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Nylon aging

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Nylon aging

Post  DougW on Mon Jun 05, 2017 12:18 pm

In the Nov 2016 Cox International Quarterly, page 9, Rusty Knowlton advised against using old Top Flite white nylon props. I read this shortly after having carefully taken the scratches out of three 5.25 x 3 examples using 320,400,600,800,1000,1500,2000,3000 and then plastic polish/preservative. It had taken quite a while, so I was reluctant to accept the advice. But I found some nylon rope test information on the Internet which shows quite a loss in strength in 10 years. Yesterday I was polishing some control rods with 0000 steel wool and accidentally gave one a little sideways knock near where it attaches to an external aileron horn. The 2-56 nylon clevis broke off the rod leaving a short length still screwed in place, and the pin also broke. They date back to the 1970's. Saw a year of use and in storage since. May have been exposed to some sun for several years in storage. The doped silkspan on the wing had split several places and needed patching.  The yoke seems brittle and in an experiment one side was easily broken off. One can get a pkg of 12 new ones for 7 dollars.
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Re: Nylon aging

Post  andrew on Mon Jun 05, 2017 1:12 pm

Nylon does become brittle with age and may develop stress crazing on the surface if bent slightly. Props and other nylon parts may (note the word "may" ) be rejuvenated by boiling in water 30 to 45 minutes. Nylon tends to lose moisture and the boiling can replace some of that; it also relieves molding stresses in props.

My inclination would be to boil the product then test to see if any surface cracks appear. If so, it's time for the trash.
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Re: Nylon aging

Post  pkrankow on Mon Jun 05, 2017 4:33 pm

Nylon that is "rotten" will not be affected by boiling. The blades will still snap when flexed.

I have about 20 Top Flight white nylon props that are fit for trash, but I don't remember if I trashed them yet. I made the mistake of buying them on Ebay since the Top Flight props I had were not age damaged and survived reasonable crashes and bad landings. I don't know why since the good props I had were kept in an attic with no climate control, and I have no idea how the other props were stored.

There were people wanting to mold off the old props and these aged out props are suitable for making molds at least.

Phil
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Re: Nylon aging

Post  roddie on Mon Jun 05, 2017 7:58 pm

I mailed Rusty an old TF 10 x 3 white nylon prop.. 3 or 4 years ago.. which generated that concern. Their frail nature due to aging was unknown to me at the time. I'm now very skeptical of using those type of props.. regardless of size.

I would suppose if they're "like-new" condition and pliable without any signs of crazing/cracking.. then they're probably fine. Common-sense should always prevail when in the vicinity of a screaming model aero-engine's propeller. Always wear eye-protection.. and be conscious of keeping your body-parts clear of the "arc" whenever possible. I use wired-clips for the glow-plug.. and always route the wire back behind the engine.. with minimal slack. All pit-gear is kept away from.. or well-behind the engine/prop. Pinching the fuel-line will quickly stop the engine.. although I continually witness modelers who stop their engines "physically" by throwing a rag into the spinning prop. That's really not a good idea.. but you don't have many options with tanked Cox Bee's or Pee Wee's that start in reverse. I've seen people grab a spinner-cone to stop the engine.. which is seriously nuts.

I am a bit surprised at the aforementioned nylon-clevis failure. All of the control-horns on my C/L models are nylon. Most are over 20 years old. A very few also use a nylon-clevis.. but most use a Z-bend formed in a music-wire pushrod. I don't like to think about a possible nylon horn, clevis or bell-crank failure due to age.. but I guess it's possible. My models have not been subjected to extreme temperatures or prolonged sunlight. Direct sunlight will just downright age any man-made surface with enough exposure.
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This and that

Post  DougW on Tue Jun 06, 2017 1:11 am

The plans for the Goldberg "Blazer" 1/2A f/f model show a timer cut off for a Babe Bee. One tank vent has a short length of closed tubing on it. The other vent has tubing going to the timer which pinches it. Would it make a difference how heavy a rag? Perhaps a piece of cheesecloth?

I never had any problems with Top Flite, Tornado, nor Cox nylon props, despite repeated bad landings, scratches, stopping with rags, running them pretty fast etc. It would not be the manufacturer's fault if nylon is not an eternal material. My props seem springy, still resilient, but I don't think it would be wise to be sentimental about them. I agree that crazing or one of a batch blade snapping is evidence against. There is no best before date on them though. I have never heard a heads up from a manufacturer. Perhaps the life of nylon was not well known in 1960. The 5.25 x 3 props might be safe now on a mild OK Cub but not on their former Tee Dee. But to me it is just not worth trying to economize on this detail considering the other costs of the hobby and the limited info available. The way I start the engine puts me in the prop plane for a while. To always stay behind would take a starter on a mount with a remote switch. A shaft run would not be good for the engine nor model I think.

