RC aircraft dyno
RC aircraft dyno
(OP)
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!
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!





RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
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?
RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
Regards
Pat
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RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
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
RE: RC aircraft dyno
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,
RE: RC aircraft dyno
RE: RC aircraft dyno
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.
RE: RC aircraft dyno
Mike Halloran
Pembroke Pines, FL, USA
RE: RC aircraft dyno
RE: RC aircraft dyno
Cheers
Greg Locock
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RE: RC aircraft dyno
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.
RE: RC aircraft dyno
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
RE: RC aircraft dyno
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: RC aircraft dyno
What I am failing to understand if using the prop as the actual break, maybe you guys can clear it up for me.
Obviously each type of prop will vary the torque readings so how do I know which one is suitable to start the conversions?
Take 3 different props and 3 different rpm readings per engine. This will give me "9 points" of collective data, now I analysed
the data to see which prop offered the highest torque reading from the load cell. Take the highest torque reading and the RPM that it made it at and plug it into the BHP formula? Do I understand this correctly?
Thanks guys.
RE: RC aircraft dyno
I don't think you will be able to achieve much rpm variation, as there is no throttle I can recall on a 2-stroke model engine? All you will be able to do is vary the mixture.
RE: RC aircraft dyno
RE: RC aircraft dyno
Agreed that you need to cool the engine during dyno runs. ... and a typical propeller is the simplest way to do that and provide a load.
Full, fix the throttle in one position, e.g. WOT, and use 3 different props to give you 3 different torque/rpm pairs. Fit that curve. Compute the HP points from that.
The HP peak occurs just a bit above the torque peak because HP = factor x rpm x torque.
Mike Halloran
Pembroke Pines, FL, USA
RE: RC aircraft dyno
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RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
That would be easier if you think it would work.
RE: RC aircraft dyno
Add a second load cell to measure thrust? This will give prop efficiency. And add a blower on the duct, to simulate at-speed performance...
I'd say you might still want to run part-throttle tests, just for the sake of completeness. Next you need a way to measure fuel consumption, too, if you want to say, find the best settings for maximum range or maximum duration flights.
But maybe all those are not big concerns for RC models.
RE: RC aircraft dyno
Thrust can easily be captured as im not concerned about that nor fuel consumption as that isn't an interest for the moment.
Thanks Guys!
RE: RC aircraft dyno
RE: RC aircraft dyno
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: RC aircraft dyno
RE: RC aircraft dyno
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: RC aircraft dyno
RE: RC aircraft dyno
Regards
Pat
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RE: RC aircraft dyno
I would suggest the KISS approach and use some kind of (wide) leather strap over a drum. Add a spring so you can adjust the braking force so you get multiple RPM test points at WOT. With a big enough drum and/or fan, it should stay cool given the test should not take more than a minute or two once you are good at it.
For your torque measurement, you can either incorporate a load-cell, or characterize the brake's torque vs knob turn-age beforehand and just do a sort of chart look-up. Depends on what kind of accuracy you need.
RE: RC aircraft dyno
Get yourself a flywheel off something like a 350ci chevy. Direct drive it from your engine. (Put a nice thick scattershield over it too).
Set WOT until max RPM is reached. Record the RPM every couple ms with a microcontroller reading from some kind of shaft encoder during the ramp-up. Do some math. Instant "inertial" dyno.
RE: RC aircraft dyno
Gas engines.
RE: RC aircraft dyno
RE: RC aircraft dyno
Well obviously you'd need to support the load (whatever it is) on its own bearings at these speeds. Being this is an engineering forum, I'd hope that much is obvious. Is this intended to be developed into a product? I'm assuming not. Have you tried RCGroups? Someone there has probably already done the leg work on this type project. Generally this forum is more aimed at pro-engineering type applications, although people here will cut slack if your topic keeps them entertained enough.
RE: RC aircraft dyno
25% 30cc 16"-18" prop
30% 50cc-60cc 22" -24" prop
38% 100cc-120cc 27"-29" prop
42% 150cc-170cc 30"-33" prop
RE: RC aircraft dyno
Anyways with the flywheel I am afraid that every time the cylinder fires there is an increase of acceleration of moving parts, with a heavy flywheel such as that 350 it will not accelerate that abruptly. The twisting stress on the crankshaft will eventually lead to failure on smaller engines. I know that this is a pro engineering site which is why I came to these forums, if I wanted information from people that don't have a clue what they are talking about I'd post on RCG. If You don't like the thread, don't post or have a MOD close it.
