DaV8or Posted June 7, 2019 Report Share Posted June 7, 2019 I have the SWTA 201 style cowling. I recently discovered after owning this plane for almost 10 years that the SCAT hose in this cowling that connects fresh, cold air from the left inlet to the muffler shroud for hot air, has been rubbing against the #2 cylinder oil drain tube and almost caused the tube to fail and leak oil. The steel wire in the SCAT hose chaffed and nearly wore a hole in the aluminum tube. This was missed in the last 9 annuals at least and I have been involved in most of them. I have since replaced the drain tube, but my question is- how important is this SCAT tube? The way SWTA made the cowling (it may be patterned after the real 201) the SCAT hose interferes with the drain line no matter what you do. It's just a bad design I guess. Rather than go though all kinds of conniptions to make the two tubes safe, perhaps KISS and skip the SCAT tube. It doesn't seem like this tube is really needed. Is there any detriment that anyone can think of for just leaving it off? All it does is, route fresh air from the inlet to the muffler for heating. I thought well, maybe it's to keep the air fresh and not full of engine stink, but then the cold air inlet for cabin air is right down in there in the lower cowling amongst the stink on the right side. So this can't be the case. I have since flown with the tube off and the heater blows like hell and heats just fine. I can't tell the difference. The only thing I'm not sure about is the increased flow of cold air to the lower cowling due to an open hole. I didn't notice anything out of order on the test flight. What do you think? Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 7, 2019 Report Share Posted June 7, 2019 I would think extra hard in the area of ways CO can enter the cabin. Bringing air into the cabin from under the cowl, wouldn’t be as good as really outside air... exhaust tubes have a tendency to leak over years... they leave stains to indicate when it is time to change the seals... It would be a better idea to put effort into protecting the aluminum tube from scat tube’s wire. how much tube wrap would that take, a few inches? Aluminum tube vs steel wire... aluminum is so soft in comparison, the steel wire probably didn’t even get polished... PP thoughts only, not a mechanic. Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted June 7, 2019 Report Share Posted June 7, 2019 There is always air circulating through the muffler shroud. It either goes into the cabin or out through the cowl flap. It cools the muffler. I think that tube is to keep the hot air off the mags and prop governor. Not super important, but it should be there. Quote Link to comment Share on other sites More sharing options...
Guest Posted June 7, 2019 Report Share Posted June 7, 2019 You can add some chafe protection to the aluminum drain line, or squeeze the Scat duct to add some clearance. Removing the line could allow engine exhaust fumes to enter the cabin heater inlet, I wouldn’t fly without it. Clarence Quote Link to comment Share on other sites More sharing options...
takair Posted June 7, 2019 Report Share Posted June 7, 2019 I agree with Clarence and Anthony....consider the effect of a secondary exhaust leak causing CO introduction. Do you have a picture of the interference? The SCAT can be “molded” such that it is a lower profile oval. I do that on my E so the heat line can better clear the muffler. 1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted June 7, 2019 Report Share Posted June 7, 2019 If you had an oil fire in the engine compartment from one of the other leaking return lines. you could have flames sucked into the cabin. Not a real possibility, but we also use protection on the fuel and oil lines to prevent burn through. Closed driver on professional course. Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 7, 2019 Author Report Share Posted June 7, 2019 OK, I will wrap the oil drain line and maybe squeeze the tube, but it'll take a lot of squeezing. I was mistaken about the cold air source and hadn't thought about muffler cooling. Thanks for the help! Question answered. Quote Link to comment Share on other sites More sharing options...
