Devcon1 Posted February 26, 2013 Share Posted February 26, 2013 Hi All, Just thought I'd share this one with you. I dusted down my Multiplex Alpina (quite old) with a view to sloping it again this year. Whilst dissasembling it and removing the wings both airbrake servo arms snapped with hardly any force being applied. Subsequent inspection showed all the other servo arms had become brittle to the point I could snap them with my fingers with no effort whatsoever. I dread to think of the consequences whilst in flight. Morale of the story, just because they look OK doesn't mean they are. This also got me thinking whether the plastic gears were capable of the same degredation over time. Now, I last flew this model about 13 years ago and I was going to "re radio" it but only because of upgrading it to 2.4Ghz and wanting to fit 6V gear, not because I thought the servo arms were unserviceable..... Regards John Quote Link to comment Share on other sites More sharing options...
Martin Whybrow Posted February 27, 2013 Share Posted February 27, 2013 Out of interest, what colour were the servo arms? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted February 27, 2013 Share Posted February 27, 2013 Some plastics degrade in sunlight - if it has been lying somewhere in the light that could be the cause. having said that some just degrade - full stop! A timely reminder for us all - especially if you're thinking of bringing an older model out of retirement - a very through check obviously needed. Take nothing for granted! BEB Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted February 27, 2013 Share Posted February 27, 2013 The gears should be o.k., as they don't see the sun. They will be greased, but if the servos are from a reasonable source they should use the matching pair (grease + plastic grade). If you use black servo arms the degradation will be reduced as the carbon black which they use to colour the plastic is also a natural UV stabilizer (degradation will happen only at the surface) Solvents also could harm plastic, but as you speak about the Alpina I don't think you ever had contact with cleaning solvents. Speaking about old models- I also noticed problems with snakes - as their tubes tend to shrink over the time. VA Quote Link to comment Share on other sites More sharing options...
001 Posted February 27, 2013 Share Posted February 27, 2013 About plastic servo arms, another thing is that if you are cutting unused arms off, don't chop them off with side cutters, it puts stresses into the hub and they can split, sooner or later. Saw them off with a fine tooth saw or, better, carefully with a minidrill using a thin rotary abrasive disc . Quote Link to comment Share on other sites More sharing options...
Charles Smitheman Posted February 27, 2013 Share Posted February 27, 2013 I have had the same experience with control horns. Luckily also on the ground..... and a nylon wing bolt on a frozen winter day. This story I can hardly believe myself, but as I have some witnesses: The plane (Hangar 9 Arresti 40 OS46) hit a frozen lump on the runway on takeoff, and behaved a bit strangely in flight. I did three gentle circuits and landed as I thought the tail was loose. As the model slowed down the wing dropped off. Phew. Pinch me am I dreaming. A little appreciated fact is that nylon material has a certain amount of water in its composition. During storage this can dry out and the material becomes brittle. Some will remember those soft white propellers that you had to boil before using. Of course we do not know what type of plastic these items are made of. So sunlight, low temperature, and dryness can degrade plastics. Charles Quote Link to comment Share on other sites More sharing options...
Devcon1 Posted February 27, 2013 Author Share Posted February 27, 2013 Hi, The servo arms were original JR white ones on JR servos. In truth the model and servos are maybe a tad more than 15 years old so one should expect them to be "not as new". The model has been stored in a loft for most of that time and subject to heat and cold. I powered the servos up and they worked and felt perfect (apart from the arms). Part of me thinks just put new arms on and obviously new batteries, harness and Rx but I don't see the point in risking the model although I'm sure the servos would be fine. (good excuse to go 6V and 2.4 with swanky new kit). I'll pull one of the servos apart and see if there are any signs of corrosion or brittleness out of interest. Regards John Quote Link to comment Share on other sites More sharing options...
Panther1 Posted July 21, 2013 Share Posted July 21, 2013 I had that happen with control horns on a 6 year old model and servo arms the same age developed minute cracks from the holes to the edges. (JR arms) These arms had not even been used. Lucky I found them before I reflew the model. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted July 21, 2013 Share Posted July 21, 2013 Posted by Biggles' Elder Brother - Moderator on 27/02/2013 00:23:23: Some plastics degrade in sunlight - if it has been lying somewhere in the light that could be the cause. having said that some just degrade - full stop! A timely reminder for us all - especially if you're thinking of bringing an older model out of retirement - a very through check obviously needed. Take nothing for granted! BEB It's for that reason BEB that I make mine out of ally! Quote Link to comment Share on other sites More sharing options...
Levanter Posted July 22, 2013 Share Posted July 22, 2013 Vecchio mentioned snakes. I am carefully checking over an Art-Tec Beaver 40 that I bought secondhand. When disconnnecting the clevis from the throttle lever the inned snake snapped and had totally lost its flexibility. After I pulled it out the inner snake had obviously had a long session with a Charmer and had partially coiled, The friction to pull it out was enormous. I think fuel had worked its way down between the two and affected the plastic. The elevator also has a snake and this seemed OK. Not taking any chances however and that is being replaced as well. Quote Link to comment Share on other sites More sharing options...
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