What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Reforming Canopy Fairing to plexiglass fit?

mfleming

Well Known Member
Patron
Reforming Windshield Fairing to plexiglass fit?

About a couple weeks ago I Sikflex'ed my windshield fairing in place. Today I pulled the clamps from around the bow. Up till now, the faring and sliding canopy fit perfectly. Something happed during the Sika process and now the canopy contacts the fairing in at least one spot.

My mistake may have been clamping the windshield around the bow. The contact is on the left side. I can get a plastic shim under the fiberglass and this allows the canopy to close.

I used West System epoxy to lay up the fairing.

I've read others using heat to reform fiberglass. To me, best way would be close the canopy with a shim under the contact point and heat the fiberglass. BUT I'm super worried that heating the plexiglass under the fairing could have catastrophic results.

How would you fix this depressing problem?
 
Last edited:
If you can fit a scrap strip of aluminum in there to act as a replacement canopy that would be my recommendation. I’d keep the cowling away from the repair altogether. That way you avoid bumping it or scratching it.
 
Oh that's a bit of a bummer, I think the way I'd approach it is firstly not to use heat for fear of cracking the plexi. (I have tried using heat to re-shape a polyester fairing and it wasn't very effective anyway).

The plans call for the fwd edge of the slider plexi to be bevelled, so I would check that's been done enough, and then also look at grinding a bit off the underside of the epoxy fairing where it overhangs the roll bar.

Have you already drilled the mounting bolts for the side roller brackets? If not then it may be possible to drop the front bow down slightly by trimming the ends of the tubes. Otherwise it would mean buying new brackets and drilling after shortening.
Good luck!
 
I’m pretty sure I’ve read where making minor adjustments to epoxied fiberglass was a thing. Hoping to get others experiences…
 
I’m pretty sure I’ve read where making minor adjustments to epoxied fiberglass was a thing. Hoping to get others experiences…

Yes - but frustratingly very minor adjustments. Based on my failed attempts to use heat on the first RV project's empennage fairing I no longer do this.

Carl
 
Reshaping fiberglass

I’m pretty sure I’ve read where making minor adjustments to epoxied fiberglass was a thing. Hoping to get others experiences…

I've done it many times. Never with the plexi attached.
Fiberglass parts seem to take a set if left without structure. I keep my canopy closed for that reason.
I reshaped my windshield trim but it was not on the plane. Also reshaped intersection fairings and empennage tips.

You need a heat gun and infrared thermometer.
You need a plan and any stuff like shims or clamps ready.
The part cools fast so it must be set up quickly.
Heat slowly and carefully keeping the gun moving and reading temps. Do not exceed 200 anywhere but try to get a uniform temp. Just below seems to work well. Should be hot to touch but not so hot you can't hold it.
Quickly set up the part the way you want it to be shaped. Walk away till stone cold.

No guarantees. I have no idea what effect there will be to Sika or Plexi. Suggest making a sample and testing first.
 
I've done it many times. Never with the plexi attached.
Fiberglass parts seem to take a set if left without structure. I keep my canopy closed for that reason.
I reshaped my windshield trim but it was not on the plane. Also reshaped intersection fairings and empennage tips.

You need a heat gun and infrared thermometer.
You need a plan and any stuff like shims or clamps ready.
The part cools fast so it must be set up quickly.
Heat slowly and carefully keeping the gun moving and reading temps. Do not exceed 200 anywhere but try to get a uniform temp. Just below seems to work well. Should be hot to touch but not so hot you can't hold it.
Quickly set up the part the way you want it to be shaped. Walk away till stone cold.

No guarantees. I have no idea what effect there will be to Sika or Plexi. Suggest making a sample and testing first.

The clamps around the windshield bow were left on for a couple of weeks and may have contributed to the change in shape.

So I've been thinking of how to do this all night.

The part of the fairing that is slightly deformed and contacts the sliding canopy is the aft (overhang) section of the windshield fairing. It contacts the canopy on a small area, maybe 1".