Bob_Belville Posted June 8, 2019 Report Share Posted June 8, 2019 Most every time I have the cowl off I spend several minutes looking for potential rubbing of hoses, wire bundles, and metal. After 7 years I am still finding stuff that can be routed more elegantly, tied back, or set off with, clamps, tie wraps, or rtv.Mooneys are tightly cowled and there’s a lot going on.Sent from my iPad using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted June 8, 2019 Report Share Posted June 8, 2019 On 6/7/2019 at 12:35 AM, DaV8or said: I recently discovered after owning this plane for almost 10 years that the SCAT hose in this cowling that connects fresh, cold air from the left inlet to the muffler shroud for hot air, has been rubbing against the #2 cylinder oil drain tube and almost caused the tube to fail and leak oil. The steel wire in the SCAT hose chaffed and nearly wore a hole in the aluminum tube. I had this happen in 05 when I owned an F with the ARI cowl closure. I chased a slight oil leak forever, until I found the culprit to be this exact problem and replaced #2 drain tube. Prevention was repositioning the scat hose for more clearance plus wrapping the drain tube with UHMW tape from McMaster Carr where it could potentially touch. Finding leaks is easy now that I have discovered magnaflux developer, Thoroughly clean the engine and spray this (or spray foot powder for CB's) around the suspect area. Run hard on ground for a bit, decowl and you will see where the oil is coming from. 1 Quote Link to comment Share on other sites More sharing options...
JimB Posted June 8, 2019 Report Share Posted June 8, 2019 While I was at work yesterday I was checking new posts here and saw this post. Didn't really think much of it at the time since I don't have the SWTA 201 style cowling but last night I was at the aircraft finishing up my JPI EDM-900 installation and I recalled this post. I decided to take a look and found the same thing on mine. Be a good idea to look. It isn't a pressurized line and probably wouldn't be catastrophic but.... Thanks DaV8or for sharing! This place really is fantastic! 1 Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 8, 2019 Author Report Share Posted June 8, 2019 28 minutes ago, JimB said: While I was at work yesterday I was checking new posts here and saw this post. Didn't really think much of it at the time since I don't have the SWTA 201 style cowling but last night I was at the aircraft finishing up my JPI EDM-900 installation and I recalled this post. I decided to take a look and found the same thing on mine. Be a good idea to look. It isn't a pressurized line and probably wouldn't be catastrophic but.... Thanks DaV8or for sharing! This place really is fantastic! Mine was worse than that. I don't know how many hours it would have been until failure, but not many. You are correct in that it's not technically pressurized, but I suppose it does have some pressure behind it just from crankcase pressure. I really have no idea how bad the leak would have been. I guess Mike's above wasn't that bad, just annoying. Quote Link to comment Share on other sites More sharing options...
rbridges Posted June 8, 2019 Report Share Posted June 8, 2019 I have several areas where scat tubes rub. I've added silicone tape to prevent it. It works well. 1 Quote Link to comment Share on other sites More sharing options...
Shiny moose Posted June 9, 2019 Report Share Posted June 9, 2019 Found this same rub on my first annual on my F with OEM cowl, split rubber hose over the aluminum, High temp RTV, and a slight squeeze on the scat. Easypeasy Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 11, 2019 Author Report Share Posted June 11, 2019 I ended up using nylon spiral wrap to protect the new line. This stuff- I also gave the SCAT a bit of a squeeze to flatten it a bit and relieve some pressure as others suggested here. However to make it no contact I would pretty much have to stomp it flat. Bad design IMO. Sorry that these images are sideways. For some reason the forum software wants to take my portrait pictures and make them landscape. I don't know how to fix it. Here is how it looks and also my old tube- Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 11, 2019 Report Share Posted June 11, 2019 Gravity on... -a- Quote Link to comment Share on other sites More sharing options...
