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Oct 23, 2003, 07:43 PM
Registered User

Quad City Aircraft Corp. Challenger I Model question

I am currently designing a 1/6 scale model of the Quad City Challenger I Ultralight. It will have a 63" WS, hopefully almost all carbon-fiber structure, and hope to power it with either a Super Cobalt 400 or a 540 style car motor (both geared). I may need to up the power a bit, but I want it fly as scale as possible, meaning I don't want a brushless motor that will give it 3D performance. One thing I really don't know about scratch building a model is the airfoil. When it come to Renelds(?) numbers and the like, I get lost. What would be a good airfoil to go with for fairly slow flight with a weight around 30 oz?

Also, if anyone knows where I might be able to find carbon fiber rods, then I would like to know. I tried looking on a search engine and all I could find was carbon fiber car parts, i.e. CF hoods, Tachs, etc.

Here is a picture of the Challenger. I think this is a Challenger II 2 seater, but the I is nearly identical, only a little shorter.

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Oct 23, 2003, 08:17 PM
Visitor from Reality
Clark Y, Clark YH (same thing, bit of "reflex" on the last 30%), NACA 23012 if you want to zip a little more. Getting hung up on Reynolds numbers is fun for some, but mostly delays the test flight

For CF, try kite manufacturers - "Into the Wind Kites" springs to mind:

With a geared motor and that layout, you'll need to watch that your prop diameter limit is met! The nice skinny inline boxes that look like they'd fit that skinny nacelle aft of the wing end up needing huge prop diameters.


Oct 23, 2003, 08:46 PM
Registered User

Thanks for the info. I new the prop might pose a problem, but I think I can get around it. If I have to go with a non-scale gearbox, that's not a problem. Hopefully I will have some pictures or info on the design in the near future.

Oct 23, 2003, 08:48 PM
Registered User
What does the "bit of reflex on the last 30%" do to the Clark YH?

Oct 24, 2003, 09:33 PM
Visitor from Reality
Standing by to be shot down by someone who can spell "aerodynamics" without frowning, but I understand it reduces the centre of pressure shift with changes in angle of attack. I think that translates loosely into "Makes it a bit more stable in pitch, but is harder to build at model sizes as it ain't got a flat bottom"!

On reflection, I'd go with Clark Y, but if it looks too fat for the model, thin it down some. Unless you use something horrific by way of a wing section, it's good enough for most practical purposes.

If you want to scrat through wing sections, look up a great little freebie called "Profili". This has a library of wing sections, can print out basic sections to your sizes and now I understand has a lot more capability for the payment of a pretty trivial sum, though the basics of Profili is still freeware. For example, I use the freebie version to create .DXF files to import into my CAD program plans.

Even if you don't use CAD, Profili is real handy to print out sections at whatever size, then you add the spars and stuff with a pencil. With a constant chord wing, that's real easy going.

It'll be a pretty little model, looking forward to seeing how you get on.


Oct 25, 2003, 02:20 AM
Registered User
Thanks again Dereck,

Belive it or not, I actually did exactly what you said there. I found Profili while searching for a wing designer. I then used it to get the airfoil that I want (Clark Y) and imported it into TurboCAD to do the rest of the wing. I think I have the wing's plan done now. This is the first plan that I have ever drawn, so it may not be right, but I think it will work.

I hope to have all the plans done by next weekend. The hard part will be the fuselage. All I have to go on for a reference are a few bad photos off the internet and a Flight Sim 2004 model of the Challenger II. Not much in the way of reference on the shape of that fuse, but I think I can work it out. I am working with the folks that built the model for FS now to see if I can get any more detailed info about the plane.

I will keep yawl posted on the progress. I may pause on it from time to time, and it may take me a bit longer to build than most of the scratch builds that I see here, but I hope to get it done soon.


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