2000 GMC FastBack AeroCap Project

[ChazInMT]

Thanks for the tips Aloha.

Unfortunately, I can't afford to buy a regular car right now, I was a builder for 8 years and now travel around the country working at Nuclear Power plants during scheduled outages. So, I am forced to use my truck to travel. All my crap fits inside the cab of the truck, and if I did need to put something in the back, I could, it would just be a bit of a pain.

A pole and tarp system sounds OK to test a theory I suppose, but I plan on driving 6000-7000 mostly highway miles in the coming months. I don't think I could engineer a pole & tarp thing to hold up. Not to mention the noise coming from such a thing would likely drive me nuts.....or I suppose you could say, More nuts.

[alohaspirit]

rough. too bad you cant sell the truck for something better on gas.

the tarp isnt too bad if its tight enough i guess

http://ecomodder.com/forum/showthrea...-cap-5640.html

http://ecomodder.com/forum/showthrea...aero-1224.html

http://ecomodder.com/forum/showthrea...-cap-3539.html

[Rokeby]

Originally Posted by aerohead

With respect to weather-proofing the wood,I can only recommend
something like West Systems epoxy.I've tried many of the polyurethane
spar varnishes,from cheapest to most expensive,I think they're all
crap.

Aerohead, other readers,

I'd like to share some of my expertise as a boat builder in payback for the
aero knowledge you share with us every day. (BTW, many thanks.)

There is no way to permanently stabilize the surface of fir plywood. No
matter what you put over it, even a layer of epoxy impregnated fiberglass,
in time it will "surface check." That means the face ply will crack and pull
apart, up to 1/8 inch. It will tear the fiberglass. You can put on multiple
layers of 'glass, but the cost and weight get prohibitive.

A better choice for a wood-only construction would be ply made from okume
or sepele, these are standard marine construction materials. The are quite a
bit more expensive, and they do surface check, but the checks look like
razor blade cuts. The are easily filled-in/repaired during a second paint job.
One nice feature of these plywoods is you can sometimes get it in 5 ft by 10
ft sheets. The cost can be surprisingly high, but a standard sheet is 32 sq ft,
and these are 50 sq ft, 56% greater area.

For a truck cap, I would recommed HDO Overlaid fir ply -- High Density
Overlaid. It has one or both faces covered with a layer of resin impregnated
film, heavy kraft paper I think. The key here is the layer is fully water tight,
and the face ply doesn't check. It takes paint well, no sanding, and the grain
in the ply is pretty much subdued.

A heavier duty version of this is Signal Overlay. It's the stuff the big
overhead freway signs are made of. It is fir ply with a hardwood face ply,
and a HDO on top of that. Excellent paint surface, no grain "show through."

[Bicycle Bob]

[QUOTE=Rokeby;152783]Aerohead, other readers,

I'd like to share some of my expertise as a boat builder in payback for the
aero knowledge you share with us every day. (BTW, many thanks.)

There is no way to permanently stabilize the surface of fir plywood. No
matter what you put over it, even a layer of epoxy impregnated fiberglass,
in time it will "surface check." That means the face ply will crack and pull
apart, up to 1/8 inch. It will tear the fiberglass. You can put on multiple
layers of 'glass, but the cost and weight get prohibitive. "

There are ways to defeat epoxy encapsulation, but it isn't easy if you work indoors and follow the instructions. Fir ply is seldom bright finished, but it has always worked for me.

[aerohead]

Originally Posted by Rokeby

Aerohead, other readers,

I'd like to share some of my expertise as a boat builder in payback for the
aero knowledge you share with us every day. (BTW, many thanks.)

There is no way to permanently stabilize the surface of fir plywood. No
matter what you put over it, even a layer of epoxy impregnated fiberglass,
in time it will "surface check." That means the face ply will crack and pull
apart, up to 1/8 inch. It will tear the fiberglass. You can put on multiple
layers of 'glass, but the cost and weight get prohibitive.

A better choice for a wood-only construction would be ply made from okume
or sepele, these are standard marine construction materials. The are quite a
bit more expensive, and they do surface check, but the checks look like
razor blade cuts. The are easily filled-in/repaired during a second paint job.
One nice feature of these plywoods is you can sometimes get it in 5 ft by 10
ft sheets. The cost can be surprisingly high, but a standard sheet is 32 sq ft,
and these are 50 sq ft, 56% greater area.

