2000 GMC FastBack AeroCap Project

[aerohead]

Originally Posted by ChazInMT

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

I've been enjoying mine since 2004,I think you'll like your's!

[bondo]

ChazInMT,

Just read you post on the aerocap you were thinking about building. Your sketch is very good and I know how it is when you have a good idea and just don't have the time to build it. Believe me, I also know how it is to travel long distances in your work. An aerocap would save you alot on fuel.

Back to your sketch. It reminds me alot of one a friend of mine designed several years ago. He lives here in Little Rock and is in the aircraft design biz. Your sketch looks alot like his design which I always thought was pretty cool. I scanned the rendering he did and post it now.

Good luck with building your cap and if I can lend any advice on the build, just PM me and I'll be glad to help if I can. It is great to see such an interest in aerocaps and I have a great deal of respect for anyone who has built or plans to build their own aerocap.

Bondo

[Big Dave]

ChazInMT:

Your drawing looks a lot like my fairing.

[ChazInMT]

OK, I been thinking hard about how to cover my AeroCap. I've come down to 2 alternatives.

* 6 mil black polyethylene from Hardware store, or
* 7 mil White Marine grade polyethylene from a ebay store that sells it by the foot.

$25 cost if I use 6 mil black Polyethylene from my local lumber yard, it's enough to cover my cap 7 times, 10' x 100'. ( I wouldn't put 7 layers on, I could screw up 6 times and still have one shot is what this means)

Good
It's cheap.
I think the black will look good on the back of my truck.

Bad
I'm afraid of 2 things,
- Will it heat shrink well enough? The guy in the store tore a bit off and we put his lighter to it and it shrank, so I think I'm OK here.
- On hot sunny days, will the heat from the sun cause it to get real loose and baggy?
- On hot sunny days will it heat up my bed area too much & stress the wood shell?

For $30 I get enough to cover my cap once, 10' X 16', with the marine grade 7 mil, and I have a 5 x 10 chunk left over to play with. (More like I play with the 5 X 10 chunk to get my technique down then do the job for real)
For $40 I could get a chunk that's 16' x 16' and I could wrap my cap twice.

Good.
- It's UV protected to last 1 year.
- I know for sure it'll work. (98%)
- It's white, so it will heat up less in the summer, keeping the bed area cooler and being less stressful on the substructure.
- I think it will be more stable thermally and less likely to get baggy on me on a Sunny 95F day.
- It is 1 Mil thicker & probably better quality.

Bad.
- It costs more.
- If it doesn't work, I'm really out $30-40. ( I could always use the black poly for something)
- The white color won't look bad, but I don't think it will be as stylish as the black. Although I could paint the white with Krylon Plastic Fusion paint ($20)


What do you all think? Should I not be such a freakin cheapskate and get the white? Or go with black, knowing I could always tear the black off and get the white later if the black fails me?

[Fubeca]

My vote is for black

It is cheaper, you have more chances to get it right and I think it looks better.

I thought about going with white (same stuff you are looking at) but it would have taken too long to get for my timeframe. I don't really think the boat stuff is significantly better quality.

One question, how are you planning to get the plastic to stay tight to the contours near the sides at the back where the flat section meets the curve? I couldn't think of an easy way to make shrink plastic work with that design (hence, my current cap doesn't taper in at the sides).

[ChazInMT]

Thanks for the reply Fubeca.

I am going to make the concave part in one piece and the flat part in another. Then I will wrap them individually and put them together.

Like this:



Kinda..Maybe. I think it will work. The flat part will be about this size & shape to act as a support platform for the back 4 feet. It will also provide a fair bit of "anti spread" strength at the caps mid point. Over engineered? Probably .....it's kinda my thing.

I have changed the back of the concave part to have a 3" flat area on the aft end. I did this for ease of construction. I couldn't get my head around making it taper flat and still have something to nail everything down to. This way I can make the last "rib" out of a chunk of 2x4 for my final tie in.

I don't think it will cost me any efficiency at all.

Status Report:

I have the ribs all made, I plan on making the flat parts for the ribs to rest on tomorrow and putting together the flat deck too. I'm using 1/2" OSB for everything so far to keep the weight down. I have 2 sheets of 1/4" CDX for the skin, it's pretty rough but it was half the cost of anything else they had at the lumber yard which I would consider using. I may just need to plaster on a few glops of Elmers wood filler to fill in some knots in the CDX, or not. I don't think they'll be seen through the shrink wrap. I have taken some pictures which I'll post when I get the frame together and before I put the sheeting on.

I changed the shape of the top profile of the cap, I was going to make it rounded to match the roofline of the truck, but since I have a fairly pronounced aero shape when viewed from the side I thought trying to get the 1/4" CDX to compound bend would be difficult. So now I basically have a 2 foot wide flat area on the very top of the cap which will go from stem to stern. On each side of that is a 1 foot wide flat spot that tapers for the final 3 feet, it is about 10 degrees sloped in relation to the 2 foot wide area. I figure it'll make the application of the sheeting a cinch and still match the profile of the roofline within 1/2 inch or so. See the illustration of the rib profile for a better idea.



Thanks for your input. I suppose I can keep a bunch of the Black Poly in my truck and if it gets too loose & baggy I could always cut new pieces to overlay and slap staple the crap out of them, it would look like hell but would work.

[ChazInMT]

Status Report:

Thought I'd post some pics.



Here is the Rib Template I had made at Kinko's. Since I designed everything using Microsofts Draw program, I thought it would make my life a bit easier to have a full scale drawing to work from. I was able to scale it up perfectly from a 1" = 1' scale drawing I made in a word program. I converted this into a pdf file and the Kinkos guy was able to print it on his 36" roll feed printer/plotter thingy. $9, well worth it!



I didn't want to cut the template up, so to make life more difficult on myself, I made patterns out of it by tracing some Tyvek house wrap I had laying about.





I then traced the tyvek templates onto the 1/2 osb. This was my first trace and I was trying to use tape.....not so good, I ended up using my slap stapler for the rest to hold the pattern in place.



Then I cut the ribs out with my Mk 47 jig saw.

I spent a good number of hours sorting the ribs out with a belt sander to get the shapes all matched up. Then I started on the base for the ribs to rest on.

I'm using all 1/2" osb to save weight. I think the frame when complete won't be very sturdy, but once it is sheeted with the 1/4" plywood, I think everything will work together to make it quite tough.

I had a $20 home made tonneau cover which I used as a platform in place of building off of my truck bed. Today I was able to dry fit the ribs onto the base to see what sort of shape I had. The following are pictures of this dry fit, everything is just sitting there loose, no nails or glue or nothin yet. I'm happy so far.

I'm a bit worried about the plywood for the sides, I know I can kerf the back with my circular saw to help it bend into shape. What I'm afraid of is when I bend the plywood around the back AND I twist from 70° to 40°, is the wood going to want to "dive down"?...Just thought of how to solve the problem. I'll make another Tyvek template and play with that, whew.

I'll post more pics as I progress.

[Fubeca]

I'm very excited to see this progress. For some reason - I can't see any of the pictures but it sounds like you are making very good progress. I think your attention to details will make your top much more finished looking than mine!

[Fubeca]

I see them now - Looks great! I look forward to seeing your technique with the plywood covering. I had a hard time getting even the minor compound curves bent in mine.

[repete]

Very nice!