dckrsn

Has anyone else seen this?

http://www.lib.umd.edu/drum/bitstrea...i-umd-4031.pdf

gkamysz

My Feedback: (19)

Wow, that's a great find.

build light

Ditto! One hundred and forty five pages!!!!!! (should there be 145 exclamation points?)
Never seen this one before.

Robert

DeviousDave

Or, at least it would be for me if they had tested it past 18k.... Unless I missed something (and I scrolled thru the pertinent parts) they extrapolated their data for higher RPM power. I sure wish I knew where that power was made so I know when to stop carving on props.....

Make you wonder if they ever bothered to run the darn thing with a prop on it. Obviously, if your test equipment drags what you are measuring down there is a problem..

ffkiwi

'Aeromodeller' tested the TD 010 in October 1961-and produced a full BHP curve-they credited the engine with 0.028 BHP @ 32,000 rpm. IIRC 'Model Aircraft' the other UK magazine, obtained 0.031-so the figures were consistent. Given that the two respective testers were respectively Ron Warring and Peter Chinn-with decades of engine experience behind them, their competence is beyond question.
Also suggests that Cox did know what they were doing when they designed the 010 prop-if it ran 27,000 on the ground(the figures given in the 010 brochure)-allowing for a 10% unload in the air would put the engine bang on its BHP peak in the air!

Makes you wonder what those university idiots were a) trying to demonstate, and b) thought they had achieved. Makes as much sense as rating car engines on the BHP produced when idling!

ChrisM
'ffkiwi'

gkamysz

My Feedback: (19)

It's not really about the HP curve to me. There were several sources cited that were valuable to me. I'm working on a dyno for model engines and this, whether done correctly or incorrectly, is valuable. I can decipher validity just like anyone else can. I have a university paper saying an OS FS-30 makes about 80W output at the crank. We as modelers know very well it makes 300W+. I don't know where they went wrong, just that they are wrong. The FS-30 experiment was not nearly as well documented as this one. I'll have to agree that they did a poor job determining what was needed to accurately measure the performance of the .010. Having historical data on the power output, they should have easily determined the expected torque output and realized very low parasitic drag would be necessary in the dyno. Why they accepted the data set they collected and did not make more attempts to validate it against existing data, I don't know. The paper was probably due and there was no time left.

DeviousDave

Greg: I would think that a slotless brushless motor as a generator might be an avenue for a low torque motor dyno.. Any ideas?

Silvaire

My Feedback: (50)

A possible way to measure engine output might be to get an RPM reading for a particular prop, and then install the same prop on an electric motor. You could then adjust the voltage to attain the same RPM as the engine. Based on the measured voltage and current (and including some sort of factor of the motor's efficiency at that approximate power level), you could then calculate the power output of the engine.

With something as small as a Cox .010, the power losses with any sort of a physical coupling (with even the slightest misalignment which would surely be present) would likely be a significant percentage of the engine's output.

On the subject of measuring power, I remember once seeing a set of special propellers made specifically for measuring engine power output. Along with the propellers there was a set of tables to correlate RPM to power for each prop in the series.

Arlen

gkamysz

My Feedback: (19)

I think a coreless brushed motor would have been most appropriate for the .010. A brushless motor would have been fine also and the paper noted that would be a better choice. I'm surprised no flywheel was used on the crank. I also surprised they didn't attempt to run the engine on the dyno with the prop.

I saw one of those machined load prop sets on thebay a year or two ago. I shouldn't have passed them up.

Running a prop on an electric motor to determine power output is not going to be any more accurate than what they did. The biggest problem is determining the efficiency of the motor. In reality the motor efficiency must be tested on a dyno so that puts you back to square one.

I was expecting to see some mention of the AE 0.1 diesel in there. I guess they really aren't that common enough to be considered a production engine.