Help with son's science fair project (airfoil designs)

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John, I agree that reading the label is very important - polyurethane does give off toxic fumes. But, from Dow's website, when they refer to Styrofoam they say "Styrofoam rigid foam insulation" or "Styrofoam extruded polystyrene insulation". And the sheet of blue Styrofoam I'm looking at is marked "Extruded polystyrene insulation" as have been all other sheets of blue rigid Styrofoam I've ever seen, including at Home Depot. Can't remember if this particular sheet came from Home Depot. There might be blue rigid foam insulation at Home Depot that is polyurethane, but I doubt that it's also Styrofoam. Kerry
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Kerry Montgomery wrote:

Dow Corning TUFF-R.
I don't understand why you're so resistant to the notion of specifying the foam by chemistry, which is on the label on any foam sold commercially, instead of by the intended use "house insulation" or the brand "Styrofoam".
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John, Not resistant at all to specifying foam by chemistry, but the brand Styrofoam is a perfectly adequate way to specify Dow brand rigid Styrofoam, which is what I suggested to the OP as a material to investigate. The only TUFF-R that I know of is insulation clad on both sides; don't remember what color the core is, but it's not labeled Styrofoam. And wanted to correct any misconception that you may have caused by saying that there was "...blue Styrofoam at the local Home Depot is polyurethane, not styrene.", as there isn't any such thing. Kerry
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Kerry Montgomery wrote:

If you had said "Styrofoam _brand_ blue insulating foam but make sure that it's really Styrofoam brand and that it's really polystyrene" I wouldn't have had any problem with what you said, but walking into a store and asking for "styrofoam house insulation" is just too likely to get the wrong stuff.
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All the rigid board is extruded polystyrene. http://www.dow.com/styrofoam/na/res-us/products/
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wrote in message

Edwin, Actually, Bayer makes rigid board polyurethane insulation: http://tinyurl.com/2rytbj but it's not going to be marked Styrofoam. Kerry
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Correct, I was referring to the Dow products. Thee are plenty of other materials available.
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And the toxic from polyurethane is cyanide......like you used to see used in the spy movies. I was refering to Dow blue polystyrene because of the extra density needed for the blades and the ability to hot wire. Pvc and nylon does pretty well on the hardpoints if he doesn't like hardwood.For the added compression strength needed for bolts to attach the blades.Full size helicopters.... you also have different metals used for hardpoints.
At the same time, I have used polyurethane,nylon , wood, and pvc in building composite structures. On models I have even used cotton/linen rags instead of fiberglass. As well as honeycombs made out cardboard,tinfoil, fiberglass,and kelvar. Each have advantages and disadvantages. Both models and full size aircraft.....though most of my experience is limited to rotorcraft and hovercraft.

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Edwin Pawlowski wrote:

I give up. I tried. If the kid ends up gassing himself on your head be it.
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In 1970 I started working for a company that molded foam and the sister company made model airplane wings from foam. I've been in the industry for the past 37 years. I've built many model airplanes that included foam. I've built hot wire cutters. I insulated my house with eps foam. I'd not suggest anything that is harmful.
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Here's a wind tunnel made from some planks of wood, a fan, a hacksaw blade and some bicycle spokes. If it was good enuff for these guys...
http://www.wrightflyer.org/WindTunnel/testing1.html
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Hi MB;
> Here's a wind tunnel made from some planks of wood, a fan, a hacksaw > blade and some bicycle spokes. If it was good enuff for these guys... > > http://www.wrightflyer.org/WindTunnel/testing1.html
Very cool picture. This is a replica of the original lost to history.
Some say the true invention of the Wright Bros. was their wind tunnel which allowed them to make very accurate measurements. They corrected the lift tables of Lilienthal. http://www.first-to-fly.com/History/Wright%20Story/tunnel.htm
The measurements were so accurate because they used a kind of force balance that compared each reading with standard unit flat drag surfaces in the same air flow.
This balance scheme did not require difficult to calibrate force scales. Calibration was mostly done by accurately cutting and measuring the standard flat drag surfaces.
Air velocity in the wind tunnel was hard to measure accurately. The drag balance devices were insensitive to small errors in air velocity.
These guys were geniuses.
Duane
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no spam wrote:

Try rec.models.rc.air
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A dremel on balsa wood? Save your time and just toss the balsa into a wood chipper.
Try an X-acto knife.

<http://www.google.com/search?rls=en-us&q rving+a+balsa+wood+propeller>
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Draw the airfoils on the ends of the wing blank, then connect them with an oversized sanding block, say, a 9 x 12" piece of flat plywood with a whole sheet of sandpaper spray glued on top. Lay the sanding block on the bench grit side up and have at it. Make a couple of test pieces before carving the actual wings, just to get the hang of it.
As for a Dremel tool, 60 grit sandpaper will cut balsa faster and more accurately. Save the Dremel for what it's best at, cutting small bolts or reslotting gnarled screw heads.
This was basically the same trick I used to carve ribs for balsa airplanes 30 years ago. Clamp or bolt a stack together and sand them all to profile at the same time. This worked equally fine for straight or tapered wings or fuselages.

You can freehand draw the cambers close. Eccentric curves are among the easiest to sketch. Sanding will get them fair.

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