One used to be advised to boil 10-15 mins even brand new not dried out props if one desired more flexibility, breakage resistance.

The plastic (ABS?) fuselages on my Graupner and Kyosho Cirrus gliders degenerated fairly rapidly, after a few years the the built in stabilator horns snapping on hard landings and other problems up to reasonable fear that the tail boom would snap. I seem to have applied fibreglas to one with epoxy or polyester.

Doped nylon covering on one ancient model still seems fine.

My 30-40 year old balsa, spruce, plywood and maple hand launch gliders, glued with white glue, Ambroid and epoxy, doped, show no signs of weakness, still fly fine. I wonder how cyano/carbon fibre/mylar will do in the distant future.

I hope to buy a package of clevises to see how new ones feel, and then, while replacing the clevises on several models, will test the old ones to destruction and let you know my results.

I have a "Lark" r/c helicopter .20 cu. in. glow which uses many molded plastic bearing pillow blocks, bell cranks, and a large nylon crown gear. By now it is probably only safe to fly in complete isolation from other people while wearing a Kevlar vest and crash helmet.

I wonder whether vibration has any effect on nylon.

Rohm & Haas made a special grade of plexi which was claimed to be UV resistant. Not sure if this was just for not yellowing, or for strength too.
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Re: Nylon aging

Post  GallopingGhostler on Tue Jun 06, 2017 1:32 pm

I gather that nylon was a wonderful substance when it first came out, but loses strength through the aging process. Since props and flight control hardware are reasonably cheap, there is no compelling reason to fly with old nylon. Failure occurs without much advanced warning or none at all. Replacement certainly beats being hit by a piece of nylon shrapnel or having a failed control surface while in the air.

I remember the old asbestos cloth covered rubber insulated facilities wiring prior to the 1960's. Back in the 1980's, we had a house built in 1926 that had been rewired a couple times. Portions were still in knob and tube. Rubber at least in the outlet boxes seemed still reasonably flexible, but had we kept the house we would have been faced with a complete rewiring job somewhere down the road. Recently I looked at 30 year old THHN wiring in our attic. It is still as flexible as it was 30 years ago. Newer plastics are technology superior to old.

Old glue joints come apart. I have a 45 year old tenor ukulele, a Duke Kahanamoku that needs the body to be reglued. Old has failed and seams are separating. The newer glues of Aliphatic resin seem to be longer lasting. Some have observed their old acetate based glue joints (Ambroid, Comet, etc.) failing.

Overall, we have better materials than eons ago, but that it to be expected, I imagine. Tired w/ Coffee Read Smoking

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Re: Nylon aging

Post  gcb on Tue Jun 06, 2017 3:53 pm

I doubt that any of the nylon prop manufacturers took into account that their props would be hoarded and used fifty or sixty years down the road. Smile

BTW, I have some too. Sad

George
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Re: Nylon aging

Post  RknRusty on Tue Jun 06, 2017 4:32 pm

If anyone wants to try Andrew's idea that boiling "May" restore some moisture, I would recommend letting the props cool in the water rather than in the air. I know from cooking that if food is boiled in spiced water, that if you take it out of the water it will be bland. But if it has time to cool, it takes on water and spices. Boiled peanuts 101... let 'em soak and sink.

I don't think the 212F heat induces any re-polymerization.
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Re: Nylon aging

Post  pkrankow on Tue Jun 06, 2017 4:56 pm

Celluloid goes bad and releases an acid which can degrade surrounding metals. This is well documented on the various straight razor forums. I am convinced it holds true with celluloid based glue. The worst part is it is "contagious" meaning that storing a degrading celluloid item with a good celluloid item will cause the new item to start degrading. The next worse part is that the acidic off-gassing will cause steel blades to rust and perforate! (actually I am on the fence about which of those are really worse, the level of rust, or the contagious effects, the blade can be rescaled if it isn't rusted)

In my opinion, the "contagious" aspect applies to celluloid glues and is very concerning with old airframes that need reglued. I have not decided on a "best way" to deal with this, or any knowledge of how long the new glue will last before deterioration.


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Re: Nylon aging

Post  David Ingham on Tue Jun 06, 2017 5:24 pm

I have some old Cox engines and a recently bought Wen-Mac with propellers, so this is interesting. I remember from about 1979 propellers being polypropylene, but I suppose the Wen-Mac propeller must be nylon.
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Re: Nylon aging

Post  GallopingGhostler on Tue Jun 06, 2017 7:46 pm

I've got a Tornado white propeller from about then, think it is a 5x4, it is of a different plastic than nylon, somewhat softer and more pliable.

