Love2FlyMN

Hey everybody. I think this would be the right place to post this. I'm going to be doing some research for my advanced physics lab for second semester and I was going to be hopefully designing a model from scratch, building it, and flying it. I already own 3 nitro planes and I have quite a bit of experience with airplanes. I have built 2 kits so far and in the future I'd like to be a designer for model airplanes so I figured this could be a good jumpstart to that.
Anyways, my professor said something about a wind tunnel. I was just wondering if anyone has any information for me on anything,it would be greatly appreciated so I can get rolling on this. My prof also said something about writing for a grant to buy a wind tunnel and maybe get one that way or build my own. I would probably have to scale it down to like 20"x20" and maybe get a max wind speed of 40 mph? I have no idea, any thoughts??

All Day Dan

My Feedback: (5)

Here's an old article that can get you started when you design your airplane. Dan.

iron eagel

http://www.science-projects.com/WindTunnel/WF.htm

http://www.physicsforums.com/showthread.php?t=191978

http://www-htgl.stanford.edu/bradshaw/tunnel/

http://www-htgl.stanford.edu/bradshaw/tunnel/intro.html

http://www.techdirections.com/BuildAWindTunnel.pdf

BMatthews

Often folks that don't really know about aerodynamics will assume you need a windtunnel to design a model... But t'ain't so. The wind tunnel work has already been done for you by that great group over at University of Urbana Illinois under the leadership of [link=http://www.ae.uiuc.edu/m-selig/people/selig.html]Michael Selig[/link]. In addition if you want to try your hand at your own airfoil then the physics of lower speeds has already been simulated by a few programs. One that is easy to access and use is X-Foil. It is embedded in Profili2 available for download at www.profili2.com and you can unlock the Xfoil portion with a rather modest fee paid to the Profili writer.

From there it's all about sizing the design's other attributes and dimensions to achieve the proper damping of the wing's pitching moments (stability related) and to provide the control torque values to suit the style of flying. For example big surfaces with lots of travel for "washing machine" like regurgitation and far more modest for soaring where control is good but too much is worse.

All of this can be done without the need for a real wind tunnel of your own. And really to take advantage of any such tunnel you've got a HUGE amount to learn on tunnel turbulence and avoiding it, learning to fabricate or select the instrumentation needed, testing to determine how far from the walls of the test cell you need to avoid surface influences and a host of other wing tunnel only related issues that are just as harsh on learning to deal with as the results from a wind tunnel itself would be.

Tall Paul

Wind tunnels are pretty useless without the balances needed to measure the forces.
For model purposes, these forces are very small, particularly the drag force, and the balance needed to detect changes must be very sensitive.. which means delicate and -expensive-!
Blowing the fan thru the box, typical of model tunnels only gives gross indications of what the model is doing.
The computer simulations do it a lot better for model sizes and modellers budgets.

OffroadBEAR

My Feedback: (2)

Where do you go to school? I had a semester long course about the setup, calibration, and experimentation with a wind tunnel. Ours had a test section of 4 ft tall x 6 ft wide. If you are an aerospace engineering student, a wind tunnel course should be mandatory. If you are studying other disciplines, you should be able to take one as an elective.

As far as computer simulation, X-foil and javafoil are the most useful for modeling purposes. If you are doing a design report or technical documentation, something a little more advanced like Fluent/Gambit (or any other CFD software combination) would be a little more appropriate. Although you will find that with more advanced computer simulation, you should substantiate it with wind tunnel testing or hand calculations, or something else to confirm that the simulation was setup correctly and that it correlates with another approach to solving the problem.

A good bit of advise for designing model planes: basic theory, common sense and logic, and Microsoft Excel are your most powerful tools.

da Rock

Building the tunnel would be more than enough of a project. More than enough.

To get a good idea of how to go about your original idea, get "BASICS OF R/C MODEL AIRCRAFT DESIGN" by Andy Lennon. It'll be the best money you spend on the project. It's published by Model Airplane News Publishers and is easily available.

iron eagel

What he said...
The book is priceless as a reference and tutorial on how to design airplanes.
another good source for info on design is:
http://www.airfieldmodels.com/inform...sign/index.htm

Love2FlyMN

Wow.... To be honest I wasn't expecting this much feedback! Thank you guys so much for all the help so far. I'm actually an Applied Physics student at University of Wisconsin River Falls. Applied physics is just pretty much pre-engineering with more physics. I can't wait to get this project started!! I'll have to get those books and look into more of those links when I get more time. I'm actually in my senior year of playing football here so we put like 25+ hours a week into that and this lab course I'm taking we're supposed to cram another 15 hours outside of class to get it all finished. Plus a ton of other stuff... But yeah, anyways...I'll hopefully get around to reading more specifically later!
Thanks to all those who have responded!


