Caravel Door Window

[Zeppelinium]

I'm a little peeved that I don't have a window up front on the door side, so I get to thinking about airliner windows, slightly curved, maybe...maybe...

Here goes! Standard airliner window (this is from a 737), front and back:



Turns out the pressure window (not the one you can touch from inside, I assure you) is actually a double pane plexiglass panel with a nice rubber grommet in between them. It's held in the frame by 10 clips:



But the frame is unbelievably difficult to remove from the aircraft skin. All those fasteners are steel hiloks, which don't drill out very easily. So out comes the small high speed grinder with a thin cutoff wheel. The hilocks can be sliced and then the colar can be removed with a cold chisel and the hilock stud punched out from the back:



You can see the frame emerging, with a nice lip that will allow it to be installed flush, just like on the plane. The aircraft skin looks to be about 0.100", so I'll need to put a shim in between the frame and the door skin. Once I get the whole thing free and the caulk off, I'll sand it and alodine it before installation.



I haven't quite figured out how to make the collar and flange for the inside skin yet, but I've got some ideas. Standby. If others are interested, I may be able to get a few more of these, but you have to take them apart yourself. It's a 4-hour job to get the frame off the aircraft skin.

Zep

[Fyrzowt]

Cool idea!
I'd be interested in learning more. Like $$, how much trouble it would be to get one, etc.
Dave

[Sugarfoot]

Now that's ingenuity at work. And appropriate with the Airstream~aircraft ties of early days. Can't wait to see the finished project.

[Aerowood]

There is no need to cut the stud with a saw. Those fasteners are called "Huck Bolts" . To remove them just take a sharp chiesel and split it fron thre side, at that point it should rotate and then you just split the collar again 180 degreees from the first split. The stud should then just punch out. The studs will be tight due to the fact that they are installed .002 interferance fit. I'd be interested in obtaining one if you got a good price. It looks like you are close to needing that "bucking" class. Let me know when. Are all those planes missing the interior trim panels? It would be easy to cut the window recess out for the trim panel. these panels have the interior window and the shade attached.

Kip

[Zeppelinium]

Some trim panels may be available. I took a look at the trim and decided that since it was, well, complicated and maybe even flat in the place you'd think of attaching it to the inside Airstream door skin, maybe I'd try to whip up a fiberglass shroud instead. I'm at Scaled Composites this month and they are very nice to employees--you get to use the shop in your off hours.

The shade mechanism is a roller, not a slide. When I checked door curvature last night, the door is too flat if you center the window between the handle and the top--you have to put the window up almost as high as you can (with a few inches to spare so it looks OK) to match the curve. The door gets curvier as you go up.

I'll try splitting the collar--it's definitely made of softer material (I assume aluminum) than the stud (steel for sure). They do punch out nicely with a solid tap, except where at the top and bottom of the frame, where there are channels and doublers. The extra thickness really grips them tight. Big hammer required.

Zep

[Aerowood]

The wide body (747) windows have a larger radius then the narrow body windows, if you can get your hands on one of those.

Kip

[Zeppelinium]

Good news. The frame fits the door when placed with about 3" of clearance at the top. This is about optimum so I think the small body windows are perfect.

The windows, as you probably know, are plexiglass and after years of service the outside of the outside window can get a little scratched. The inside window is protected from the passengers by another sheet of plexiglass that's part of the shroud, so the inside window is always protected and most of them are in great shape. Nevertheless, here's my quick analysis of fixing a scratched plexiglass window. (Aerowood is probably going to chime in and tell us all -- and we welcome it, Kip -- how I could have saved a lot of elbow grease, here )

First, the whole window with some sanding already done. It was badly scratched over the whole center, but you can see I've removed most of the scratches to the right with grade 220 sandpaper. The closeup gives you a better idea of the scratches. They are deep enough to feel with a fingernail, but not more than 0.01" and probably less.



Ater sanding and doing some polishing using a rotary polisher and some Nuvite, I could see through the window pretty good, but only when looking pretty close to 90 degrees incidence. I had run the polisher way too fast and the surface got quite warm. This created something like a micro diamond plate surface, or like the washboards in a dirt road. Not really visible, but enough to cause optical degradation at any off angle.

