How to Make (or Buy) Plexiglas Covers for Wingtip Lights

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wsimpso1

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Scheming out my wingtips and the Plexiglas covers that go over them. So, given that the airplane is a one off, and the tips are compound convex shapes (much like the ones used on RV's). They will be about 10" long, 10" wide, and about 5" deep. So let's get into PROVEN methods of how:

Do we make or buy, and why?
If we are to buy, Please supply recommended shops. Extra points for SE Michigan;
If we are to make:
Do I attempt to simply drape frame over a male mold?
Do I make an over-height male mold, then heat the sheet in a frame and then stretch form?
Do I vacuum assist onto the male mold?
Should I go female mold and vacuum assist into the mold?
What thickness would you use for the sheet?

I am also figuring that I will have to work it out, and when it does work, then I can put in the offset in the tip molds and build tips, then maybe iterate... I would like to reduce the "development" by using PROVEN methods.

So, let's hear it.

Billski
 

pictsidhe

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Think of it as a mini canopy...
If you want them optically clear, you'll need an optical grade mould, or blow/vacuum a bubble. If you are ok with slight ripples and marks etc, a mould is an option. I would be grabbing a heat gun and just trying stuff out and refining until I made something I am happy with. By just blowing it, you will have a hard time getting an exact shape, so I'd try a mould first. Expect scrap...

Something I've done on motorcycles: I made glass fibre lens. With a clear resin they are very good at transmitting light.
 

Topaz

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I recall one or more articles on this very subject in Sport Aviation from years past. The idea was to create a wooden male mold, heat the plastic in the home oven, and simply drape it over the mold.

There may even be information on this in Bingelis' books. I can check that. Hang on. Will update when I have an answer.

UPDATE: Nothing in Sportplane Construction Techniques. I'm sure I saw an article on this in Sport Aviation. Would've been in the 80's-90's. If you have access to the EAA library, it's a place to look.
 
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Turd Ferguson

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The Bingelis article on stretch forming was March 1988 issue of Sport Aviation. Anyone with a current EAA membership can look up the article online.

He made the light lenses for his Falco this way.

Correction: Typo on the yr. It was March 1988, now corrected.
 
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BoKu

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I made a male mandrel, sent it to Cee Bailey, and got three sets of great looking lenses that fit perfectly for $75 per lens. If I had to do it again I'd ask if they could make them out of polycarbonate with a UV coating.

79425869_1762464190565254_3427058201953042432_o.jpg
 

Toobuilder

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Whats the general configuration of the lens? Is it the whole fwd/outbd 25% of the tip or is it more of a flat wrap?

There are a bunch of wingtips in the kitplane world - maybe find one on an existing airplane thats close enough for you to take a section from and adapt. Conversely, you might be able to alter the OML of your tip to match an existing lens. Much easier to have a supply of lenses available than crank out a one off when it cracks (and it will).

I have had some success with vacuum forming parts like this. A vacuum base is easy to make and a shop vac provides enough sucking power.
 

wsimpso1

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Whats the general configuration of the lens? Is it the whole fwd/outbd 25% of the tip or is it more of a flat wrap?
Looks like an RV, compound convex shape, forward quarter of the tip, like the picture in BoKu's post.

There are a bunch of wingtips in the kitplane world - maybe find one on an existing airplane thats close enough for you to take a section from and adapt. Conversely, you might be able to alter the OML of your tip to match an existing lens. Much easier to have a supply of lenses available than crank out a one off when it cracks (and it will).
Needs to have a chord of 32" and Riblett 37A315 foil. Not much of a chance.

I have had some success with vacuum forming parts like this. A vacuum base is easy to make and a shop vac provides enough sucking power.
Now that sounds like a plan. Seems like the big deal is getting the frame sealed fast so you can pull it down. Any good websites or articles on how to do this?

Billski
 

wsimpso1

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The Bingelis article on stretch forming was March 1988 issue of Sport Aviation. Anyone with a current EAA membership can look up the article online.

He made the light lenses for his Falco this way.

Correction: Typo on the yr. It was March 1988, now corrected.
I shall look it up. Thanks.
 

wsimpso1

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The Bingelis article on stretch forming was March 1988 issue of Sport Aviation. Anyone with a current EAA membership can look up the article online.