-Jesse

Love2FlyMN

You know...I was just thinking after reading in the link of that last post. When I was younger one of my friends had come up with a design for a RC UFO. Basically you'd mount the engine in the middle blowing air down and using servos open and close holes in the bottom to give it lift and pitch etc. I think it would take a very good radio wtih some good mixing to get it to work but does anyone know of such a craft?

I built a hovercraft last spring that turned out pretty sweet. I'll take some pics and post them if you guys want.

Love2FlyMN

Here's some pics of what I was talking about.. Got to thinkin and had to draw it up... It'd definitely be a project and I'd have to do some preliminary experiments on it first.

iron eagel

here is something similar to your idea...
http://www.rcuniverse.com/forum/m_7673332/tm.htm

Love2FlyMN

that's different from what I'm thinking.. I'm going to be doing a flying saucer type thing. I was talking to my roommate last night and we sparked the idea of using electric motors and I think that might be a better idea since I won't have to tune the engine when it's in the craft. Electrics I'd set a few of them in there, or one big one, depending on the best ratio of thrust/weight (all to be figured). That way I could set the throttle channel as a constant and use the left stick for up/down and the right stick to tilt.

I was actually up last night drawing out what it woudl look like. Maybe I'll post some more pics of my drawings if I have time. I'm totally excited for this.

iron eagel

The interesting part of the set up of the fan in a shroud setup is the vanes are placed directly behind the prop which gets them in the strongest part of the airflow and reduces the swirl of the prop blast.
The idea you have is similar to the "Avro car" (I think that was the name) built in the 50's up in Canada. Of course that was built with a turbine but used vents and vanes to direct the thrust for lift, thrust and directional control. They scraped the idea because they could not produce enough thrust to get it much higher than a few feet off of the ground. Back in the 60's there was a design that was called the Plato that was used in RC, it was a disc or saucer that flew like a conventional aircraft (forward facing motor) that was a saucer shape, much like the flying disc today with conventional control surfaces, a horizontal stab and rudder, along with elevators. Another aircraft in development today uses several engines and vectored thrust for VTOL and normal flight it is being developed by Moller international on the west coast, I think it has been shown on some science programs on tv a few times.
With the computer radios of today not to mention power systems both conventional and electric it would be interesting to see what can be done.
I myself am playing around with a vectored thrust design that is listed in the forum as oddball design 101, it has been on the back burner for some time now but I am going to play around with it a bit this winter. It is not designed for VTOL just STOL and I have no idea if it will really work at all.
I think the only issue that you have with the VTOL setup is getting enough HP to get the lift youneed and being able to control it. It should be an interesting project none the less, worst case you get a real nice hover car type of craft.
Good luck and have fun...
I just mentioned the other craft as some references for you to look at...

Love2FlyMN

thanks again... I was talking to my physics prof about it today. I think what I would need to do is set up one engine in the middle for thrust alone, then 1 or 2 more engines on the outside edge for tilting it. I think I would have to use gyros to stabilize it otherwise it would be impossible to fly. Can you pretty much do anything these days as far as mixing with radios?

iron eagel

There are others who know a lot more about today's radios than I, so I can not answer that question. I do not know how advanced the mixing features can be but I would suspect some of the higher end radios that have 8-12 channels can do some amazing things. I only know the most basic operations of the new computer radios and have not really used even my six and seven channel setups to do all that they can do. One of these days I have got to take the time and sit down with the manual and figure out all that I can do with them. For the most part any mixing I ever dealt with was mechanical in nature because I was lucky to have even a three or four channel setup and for the most part that is all I ever used of the radios I have today. Now that they have the new 2.4 ghz stuff is, and I still haven't figured out the new 72 Mhz ones I have...
But having bought 3 new radios over the past 5 years I not going to rush right out and but a new one till I need something real wild with 8-12 channels.

Avaiojet

In some cases, a wind tunnel is necessary!

I have a design that I've been putting off for at least a dozen years because I don't have access to a tunnel. This particular design, extremely unusual as it is, would not work with normal aerodynamics. The fuselage offers unusual drag in various pitch and yaw configurations.

To rent time in a tunnel is expensive. My only hope is to mount the "mark-up" on the bed of a pick-up truck, but that's not accurate either because the model is stationary and not climbing when pitched.

Do I make any sence?

iron eagel

You do not need a wind tunnel to build any aircraft of any design.
Easy way is just to get some balsa or foam (or both) and build it say 1/3 scale.
Then go fly it.
If it works scale it up to 25%.

If it doesn't make sure to video tape your flight and see why it did not work.

I am working on an oddball design myself and that is what I am doing.
If it works cool.
If not, I will find out what issues it has.

