hhobbit Posted January 26, 2011 Report Share Posted January 26, 2011 Hi All, I am looking for where it says in any FD manual to use of loctite on the spinner backplate rivnuts. It’s something I think I read, but now cannot find it, in the maintenance manual or anywhere else for that matter, despite searching all my files on the computer. I better not tell the doc just in case he says I’m getting too dumb to fly. In case you are in doubt, this little tale has an unhappy ending. Last June I re-pitched my propeller from 19 to 17.5 degrees and got about 5400 in level flight at 2000ft and about 15deg C. Not the 5500 one sees recommended, but there was an improvement in speed and climb rate compared to the previous 5200-5250 I was used to seeing. When removing the spinner, one rivnut was turning, and the long nosed pliers was barely able to restrain it, but I managed just about. I gather that the use of loctite for reassembly here is double edged to put it mildly. You don’t get to see a loosening M5 screw sail into your windscreen, but the fun certainly did begin when I went to re-pitch again. Although I had applied the loctite to the first two threads only, they all grabbed on too strong, and began to rip into the inside face of the spinner and wreak havoc during removal. Most of the 5mm holes enlarged to the diameter of the outer rivnut face. I am now having to repair and reinforce the damaged attachment holes, and reckon a 20mm flat washer 1 mm thickness, epoxied on the spinner’s inside face, and a plastic washer under the head of the screw should do it. The turning rivnuts did not seem to damage the backplate, and using a standard Allen bolt, washer and grease it was easy to reset them in place. Should have left the prop alone! Except that Warp drive say check torques regularly, which I did once or twice, and was glad because there were bolts that were slacked right off. Ok men, any further insights? Link to comment Share on other sites More sharing options...
Roger Lee Posted January 26, 2011 Report Share Posted January 26, 2011 Sorry to hear about your problem, but absolutely do not use any Loctite on the spinner screws or you will be stripping out the Rivnuts and or replacing them. If one comes loose you may be able to save it once you get the screw out. You can put a little of the Loctite 480 that you use on the flap and aileron bearings around it's edges and then use the Rivnut tool to try and squeeze and expand it out a little more. This does work many times. Just tighten the screws hand tight. Don't worry if one does come out it will fly off into space laterally from the plane and not hit the windshield. I have only seen one missing in my shop and have never had one that I put in come out. Take out between 1/4 - 1/2 degree from the prop pitch and you'll be setup good on the rpm. Link to comment Share on other sites More sharing options...
sandpiper Posted January 26, 2011 Report Share Posted January 26, 2011 Like Roger, I never put loctite on the spinner screws. I don't put it on the wheel pant attach points either. Just pay attention on preflight. I haven't had any spinner screws come loose but the ones on the wheel pants do. Link to comment Share on other sites More sharing options...
Tom Baker Posted January 26, 2011 Report Share Posted January 26, 2011 I've always used a little blue loctite on the spinner screws because I had problems with them backing out. I've never had a problem getting the screws out either knock on wood. Tom Link to comment Share on other sites More sharing options...
hhobbit Posted January 26, 2011 Author Report Share Posted January 26, 2011 @Tom Baker did you put the loctite on on your own initiative, or follow some advice? I am scratching my head to find any reference to this practice. Link to comment Share on other sites More sharing options...
Roger Lee Posted January 26, 2011 Report Share Posted January 26, 2011 Hi Hobbit, It isn't in the manual. If they are tightened down they won't come loose. Loosening up a Rivnut and trying to get the screw out or even fix it is a PITA. In some places you can't even get to the damaged Rivnut. Don't ask how I know, I don't want to re-live any nightmares during the daytime. Link to comment Share on other sites More sharing options...
hhobbit Posted January 26, 2011 Author Report Share Posted January 26, 2011 Yes Roger I have had that nightmare. I solved it with heat from a portable soldering iron, first with the solder tip. It was slow because it did heated up the screw only a little, until the loctite re-hardened. Later, when a few threads were exposed, I was able to get an improvised heat shield under the screw head, and use the micro blow torch; got 3/4 turn before I had to re-apply heat. There was a small amount of scorching, not much, but either way I think the spinner needs repainting. Someone leaned on it and it flexed enough to crack the paint. I used a machine screw to retighten the rivnut, seems to have worked but we'll see... Link to comment Share on other sites More sharing options...
Tom Baker Posted January 26, 2011 Report Share Posted January 26, 2011 Page 1-13 in the latest MM covers this. The text is located below the torque chart. @Tom Baker did you put the loctite on on your own initiative, or follow some advice? I am scratching my head to find any reference to this practice. Link to comment Share on other sites More sharing options...
hhobbit Posted January 26, 2011 Author Report Share Posted January 26, 2011 Page 1-13 in the latest MM covers this. The text is located below the torque chart. Tom I have FD CTSW LSA Manual AU 101 02000 Rev 6 2008 dated 20 Nov 2008; is that what you have, or where can I obtain a more recent version? On page 1-13, containing section 1-12, it states: (damn that protected PDF, it won't let me copy and paste) the unsecured nuts, which I take to mean rivnuts and exclude nyloc or stiffnut types, must be loctited with medium strength loctite. Is that your interpretation? I've come to the conclusion that if you stipulate use of loctite here, then a standard rivnut in thin composite is a catastrophe waiting to bite you in the ass. If such a thing as a wide head rivnut existed, and also a backing washer were to be used, then that would take the loosening torque OK. something like these rivet "burrs" which AFAIK are just big wide washers Link to comment Share on other sites More sharing options...
