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 Post subject: Re: widebody
PostPosted: May 7, 2011, 9:16 am 
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Location: central Arkansas
In a surprise development, my wife thinks fabric stretched over bulkheads and stringers would be way cool. And she wanted to know why the rest of the outer panels couldn't be done that way, too. And she can sew...

I'm not sure letting her watch old British cop shows on the right-hand monitor while I'm surfing the web is a good idea. Last month she saw me looking at pictures of old Soviet DP-28 machine guns, decided they were "cute", and bought one.


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 Post subject: Re: widebody
PostPosted: May 7, 2011, 2:55 pm 
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Okay, I finally realized a downside to a clamshell hood. You *could* bolt some regular lights down on the top, but that just doesn't sit well in my mind's eye. The lights need to retract, which suddenly adds a fair amount of extra complexity.

Ordinary pop-up lights like my former RX-7 used an electric motor and a stop. The motor gearbox held them up until the motor reversed and pulled them back down.

The motors and gearboxes aren't that heavy... but a friend's Opel GT had headlights that operated by a hand lever and a cable from the cockpit. That would be lightweight and simple. However, you'd have to have some way to lock the lever, and the tension on the cable would be what held the lights up. They'd probably bounce when you hit bumps.

I haven't seen an Opel GT in a long time, so it took a while before I remembered the GT's headlights rolled sideways when activated, the axis running front to back. That meant they stayed up all by themselves; all the mechanism had to do was stabilize them so they didn't fall back over.

Of course, this would involve building headlight housings, transplanting some buckets and adjusters, etc. Not a major project, but not trivial either, at least if it's to be done in a reliable, sturdy, and reasonably attractive manner.

Then I remembered the C4 Corvette lights did something similar, except they rolled front to back, on crossways pivots.
You'd still have to stabilize them somehow to keep them from bouncing, but it would be easier than a light and cover that just hinged at the back like the RX.

Assuming you used a shaped plywood section where the headlight bucket would go, you could cut the bucket out with a jigsaw. You could then attach a standard 7 headlamp to the bottom. When the light is up it would look silly, but hey, it's dark then, theoretically...


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 Post subject: Re: widebody
PostPosted: May 7, 2011, 10:30 pm 
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Location: Tennessee
Have you considered using the Miata actuators? They are pretty simple and should be cheap.


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 Post subject: Re: widebody
PostPosted: May 8, 2011, 2:42 am 
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No, but I'll check them out next time I'm at the junkyard.


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 Post subject: Re: widebody
PostPosted: May 8, 2011, 11:28 am 
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As a styling exercise for a skin-and-stringer body, the BMW Gina is the ticket. Now it was a bit hey-look-at-me-at-the-car-show with its ability to change its shape by moving the stringers on driver's command, but if you look at it in any transitional phase and ignore the fact that the stringers have motors on them (invisible under the skin anyway)...here's a short version:

http://www.youtube.com/watch?v=IGf3pzOydd0

Here's a longer version, from Road & Track, with an interview of the chief designer. My favorite part is where the narrator says the materials of today won't work for a production car but maybe in the future, high strength fabrics blah blah. Maybe in the past, dude, or maybe in your Stitts catalog right now.

http://www.youtube.com/watch?v=4YqJdGnE3Do

Anyway, the technology exists, you could make a gorgeous car, and if you go to eaa.org you can find a local EAA chapter; go to a meeting, bring a screen shot of the Gina and a pic of your car and see what response you get from the dopers.

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 Post subject: Re: widebody
PostPosted: May 8, 2011, 1:23 pm 
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JackMcCornack wrote:
As a styling exercise for a skin-and-stringer body, the BMW Gina is the ticket


Well, ain't that a kick in the head... and here I thought I was mega-retro, and it turns out I'm bleeding edge!

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Maybe in the past, dude, or maybe in your Stitts catalog right now.


There are lots of technologies that have come and gone several times. Quite often I've thought I've come up with something innovative and original, only to find a mention of the same thing from the Roosevelt administration. Theodore, not Franklin...

I eventually came to think of the art of engineering as being somewhat like a lava lamp; associated groups of technologies bubble into common awareness, spread out, and then sink down and are forgotten for a while.

Quote:
and if you go to eaa.org you can find a local EAA chapter; go to a meeting,


eaa.org sure wasn't much help there; I had to google "eaa chapter list" to find the list. Turns out there's a group only 12 miles from here. I'll email the contact and ask if they mind me dropping by the next meeting.

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bring a screen shot of the Gina and a pic of your car and see what response you get from the dopers.


From the chapter's own web page it looks like they have a lot of ultralights. I'm hoping that's just the kind of people I need to be talking to.

You know, Jack, you're not doing a very good job of talking me out of this idea...


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 Post subject: Re: widebody
PostPosted: May 11, 2011, 4:27 pm 
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TRX wrote:
You know, Jack, you're not doing a very good job of talking me out of this idea...


If you want people to talk you out of harebrained ideas, you're in the wrong place. :lol:

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 Post subject: Re: widebody
PostPosted: May 11, 2011, 10:01 pm 
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JSullivan wrote:
TRX wrote:
You know, Jack, you're not doing a very good job of talking me out of this idea...


