Paul et al,


The recent TTC engine run postings, turbo compound threads, and my own
efforts have started me thinking about an engine test stand and the
features/performance it should demonstrate.


Obviously a control/instrument panel would incorporate some of the basic parameters like...


   oil pressure

   oil temp

   engine (coolant) temp

   exhaust temp

   manifold pressure

   air/fuel ratio

   rpm

   throttle position

   fuel flow/totalizer

   time

   hobbs


   throttle

   mixture

   ignition



What other controls/measurements should be incorporated on a basic level?


What about on a more advanced, special situation level (e.g. waste gate position when testing turbos)?


Should it be easily transportable?


And what about safety features (fire extinguishers, kill switches, etc.)? What do you suggested?


Ideally a data acquisition and control system would collect, log, and display the data. I use National Instruments LabVIEW software and hardware (along with other manufacturers like Omega, Interface, Banner, etc.) for such at work. But it looks like other solutions are available through some of the systems discussed in postings here. Personally I'd prefer to use something available and proven in order to get to the engine testing instead of debugging I/O systems (even though I do that a lot with NI LabVIEW!!). What is available and what are your thoughts on that?


There are many automotive type test stands out there for basic run in testing. But I would expect an aircraft test stand to measure torque and thrust for a prop generated load. Not too many (none???) out there that I saw, but please let me know about any that you know of.


Is there any sort of "standard" test prop that would be suited for initial or comparative testing?


A DIY stand seems more practical from a cost and achieving desired capability standpoint.


Therefore, what would be a good upper limit of each value to start sizing a stand?


   Max engine torque = ?

   Max engine thrust = ?


Obviously the answers to my questions are very subjective with many variables and personal preferences that could affect the answers. At this point I'm just looking for some rough initial numbers for the upper limits and capabilities that "amateur home builder" folks like us might like to see a stand incorporate.


I think the TTC engine might be representative of such performance limits? Yes? No?


And what are the thrust and torque goals for TTC?


Is anyone else interested in building such a stand?


So put on your thinking caps, let your imagination run wild, and let me now your thoughts on this matter.


Looking forward to your responses!


Warm Regards to All,

Brad Chubb



Be careful optimizing thrust. The best static thrust is not the best prop pitch for an
airplane.


Here are some prop dyno ideas.



Airplanes fly on HP.


HP = Torque  X RPM / 5252


If you measure the torque and of course the RPM you know the HP.


An aircraft engine will increase the RPM until the prop torque requirements are met.


Paul Lamar



Paul,

Great answers and information as always. Thanks!

At work part of what I do is basically in house designed "dynos" and testing for string trimmers so some analogies are there.

By the way everyone else, please note that Paul's formula requires torque to have units of "ft. lbs."

And yes, even though an engine is operating (dynamic) system it will settle in to operate a dynamic equilibrium of motor torque = blade torque = (hopefully) reactive mount torque at any given RPM. Prop torque will basically be a function of geometry and atmospheric properties. For a given motor, motor torque will basically be a function of fuel/air volume and ratio (and what else?). Give the motor more fuel/air in a favorable ratio and RPM will increase until the increased motor toque is balanced by the prop torque.

But how do we explain increasing the equilibrium RPM when the torque curve goes flat? Is that where a variable pitch prop is reconfigured to produce the same torque at a higher RPM? What a bout a fixed pitch prop? Do we reach a maximum RPM when the torque goes flat even if the engine is not at max. possible RPM? I don't have such concerns with string trimmers!!!

I'm probably opening a very big and deep can of worms, but what do you mean by stating "Be careful optimizing thrust. The best static thrust is not the best prop pitch for an
airplane." Some more insight on that point would be useful. I could assume that to mean many different things, most probably wrong. I'm sure I could dig back into my aerospace engineering propulsion 101 books and notes and find that but that would be an even bigger messier can of worms to open!! Is it merely because static trust is not the same as thrust in flight? So who want's to build a wind tunnel to optimize prop/engine combinations (http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1066&context=aerosp and http://cecs.wright.edu/~sthomas/aronsconferencepaper.pdf for two examples)?

My first job out of college was 4 years as test, operations, and project engineer at Calspan in the 8 ft. transonic wind tunnel. Cool stuff and the greatest people, but Buffalo NY was not my cup of tea.

The addition of the vanes is an interesting insight. It would be very interesting to test the same combination with and without vanes and quantify the difference.

Regards,
Brad Chubb

You have it on the variable pitch.
Actually  ground adjustable is adequate as the rotary powered airplane usually have an excess
amount of power for take off.

Set the pitch for best cruise.

Paul Lamar

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