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Re: Nylon aging

Post  roddie on Tue Jun 06, 2017 8:19 pm

Hi Doug, This is a great thread! I find the reading of commentary with regard to the failure of any model-aircraft component/material to be very educational.  I'd guess that today's Nylon (for a given app) might have additives to slow the aging.. but we're not seeing any propellers being offered.. Laughing There are of course.. "boutique-props".. but they're not mass-produced. There was a vendor at the 92 NATS selling props. He had some glass-fiber reinforced props that were just wicked.. (Boston-slang Smile ) You could see the glass-strands through the resin.

Everything ages. It's the physical-effects of aging that concern us most with our models. Regarding our model aircraft(s).. I guess it would behoove us.. to seek/construct the general airframe of the longest-life joinery materials. The glue or adhesive.. and "how it's used". It's a science in itself. If IC engine-powered; sealing the model against the effects of fuel and oil-soaking. Load-bearing plastic-parts seem to fail with age.. as well as use. It's always best to have scads of models on deck. When they break.. just grab another one.  Laughing

Regarding modern RC gear... the battery-technology has improved "so much" (as in lighter-weight and increased-capacity)... that the modeler can now apply the weight-savings to a more "sound" overall structure. A heavy paint-finish might not matter as much. Pound per pound... an appropriate lithium-type receiver-battery vs. yesterday's NICD/NIMH 4xAA packs.. or larger old-technology RX packs is a HUGE difference in weight.

Regarding control-line models.. I tend to over-build mine. I'm going to try to correct that habit. I only have experience with 1/2A profile-type models. I design many of my models.. and many are over-weight. The earlier designs in particular. Sheet-wings having too-much area/span for their .049 reed-valve engines.. excess-weight in control-hardware.. not to mention landing-gear. Most all of my airplanes are R.O.G. tail-draggers launched by a pin-stooge. Gear-strut weight I try to keep back, close to the C of G. Wheel-weight however; is quite variable. I keep a VERY assorted stock of wheels for functional-trimming.

I really enjoyed flying a 1/2A C/L Carl Goldberg "Stuntman 23"...  powered by a Cox .049 reed-valve engine. A Cox "Golden Bee" .049 with its stunt-vented tank, will put a smile on your face!
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Re: Nylon aging

Post  RknRusty on Tue Jun 06, 2017 9:42 pm

My most recent incident with what, for lack of knowledge, I'm calling "Nylon," was the first day flying Will Davis' Tutor. I think it's a Topflite kit he built around 1980, and an ambiguous assemblage of parts, for instance a 5/8" thick fuselage. That makes sense if a little more stiffness was the reason for that. But with that in mind, the rest of the plane seems like purpose built weaknesses. That is if the kit really came with 1/16" control rods to the flap horn and elevator. Threaded for 2-56 connectors, it had white Nylon mini-clevises. Then there's the wire flap coupler that passes through the fuse, and rather than welding a metal horn onto it, it had a tall nylon horn somehow connected to it, taking on the forces of the flaps and elevator. It broke. In flight, of course.

I'll never know how that plastic horn was affixed to the coupler wire, and I sawed off its stump with my Dremel. I bolted a tall Sullivan steel horn to the flap and installed a pair of new metal 2-56 clevises from the bellcrank rod, and onto the long elevator rod. I had no 2-56 ball links. It had a standoff to brace the long rod from flexing, but it was a bit too far aft. It had been flying fine before the flap horn broke, so I left it like it was and hung it up till Huntersville two weeks later. I should have paid more attention.

In Huntersville we had two days of brutal winds and everyone who flew was giving punishing inputs to their control systems. We made it out of there in one piece, but upon my post-flight inspection the next week, I discovered that not only was the thin long rod permanently bent, bowed from the fairlead to the flap horn, but the 2-56 Nylon elevator clevis was split wide open along the threaded connection to the rod and just about to pop off, and the rod had a sharp bend right where the threads start at the elevator clevis. Good Grief! This plane did not have one more flight left in it. It now has 4-40 hardware, including ball links, and a CF tube going to the rear end. Nothing I can do about the front end, because I'm not opening the plane up to get to the crank, but at least it has a new steel clevis. No telling what's inside... I don't wanna know. I'm giving the plane back to Will pretty soon.

But if that's the same stuff the Nylon props are made from(remember, this is a TF kit(I think) ), I want nothing to do with the props.
Then again, it is 37 years old.
Rusty

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