He made the light lenses for his Falco this way.
Tony Bingelis' article covers how to stretch form without a vacuum using a male mold, frame, and a guide plate. Good background.
 

wsimpso1

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Looking like a vacuum table and male mold for these parts. It will be a rehearsal for the windshield and side windows, which will require a much bigger table then.

Thanks for the guidance!

Billski
 

Jay Kempf

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Vacuum table is a good thing to have for any reason. CNC for the buck. If you have a CAD file let me know. Been doing nothing but CNC one off molds lately. Something that size is probably a hour or so of run time to sanding tolerances in something pine or MDF like.
 

Toobuilder

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Concerning finding an existing piece from another kit... I was not suggesting adapting the entire tip - just the lens. If the airfoil is less than optimal for the last 5 inches of span is that a deal breaker?

As for sealing the frame to a vacuum box - it seems that the warm plexi will confirm to a reasonably smooth surface just fine. Not much need to get too exotic. Maybe some strips of silicone baffle material or even weatherstripping from one of the big box stores. Keep in mind the process from rubbery plexi to a molded part takes literally seconds. It's not like bagging composite.
 
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ScaleBirdsScott

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Here's how Grumman did it on the Hellcat.

(link should jump to 17:09)


Seems pretty simple-enough to replicate even this method with some work, but the vac works pretty well for sure if you can build the whole rig.
 

Iwerk

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Belovac have some good videos on YouTube - for vacuum forming basics.
 

wsimpso1

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Vacuum table is a good thing to have for any reason. CNC for the buck. If you have a CAD file let me know. Been doing nothing but CNC one off molds lately. Something that size is probably a hour or so of run time to sanding tolerances in something pine or MDF like.
Thanks for the offer. I have foam and fiberglas plugs and base molds for the wing tip on the table now, so I am planning to just pull a male mold buck from them. Attached is photo of one plug with bottom mold, before top mold was laid up.
Billski
 

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David L. Downey

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You might be able to (perhaps too large a lens and therefore not stiff enough?) use the modeling technique that takes a PET container big enough to encompass the part plug and then with judicious application of heat allows the plastic to atempt to revert to its original extruded tube size - ending up with replication of the inserted mold. Works pretty well but I don'tknow that you can find a PET container that large...
 

Tom H

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Billski, I tried to make wingtip light covers similar to what you are wanting to do. My covers are smaller, about 4" long, 3" deep, compound curves.
I tried the Bingelis method from the SA article mentioned. I could not get the lower (inboard, wider area) to pull in to the male plug.
So, I made a vac. box/base from 1x3s on the sides, ply bottom and top, with top drilled with many 1/4" holes. On one side I made a hole to receive the shop vac hose end. I put weather seal foam tape around the edges of the top to seal with the plexi frame.
The male plug was fixed in the center of the top surface, with some gap between the plug and the top box surface.
I made the plexi frame from plywood, with a matching clamping frame, held together with screws around the edges.
The frame w/ plexi was put in the kitchen oven, heated slowly until bubbles just started to form around the edges. This is the tricky part. Too much heat and bubbles form quickly through the sheet, which ruins it. The plexi drooped a good bit after getting hot.
Then, with shop vac running, I quickly placed the plexi frame over the male plug. The combination of pushing the plex down over the plug and then the vacuum assisting after the frame sealed against the top of the vac box pulled the hot plex over the plug.
Sorta. I tried about six times, but I never was able to get the whole lens cover properly shaped. One came out shaped pretty well, but had bubbles. I finally quit for the time being to think it over.
As stated in another post, the plex goes from hot, soft, droopy to firm very quickly. Maybe some way to keep it hot during the forming/vacuuming would be the trick. Maybe a couple heat guns blowing over the plex?
Or, maybe higher vacuum with a vac reservoir tank?
Or, extra heat and higher vac?

When you get a good technique developed, let us know.

Tom H
 

FinnFlyer

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A bit late on this thread. You could buy them from Van's Aircraft.

On my RV-3, I was too cheap and made them myself. Stood the wingtips in a small bucket or can with gypsum (sheetrock mud). One mold for each side.

Can't remember if used a hair dryer to blow the plexi into the mold or if I put it in an oven.

Finn
 
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