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[Motorman]

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[Tim Wescott]

Dunno -- have you seen this page on measuring horsepower?

[Tim Wescott]

Do you want to measure horsepower, or do you want to match your results to Peter Chinn's?

[Steve Helmick]

PGF Chinn used the kalibrated (sic) Kavan propeller set. Not sure what tacho he used, but suspect it was a Smith's analog direct shaft drive unit. I had a shaft drive tach many years ago, and decided it was crap when I found it would stop a good TD .049 in its tracks. Technology rolls onward.  Steve

[katana]

Dunno -- have you seen this page on measuring horsepower?

It was amusing looking at that page and the 'why not' notes of each technique especially the electromechanical and water brakes considering these are now the defacto go-to's for large scale dyno's. I have to admit engineering a small enough water brake for a 1cc engine would be tricky but see enormous scope for electromech. small scale dynos - they are virtually friction free so no losses and feed back braking can allow some serious power measurement.
For example motorcycle chassis dynos were plain inertia types limited to 200 odd hp as more power accelerated the drum too fast, then eddy current braking was added allowing these dyno's now to measure in excess of a 1000hp. The electronics behind them are well understood so i'd surmise these are liable to be the most accurate  / reliable methods currently available?

[Larry Renger]

Power is torque times rpm. We have cheap tach’s that are incredibly accurate, and setting up a test stand to measure torque isn’t rocket brain surgery.

Most of the time, all we need is comparisons between different motors with the same prop.

[BOB ALLAN]

Peter Chinn commenced testing engines for the British magazine “Model Aircraft” in about 1949. The earliest test by Chinn that I have is #5 in the July 1949 issue. Previously, these tests were conducted by L. H. Sparey, and he used a "stroboscope" to check an engines RPM. By 1951 however, a nifty hand held tach made by Smiths Instruments was available, reading from 0 to 20,000 RPM. For measuring torque, Sparey used a home made “torque reaction balance” and a photo of this device can be seen on the heading of this article here –

http://sceptreflight.com/Model%20Engine%20Tests/Buzzard%202.8.html

It’s reasonable to assume that Chinn also would have used some sort of similar workshop made device, as there would have been no commercially made units that small. In his tests, Chinn often refers to a “torque-reaction dynamometer” but doesn’t elaborate on the details.
In an article published in August 1952, Chinn states that “B.H.P. or brake-horsepower, is the power developed by an engine as measured with suitable apparatus, such as a friction brake or reaction dynamometer. B.H.P. is the difference between the indicated horsepower (i.h.p.) or power developed within the engine before accounting for mechanical losses, and the f.h.p., or frictional-horsepower, and is thus the actual power available at the crankshaft.”
By mid 1954, the other great British tester of model engines (Ron Warring) was using an eddy-current dynamometer, but as it says in the article (link below) Chinn and Warring held their cards close to their chest, and in fact, disagreed on some aspects of calculating output.

http://www.modelenginenews.org/techniques/testing.html

[Brett Buck]

Power is torque times rpm. We have cheap tach’s that are incredibly accurate, and setting up a test stand to measure torque isn’t rocket brain surgery.

Most of the time, all we need is comparisons between different motors with the same prop.

   I haven't seen any cheap tachs that are accurate and reliable, although accuracy doesn't have to be all that good. Most of the cheapies seem OK until you actually try to use them at the field. You certainly don't need it to be better than about 100 RPM (as opposed to the approximately 5 ppm/0.0022 RPM at 11000 claimed by the original TNC) but when they are frequently miscounting and getting errors in the thousands of RPM, that's a real problem.

   Also, one of the issues that I have seen with these measurement is *exactly* the notion that you don't want or care about real numbers, just relative performance. In some cases you might just want to compare RPM, but if you don't also measure the torque accurately or in real units, you can make no comparisons aside from the one you  do back-to-back, and certainly cannot determine that the data you took on one day/time is in any way relevant beyond that. You can't build up a body of knowledge that way, and you certainly aren't going to make any generally useful conclusions on one day's worth of testing.

