Inertial Mass Dynamometer

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Hot Wings

Grumpy Cynic
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Easy to build and operate but limited in the amount of Hp they can be used for due to needing too much mass to be practical (my opinion only). The ones I built were for guys building karts or RC units. Used an ABS sensor for RPM and converted the pulses to digital that was logged with a basic program and then transferred to an excel sheet. There are easier ways to do it but back then that was what got the job done.

TDK Motorsports Inertia Dyno Testing

Good 'how to' if you want to try your hand at building one. For aircraft I'd suggest a simple dyno like WW uses for Corvairs. Torque, HP and Thrust Testing at www.FlyCorvair.com

PS: if you put a brake on an inertia dyno make sure it's well anchored to the floor - even a small one :emb:
 

parkert51

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Thanks for the input, I am currently paying someone to do my dyno work. But setting up this engine shop necessitates we have our own dyno. And I want the accuracy an inertial mass can produce throughout the rpm range....
 

wsimpso1

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This gadget works fine for determining engine output in acceleration, but it has some limitations.

First and foremost, you can not do much in the way of endurance tests - the gadget relies upon its inertia to provide resistence, so you do accels, then decels...

Second is that a 12 second accel run on a 150 hp engine will require 10 times as much inertia as for a 15 hp engine. Same diameter as the one pictured in the article, but 10 times as thick, or twice the diameter and 2.5 times as thick...

Third, since it is only providing load during relatively short accels, it could be tough to program spark timing, mixture, and wastegates, although it should be pretty good for confirming the settings. Having a club prop or three to run on it in parallel with the inertia might be the ticket...

Billski
 

autoreply

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No braking set-up? I've always though that's about the simplest way to measure torque (and hp via rpm), because you only need to measure force?
 

parkert51

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I will be using a disc system to slow the drum. From what I understand this is the most accurate type dyno and you get accurate numbers throughout the run from idle to WOT.....
 

Hot Wings

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While these are good for raw Hp curves, as Wsimpso1 pointed out, they are pretty useless for development or getting other numbers like specific fuel consumption, cylinder head temps at various power settings, and other numbers that need to be collected over time.

If you want to simulate installed condition or run this engine through the ASTM or JAR 22 tests you will need a more conventional dyno. In the Hp range you're looking at I'd be looking for an old Stuska, or equivalent. They pop up in some strange places for pretty reasonable prices.

Inertia dynos are great for low hp engines when all you need to do is test a few changes and compare them to a baseline. Aside from simplicity for the DIY types the speed with which you collect the data over the entire rpm range is the main attraction for these.
 

Kristoffon

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I work with dynos and second what others said.

Also, a 200lb drum will be worthless. Start thinking about 10 times that.

For testing engines it's not a good idea. Its simplicity is only a plus when testing cars, IOW, chassis dynos.

Seek an used water brake type dyno. They're the cheapest and easiest to set up - can be made to work without any electronics.
 

parkert51

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Golconda, Il, usa
I work with dynos and second what others said.

Also, a 200lb drum will be worthless. Start thinking about 10 times that.

For testing engines it's not a good idea. Its simplicity is only a plus when testing cars, IOW, chassis dynos.

Seek an used water brake type dyno. They're the cheapest and easiest to set up - can be made to work without any electronics.

Hmmmm, I have seen several in the 200lb range. In fact the dyno we have been using is in that same range. There are plans with working dynos in that range...
 
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