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Power measurement

I-TERA

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Hello gentlemen,
I imagined measuring the power delivered by the engine using the weight variation between the engine off and the engine running measured on the two main wheels (taildragger).
I don't know how relevant the aerodynamic forces on the wings and empennage causing additional torques might be.
The symmetrical traction components should be similar on the two wheels but some difference is certainly produced by the slightly misaligned orientation of the engine with respect to the fuselage.
Has anyone done any measurements or ruled out this possibility?
Claudio
 
My goal was a simple way to measure the power output of the engine, nothing to do with prop efficiency or thrust.
The instantaneous power (W) is the torque (Nm) multiplied by the rotation speed (rev/s). Test benches usually have load cells that measure torque. Scales are compression load cells. I imagined applying different static torques to the propeller shaft and recording the weight variations indicated by the scales installed under the main wheels ( taildragger) in order to obtain an applied-torque versus wheel weight-difference graph. With the engine running, once the rotation speed is known, the instantaneous power is obtained by deriving the torque generated from the graph, without dismount the engine and putting it on a test bench. Perhaps the method introduces excessive errors and I would have liked to know if others have already tried it.
 
Talking shaft output power only

Regarding PP output, you can only directly measure the related torque. The other associated output parameters are derived. If I am understanding your original post correctly, there are so many other parameters that filtering out the related effects and the compounding error/uncertainty that I don’t know if the results would be truly useful. Let me know if I’m misunderstanding you.
 
Could some sort of twist/torque device installed between the engine and the propeller? I gather such a device currently doesn't exist and would have to be designed. Is it even a possibility?

I'm thinking of turboprops that set power by propeller torque and RPM. Doing the math on horsepower is really quite easy. Those torque measuring devices are done via the gear box, or measuring twist on a really long power turbine shaft. Not a whole lot of room between the crank and a prop. No gear box either.
 
I remember reading some years ago that some Reno racers were experimenting with strain gauge sensors that were being used to determine torque output while flying. I don't know if that is a thing anymore.
 
Not uncommon on turbo shaft PPs. Beats the older method of measuring radial stain via displacement to a reference shaft IMO. Real-time access to knowing your max torque is key to getting the most out of your prop/PP combo though many disagree with me here.
 
I think you'll find that the readings using load cells under each gear leg will be pretty noisy.

As Ralph said, TECAT made a strain gauge system for the prop shaft which included telemetry. Much more stable readings. https://tecatperformance.com/
 
I think you'll find that the readings using load cells under each gear leg will be pretty noisy.

As Ralph said, TECAT made a strain gauge system for the prop shaft which included telemetry. Much more stable readings. https://tecatperformance.com/

I don't see a price for this unit... so their claims of "low cost" probably means "low cost for professional race car teams".

But I'd think we could engineer something...
1) Strain gauges (very inexpensive)
2) Gauge amplifier / interface $8 https://www.elecrow.com/strain-gauge-module-p-735.html
3) Arduino around $20
4) Bluetooth module around $10
5) Small Battery

And a bit of software to take the reading and provide it to the bluetooth

And a bit of software for a tablet/pc/whatever to read the bluetooth data.
Could also do on WiFi.

A latching reed switch can allow turning the unit on and off using a magnet. So this could be installed into the composite spinner and activated by passing a magnet near the latching reed...

I've done Arduino programming... anyone else interested?
 
I doubt if TECAT is pocket change, especially with the long range telemetry part.

Seems like you have the skills to build your own short range system. Excellent.

I'd be interested to see what you come up with and the numbers you see.

Cool project. :cool:
 
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