just like you some day only thinner. I hope you are re-hydrated now.

If I came across that what I do is super special it was never meant that way. Sending a Fox out for rework is a pain and if I can share what I do with someone then I well. Seeing beginners struggle with Fox35 was costing us new flyers back in the early 80's so I started lapping them in and cleaning up the burr's, then I bought a reworked one from a source I won't name and it was so bad I knew I could do it better. I just get frustrated when I get personal e-mails telling me how wrong I am about the testing and they would tell me how to do it if I asked.

When it comes to motors I do my best and if someone doesn't like my product then return it for a full refund. If someone has a problem than I feel really bad but not frustrated. I've only had one customer that ever asked for his money back and he never ran the motor. The only other customer I couldn't get an engine to stay together for was Jerry Silver and after two years of warranty on his motor I gave up and offered his money back (which Jerry wouldn’t take) so I never got thick skinned when dealing with Fox reworks.

Larry

>"Wouldn't you have to add the torque required to spin the
>prop to the reading found on the dyno?"
>
>Well, yes. It's, as the British say-- Oops, we can't say
>here what the British say. It's zero.

Kee-rect. I had to think what idiot thing I said.

I knew where I was going, but I forgot to stop for directions!

LAST EDITED ON Dec-12-03 AT 11:05 PM (CST)
 
>"Wouldn't you have to add the torque required to spin the
>prop to the reading found on the dyno?"
>
>Well, yes. It's, as the British say-- Oops, we can't say
>here what the British say. It's zero.

Or rather, the result of adding the torque you read off the dyno and the torque required to spin the prop would be zero, as the reading off the dyno is exactly the same as the torque needed to turn the prop, just in the opposite direction...

The nice thing about having the dyno is that you don't need a set of calibrated props. And the nice thing about having a set of calibrated props is that you don't need a dyno. But at some point, there has to be a dyno (or torque meter) involved at some point, or you can't HAVE a set of calibrated props... it just doesn't have to be YOUR dyno.

>Thank you Preston, indeed. Called last night, you didn't
>have the foresight to be home at the time.
>
>Will you be at the Swap Meet, John Hall's place, tomorrow?
>
>Dan

WHAT???? I was going to go and I was told it next weekend!

>>Thank you Preston, indeed. Called last night, you didn't
>>have the foresight to be home at the time.
>>
>>Will you be at the Swap Meet, John Hall's place, tomorrow?
>>
>>Dan
>
>WHAT???? I was going to go and I was told it next weekend!

Scott,

Can't you ever take a hint and just let it go?

>>>Thank you Preston, indeed. Called last night, you didn't
>>>have the foresight to be home at the time.
>>>
>>>Will you be at the Swap Meet, John Hall's place, tomorrow?
>>>
>>>Dan
>>
>>WHAT???? I was going to go and I was told it next weekend!
>
>
>Scott,
>
>Can't you ever take a hint and just let it go?
>
>Dan

Scott,

I have reconsidered my position on this, although the entire Skyraiders club will surely be completely irked over my conduct.

Latest issue of Skywriter came in a couple days ago. I am certain the date of Swap Meet is December 13. Might want to check the Skyraider web site maintained by Steve-O, as I am a most unreliable source of information.

And what made you think a Swap Meet might be scheduled less than a week before Christmas?

LEO

Scott(i need younger friends)Riese