Tom Baker Posted January 26, 2011 Report Share Posted January 26, 2011 You have the most recent version of the manual. Like I said I've had problems with the screws coming out when not using loctite. Something you could try is model airplane canopy glue. Model airplane guys use it to secure screws that go in and out on a regular schedule. Tom Tom I have FD CTSW LSA Manual AU 101 02000 Rev 6 2008 dated 20 Nov 2008; is that what you have, or where can I obtain a more recent version? On page 1-13, containing section 1-12, it states: (damn that protected PDF, it won't let me copy and paste) the unsecured nuts, which I take to mean rivnuts and exclude nyloc or stiffnut types, must be loctited with medium strength loctite. Is that your interpretation? I've come to the conclusion that if you stipulate use of loctite here, then a standard rivnut in thin composite is a catastrophe waiting to bite you in the ass. If such a thing as a wide head rivnut existed, and also a backing washer were to be used, then that would take the loosening torque OK. something like these rivet "burrs" which AFAIK are just big wide washers Link to comment Share on other sites More sharing options...
Roger Lee Posted January 27, 2011 Report Share Posted January 27, 2011 You guys really don't need Loctite on those Rivnuts. You may get away with it in metal, but plastic is a disaster waiting to happen. No Joke, I just got a plane in today and had to drill out both Rivnuts on the right wheel pant. Now the owner is into me for the repair. It just isn't worth it. Link to comment Share on other sites More sharing options...
hhobbit Posted January 27, 2011 Author Report Share Posted January 27, 2011 Right let's consider the mechanics of the problem in a little more detail. You remove a cowl or spinner machine screw, do your business, then put it back in place. After a few operations, perhaps a tiny hard piece of paint debris crushes into the surface and the paint begins to flake a little. Now you are trying to get a secure fastening onto a flaky surface which is beginning to disintegrate, so what then happens is of course it disintegrates more and more. This process is accelerated by vibration in flight and so you lose the odd screw in the air. You then tighten them down even more, so much so that the paint under the head is now all gone and you have the harder kevlar or carbon to tighten down upon. After some time this also begins to fret and now it's time to do something about it. The solution nearest to hand is a nylon washer and this proves a good cure. So why did they not put them on in the first place? A couple of dozen €0.04 each for goodness sake? We are all advised to continually check under the cowl, so this problem is easy enough to anticipate. Since using these washers I haven't had any issues IIRC with these screws loosening either, that's probably because the natural give in the nylon acts like a spring washer. Funny how the little things annoy you, devil in the details and all that..(Descends from pulpit) Roger you are right it's a trap that will bite. Working on my RC helicopters, I notice that if I break the loctite bond after maybe an hour or two, the sticky and crumbly residue on the threads does a decent job of holding things still; enough remains sticking to the screws to goo up the threads, kind of more locloose than loctite. Tom - seems you are into models as well? Hard to get canopy glue nowadays since ARTFs have taken over! Link to comment Share on other sites More sharing options...
Roger Lee Posted January 27, 2011 Report Share Posted January 27, 2011 There is another trick that can be done, but I haven't had any issues so I haven't done anything. You can take Loctite 243 medium and apply a drop to any screw. Let it set out and dry. Then put it in place. The dry Loctite will keep the screw from backing out, but doesn't hold it so tight it causes things to strip. This said I have had to replace too many Rivnuts in plastic to ever want to use Loctite on plastic again. The big hassle isn't the Rivnuts you can get behind and hold to take a screw out, but the ones you can't get anything on to hold the base. Then at times It is better to use Dremel to take the screw head off to give access or take the head off and just drill a hole for a new Rivnut depending on the application. The absolute worst place to have a Rivnut turn is on the back screws of the airbox for the CTSW's. It is too hard to get to and it is double walled so you can not get to anything. You are just flat out stuck. Never use Loctite on any of these 4 screws and never over tighten them. Better for it to come out and fall out the bottom of the cowl and just replace it than to have to work on one of these. Your only hope when one of these start to turn is take a Dremel and cut the head off. Next take a Dremel with a long flex shaft and pass it up through the bottom of the engine and drill a new hole about 1" in front of the bad one. Then replace the Rivnut. It is very tight doing any of this and will test your language control. The only other way to have free access to this would be to pull the engine. (not going to happen for one screw) You can not get to the back of these 4 Rivnuts as the wall behind them is double sided. You would need to remove the entire console mushroom (That isn't going to happen for one screw either) Some things are just better left alone. Link to comment Share on other sites More sharing options...
