Polycarbonate screen damage

[Raytol]

Does not even have to be liquid petrol, just the vapour or fumes will do it.

 

 

[Raytol]

Does not even have to be liquid petrol, just the vapour or fumes will do it

 

 

[APenNameAndThatA]

The screen in the photo is a brand new polycarbonate sheet (with less than 5 hours flying time), installed as a replacement for the original screen. The factory used to fit polycarbonate as standard, but now also fits PET screens, which are more pliable but are a little more prone to scratching. The owner says that no fuel or other chemicals were spilt or used on the windscreen.

Interesting. Foxbat windscreens are an ongoing issue. Perhaps, the main weak point on the whole aircraft. I Would have thought that they could use stronger, thicker plastic if they annealed it after they bent it, or actually moulded it a bit before it was fitted. It would be more expensive, but it seems to me it would help. Maybe annealing it would help even if it was no thicker. (Disclaimer: no engineering qualifications or experience.)

 

 

[SilverWing]

Thank you to everyone for your responses. In the main, mostly confirm my own thoughts and those of plastic sheet suppliers.

 

 

[Deskpilot]

What ever you do, don't get Acetone near it. They hate each other

 

 

I'm now trying to find replacement polycarbonate at a reasonable price.

 

 

[Old Koreelah]

... Foxbat windscreens are an ongoing issue. Perhaps, the main weak point on the whole aircraft. I Would have thought that they could use stronger, thicker plastic if they annealed it after they bent it, or actually moulded it a bit before it was fitted...

I tried to "anneal" my Lexan screen to slow the process of internal stress cracking, which I blamed for the deterioration of its transparency. It was a disaster, because polycarbonate is hygroscopic, and you have to "cook" the water out of a sheet at 60 C for 24 hours before attempting any heat forming.

If attached securely, Lexan can be damned strong, perhaps stronger than other parts of the structure. It's just a bit fussy about what chemicals you inflict on it.

 

Just remember that you won't be able to smash your way thru a Lexan sheet if you prang it.

 

 

[Old Koreelah]

...I'm now trying to find replacement polycarbonate at a reasonable price.

$180 for a 2400X1200X2 sheet at Newcastle.

 

 

[Downunder]

The screen in the photo is a brand new polycarbonate sheet (with less than 5 hours flying time), installed as a replacement for the original screen. The factory used to fit polycarbonate as standard, but now also fits PET screens, which are more pliable but are a little more prone to scratching. The owner says that no fuel or other chemicals were spilt or used on the windscreen.

Whatever probably spilt or splashed (even blown) onto the screen may not have even been seen by the owner.

 

Was it parked out in the open? Near a fuel bowser? Was it taxiing behind an aircraft with overfull tanks with propwash sucking some fuel out....Parked near a maintenance facility?

 

The open space at airports allow stuff to be blown a long way.....

 

 

[Deskpilot]

$180 for a 2400X1200X2 sheet at Newcastle.

I got quoted $130 for a meter square of 1.5mm thick, way too pricey for my pockets. If necessary I'll try 1.mm but not sure if it'll be strong enough. Luckily, there no flat portion trying to push it's way through the air.

 

 

[Kenny]

Just one more problam poly sheeting can have is coming in contact with petro chemical rubbers.

 

I used some rubber mouldings from Clark Rubber to finish of the fitting of a screen on my Savannah where an alumineum flashing was touching the screen I used the moulding to give it a nice looking finish, after a while the poly became crazed where it was touching the rubber.

 

Two years later it is still holding together

 

Cherrs

 

Ken

 

 

[Kenny]

PS Re pricing, the place in Caboolture wher I got mine 2 mm thick, from memory it was under $100 for a full sheet

 

 

[ISA]

I'm not sure that Windex would be culpable in this situation. I use it all the time. Saw Dick Smith years ago cleaning the bubble on his helicopter using Windex and following up with Mr Sheen.

I've been using Mr Sheen or similar for many many years, in fact I treat my whole plane with the stuff, smooth and shiny results -:)

 

 

[Phil Perry]

It's caused by spilling fuel on the windshield. The rapid cooling of the fuel evaporating on a curved (i.e. stressed) polycarbonate windshield wrecks it in seconds.Generally they don't break inflight afterwards but would need replacing asap.

Polycarbonate really Doesn't like any kind of reactive solvent anywhere near it. It is incredibly strong physically, compared to acrylics like Perspex, which is very brittle, but solvents and Fuel should be kept well away from it. I used to manufacture Illuminated sign faces using Poly in High Vandalism risk areas. . .it withstands a lot of punishment. . .But if you wipe it clean with a solvent, like paint thinners, it melts the surface. Not good for windows in aircrft. . .Nice and bendy though, even at 1 mm thickness, and still strong enough to thwart small birds. . . .

 

What we REALLY need is that Star Trek 'Transparent Aloominum' stuff. . . .

 

 

[Phil Perry]

What ever you do, don't get Acetone near it. They hate each other[ATTACH=full]61588[/ATTACH]

 

I'm now trying to find replacement polycarbonate at a reasonable price.

