Polycarbonate screen damage

[SilverWing]

I recently noticed this damage to a polycarbonate windscreen. Definitely not stones - the screen remains smooth to the touch inside and out. Questions: (a) anyone any ideas as to what's causing this? (b) Is it dangerous - ie might the windscreen break in flight? © How to prevent in future? All helpful comments gratefully received!

 

 

 

[BirdDog]

Hmm... I am no expert (and someone else may add) but that looks like stress cracks. If the out and in and are still smooth, then it's obviously internal.

 

It looks similar to what happens when you heat and cool plastics rapidly. like this image...

 

http://www.annealingplastics.com/glass.jpg

 

 

[BirdDog]

This is also a good read....

 

It talks of chemical use, and causes etc.

 

Environmental stress cracking - Wikipedia

 

 

[SilverWing]

Hmm... I am no expert (and someone else may add) but that looks like stress cracks. If the out and in and are still smooth, then it's obviously internal.It looks similar to what happens when you heat and cool plastics rapidly. like this image...

 

http://www.annealingplastics.com/glass.jpg

Many thanks BirdDog - i'll put it in the mix

 

 

[Head in the clouds]

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.

 

 

[rgmwa]

Did you spill any drops of mogas on it? That will cause almost instant cracking.

 

I'm about to replace my rear window for the second time for that reason. I wouldn't be too concerned about your window failing in flight.

 

 

[facthunter]

I think the fine cracks that all go in the one direction are stress cracks, maybe as the result of vibration.. Fuel leaves an Opacity/ Dulling of the place where the fuel went. I feel the cracks weaken it to an unknown extent There is no way they wouldn't. Nev

 

 

[Downunder]

I recently noticed this damage to a polycarbonate windscreen. Definitely not stones - the screen remains smooth to the touch inside and out. Questions: (a) anyone any ideas as to what's causing this? (b) Is it dangerous - ie might the windscreen break in flight? © How to prevent in future? All helpful comments gratefully received!

It looks like a chemical has sprayed or been blown across the screen. People using carb cleaners (acetone) in pressure packs need to be careful on Rotax engines it doesn't blow on the screen....

 

Carb cleaner is also sometimes used to remove PULP/98 stains around fuel tank fillers, and again, can blow over the screen/windows.

 

 

[M61A1]

A cut and paste from a UK website about chemical resistance of Polycarbonate.....

 

I think someone spilled fuel on it. I've had it happen myself. Doesn't matter how quick you clean it, it still happens.

 

The third type of attack is often the most difficult to predict since environmental conditions dictate whether or not the plastic will be affected. Combinations of certain environments, coupled with stress and/or strain upon the material, cause stress cracking or crazing of the polycarbonate sheet. Crazing can be induced at moderate to high stress levels by low molecular weight hydrocarbons. Products such as acetone and xylene may cause stress cracking even at very low stress levels and should therefore be avoided.

 

 

[Head in the clouds]

M61 is spot on. I conducted a series of test when this was discussed on HBA. If the poly sheet was not curved the petrol did not attack it whether fully immersed or whether sprayed on/spilled on and allowed to evaporate and there was no sign of any chemical attack (mistiness/cloudiness of the surface etc).

 

However some products, acetone maybe, (I didn't find Xylene to be a culprit but one of the paint thinners was), would attack the surface slightly even when the product was not under bending stress.

 

When petrol has been spilled on curved/stressed polycarb sheeting and the stress fractures have appeared, there was sometimes evidence of the spill on the surface and sometimes not. This wasn't as a result of my experiments but shown in photos sent to me by others, of typical fuel spill damage. I was not personally able to replicate the surface evidence with petrol (such as FH described earlier), however, on the windshield of the Kestrel ultralight I bought recently there is a small patch (100mmx50mm) of stress cracking which is directly below one carby overflow and it does show some surface degradation. Perhaps that is from aromatics in a different grade of fuel from that which I used for my tests a few years ago.

 

 

[ClintonB]

I recently recieved a bulliten about plastic windows in Caravans from one supplier. We were seeing an increase in warranty claims for crazing around the mounting and lock points. Turns out the solvents in a lot of cleaners are bad for plastics. Recommended using specialist cleaners like Vuplex or plain old warm water and mild dishwashing soap. I immediately took the windex out of my travel tool bag and swapped it to Vuplex and microfibre for the windshield.

 

 

[Methusala]

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.

 

 

[Downunder]

I think windex contains ammonia. Pretty bad for ploycarbonate/plastics.

 

It is a GLASS cleaner.....

