I'm very close to starting a quarter scale foam and fiberglass model -- a friend is plotting the twelve 30"x42" sheets of the 53 sections. Also, I am refining the articulated front wheel skirts -- the front wheels are turned 33 and 28 degrees (inside and outside, respectively), and I completely remade the front fender, so it is much smoother and curved better. The skirts are smaller diameter, as they were bigger than they needed to be. I still need to pivot the skirts themselves (so they cover the wheels!) and the strakes are not quite right, yet -- see attached thumbnail pictures.
Im just catching up on some of the older posts, and saw the thin plywood discussion.
I did a lot of reading and research regarding my homebuilt car and came to the conclusion that 5mm luan was the way to go, arguably stronger and lighter then "hobby ply" and plentiful at pretty much any Lowes or Home Depot for about $20 for a 4x8 sheet.
I've started a quarter scale model of the CarBEN EV open source design:
The first two sections are at the tallest part of the roof, and the red marks are the edges of the windows. The lower parts of the section will go under the longitudinal section later. Five sections cut, and 48 to go... Then I'll fiberglass the skin, and be able to either tuft test it (on the roof of my car?) or maybe get it into a wind tunnel?
I'm building a quarter scale model of the CarBEN EV:
I have a little problem: the thinner foam is sold as 1/2" thick, but in reality it is over 9/16", so the horizontal scale of the front and to a lesser extent the back, are longer than intended. You can see the longitudinal section at about the floor height that is the intended length. I'm gonna' be doing some carving, and filling -- I kind of like the extra length, and this model is for aerodynamic testing (I'm going to make a small wind tunnel!) and I'll see how it works, and go from there.
I found that Elmer's Multi-Purpose Spray Adhesive does not melt EPS foam -- this is great. It is also low-tack glue, so spraying both surfaces and then letting it dry slightly, may be the best bond.
I am epoxying the major gaps on the 1/4 scale model with Loc-Tite "Extra-Time" 60 minute epoxy, and it is taking at least SIX HOURS to cure. So it settles and smooths nicely, but it also leaks.
I bought 8 ounces (4 ounces of resin and 4 ounces of hardener) for ~$18 at Lowes -- is this a reasonable price for epoxy? Would this work on the fiberglass? I like that it is very low VOC -- it has virtually no smell, and it washes up with soap and water fairly easily.
Edit: I realized I left out some details on how I built the 1/4 scale model. I used a hack saw blade with a small handle to cut the sections to the edge of the paper cutouts. I used waterproof yellow Elmer's glue. The roguh forming was done with a small curved Stanley SurForm (which may be discontinued?) and a medium flat SurForm (about 6" long). These would very well on the flatter faces, and if you go "up" the steeper curved faces, so the corners are not torn off. Then I've used 100 grit sandpaper to smooth things. This seems to be as much as I'll need to aero test or fiberglass.
I'm going to aero test with leaf blower(s?) before fiberglassing, so I can modify it more easily. I need to buy a small (HD?) video camera to document the tuft testing. :-)
I will be sending them an email, or a call as soon as I have done some initial testing. I need to find out what the requirements are for the model -- they have two PDF's on their web site that have a fair bit of information, mostly about airplane models. They do cars and bicyclists and probably any sort of project that can fit in their tunnel.
The leaf blower I have is capable of very high velocities, by the way -- like 200+mph, they claim. This is a great suggestion (by someone here on EM), and I plan on trying some tuft testing soon -- I also picked up a HD pocket video recorder last Friday for $100... amazing.
This is the quarter scale model, with partial number of the tufts needed; and with only one leaf blower. I think I'll need (at least) two to get anything useful.
I apologize in advance for the loud noise of the blower itself -- please TURN DOWN THE VOLUME or turn it off, altogether. In the future, I'll record them w/o sound...
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