For a truck cap, I would recommed HDO Overlaid fir ply -- High Density
Overlaid. It has one or both faces covered with a layer of resin impregnated
film, heavy kraft paper I think. The key here is the layer is fully water tight,
and the face ply doesn't check. It takes paint well, no sanding, and the grain
in the ply is pretty much subdued.

A heavier duty version of this is Signal Overlay. It's the stuff the big
overhead freway signs are made of. It is fir ply with a hardwood face ply,
and a HDO on top of that. Excellent paint surface, no grain "show through."

Rokeby,would you use a sanding-sealer and then a marine grade paint,as one might use on an all-wood Chris Craft?

[Rokeby]

Originally Posted by aerohead

Rokeby,would you use a sanding-sealer and then a marine grade paint,as
one might use on an all-wood Chris Craft?

Aerohead,

I can't tell which one of the options I gave you are asking about.

So I'll address them in turn.

One point on using any type of plywood. Plywood failures typically start at
panel edges that aren't part of a properly executed "two step" epoxy joint.
This due water getting into the end grain in the interior plys. This due
careless prep of the edges. You have to seal up the end grain so it can't suck
up water. This take 3 or 4 coats of straight epoxy. Keep on coating until
when you sand lightly with 100 grit paper there is no indication of the end
grain... smooth and even. Only then is it time to begin the painting preps.

I wouldn't use fir plywood... too much trouble downstream.

On HDO and Signal HDO, you don't need or want to sand, that will just fuzz
up the overlay. Go straight to a good grade oil based, "alkyd," primer. Two
thin coats dry faster/harder than one thick one. Lightly smooth/skuff the
surface with 120 grit abrasive, "sand paper" to most folks.

Then on to high quality alkyd, or one part polyeurethane, top coats. Marine
grade paint is considered the best. But at least when it comes to alkyd paint,
there is general belief that "porch paint" is the same as marine grade.
Sand with 220 between coats.

Painted surfaces that will see service out in the real world will last longer,
and require less downstream upkeep if allowed to dry for 30 days before
being put into service... yeah, not likely. But a week at least.

As to the finish on a classic Chris-Craft type hull, that would be a whole
different world. First off, the hull may be a single layer, or even laminated
of 2 or 3 layers. For the most part it would be treated as solid wood. Some
folks would start with a single purpose sanding sealer. Others start with a
25% varnish, 75% thinner first coat. This just to get the fuzzed up wood
fibers to stand up for sanding, subsequent "prep" coats at 50/50 and then
25/75 thinner/varnish. Further "full strength" varnish coats until the grain is
filled, as many as it takes. (Actually the varnish is thinned 10-15%, and
plasticicers and drying agents are used to doctor the mix to ambient
conditions.) Sanding at this stage with 150.

Only when grain is filled do you start counting varnish coats. How many?
How much time/money do you have to spent? At least 20, 30? Abrasives
gradually get less gritty; 320, 400, 600. Most folks stop there, higher grits
tend to polish as opposed to smooth. Could take 15,000 sheets on a 30 ft
hull.

Down stream, you'll need to do some top coating every year. Varnish just
disappears, it ablates. How many coats depends on UV levels. You want to
be slowly building up, never thinning the total film thickness over time.

Sort of like the 50's era "hand rubbed lacquer" auto finishes.

And that's the short course!

[ChazInMT]

Here is a basic line drawing of the FastBack AeroCap I'm thinking to build.

[MetroMPG]

Chaz: line drawing didn't show up. Were you posting a link or attaching an image?

[Fubeca]

I see the drawing now. I like it! This is what I was looking to build but I couldn't come up with easy/cheap way to do it on my budget and timeline.

I am excited to see your progress - I think my version 2.0 will look more like this.

[ChazInMT]

Thanks Fubeca! I'll take a bunch of pics. Your build has given me the inspiration for the construction technique. I am going to go buy a roll of butcher paper, or craft paper and I'll trace each part as I make it. This way I can either copy the work, or have a basis to tweak it.