Plastic Degradition - UV? - Aging?

[John-Frederick Davie]

Hi Folks - Im a self-confessed buyer of old E-bay and the like - 20th hand aeroplanes.

I have noticed a worryingly large number of plastic component failures. notably, control horns. I have not had a flight failure - more often than not when hooking up control rods etc.

Another notable was the tailplane breaking up, on both a plastic 'Jupiter' and its high wing mate, a Ready. Just a light tap and the surface shatters.

One material I know (professionally), that is damaged by UV is Kevlar. It has to be protected - early test specimens failed at half the expected load after UV exposure.

The trick is there would appear to be plenty of plastic components that DO-NOT degrade with UV exposure or aging - any recommendations guys, as what to go for?

RamseyMAC - J. D.

[J D 8]

I have a twenty year old ARC Jupiter, Probably my most flown aircraft . I I recon it has only lasted this long because when new I gave it a coat of paint and the hollow tail plane is still pliable.

[Graham Davies 3]

Hi JD,

I have some professional knowledge of plastics, and I'm afraid there isn't an easy answer. All plastics tend to be degraded by UV; some worse than others. ABS tends to degrade quickly, Polycarbonate less quickly. HOWEVER, there are grades, brands etc that have anti-aging additives that greatly slow this process. The problem is, how do you know? Well, you don't! To further muddy the water, in processing the scrap material from moulding is often ground down and added to the mould material (called regrind). This is normal, and has minimal effect if kept below around 20% by weight. Low cost economies have been known to use a great deal more than this, sometimes 100%, as it saves a lot of money. This leads to embrittlement, and a very short UV lifespan. Again, the problem is you will not know!

Painting plastics CAN extend the life, but we then have to worry about chemical activity potentially making things worse...

Not all UV-aging is structural though. Sometimes the failure mode is colour degradation. However, embrittlement tends to occur sooner or later.

My advice; keep plastic out of UV light where possible, and regularly test plastic parts. Particularly 'mission critical' parts...

Graham

[Pete Collins]

Hi, I had this problem myself. Not on an ebey bargain but on a model of my own, a loft queen that I resurrected after the odd 40 years or so. I had been flying it for a couple of weekends when I found that the aileron response went very vague and weird. I landed immediately and checked. Sure enough one of the aileron horns had broken off completely. I gave the other one a gentle tweak and it sheared off like a carrot. I checked the rest of the linages and a couple of others were in the same state. Moral - don't trust old plastic linkages! The solution however, is simple - just give them a bend in your fingers and you'll soon see if they are in decent condition. And, of course, if in doubt replace them.

[Stuphedd]

Whenever I bought a "pre-owned" plane from Punctillio Hinckley , Justin , (the owner) would always check the plastic horns and exterior plastic bits for age hardening on older models ,and then sold you the new ones to replace the ones that failed !!

The good old days

[Robin Colbourne]

Its worth noting that most threadlocking compounds have a similar effect to UV damage on most plastics. Loctite do sell a 'plastic safe' threadlocker, Loctite 425 Assure, which is basically cyanoacrylate adhesive.

Plastic-safe threadlocker

You don't have to actually get a blob of thread locker on the plastic to do the damage, the vapour will be sufficent.

[Allan Bennett]

Several of my models are stored in a 'summer house' shed, and I found the Solarfilm covering (they're all balsa) was degrading over time to the extent that on open structures it just disintigrated when touched. I solved that problem by putting tint film from Halfords over the shed windows.

[robert chamberlain]

I have several Futaba " new in box" servos that I bought 20 years ago. Of course, they have not been exposed to the sun, but I was wondering about natural degradation of the plastic gears. New servos are so cheep it hardly makes sense to take a chance, but I hate to throw away 6 "new" units. any thoughts?--Bob C

[J D 8]

I have many Futaba servos of that age and older that that are still in service and have been for all that time, also have some 80's Fleet servos still doing their job.

If you ask me many of the lower price servos available today are not as good.

 Jupiter in pic above has Futaba 3001's and 148's in it and all are original.  RC changed to 2.4 some years ago.

Edited By J D 8 on 22/01/2021 08:50:20

[Engine Doctor]

As already pointed out painting plastic to protect it will only work if a suitable paint is used. Many years I painted some Flair Vintage wheels with Solarlac paint . Within a year they became brittle like an eggshell as the paint or the solvent had denatured the plastic. I replaced them and painted the replacements with Humbrol and they were fine years later. Some exterior paints particularly those fast drying types with an aggressive thinners like cellulose or solvent acrylic and similar may have UV stabiliser added but can still damage or denature the plastic that then becomes brittle A plastic enamel like Humbrol should be OK but even that seems to have changed over the years so beware. .