If you want people to talk you out of harebrained ideas, you're in the wrong place. :lol:


:rofl: Amen, Brother!!!

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 Post subject: Re: widebody
PostPosted: May 12, 2011, 3:38 am 
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TRX I do a lot of my bodies over the years with string, rope and cloth.

The entire basic body panel shapes for this were done 100% with 8mm rope and 8mm steel rod strategically positioned to run the rope over/around etc. Many hours of wrapping rope and then simply add f'glass resin and a single layer of mat to harden it all up and run over it with body filler to smooth it all up and make your molds from.

Sad part is then getting a large hammer and destroying it all when you're finished.


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 Post subject: Re: widebody
PostPosted: May 14, 2011, 1:47 am 
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Have you seen any of the geodesic airolite boats? http://gaboats.com/construction/ These are built with light wood frames braced by kevlar string and then shrink wrapped with dacron. I remember drooling over these in Wooden Boat twenty-something years ago.

I never thought about using it on a car until now, but it might work nicely so long as you avoid too many bulges and scoops. I'm also starting to wonder if this is flexible enough that it can just shrug off minor impacts and parking lot whacks without suffering the dings and scrapes so many custom car builders fear.


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 Post subject: Re: widebody
PostPosted: May 23, 2011, 4:08 am 
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If you do some searches for ceconite, stitts system, or Hypec. you should find info on the process as well as a few builders websites. Stitts has a good manual that you can either get sent to you or download . Used to have to pay for it, think it is free now.

If you just happen to be on the cheap side of things you can get unshrunk dacron cloth from the fabric store for a fraction of the cost of the certified cloth. Basically there are different weights 1.7 2.7 and 4.7 oz per sqr ft. Don't worry about those unless you plan on going over about 200 mph. The dacron aka polyester cloth is the same basic stuff as the certified, the things to watch for are pre shrunk and sizing. Pre shrunk is useless for obvious reason and the sizing can cause paint not to adhere well so you have to care fully wash it in very cold water. As far as paints the cheap trick is to use exterior latex paint with flotrol and you can get a smooth gloss uv proof covering. A lot of guys have used that and have found the same quality/finish and durability as the commercial stuff for a very small fraction of the price. And a few have over 10 years of it sitting out in the sun at the airport so on a car it should live a while.

You can stitch, rivet, screw or even glue the fabric in place. Glue us the smoothest of course and the easiest. Polytak is on of the brand names that pops to mind (Stits system) Galu is Hypec;s version. Either needs lots of ventilation or you may get "stranger" ;-]. Once its attached you use a 350°F iron to shrink it. You just shrink it tight. You can actually damage a wing by over shrinking. It will quite happily bend the crap out of a wing or parts of. Easiest way to practice and test your system out is just make a square wood frame out of 1x1's. Then staple, or glue or whatever attach the cloth then shrink and paint it. If you mess up you have killed a square foot of cloth not something important.

Problem with EAA is a lot of the good stuff tends to be members only. Look at www.wicksaircraft.com or www.aircraftspruce.com or just aircraft fabric covering. From there you can track down the brand names and to the web sites. There a few more systems out there including a few that use water based epoxies (no idea how good that one is). Your local EAA chapter is a good place to do some hands one and maybe score a bit of left over fabric. They usually meet once a month. You should be able to find the contact numbers for the various chapter officers and give them a yell.

With good fabric and paint this is tough. You can push a finger into it and as someone said it will even back out on it own. The fabric gets tested using what is called a punch test. Basically a finger sized rod is pushed into the fabric with about 70 pounds of force. If it punctures time to replace other wise you keep on flying. On a properly done cover that's 15-20 years to get to the point of replacement.

This stuff is also used on strip lath kayaks but end up with either epoxy or polyester resin to seal. Very tough and light.


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 Post subject: Re: widebody
PostPosted: May 23, 2011, 5:24 pm 
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Cheapracer, Wump, Wragie:

Thanks, guys! I'll follow up those pointers.


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 Post subject: Re: widebody
PostPosted: June 2, 2011, 2:44 pm 
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TRX, have you seen this forum? viewtopic.php?f=23&t=8045 (Low Drag Body Done Cheap)

It doesn't talk about cloth skin, but on pages 3 & 4 they discuss a few ways to make a fairly graceful shape using mostly flat sheet with a few fiberglass fender caps to break up the blockiness.


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 Post subject: Re: widebody
PostPosted: June 5, 2011, 5:56 pm 
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Location: central Arkansas
Well, lookie what I just found:

Attachment:
velorex00.jpg


http://microcarmuseum.com/tour/velorex.html

I was thinking more of tucking the cloth around the bottom and lacing it up from underneath, but this is the same general idea.


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 Post subject: Re: widebody
PostPosted: June 7, 2011, 2:01 pm 
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The methods used on aircraft are designed to prevent the cloth from flapping and separating during flight (bad). Since you life doesn't depend on it, you might try the stuff used on models.

Google Monokote and Solartex,. Those and other similar coverings do a great job on model airplanes. You just iron it on and it adheres to the frame and shrinks up tight as a drum. Many colors (even chrome and brushed alloy) are available. Or you could do it all in the transparent version.

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