My plan is this:
  1. Make a shim that matches the curve of the canopy.
  2. With the canopy open and away from the fairing, heat the fiberglass contact area to the desired temperature.
  3. Quickly close the canopy while installing the shim.
  4. Allow to cool.
  5. Repeat with thicker shims if necessary.

Also I plan to make a test article and measure the softening characteristics of the fiberglass using a combination of thermal gun and temp probe on my multimeter. Fortunately I have plenty of scraps of the fiberglass layup and canopy plexiglass to work with.
 
Last edited:
Shim

The clamps around the windshield bow were left on for a couple of weeks and may have contributed to the change in shape.
<snip>
My plan is this:
  1. Make a shim that matches the curve of the canopy.
  2. With the canopy open and away from the fairing, heat the fiberglass contact area to the desired temperature.
  3. Quickly close the canopy while installing the shim.
  4. Allow to cool.
  5. Repeat with thicker shims if necessary.
<snip>

Clamps are the culprit. Fiberglass will take a set.
I recommend something less conductive. A metal shim will suck heat and transfer it to the canopy side. I would make something and try to reshape it without closing the canopy. Maybe a wood block the correct shape. Clamp that in place. No issues with the plexi of the canopy getting locally heated.
Just a thought.
 
Fairing

I think you have a good plan Michael. I wouldn’t use a metal shim.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Clamps are the culprit. Fiberglass will take a set.
I recommend something less conductive. A metal shim will suck heat and transfer it to the canopy side. I would make something and try to reshape it without closing the canopy. Maybe a wood block the correct shape. Clamp that in place. No issues with the plexi of the canopy getting locally heated.
Just a thought.

I think you have a good plan Michael. I wouldn’t use a metal shim.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

Good advice on not using a metal shim. I'm looking around for something suitable thats thin and has some insulation value....
 
Hey Michael- Maybe a dumb question, but if it's just an inch of slight interference, would it be possible to just locally sand the underside of the fairing in that area to make it a little thinner there?
 
Hey Michael- Maybe a dumb question, but if it's just an inch of slight interference, would it be possible to just locally sand the underside of the fairing in that area to make it a little thinner there?

Not in this case. The deformation is such that the top of the fiberglass is almost flush with the canopy.
There are several areas that deformed, this being the worst...all right under where a clamp was placed.
 
I had good results re-forming my empange fairing with heat. Used a heat gun and infared thermometer to check even temperature. As I recall, it took about 240 F to get it to move and then secure to shape untill cool.
 
Last edited:
I would go with Terry’s suggestion & explore the sanding option. I also would caution shimming the w/shield at this late stage for fear of creating pressure spots & potential future cracking.
Slowly grind out the low spots with a sanding drum on a drill, than build up the top with a few layers of glass where needed.
 
I would go with Terry’s suggestion & explore the sanding option. I also would caution shimming the w/shield at this late stage for fear of creating pressure spots & potential future cracking.
Slowly grind out the low spots with a sanding drum on a drill, than build up the top with a few layers of glass where needed.

So the plan is not to shim the windshield.

The shim will only be used to create some space between the fiberglass and plexiglass while the fiberglass cools off, the shim is then discarded.
 
I had what sounds like, the exact same thing happen on my RV6 slider, except I didn’t use Sika to attach the windshield fairing. My slider fit fine at first, but then a couple weeks later the slider contacted the windshield fairing on the lower right side on a small area that prevented closing it all the way unless I pried the fairing out just a little. I don’t remember how many layers of glass I used when I made the windshield fairing, but it was thick enough that I could just sand the fairing a little on the inside to regain a perfect fit. The fairing that was left was a little thin right there so I layed up a couple short layers of 9 oz cloth on the outside of the fairing and then faired it in with micro. You can’t even tell now where that layup is, and the fit is still perfect.
 
Finally I'm able to turn my attention back to fixing this issue. Yesterday I experimented with heating fiberglass scraps and measuring when they are malleable enough for the fix.

The one part of the puzzle that I haven't figured out is a non metallic shim. I've tried some cutting mats that may be able to be used but they get soft at the heat levels needed.

Any ideas for non metallic shims would be welcome. Approximately a 1/16" shim is needed.
 