Thanks to the guys who offered comments that lead me in the right direction. I will update you guys on the build as my parts arrive, hopefully this week. :)
RE: RC aircraft dyno
Very well. I have a 72" Suhkoi I was basing my mental guestimates on. That runs a 1.2cu 2-stroke that swings a 16" prop and puts out a measly 2hp or so.
Still, don't discount an inertial setup. It can give you a nice smooth curve over the entire speed range and does away with the "what to do with all this heat?" problem, as well as steering away from expensive load-cells.
RE: RC aircraft dyno
An inertia dyno does not really measure steady state hp. it measures acceleration. Two similar powered engines can have considerably different acceleration due to different inertia within each engine. On engines with all identical weight rotating and reciprocating parts it will serve as a good ranking system.
Regards
Pat
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RE: RC aircraft dyno
The propeller used to absorb the engine's power does not have to be a genuine "flight" propeller. Test "club" propellers are used for ground testing of full-size aero engines - and I have heard of their use on model engines.
http://www.casa.gov.au/scripts/nc.dll?WCMS:OLDASSE...
RE: RC aircraft dyno
Thanks
RE: RC aircraft dyno
Why not just accelerate a big flywheel and then measure the reaction torque and rpm which gives you all the data you need?
I'd watch the comments. You really don't have a soapbox to stand on, considering you're here with an obvious hobbiest question which is against the forum rules.
RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
Do several samples at progressively higher rpms. plot it on a graph, and you can interpolate rpm vs load (HP)
This is how power settings are determined on simple, fixed pitch prop recip powered airplanes. (Turbofans too, for that matter)
regarding torque indicating systems on propeller driven aircraft, A driving/driven helical gear set, driven from the prop gearbox, that moves a piston in response to the thrust loads the gears generate under power. This piston ports, or unports a chamber referenced to engine oil pressure, metering it into "torque pressure" This is read either on a transducer fed electric instrument, or a simple bourdon tube indicator, calibrated in ft/lbs, or % of torque.
There is another system, that measures the angular difference between a driving power shaft, and the driven prop gearbox. Measures the "twist", if you will. It also works by the variable orifice method, ending up with a fluid pressure that varies in a linear fashion with load on the prop.
RE: RC aircraft dyno
Regards
Pat
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RE: RC aircraft dyno
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RE: RC aircraft dyno
The basic formula is as follows;
P=(inertia x N2^2/2 - inertia x N1^2/2)/dt
inertia = inertia of the flywheel. Should include inertia of the motor if the flywheel isn't 20 or 30 times larger.
N2 = final rotating speed
N1 = initial rotating speed
dt = time to go from initial speed to final speed.
As you can see, something to measure the rpm and an accurate clock will give you the power.
Personally, I'm thinking that a hybrid dyno would be easiest in your case. Use your mount to measure torque and the pickup to measure rpm. Connect the engine to a big flywheel of some sort as a load. Get it running just off idle and then open the throttle and start measuring rpm and torque points until you hit max rpm. Of course, some kind of PC board logging the data would make it very simple.
The manufacturers of inertia dyno's to measure the RWHP of a vehicle don't provide any details on their systems so only they know what causes the errors. However, I would suspect an honest owner/operator who uses all the correct info could get accurate results.
RE: RC aircraft dyno
RE: RC aircraft dyno
No having any real clue as to the measuring capability of the equipment the OP is building means it's hard to comment on that as well. If he's rigging up some rather difficult to read gauges then using a number of props is likely the best. If he's rigging up some equipment with better and quicker measuring capabilities then using a flywheel load might be the easiest.
I haven't seen a commercial load dyno that normally tests at steady loads either. Most engine dynos sweep through the test rpm range during the testing.
RE: RC aircraft dyno
On these dynos, light weight internals in the engine make no difference.
On an inertia dyno, I have seen no suitable explanation as to how using light weight components does not change readings and show as more power.
I do accept that the higher the load, the lower the %age difference until a point where it becomes insignificant.