    Brett

[Larry Renger]

My Electrical Engineer brother (Masters degree, Caltech)  built me a tach checker one year for a birthday present. It uses a crystal controlled circuit to flash an LED. It has several ranges up to 60K rpm.  All but two tachs I have checked were within 5%. The only two that were farther out were a TNC at about 10% and a Heathkit that was 8000 rpm high at 21,000 (the owner, who shall remain nameless, was always bragging about the astounding rpm his engines turned  ).

To get good readings from my tach, I added a "snoot" painted black on the inside and added a lens that focuses directly on the detector. This puppy will read reliably at about a foot away from the prop!

[Lyle Spiegel]

Is anyone familiar with this torque stand? Don't know if it is still available or if it is something to consider.

AMERICAN HOBBY PRODUCTS
12 West Hill Circle, Reading, MA 01867
Dyna Torque Test Stands to measure torque and HP on engines from .049 to .90 - $129.95
Thrust Finder to measure propeller thrust in pounds and ounces up to 15# for engines from .10 to .90 $124.00 Phone: 781-944-8316 Fax: 781 944-3585

[Lyle Spiegel]

Google search showed up Business owner  of American Hobby Products is
 Gilbert Greenberg

[Ara Dedekian]

        Gil Greenburg passed away about five or six years ago along with American Hobby Products. Gil had a woodshop in his basement near Boston where he made his test stands and dynos. He had some impressive non-modeling customers using the dynamometer including, I seem to recall, MIT and the Israeli military.

        Ara

[Brett Buck]

My Electrical Engineer brother (Masters degree, Caltech)  built me a tach checker one year for a birthday present.

   Right, and all of my cheap tachometers would work fine when I pointed them at calibration sources. But none of them reliably worked at the field.

     Brett

[RandySmith]

Is anyone familiar with this torque stand? Don't know if it is still available or if it is something to consider.

AMERICAN HOBBY PRODUCTS
12 West Hill Circle, Reading, MA 01867
Dyna Torque Test Stands to measure torque and HP on engines from .049 to .90 - $129.95
Thrust Finder to measure propeller thrust in pounds and ounces up to 15# for engines from .10 to .90 $124.00 Phone: 781-944-8316 Fax: 781 944-3585

Yes  I have sold many of them,  I think I still have  both on stock

Randy

[Larry Renger]

That’s why I modified my tach to be a more direct detector. The broad reception of a raw detector is too susceptible to outside stuff, and insensitive to what you want to detect. The tach is not at fault, it is the way the signal is detected.

A cheap lens and snoot make all the difference! It would add very little to the cost and, thus, the price, to add this to a production tach. And it is easy enough for a modeler to make these modifications. Lens Crafters can make a lens if you don’t have a cheap plastic magnifier to cut down, or hack up a set of dollar store reading glasses.

Not rocket surgery!

[Brett Buck]

That’s why I modified my tach to be a more direct detector. The broad reception of a raw detector is too susceptible to outside stuff, and insensitive to what you want to detect. The tach is not at fault, it is the way the signal is detected.

A cheap lens and snoot make all the difference! It would add very little to the cost and, thus, the price, to add this to a production tach. And it is easy enough for a modeler to make these modifications. Lens Crafters can make a lens if you don’t have a cheap plastic magnifier to cut down, or hack up a set of dollar store reading glasses.

        I think most of what is needed on the optical side is a baffle to avoid picking up glint, reflections, or shadows. That was my fix for the Fromeco, that they later attempted to replicate - by burying the sensor inside a SHINY, MIRROR-FINISH metal tube!  The TNC and Fromeco sensor already had a lens.
 
    The other problem we found with the cheapies is that the temperature seemed to cause the reference to drift all over the place, no matter how you calibrated it in the cool of your living room. I convinced myself by leaving it in the freezer for a few minutes, calibrating it, then putting it in the sun, and checking it. 3600 rpm cold was 2900 hot. That's ~20% error and that was not the worst case, the difference between 11,000 and 9000 rpm, meaning *utterly useless* for even relative RPM checks from morning to afternoon.

     Brett