FastEddieB Posted January 27, 2011 Report Share Posted January 27, 2011 As a data point... ...my Sky Arrow uses a Warp Drive prop and UHS spinner. The installation sheet for the spinner says Loctite or equivalent MUST be used. Since those screws are so small and subject to a lot of vibration, and since a spinner coming loose could be worse than a power failure, I think its probably a good idea to use Loctite, unless an installation already uses some other locking method (lock-nuts or similar). But That's Just Me!™ Link to comment Share on other sites More sharing options...
hhobbit Posted January 27, 2011 Author Report Share Posted January 27, 2011 Roger your experience points to the problematic nature of rivnuts when they loosen. I want them to make special wide topped ones with underneath serrations, that grip the plastic part a lot more than the present design which works well enough in metal which can be squeezed more. Manufacturers /specifiers please take note! @ fast eddie b CTSW spinner has a spigot which pretty much guarantees the spinner would stay in place even if all the screws backed out. Oh that brings on the question why have a backplate I suppose..I guess a solution not involving rivnuts would be ideal. Link to comment Share on other sites More sharing options...
Runtoeat Posted January 27, 2011 Report Share Posted January 27, 2011 I have applied Loctite as Roger suggests - put a little on the fastener. Put the fastener aside until the loctite has dried, then install. This seems to work for me. Consider that we use the nyloc torque prevailing nuts on critical locations on our CTs and these work on the same principle - a polymer prevents back-off of the fastener by friction rather than by glueing one metal to another. Actually, there are nyloc screws and bolts that have a nylon insert. These would be ideal for applications such as the spinner where rivnuts are used. Of course, we would be wise to only use these screws once as is done with the nuts. Hobbit's suggestion to use rivnuts with increased bearing surfaces for composite applications is a point that all manufacturers should take note of and incorporate. Link to comment Share on other sites More sharing options...
Roger Lee Posted January 27, 2011 Report Share Posted January 27, 2011 There have not been any CT's that have had a spinner separation and I never seen one with more than 1 screw missing or loose. We should not make a mountain here with nothing more than speculation. There is not any real problem here. Just tighten the screws on the spinner down. They have been on your planes this long, they aren't likely to go any where now. Link to comment Share on other sites More sharing options...
hhobbit Posted January 27, 2011 Author Report Share Posted January 27, 2011 Roger I hope you are not actually recommending not to use any form of threadlock, because by my reading of the manual they say you must. We are all aware of the problems of using too much of the stuff and I like your idea of letting the 243 dry out before installing. I think there is merit in oiling the mating surfaces to reduce the bond strength, but would like to prove it by careful experiment first. If that worked it would be possible to follow the mfr's guidance without slowing up the job. I have a damaged spinner which needs reinforcing around the holes, and maybe this thread will prevent some unwary soul messing up when he inspects the prop bolt torques or whatever. BTW this could be of use: rivet "burrs" Link to comment Share on other sites More sharing options...
Roger Lee Posted January 28, 2011 Report Share Posted January 28, 2011 Hi Hobbit, I see no where in the maint manual where it says to apply any Loctite on the spinner screws. Section 7 is for the prop and there is nothing listed there. The only place it says to apply any Loctite is for BOLTS that run through plastic with no back up nuts. These are screws not bolts. I haven't seen any Loctite on any spinner from the factory. There is no documentation to support using Loctite on spinner screws. If you needed Loctite as you point out through the plastic screws then why not take that and put it on the instrument panel screws? (According to the manual) If the maint. manual says this please point it out to me. Link to comment Share on other sites More sharing options...
hhobbit Posted January 28, 2011 Author Report Share Posted January 28, 2011 Hi Roger Very interesting to read your observation. No I don't use loctite on the panel screws, nor was there any there from the start AFAIK. If the factory does not use it, then as I read it that contradicts what section 1-12 says. They should be more clear and state do not use. And that would be a great relief! Link to comment Share on other sites More sharing options...
Mac Bowden Posted January 28, 2011 Report Share Posted January 28, 2011 I've never used Loctite on any of my hex headed screws and that includes the spinner. My plane has done 250 hours in just over a year, the top cowling is off frequently and the bottom cowling is off about once a fortnight or so. In all that time I've had a couple of screws go loose on one spat. I see the preflight and post flight as an opportunity to run my hand over the screws as I walk around and I for one won't be glueing any screws. Besides, it always pays to check your nuts ! Mac Link to comment Share on other sites More sharing options...
Tom Baker Posted January 28, 2011 Report Share Posted January 28, 2011 I started using the thread locker on my first airplane. It would have a couple screws backed out after just about every flight. It didn't matter how tight you had the screws. There have not been any CT's that have had a spinner separation and I never seen one with more than 1 screw missing or loose. We should not make a mountain here with nothing more than speculation. There is not any real problem here. Just tighten the screws on the spinner down. They have been on your planes this long, they aren't likely to go any where now. Link to comment Share on other sites More sharing options...
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