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Where do Stats come from?

Old 04-03-2013, 01:21 PM
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James c harrell
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Default Where do Stats come from?

Just curious as to where the people that put the stats out on engines get their facts from and whether there are any set standards for them. You know, the engine HP or the RPM and such. I have seen alot of "Brags" on a engines HP or top RPM, even the ones listed on here if you look them up that I just can't believe. Example: I have a O.S. 46FX with a pipe that I think turns pretty hard, and it is fast, but it can only do about 15500. That's on a pipe. The RCU listing on it says it has a top RPM of 17000. Seen alot of engines listed with HP listings that are just un-real. What gives?
Old 04-03-2013, 04:28 PM
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Default RE: Where do Stats come from?

If someone says they are doing a certain rpm on a certain prop. it is likely right unless they are just bragging or liars. A manufacturer may give a hp figure. I would not believe that. If they say 2,000 to 18,000 rpm. it means they think that is the range it shoud be. A peak figure may be say 16,000 where they may have calculated the peak hp from. The 'Powerband' you would want to pick your prop. for. I would think that in this case not going over the 18,000 rpm would be wise. A motor would pick up 1000 to 3000 rpm in the air too depending on the pitch, and the plane etc. Pipes can really confuse numbers too with different lengths and props.
Old 04-03-2013, 05:48 PM
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Default RE: Where do Stats come from?

The stats they publish need to be read carefully. Usually horsepower goes hand in hand with peak RPMs. So they run a smaller not very useful prop to get the RPMs up there and then calculate the horsepower based on the prop size, pitch and RPM.  But you may not know what fuel they used, brand of propeller, prop size and pitch, temperature, humidity, altitude and barometric pressure either. Plus the OEM muffler may be terribly restrictive so they run no muffler or use something else like a tuned muffler or a tuned pipe or a tuned straight tube too.

Many of the real world numbers come from guys running a certain more useful size prop at lower RPMs where the engine is within its normal power band. Thus the power is lower as is the RPMs. Plus using the stock OEM muffler is guaranteed to cause the RPMs to be lower.

Peak RPMs might be achievable, but the engine won't develop any real world useful power like that, and worse it usually will not live long at those speeds either.

For example, years ago they had a big .60 engine shootout performance review article using ten different .60 engines. They used a 11x6 prop on all of the engines and ran 20% or 25% nitromethane fuel in all but one of the engines. But at the time, the smallest useable prop was a 11x7 or 11x8 prop on those engines. The planes of that period would have all flown like crap if you used a 11x6 prop on a .60 engine on them.


Old 04-03-2013, 08:44 PM
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Default RE: Where do Stats come from?



No standards for model engines as with automobiles. They can make up any number they want.

Old 04-04-2013, 03:16 AM
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Default RE: Where do Stats come from?

The numbers to trust are the numbers guys like Dub Jett publish. OR the RCU tach forum is a other good place to find real world rpm figures.

Anything numbers the manufacturer puts out is bogus 99% of the time. Also, the rpm range the mfg puts on the engine means little as well. A tuned muffler can push an engine over the 'max' rpm easily. Doesn't hurt the engine unless you're trying to hit 20k on a 16k engine. I degree all of my engines to get a sense of where the powerband should be and prop them accordingly.

Old 04-04-2013, 06:46 AM
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Default RE: Where do Stats come from?

With most model engines, the RPM range is the range of RPM where the engine has been run with some propeller. The upper and lower ends of the range may not have been achieved with the same propeller. The top-end is usually the same as the "red line" RPM you'd have on a motorcycle or automobile engine. Run very long at or close to that RPM and your engine won't last.

If you can achieve the lowest RPM reliably, you won't be able to get the top-end RPM with the same setup. The same for the top-end RPM. You can't have both at the same time.

Horsepower is a calculated number based upon torque and RPM. You run the engine on a torque stand and measure the torque at various RPM. You have to use different loads to achieve the different RPM levels. You plot torque versus RPM. Then you calculate the horsepower at the different RPM levels. Plot the curve to see where the peak lies.

The formula for power is:

Hp = (Torque x RPM) / 5252
Old 04-04-2013, 08:03 PM
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Roary m
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Default RE: Where do Stats come from?

I used to trust the published stats until MAN did a 60 size engine shootout, sometime in the 90's and the no name brands came out on top. ST and OS also had identical numbers which I found interesting.

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