RC aircraft dyno

[FullSpool]

I was looking at building a hydraulic brake dyno for rc gas aircraft, the engines are 2 stroke with a HP not exceeding 12-13. I am trying to figure out
what I want to use as my brake and was exploring the possibilities of using turbo parts as the exhaust wheel/shaft and housing would make a decent starting point.
Do you think I would be able to exert enough load on the engine to take torque measurements with this configuration or should I look into a mass produced toroidal?

Thanks!

 

[ivymike]

how many rpm?

 

[FullSpool]

Smaller engines around 2-3hp see up to 8500 larger engines see 7k usually.

 

[ivymike]

hm. That's 13.2 N-m, right?

I have no idea how well a turbo would work as a water pump. It would definitely move water, but I would worry that it would erode or otherwise fail. My first thought was that you'd be better off with a hydraulic pump or (regular) water pump, but you probably won't find one big enough that you can direct-drive at that speed.

I imagine you'd want to measure torque (as force) at the corner of an engine platform while driving a bench-mounted pump of some sort. Maybe you could use a belt drive for speed reduction?

 

[FullSpool]

I would use Hydraulic fluid instead of water if I go the turbo route so that should take care of the corrosion issue. If I use the compressor wheel I can use water with a custom aluminium housing as the compressor wheel is AL however if I can use part of the cartridge and the exhaust wheel the assembly would be much easier to construct.

 

[ivymike]

I said erosion...I didn't mean corrosion. I was thinking about bits of metal being removed by localized cavitation or other processes (high velocity over the surface) . Water and oil have vastly different viscosity than air, so I'm suspicious that the geometry won't be appropriate.

 

[FullSpool]

I totally spazzed out on that I am sorry LoL.... Long day at work, I am looking for a different pump but having a hard time finding anything that I feel would be an acceptable to act as a load control valve. I had the old used t70 turbo laying around the shop so thats why I thought about using it.

 

[FullSpool]

I totally spazzed out on that I am sorry LoL.... Long day at work, I am looking for a different pump but having a hard time finding anything that I feel would be acceptable to act as a load control valve. I had the old used t70 turbo laying around the shop so thats why I thought about using it.

 

[patprimmer]

Any load can work. It does not have to be pump that is pumping liquid. A variable fan pumping air will do it, a clutch pack from a small motor cycle or even moped could do it so long as the transmission fluid was circulated and kept at reasonable temperatures.

Regards
Pat
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[FullSpool]

ummmmmm....... I suppose I could measure the torque via load cell that prop exerts. Im just not sure how much torque can be measured with that method or if it would give a stable data.

 

[ivymike]

You would still measure at the engine support, I think

 

[berkshire]

Aeromodeller magazine in the UK., used to publish plans for an engine dyno, that used a beam balance reacting the engine against a known fan.
This was for much smaller engines than the one you are testing. But it may be an idea worth looking into.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[BrianGar]

Has been covered before a few times, granted on a larger scale, but a little bit of 'adjusting' could bring into your range,

http://www.eng-tips.com/viewthread.cfm?qid=84432

http://www.eng-tips.com/viewthread.cfm?qid=125098

Further searches will provide more info, use key words, water brake, engine dyno, etc...

Brian,

 

[BigClive]

Unless I am mistaken - I think a lot of propeller-driven 'planes do actually have a load cell in the engine mounts to give an indication whether the engine is producing full power.

 

[LionelHutz]

You could find an ~30hp 3-phase motor and feed DC into 2 of the leads to get a brake. It can't be run continuously because it would overheat but it would give you braking for long enough to do the tests you'd likely want.

You can also accelerate a flywheel and count pulses from teeth on the weight using an accurate clock. Figure out the inertia of the flywheel and you can calculate the torque and power curves.

 

[MikeHalloran]

I'm failing to understand how an instrumented stationary engine mount, and a selection of propellers in the range of interest, could not give you all the data of practical significance.



Mike Halloran
Pembroke Pines, FL, USA

 

[ivymike]

I was thinking that perhaps he feels safer without spinning blades, but a guard could fix that.

 

[GregLocock]

A 3 hp fan will be generating a fair old draft.

Cheers

Greg Locock


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[FullSpool]

Wouldn't the wind conditions affect the prop readings? How many props would it take to get reliable data? So for each size engine I would need X amount of props, that could get expensive quick.

Can someone explain to me how I would collect that data to usable HP ? Thanks for all the help thus far guys, I really do appreciate it.

 

[MikeHalloran]

You get HP by measuring rpm and torque and doing a little math.
RPM can come from a photo tach aimed at the prop.
Torque can come from an engine mount that is free to rotate except for where it's restrained by a load cell or a scale.

I.e., you don't have to measure the torque between the engine and the prop, you just measure the torque that's required at the engine mount to keep the mount and the engine from rotating.


Mike Halloran
Pembroke Pines, FL, USA