Creating/building a wind tunnel test model. Help a student out!

[Apford]

Hello all,

I'm currently a senior perusing a BS in Mechanical Engineering at the University of Mass. in Lowell. As part of my senior project, myself and a few others are attempting to build a scale model of a Cessna Citation I to be tested in our low speed wind tunnel. The model will ideally have a wingspan between 18 and 22 inches.

My question is this: what is the best way to approach a project like this? I have been trying to find information on the geometry of the plane so we could make an accurate scale model. So far, all I have is general length and wingspan data, and the types of airfoil used for the wings (NACA 23014 and 23012). After looking through your forum area, I've noticed that there are a number of programs available to help create scale models. Is there anything on the market that might be able to help me create a CNC file so we could mill the model pieces out of Lexan?

A secondary goal for this project is to equip the model with operational control surfaces. We would like to have something to control them from outside the tunnel, so we wouldn't have to shut down between adjustments, but this may be out of our scope for this project.

I have taken an introductory course on aerodynamics and flight mechanics, so I have a fair grip on the science of the project, its just the construction of the model thats causing me to fall short.

Any suggestions or input would be greatly appreciated. Thanks so much for your time!

[nmasters]

http://www.google.com/search?q=rhino+3d

[BMatthews]

With more data and some CAD or Solidworks or Rhino skills you could model the Citation in the program. But it's you that needs to make the model using the tools. You can't just load in some sketches or pictures and press a button and out comes the 3D virtual model. It's a pretty serious learning curve to get good with any of the programs well enough to let you do a model of the Citation to that degree.

Then there's the machining of the model. It's not likely that you can do it in one piece. That means splitting the CAD model into parts that you can manage. And to move the controls from outside that means your model will need to be hollow and have arrangements for servos to move the surfaces. All that needs to be allowed for in terms of linkages and room for the servos.

[Apford]

I guess i should re-phrase my question. I need to know how you model builders get your dimensions for your projects. Are there plans you can find online, or do you extrapolate from other sources? I have plenty of Solidworks skills and the construction of the model will not be the problem. Our problem is not being able to find accurate dimensions for all the different geometries of the plane. We want to make our scale model as accurate to the true shape of the plane as possible.

If you were going to make a regular hobby scale model, how would you go about doing it?

[furyflyer2]

If you need more info their is a wealth of info here- http://cnczone.com

[Gary Warner]

I purchased a copy of this CAD file (http://www.turbosquid.com/FullPreview/Index.cfm/ID/235963) of a Beechcraft B200 and was amazed at the detail. I used it to extrude the fuselage cross sections and make a foam plug of the fuselage. Things have gotten too hectic to make more progress on it right now. If you are looking for fairly accurate CAD files, checkout Turbo Squid (http://www.turbosquid.com/) (that’s where I got the B200 files) or any of many such 3D modeling web sites. If you are flexable with the model of jet you want to build, there are some great examples at Turbo Squid, though some are not as accurate as others. In general, you'll get what you pay for in quality (or lack there of).

[portablevcb]

Your best bet might be to contact someone at Cessna with your problem. Maybe even contact someone on their engineering staff. You might even get a 'sponsor' from Cessna to advise you on your research. Corporations frequently support student research efforts, including the use of company resources in experiments. Sometimes these kinds of collaborations result in internships and jobs following graduation.

charlie

[Stalled]

Would this be of any use?

http://www.rcuniverse.com/forum/m_3473532/anchors_3473532/mpage_1/key_/anchor/tm.htm#3473532

http://www.warplanes.com/store/index.asp?department_id=39&pg=all

http://www.rcuniverse.com/forum/m_6451773/tm.htm

Stalled

[BMatthews]

Apford, it's definetly a case of GIGO. You are right in that you need to have truly accurate information at the start. For world competition caliber scale models the documentation is very stringent and even the validity of the information sources needs to be verified. Without verified documentation that the judges can use to measure against the actual model the scores fall or the model is disqualified.

Depending on your required fidelity to scale the others are right about contacting Cessna for more information. Otherwise we are in the same boat as you are if there is a lack of solid and accurate drawings out there. Certainly the requirement for it to be scale to a high degree means you will need far more accurate and detailed CAD or paper drawings than all the casual 3 views and photos can possibly provide.

That's not much help but at least you know that we are in the same boat when it comes to this sort of thing. Our only saving grace is that many of us just shoot for what we call "stand off scale" where the model is often made to look as much like the original as the poor small 3 views with a few sections and some photos will allow. In some cases they come out more like "stand WAY back and squint scale" but once in the air many evils are not visible to the eye of the creator or the audience and it's alll good. Models done to the level of accuracy you require are left to the contest participants as a general rule. Often the choice of what model to build is based on which has the best documentation for it.

[markschaffin]

Another option that you might want to consider is talking to the education outreach folks at NASA, particularly NASA Langley. These guys love to help students. I can almost certainly tell you that they would be able to release geometries of aircraft (probably concepts, not production) that they have tested. Search the old NACA reports and you may find some of these yourself. They may even have a generic business jet model.

[kcaldwel]

Sounds like you can get a detailed 3-view from Cessna. or through some XPlane guys:

http://forums.x-plane.org/index.php?showtopic=15604

Kevin

[N9DP]

I’m curious why you chose a jet (Citation) to study. Your low-speed wind tunnel will not be able to tell you much about the Citation’s flight characteristics, will it? Won’t the small Reynolds’s number of the model coupled with the low flow-rate mean that you will be studying the Citation’s flight regime at equivalent taxi speed?

If I were your advisor, I’d suggest you put a full-size RC model in the wind tunnel. And study flight characteristics at actual flight speeds. The flight surfaces would be controlled by the RC transmitter. I’m willing to bet there are a host of model manufacturers who would gladly supply assembled model (RTF) with Tx and Rx in exchange for free use of your results in their ads. Your report/thesis would be a marketing guy’s dream!

Good luck in your project!

Dennis