16 Year Old Research Project

[smed]

I am a sixteen-year old high school student and am currently working on a two-year research project on propellers. I just found this forum, and hoped that you guys would be able to help me.
I plan to test the efficiencies of propellers using several different methods. I would also like to analyze studies on the Theodorsen-Betz propeller research by building a Theodorsen-Betz propeller according to minimum induced drag theory.
At first, I was interested in performing tests on indoor propellers. In time though, I realized that performing tests on outdoor propellers would be much more practical, especially considering the scale of my research. I learned that there is little, if any information on drag at such low Reynolds numbers, and that there are many more applications for research on outdoor-type propellers. I also was made aware that my computer program does not yield accurate results at such low Reynolds numbers, however it does for the Reynolds numbers of outdoor model airplanes.
I have developed the following plan for experimentation with my mentor, a superb indoor and outdoor modeler. I would like to conduct outdoor flying tests, using an all-round A.R.F. fitted with propellers of the same diameter but of all different designs (including a Theodorsen-Betz propeller, which I shall build). Power will be supplied by three different engines: a high torque/long stroke engine, a high rpm/low torque engine, and a standard-task engine. I will then find the best combination to evaluate the performance of each propeller under certain tasks. The tasks will be acceleration from a standstill, shortest distance over an obstacle, and highest overall speed. All of the data will be carefully measured and the wind velocity will be recorded. Overall, I hope to find the most efficient propeller for a certain task, and maybe even find a correlation between the propellers.
In addition to the flying tests, I am considering conducting tests with a wind tunnel, homemade or not.
Does this sound like a viable research plan? Do you know of any previous work in this field? I would really appreciate any help you can give me.

Thanks in advance

[Peter Young]

Adam

I can't help - sorry - but you might also want to try the Modelling Science forum in electric flight. The e-zone has a lot more traffic (although this forum is growing - it's amazing what a free gift will do).

Peter

[Don Sims]

Good luck on the project! I'm going to copy this to modeling science since we haven't gotten any replies here.
Don

[Gerald]

Adam, that sounds like a fairly advanced research project for a 16 year old :)!

Propeller science is not widely understood, and probably even less applied by model propeller manufacturers.

I'm not familiar with the Theodorsen-Betz propeller that you mentioned. Does it have any distinct feature or is it simply a propeller design which has been optimized through the application of Theodorsen's and Betz's research?

Though you are planning to use reciprocating engines in your study, have you thought about including electric power? You will find that there are many aspects of propeller design that are unique to each.

For example, the props for engine powered models are designed to stand up to stressful engine vibrations. This reduces the aerodynamic efficiency since it is a compromise for strength. Some of Theodorsen's work was evidently directed at studying the effect of vibration in airfoils which would not only include engine induced vibrations but also resonant effects.

In electric powered craft, the vibration of the motors is almost insignificant and propeller designers can apply much more efficient airfoils suited to a particular application. Of course 'flutter' or resonant type vibrations can still occur.

It sounds like much of your research will involve experimental testing, so how does that inhibit you from studying 'indoor' propellers? Do you also plan to undertake a theoretical analysis of the different propeller's behavior? If so, then I can understand that the mathematics will be more manageable for larger conventional propeller designs which are likely what your computer program is capable of handling.

I suspect that the very small or thin airfoils used in 'indoor' flight may require analysis that takes the boundary layer conditions into much greater consideration closer to the 'molecular' level.

I have not really studied propellers but know a bit about the analysis of airflow over small surfaces which are not well characterized by use of Reynolds numbers. I used to work with the design of disk drive read/write heads which have to 'fly' over the surface of the disk at 'micro-scale' distances. In these cases it was a study to combine the application of Reynolds numbers with the use of Boltzmann's mathematics to describe the boundary layer conditions at the molecular level. This was being applied to relatively simple structure shapes and was quite difficult about 18 years ago when I was last involved in it. Perhaps the present day computers are more suited to the task of applying it to a complex surface such as a propeller.

Perhaps you should contact some of the model propeller manufacturers such as APC for example. It seems that every one of their propellers is different and they claim to use advanced CAD modeling techniques to derive their propeller profiles. http://www.apcprop.com/Engineering/engineering.html

Good luck!

[Sparky Paul]

"The tasks will be acceleration from a standstill, shortest distance over an obstacle, and highest overall speed. All of the data will be carefully measured and the wind velocity will be recorded. Overall, I hope to find the most efficient propeller for a certain task, and maybe even find a correlation between the propellers. "
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This will turn into a very lengthy investigation, you'll find.
Consistency in performing each phase of the test is imperative.
Engine power setting, airplane weight, wind direction and velocity, smooth flying in a repeatable manner..
Having the proper instrumentation to record the variables.. static thrust and rpm are easy. Airspeed, and inflight rpm are not and are what you will need most to get results.
The "most efficient" prop for one task.. such as acceleration, will be quite different from the prop that gives the highest speed.. It will take a bucket of props to cover the performance envelope you wish to test.
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At the very least, if you conduct the testing consistently, you will find the correlations between the props... but we already what those are.
That's why we -have- buckets of props at the field! :D
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Eliminating as many variables as you can will ease the task. The wind tunnel will do this, propellor rpm can be directly observed.. but then applying the wind tunnel results to actual performance should also be done.
As the forces involved are small, getting a good wind tunnel balance will be critical. I'd look into using strain gauges on the support instead of any direct measurement of weights etc.. much more consistent results and less intrusive in the test itself.
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[Sparky Paul]

Check this stuff out to see what I've been doing along these lines over the past couple years..
http://www.angelfire.com/indie/aerostuff/PropellorTest.htm

[Larry Dudeck]

Have you considered down loading one of the calculation programs such as electrocalc or Motocalc? Do a search in this forum and you can find the correct URL for a trial download.

Although the programs are written around the use of electric motors you may be able to glean some useful information from them as you could fix one variable (the motor) and change the prop's diameter and pitch easily.

For the $30 or so, you could 'fly' hundreds of different props, get all kinds of theoretical performances. The output of these programs can be graphical or tabular, probably exportable to an Excel spread sheet.

Another thought is the purchase of one of the flight simulators. Don't know if you can change props or not in all of them but I do know the Dave Brown Flight Simulator allowed the user to vary prop diameter and pitch, as well as all other air frame parameters.