Last edited:
Shim

Finally I'm able to turn my attention back to fixing this issue. Yesterday I experimented with heating fiberglass scraps and measuring when they are malleable enough for the fix.

The one part of the puzzle that I haven't figured out is a non metallic shim. I've tried some cutting mats that may be able to be used but they get soft at the heat levels needed.

Any ideas for non metallic shims would be welcome. Approximately a 1/16" shim is needed.

Thin aluminum with a piece of cereal box on the hot side. Cut a section from an old CD box. Lots of options.
 
Thin aluminum with a piece of cereal box on the hot side. Cut a section from an old CD box. Lots of options.

Boy, I tell ya……. that Larry Larson has so many good idea tricks. A cereal box. We don’t need to waste money figuring this out, because this one (and others) is free. On one of his videos Larry suggested using the small individual yogurt containers to mix batches of epoxy. I’ll bet I’ve used 100 of these containers. I now eat yogurt for breakfast at least 4 times a week. I’m healthier today because of this great idea……. thanks Larry!

Sorry - didn’t mean to hijack your thread…….
 
Last edited:
Cheap

Boy, I tell ya……. that Larry Larsen has so many good idea tricks. A cereal box. We don’t need to waste money figuring this out, because this one (and others) is free. On one of his videos Larry suggested using the small individual yogurt containers to mix batches of epoxy. I’ll bet I’ve used 100 of these containers. I now eat yogurt for breakfast at least 4 times a week. I’m healthier today because of this great idea……. thanks Larry!

Sorry - didn’t mean to hijack your thread…….

Nice to know my tips are keeping you healthy. :D
I'm cheap!
It's actually an old wrench head trick. When you don't have gasket material, a cereal box works pretty good. I've stolen a few boxes from the kitchen. :D
 
Big risk

I used nylon washers - a little hard to find, but cheap when you do. I use then under screw heads to avoid paint damage and shimmed a few places on my canopy to match contours.

On your heat. I have mixed success on this. I deformed a small area of canopy accidentally when removing some crappy west epoxy that would not cure. So be very very careful around that plexiglass, it will deform at much lower temps than the epoxy. Big risk.


And - heat reforming might just return after sitting in the OSH sun.
 
I have reformed a number of fiberglass parts using heat. The results depend a lot of the specific resin and how the part was cured to begin with. In my experience, For wet layups with epoxy, you can reform once. After the post-cure caused by the heat, you are done. The problem in your situation is the amount of heat required. Epoxy post-cure temperatures generally range around 200-300F. The glass transition temps for acrylic are in the 200-220F range. So the risk of deforming the acrylic is very high.
 
About a couple weeks ago I Sikflex'ed my windshield fairing in place. Today I pulled the clamps from around the bow. Up till now, the faring and sliding canopy fit perfectly. Something happed during the Sika process and now the canopy contacts the fairing in at least one spot.

My mistake may have been clamping the windshield around the bow. The contact is on the left side. I can get a plastic shim under the fiberglass and this allows the canopy to close.

I used West System epoxy to lay up the fairing.

I've read others using heat to reform fiberglass. To me, best way would be close the canopy with a shim under the contact point and heat the fiberglass. BUT I'm super worried that heating the plexiglass under the fairing could have catastrophic results.

How would you fix this depressing problem?

Here’s my follow-up on fixing this issue.

Using heat sounded promising so I practiced on some test articles. In the end, this method was abandoned because I couldn’t get the test article to stay re-formed without using excessive heat.

So here’s what worked. I had some really thin acrylic sheets laying around, about 0.040”. These sheets are super flexible and not brittle at all. Theses would be used as temporary shims. I cut some lengths that matched the areas that the canopy was contacting the fairing. The canopy was slowly closed while the shims were hand held in position. The fairing flexed out just a bit to accommodate the shims. The shims were left in place for over a week with the canopy fully closed and latched. This improved the fit a bit, so I reinstalled the shims and every time I was at the hangar, the hangar heat was turned up to help the fairing to reshape around the shims.

Now the canopy closes with just a little jiggling to fully close. Not perfect but it’s fully functional :)
 
Last edited:
Back
Top