 

 

[facthunter]

Be pretty careful what you use. I have only ever used "aero" recommended products. Might cost a bit more for the product but less in the long run. Nev

 

 

[Old Koreelah]

Very useful thread; the good news is that the price of polycarbonate sheets has more than halved in recent years.

 

If in doubt, just replace it.

 

 

[Methusala]

1. Thoroughly rinse windshield to wet the surface and to float off dirt and mud.
    
    
   
2. Using a damp soft or microfiber cloth, clean the windshield side to side with warm water and a gentle soap or detergent. ...
    
    
   
3. Thoroughly rinse with clean water.
    
    
   

 

 

I humbly stand corrected...ahem!

 

 

[APenNameAndThatA]

There is a post about cleaning these windscreens on Foxbat Pilot. Apparently, they are PET, and not polycarbonate at all. I would email Foxbat to see what they thought. (I follow my own advice and have emailed them lots of times. Unlucky for them, but they know their product really well.)

 

 

[M61A1]

Not according to the A22 manual....

 

AEROPRAKT-22LS Airplane Maintenance Manual A22LS-AMM-02 13 3

 

Structures

 

The airframe of A-22LS airplane includes the following parts: fuselage with polycarbonate glass windscreen and rear skin panels, wings, wing struts, horizontal and vertical tail units (HTU and VTU), wing fillets, strut fairings and engine cowling. Fuselage with fin, wing struts and stabilizer are made of aluminum alloys

 

Nor the A32 manual...

 

AEROPRAKT-32 Airplane Maintenance Manual A32-002-AMM

 

13 3 Structures

 

The airframe of A-32 airplane includes the following parts: fuselage with polycarbonate glass windscreen, wings, wing struts, all-flying horizontal tail (AFHT), vertical tail unit, wing fillets, strut fairings and engine cowling. Fuselage with fin and wing struts are made of aluminum alloys.

 

 

[APenNameAndThatA]

Not according to the A22 manual....AEROPRAKT-22LS Airplane Maintenance Manual A22LS-AMM-02 13 3

 

Structures

 

The airframe of A-22LS airplane includes the following parts: fuselage with polycarbonate glass windscreen and rear skin panels, wings, wing struts, horizontal and vertical tail units (HTU and VTU), wing fillets, strut fairings and engine cowling. Fuselage with fin, wing struts and stabilizer are made of aluminum alloys

 

Nor the A32 manual...

 

AEROPRAKT-32 Airplane Maintenance Manual A32-002-AMM

 

13 3 Structures

 

The airframe of A-32 airplane includes the following parts: fuselage with polycarbonate glass windscreen, wings, wing struts, all-flying horizontal tail (AFHT), vertical tail unit, wing fillets, strut fairings and engine cowling. Fuselage with fin and wing struts are made of aluminum alloys.

That’s my point. Apparently the manuals are wrong.

 

 

[M61A1]

Well, someone's wrong...the transparency in the OP's pic looks exactly like polycarbonate after having fuel spilled on it.

 

 

[APenNameAndThatA]

Well, someone's wrong...the transparency in the OP's pic looks exactly like polycarbonate after having fuel spilled on it.

Did you click on the Foxbat Pilot link in my earlier post? The blue looks a lot like black.

 

Too, if you Google "Poly-Ethylene Terephthalate stress crack", you end up with the link below. It seems that polycarbonate and PET both get stress cracks if you spill solvents on them. (Also, apparently, PET does not like alkalis or UV light)

 

Trelic's picture of the week 05/2018 - Trelic

 

 

[Yenn]

Did you spill fuel on it. I did that with my drifter years ago and got what you showed. the experts may say it couldn't be fuel spillage, but experience says it could well be.

 

 

[M61A1]

No, sorry, didn't see it there.

 

anyway here's a chart that compares the two (and many others).

 

Plastics Chemical Resistance Chart | Plastics International

 

 

[kgwilson]

The 2 most common clear plastic sheeting used use in aircraft windscreens are polycarbonate & acrylic. Polycarbonate is much stronger but has slightly poorer transparency and deteriorates over time by yellowing. Polycarbonate scratches more easily than acrylic and is hard to fix whereas acrylic scratches can quite easily be removed. Strength is hardly an issue so I'd go with Acrylic every time as I can easily polish out scratches. I only use acrylic cleaners and polish on my canopy or mild soap & water. Never use ammonia or glass cleaners on acrylic. There are a number of brands of Acrylic. Plexiglas, Acrylite and Perspex are just 3 of them

 

 

[SilverWing]

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.