Correction factors are always a risk for fudging the figures no matter what type.
You can also fudge a brake by sudden application of load to bounce the load by inertia effect however this is obvious if you are present and watching.
Unfortunately for dyno operators, a happy customer means a customer with high numbers to brag about rather than accurate numbers. I know some many make "commercial decisions" re the corrections to the reported numbers.
In this case a flywheel should rank engines accurate with a very heavy flywheel. Yes I guess that's a back-flip on the issue.
Gearing can also be used to match flywheel weight to required load and SAFE rpm limit for the flywheel. I would much prefer to see steel rather than cast iron if the wheel is to be spun at high rpm. It could be something as simple as a large truck or tractor wheel mounted on a front hub with a chain drive.
Regards
Pat
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RE: RC aircraft dyno
This is my assembly thus far in a nutshell, I am up for suggestions if anything sounds problematic . As far as applying the load I think using propellers would be the easiest method however it would be nice to adjust the load on the fly.
RE: RC aircraft dyno
I am not sure you really need automotive-type dyno graphs of torque and HP for a model aero-engine.
I think you have to keep in mind that for aero-engines (both full-size and model) things like good mid-range or low RPM torque (and a smooth idle) which are important in a car don't matter as much in a 'plane. Maximum power output and fuel consumption at cruise power (in a full-size engine) are the important features.
RE: RC aircraft dyno
http://www.magtrol.com/motortest/ed_dynamometers.h...
IMHO, this is the way to go if you are serious about developing a small aircraft motor for use in a long endurance uav or other military/commercial application. It may not make sense if you are a hobbyist.
RE: RC aircraft dyno
Perhaps a squirrel cage motor with DC on the poles
Roy
RE: RC aircraft dyno
RE: RC aircraft dyno
RE: RC aircraft dyno
Steady state dynos have their place and are the most widely used. But the inertia dyno will tell you more about how the vehicle will perform in your "real world" applications.
Just depends on what information you need to do what you need done.
Take care, K
RE: RC aircraft dyno
P=(inertia x N2^2/2 - inertia x N1^2/2)/dt
inertia = inertia of the flywheel.
N2 = final rotating speed
N1 = initial rotating speed
dt = time to go from initial speed to final speed.
I got looking at your formula again and I am interested to see how this might work for my application.
Can someone tell me if N1 and N2 are for the engines RPM or the flywheels rpm?
Thanks Guys for all the help, with out you this project would have never got to were it is now.
RE: RC aircraft dyno
RE: RC aircraft dyno
The inertia would have to be translated through any speed changing devices (ratio^2) if you want to use a different speed measurement than the flywheel speed.
RE: RC aircraft dyno
What you want is a rpm vs power curve. You only need the instantaneous torque reaction and rpm recorded together. It doesn't matter much about the flywheel mass except that the reading will be smoother with a heavier flywheel (geared or not doesn't matter) that will be slower with more readings per rpm. The torque reaction is against ALL inertial mass, flywheel plus internal rotational inertia.
What am I missing guys??
RE: RC aircraft dyno
I don't think you missed anything.
Torque reaction against the load is the best gauge. A snapshot of torque reaction vs rpm gives power at those rpm.
Regards
Pat
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RE: RC aircraft dyno
You typically count pulses and calculate rpm, so your rpm number is already the average rpm over an interval. How can this be right but calculating the power over an interval be wrong.
The only difference is that measuring torque will account for losses in the dyno, assuming you measure torque accurately enough.
RE: RC aircraft dyno
RE: RC aircraft dyno
Regards
Pat
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RE: RC aircraft dyno
Even industrial-strength dynos are traditionally back-to-back comparative tools. Just needs to be consistent with itself.
RE: RC aircraft dyno
RE: RC aircraft dyno
Listen, you can do it either way.
Measure force and pulses and calculate rpm and torque and use that to calculate power.
or
Find the inertia of the flywheel and then count pulses and calculate rpm and power and use that to calculate torque.
Both require an accurate time reference to calculate the rpm from the pulses and either will work to give data.
RE: RC aircraft dyno
Regards
Pat
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RE: RC aircraft dyno
http://www.dtec.net.au/Inertia%20Dyno%20Design%20G...