Worst case I will be out the materials and time...

But either way I learn something and that is a plus.

Avaiojet

Iron,

Yes I understand all that, and it's good advice. However, in this particular case it would be costly and time consuming even to build a smaller model with these characteristics.

With all do respect, with this particular model design, real life aerodynamics alone won't work. There's other factors involved.

I do have a good background in model design and applied aerodynamic math and principles. Actually a really good background. This being what it is, I must ask you believe me.

Eventually I'll surface with the design. Then you will be taken back a bit and understand why "normal" principals are applied, buy not applied.

It is quite the thing, and destined to make the cover of all modeling magazines. Not my goal actually or I wouldn't kept it on the drawing board a dozen years.

I need help and someone I can trust. This could be quite the money maker. like that great Gee Bee R3. I actually purchased one. Interesting design. realisticly functional, yet has the appearance of a radical design when it isn't. The Designer did an excellent job.

Love2FlyMN

OK...I'm in my class now, time to design a wind tunnel.. I'm not necessarily making a super high end wind tunnel for measurements. I basically just need to get one quantitative measurement (reduction in drag with different wing tips) which I can do with a computer program (I think? Does profili2 do this?) I want to just build a simple wind tunnel for a qualitative analysis of the turbulence that gets reduced with the winglet by using a smoke trail.

How fast should the air flow through to get a good visual of turbulence created by the wing tip vortex? If I have a 15"x15" cross sectional area, how big of fan/motor will I need to push the air at that speed?

I'm probably going to use straws stacked in a honeycomb formation to reduce the turbulence from the fan which will probably be a centrifugal fan hopefully. I might just be able to pick up an old furnace blower for free and use that and scale it to that...maybe a couple of them together. Any other suggestions?

BMatthews

No, Xfoil in Profili2 won't do wingtip analysis. It's geared up for strictly 2 dimensional flow over airfoil models.

I'm sorry but did you read the replies above? The size of tunnel you're talking about will require some really delicate and sensitive measurement balances. Smoke trails are nice for showing the amount of turbulence but the smoke trails mean diddley otherwise. Any reduction in drag is going to show as a change in the scale or strain guage you setup to measure the force trying to push the wing model down the tunnel.

Furnace blower or prop blade. You'll need to set it up with a bunch of different options to even up and straighten the airflow to achieve a turbulence free flow. That takes room. I'm strictly guessing here but from what I've read in books about wind tunnels and seen from others on this forum that have worked with wind tunnels all this flow straightening and wake reduction takes room. If you want your test area cross section to be around 15 x 15 inches then the upstream tunnel will need to be a good 8 to 10 feet long with the fan on the end. Along that length will be a fly screen or two and a bundle of drinking straws followed by a few feet of open tunnel to let the "noise" from the drinking straws subside. And maybe another layer of fly screen a foot or two before the test area.

You may not think you need a high end tunnel but even if you only want to see smoke trails you will soon find you need a high end tunnel or the smoke trails will just be a fog in the wind.

allanflowers

You could do a modern version of what the Wright Bros did, testing on a bicycle. Do it with a rig attached to a car or truck instead. It would have to be high enough to be out of the main flow disturbance created by the vehicle. The Wrights use a balance which had a flat plate on one side and the test object on the other. By shifting the position of the flat plate, they could compare drag. The whole thing could be built inside an open ended box which becomes the test section, in which case it could be closer to the vehicle - with maybe just 6 inches or so separation. There would be no need for honeycomb flow straighteners, etc.)
The passenger would run the tests using pulley or something to move the position of the flat plate to do measurements. All measurements would be relative although you can probably find standard data on flat plates of a given size.

Love2FlyMN

Yes I know I will need sensitive equipment and a large area to make the wind tunnel. I have the size issue covered. As far as the smoke, all I want is a visual representation of what the vortex does with and without the winglets.
As far as measuring the drag forces, I'll design something so I can measure it, whether or not I get good results isn't a huge deal.

I'm just looking for information like Bmatthews said about how long to make the tunnel before the test section to reduce turbulence and to have 2 honeycomb straighteners and 2 screens etc.
Thanks again for all your help!

donnyman

Hold on, I think I have what you need It's cheap simple and direct. won't kill your wallet. I need to get my scanner on line so maybe later today before I post it. I am A believer in the K.I.S.S. principle whenever possible.

donnyman

these are foto copies of and OLD article which you can may care to use, I had to use pictures because scanned files are too large.

look it over if you are interested I will be glad to mail you a copy.

you will probably make a few changes like a squirrel cage blower but the basic Idea is very sound and can be up graded to suit your needs, more important it wont bust your piggy bank, note the date on page three

Donny