The 'Big Two' brands in the UK are MAKROLON. .and LEXAN. I don't know if these brands are available in Australia. . (Try Mr. Google) I've used both coloured and clear MAK for impact resistant illuminated shopfront signage, and lots of Clear LEX for replacement screens on many Ultralight / Microlight aircraft as.it's normally available in useful thicknesses like 1 and 1.5 Mil. Treat it like Timber when drilling fixing holes though, ie Slow speeds, otherwise it melts the material. I've used a good pair of tinsnips to ( carefully ) cut out screens using the flattened out old one as a pattern, in the event of a missing screen, made templates out of card.

 

 

[Phil Perry]

I got quoted $130 for a meter square of 1.5mm thick, way too pricey for my pockets. If necessary I'll try 1.mm but not sure if it'll be strong enough. Luckily, there no flat portion trying to push it's way through the air.

Bloody 'eck Doug. . . .that's disappointing. . .3 months back I bought a full sheet of 1.5 Mil clear ( 2440 x 1220 mm ) for £36.00 to replace 2 badly crazed side windows on a Rans S6 . .

 

I guess there is a greater demand for the stuff in the UK, which reflects on the pricing structure. . . .

 

 

[M61A1]

The 'Big Two' brands in the UK are MAKROLON. .and LEXAN. I don't know if these brands are available in Australia. . (Try Mr. Google) I've used both coloured and clear MAK for impact resistant illuminated shopfront signage, and lots of Clear LEX for replacement screens on many Ultralight / Microlight aircraft as.it's normally available in useful thicknesses like 1 and 1.5 Mil. Treat it like Timber when drilling fixing holes though, ie Slow speeds, otherwise it melts the material. I've used a good pair of tinsnips to ( carefully ) cut out screens using the flattened out old one as a pattern, in the event of a missing screen, made templates out of card.

Both of those brands are available here Phil. I found sign making shops the best source too. Done properly, using a dull bit at a high speed will melt the edges of the hole a bit, this isn't bad, it helps stop cracking. A good quality step drill is also good. Snips work well for cutting, but the edges still need to be finished on a linisher or such to prevent cracking.

If it is being riveted, always make your holes oversize and use a large flanged rivet or a washer so to help prevent cracking out from the holes.

 

 

[Phil Perry]

Both of those brands are available here Phil. I found sign making shops the best source too. Done properly, using a dull bit at a high speed will melt the edges of the hole a bit, this isn't bad, it helps stop cracking. A good quality step drill is also good. Snips work well for cutting, but the edges still need to be finished on a linisher or such to prevent cracking.If it is being riveted, always make your holes oversize and use a large flanged rivet or a washer so to help prevent cracking out from the holes.

ALL agreed mate,. . I just thought I might be getting a bit boring. . . . .

 

Big signmaking shops are great. . .just ask if you can scourge their skips for bits. . . .the stuff that they chuck out are horrifyingly nice and very useful. . . .I just got asked to make some taxiway directional signs for a regional airport ( repeat work ) and checked the local skips and found sufficient 10mm foam board to make all of the signs at NO cost for the frangible Foam board faces,. .

 

I only have to buy the 25mm Cliprails which are rivetted to the rear for fixing.to the support poles. Plus the Reflective yellow, red and white self adhesive vinyl material to make the background and lettering for use at night.. . . .saves me a load of dosh and increases the margin.

 

 

[Old Koreelah]

...If it is being riveted, always make your holes oversize and use a large flanged rivet or a washer so to help prevent cracking out from the holes.

That's pretty much what I plan to do with my Perspex canopy when I renovate my beast. I hope to replace the ugly big stitching screws with wide flange rivets- after I've done a few tests with some scrap.

 

Have you had any experience riveting acrylic?

 

 

[Bruce Tuncks]

Sailplane canopies are acrylic. They are generally attached with epoxy flock, and the bond is such that it is hard to clean off the residue of a broken canopy. Initial fixing is done with countersunk screws, but these really only hold the canopy while the epoxy is wet.

 

My early Jabiru kit was supposed to have the acrylic windscreen attached with silicon and screws. This leads to cracking at the edges of the screen due to tiny movement permitted by the silicon.

 

Because of my glider experience, I epoxied the screen in place and it has been ok for 18 years now. Also it is is more a part of the structure than if it were siliconed in.

 

 

[Bruce Tuncks]

Don't just drill holes in acrylic without learning the traps... it is easy to ruin the job.

 

 

[Old Koreelah]

Blunt drill melts a hole via friction rather the cutting.

 

 

[fly_tornado]

dull your drill bits on concrete

 

 

[kgwilson]

A sharp drill will bite and pull the bit through if you have too much pressure on it and the hole will be the shape of the fluted drill. If this happens you will need to reverse the drill out (slowly) and redrill very gently at high speed. If you don't reverse the drill out & try to cut the hole you will crack the perspex. I did this with my first hole on a sample piece of perspex to find out how it would drill. After a couple of goes I got it right. Sharp drill, high speed, very light pressure & once drilled some honing with the same bit. The holes were for AN3 bolts & the honing made them just oversize which was perfect.

 

 

[Bruce Tuncks]

Of course, I was referring to acrylic bonded to fibreglass. If you have to fix the screen to metal, then the problem is much more difficult . I guess that is why those foxbat planes have so much trouble.

 

 

[tillmanr]

If you take the sharp cutting edge off the drill similar to drilling in brass the material is scraped out rather than cut out. This stops the drill from biting in and cracking the material.