So I went back and sanded with 220, 320, then 600, and in only about 15 minutes it was ready for the polish! The 600 allowed me to look through the window like a foggy day. Then I applied "S" grade Nuvite. Viola! Clear as plexiglass. You can still see a few scratches--I wasn't trying for a finished product, just to see if I could repair the washboard in the middle. Worked great.



What looks like haze in the above photo is really just bright Mojave sunny day (like 80 degrees here today) and reflections of the sky and nearby RVs. the plexiglass looks good--not 100%, more like 99 and 44/100ths (boy, where did that pop up from?).

Zep

[Zeppelinium]

The bad news is that the airplane frame is about 1-3/8" thick. My door casting on the Caravel is only about 1-3/16" thick. This means the frame will be "proud" inside the inner skin about 1/4". I'm working up a fiberglass mold for a shroud that will take care of that, but I may not be able to get it done before I leave in a week. But eventually....



The shroud does two things--it hides the frame on the inside of the door and replaces the clips that hold the glass in the frame. I didn't take the time to draw the nutplates along the outer edge of the frame, but they are depicted by the callout and arrow. A little strip of 1/8" weather seal along the glass edge of the shroud and everything should be nice and tight.

Oops, didn't label the frame. It's the other crosshatched item in cross section. You can see the lip around the glass that will be a little proud of the outside skin, but I think it will look at lot like the 70's frames around the windows. The glass is actually flush with the lip, forgive me for not taking the time to make this PERFECT.

Zep

[Fyrzowt]

Great work Zep, great idea.
Dave

[Aerowood]

There is a Plexiglas polishing kit called "Micro-Mesh" that has all of the different grit sandpaper for these windows. I've used a pneumatic DA to sand them out and done a lot by hand also. You did everything right in polishing them out Zep. No need to get out the optical micrometer to measure the deep of the scratches to see if they are still airworthy, because I don't think they will see FL 36 again.
Kip

[Sugarfoot]

I'm impressed, I had no idea there were methods that worked so well to polish out scratches from Plexi-glass.

[Zeppelinium]

I didn't get the shroud from the airplane, so I'll have to make one. I didn't think the airplane version would fit, anyway, since the window frame is about 1/4" thicker than the door--no room for the fancy roller shade, either.

First step is making a mold. Fortunately I'm in a place where I can pick up 16 lb foam from the trash bin. In order for the shroud to push on the window plexiglass and hold it in place, it needs an inside "leg" that's 11/16" deep. In order to reach down to the inner door skin, the outside "leg" needs to reach down only 1/4". The trick will be to form some 3/4" thick foam in the right shape.

I started by making a curved surface slightly larger than the frame. You can see the frame fits snugly onto this surface. The back side is heavily reinforced with thick blocks of foam. I thought that the thick pieces would require lots of sanding, using the frame as a block for the sand paper. I was pleasantly surprised to find that cutting the curve by hand using a bandsaw was plenty accurate. Everything is glued together with "5-minute" epoxy.



Now to make the mold. I used the frame (for the inside curve), the glass, and the round edge of a plastic bucket lid (it was just the right radius to make the outside curve) to draw the desired shape on both the curved surface that was going to receive the mold pieces and the pieces themselves. In order to get the specified 50/50 mix and not use too much resin, I filled small cups first, then mixed them in a large cup.



This stuff seems very viscous, but it's also slippery when trying to keep the pieces in place--so I did one piece first so I'd have something to push against. Five minutes wasn't too long to wait to start the second set. You can see one side epoxied in place in the left photo and the finished and sanded mold on the right. Well, not quite finished--it needs to be coated with several coats of resin and then covered with a waxy mold release coat.



Next step is to do a contact layup over the waxed mold. I should be able to get multiple shrouds out of this "tool." The fiberglass will drape all the way to the curved surface on the inside and only 1/4" down on the outside. Actually, it will be past that point and cut off at 1/4" with an abrasive cutoff wheel after it cures. The inside will have a "foot" that extends horizontally across the curved surface for 3/8" in order to apply a distributed force against the plexiglass--more on that when I actually do the composite layup.

Zep

[Aerowood]

How's your window project progressing?