---------------------------------------------------------- Europa-List Digest Archive --- Total Messages Posted Thu 01/30/20: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:43 AM - CKT exhaust springs breaking (JonathanMilbank) 2. 07:30 AM - Re: CKT exhaust springs breaking (tennant) 3. 07:55 AM - Re: CKT exhaust springs breaking (clivesutton) 4. 08:03 AM - Re: Re: CKT exhaust springs breaking (Kevin Challis) 5. 02:21 PM - Re: CKT exhaust springs breaking (SPURPURA) ________________________________ Message 1 _____________________________________ Time: 05:43:54 AM PST US Subject: Europa-List: CKT exhaust springs breaking From: "JonathanMilbank" Over the last couple of years, my CKT exhaust system fitted to a Europa with Rotax 912ULS has broken a few springs and not in the same location each time. I never seem to be able to fly for more than about 30 hours before I find another broken spring, each time with a short 1/2" straight piece remaining after the hook has disappeared. The coils never break. As per CKT instructions, I never use metal tools like vice grips and only use a plastic cable tie for pulling the spring onto the welded anchors. The last time when I replaced a spring, I cut lengths of old metal brake hydraulic tube to fit inside the spring coils before passing locking wire through for safety. This attempt at vibration damping obviously didn't prevent another breakage. The aircraft carburettors are well balanced using Carbmate and the Airmaster propeller is also well balanced, so my aircraft runs "sewing machine" smoothly. The replacement springs from CKT were bought as a packet of 8, if I recall correctly and are the simple type with a hook at each end. I would prefer the more complicated type which act differently and have closed 'U' loops at each end, but don't know where to find them. I'm also considering to copy the 2-stroke microlight flyers, by wiping a thick bead of high temperature silicone rubber sealant along the length of the spring coils on the side furthest from the exhaust header tubes, which after setting will hopefully act as a vibration damper. Dow Corning Momentive RTV106 red silicone sealant is what I have in mind and works at a temperature of up to 260C ( 500F ). However if I could obtain the more complicated exhaust springs, I'd try those first before experimenting with RTV106. Your advice please, thanks. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=494524#494524 ________________________________ Message 2 _____________________________________ Time: 07:30:34 AM PST US Subject: Europa-List: Re: CKT exhaust springs breaking From: "tennant" Hi Jonathan, I had a similar experience in the beginning but not with a CKT exhaust. The springs were stainless steel. Stainless steel does not like contact vibration and the constant contact microwelding quickly rubs through the wire. I have used galvanised spring steel for about 15 years without a breakage. Don't ask where I got them as it must have been some DIY store!! Your idea of a silicone damper sounds like a good idea though. -------- Barry Tennant D-EHBT At EDLM - Germany Read this topic online here: http://forums.matronics.com/viewtopic.php?p=494527#494527 ________________________________ Message 3 _____________________________________ Time: 07:55:17 AM PST US Subject: Europa-List: Re: CKT exhaust springs breaking From: "clivesutton" Hi Jonathan, I've had the same problems for some time - and they persist despite trying more than 1 CKT design of spring, lining the 'hole' down the middle of the spring with silicone tubing held in place by a combination of Red silicone and adding a length of central locking-wire as you describe. In an effort to try and get to the bottom of the problem I have measured the natural frequency of the 8 springs fitted (try recording the twang emitted when you ping the springs, with your mobile phone on the ground) - so that i can draw up a Campbell Diagram - that compares the spread of spring resonances with the forcing frequencies generated by the engine (i did this stuff for a living once). Here is an example diagram that possibly illustrates the concept better than my text: https://www.originlab.com/www/products/GraphGallery.aspx?GID=130 The idea is that the natural frequencies of these springs [like everything else on the aircraft btw], sit waiting for excitation by forcing at the same frequency - in our case, by an out-of-balance (OOB) force from the engine (these OOB forces are normal - though relatively small, in all engines btw). Typically, when something goes into resonance, just a small level of excitation can result in a large motion - and a commensurate increase in the amount of strain, and therefore stress, in a component - depending on how it is mounted and how it is vibrating. Excessive vibration does not always result in breakage, it may just be irritating of course. The implication/potential remedy is that there are probably a few engine speeds that are best avoided for e.g. cruising - if we are to avoid exciting the exhaust springs into resonance. BTW, i also notice that the points between my springs and their exhaust pipe/silencer 'hook stubs' are worn away/thinner - which hints at the failure mode. My gut feeling is that in addition to the heat in service and possible fatigue damage initiation caused by e.g. use of a screwdriver to fit a spring [which like you, i never do], material thickness reduction is probably what happens to induce a spring to 'let go'. With this in mind, I have been playing with putting a blob of CKT's graphite exhaust socket grease in this area - but the results are inconclusive so far. Damping = generally good, as it generally reduces the levels of vibration amplitude, though it also can 'lower' the frequency of resonance as well. Apologies, a bit of an edict . . . More to follow. Clive G-YETI Read this topic online here: http://forums.matronics.com/viewtopic.php?p=494528#494528 ________________________________ Message 4 _____________________________________ Time: 08:03:47 AM PST US From: Kevin Challis Subject: Re: Europa-List: Re: CKT exhaust springs breaking I have had lots of CKT springs break. I have tried heat resistant silicon made no difference. I have a complete spare set in the aircraft and change regularly. I was told it was an old problem and the new springs would be ok. They arent and I am glad its not just me experiencing issues. Engine is smooth with no different vibrations than any other 912ULS. Kevin Challis > On 30 Jan 2020, at 16:33, tennant wrote: > > > Hi Jonathan, > > I had a similar experience in the beginning but not with a CKT exhaust. The springs were stainless steel. Stainless steel does not like contact vibration and the constant contact microwelding quickly rubs through the wire. I have used galvanised spring steel for about 15 years without a breakage. > Don't ask where I got them as it must have been some DIY store!! > Your idea of a silicone damper sounds like a good idea though. > > -------- > Barry Tennant > D-EHBT > At EDLM - Germany > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=494527#494527 > > > > > > > > > ________________________________ Message 5 _____________________________________ Time: 02:21:33 PM PST US Subject: Europa-List: Re: CKT exhaust springs breaking From: "SPURPURA" I have over 500 hours on my 912s and some of its stainless springs are wearing a bit. When I replace them Ill use part # 3114T111 from McMaster Carr. My hooks are 4 apart. I think the black oxide will be better as Rotax sells these for replacement at a much higher price. -------- N951EU - Tri-gear & 912ULS, N77EU- Mono & 914 I'D RATHER HAVE A BOTTLE IN FRONT OF ME THAN A FRONTAL LABOTAMY. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=494532#494532 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message europa-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Europa-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/europa-list Browse Digests http://www.matronics.com/digest/europa-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.