EricJ Posted June 11, 2019 Report Share Posted June 11, 2019 45 minutes ago, DaV8or said: I ended up using nylon spiral wrap to protect the new line. This stuff- I also gave the SCAT a bit of a squeeze to flatten it a bit and relieve some pressure as others suggested here. However to make it no contact I would pretty much have to stomp it flat. Bad design IMO. Sorry that these images are sideways. For some reason the forum software wants to take my portrait pictures and make them landscape. I don't know how to fix it. Here is how it looks and also my old tube- Keep an eye on that stuff to make sure it doesn't shrink. It may be okay, but I've used it in some apps (brake lines on a race car), where the heat destroyed it. It basically shrinks into a skinny, useless string. Brake heat >> engine heat, but I'd keep an eye on it, anyway. Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 11, 2019 Report Share Posted June 11, 2019 Also keep in mind what plastic it is made of... Avoid the situation that nylon ty-wraps cause..? Apparently some ty-wraps have been known to cut through things... The melting point of some nylons (nylon66) is 255°C. It may soften at a temperature much lower. Above the softening point, it will release stress and shrink and shrivel.... So keep an eye on it for a while.. if it creates a lot of Back dust and the tube stays polished shiny... the wear is taking place again... PP thoughts only, not a polymer engineer anymore... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 11, 2019 Author Report Share Posted June 11, 2019 47 minutes ago, EricJ said: Keep an eye on that stuff to make sure it doesn't shrink. It may be okay, but I've used it in some apps (brake lines on a race car), where the heat destroyed it. It basically shrinks into a skinny, useless string. Brake heat >> engine heat, but I'd keep an eye on it, anyway. Yes. Now that I'm aware of the issue, I'll be watching. If it fails, I'll do something else. It took nearly ten years or more to get to the point it did, so I'm not super worried. If the nylon fails, I'll find something better. Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 11, 2019 Author Report Share Posted June 11, 2019 54 minutes ago, carusoam said: Also keep in mind what plastic it is made of... Avoid the situation that nylon ty-wraps cause..? Apparently some ty-wraps have been known to cut through things... The melting point of some nylons (nylon66) is 255°C. It may soften at a temperature much lower. Above the softening point, it will release stress and shrink and shrivel.... So keep an eye on it for a while.. if it creates a lot of Back dust and the tube stays polished shiny... the wear is taking place again... PP thoughts only, not a polymer engineer anymore... Best regards, -a- Do you have something better to suggest? Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 11, 2019 Report Share Posted June 11, 2019 2 hours ago, DaV8or said: Do you have something better to suggest? Unfortunately, I don’t... But, I do know somebody that might.... One thing to look at could be putting a piece of rubber over the hard wire coil that supports the SCAT(tubing). Possibly a sleeve(?) The rubber of choice would be something like the materials used for baffling. High temp resistant with known longevity...typical of the red silicone stuff... It is the hardness of that wire that did all the cutting of the softer aluminum... Ask @M20Doc the best way to protect the aluminum tube from rubbing against the steel(?) wire support of the Scat hose... Clarence has the experience and ability to make these types of recommendations. I am only a PP, not a mechanic at all... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Guest Posted June 11, 2019 Report Share Posted June 11, 2019 There is a high heat version of spiral wrap. If you can’t get it, you can take a short pice of Mil H 6000- 6 hose, cut it lengthwise and slip it over the aluminum tube. Clarence Quote Link to comment Share on other sites More sharing options...
Bob_Belville Posted June 11, 2019 Report Share Posted June 11, 2019 1 hour ago, M20Doc said: There is a high heat version of spiral wrap. If you can’t get it, you can take a short pice of Mil H 6000- 6 hose, cut it lengthwise and slip it over the aluminum tube. Clarence ASpruce shows PTFE that has an operating range up to 500F. https://www.aircraftspruce.com/catalog/elpages/spiralwrap.php?gclid=EAIaIQobChMIr7D5lq3h4gIVFoGzCh2SdweFEAYYAiABEgL3ZPD_BwE Quote Link to comment Share on other sites More sharing options...
HRM Posted June 11, 2019 Report Share Posted June 11, 2019 Jeez-Lou-eez! I am going flying tomorrow morning and first thing I plan to do is take a look (I have the SWTA mod). Thanks guys!!! Quote Link to comment Share on other sites More sharing options...
DaV8or Posted June 11, 2019 Author Report Share Posted June 11, 2019 10 hours ago, Bob_Belville said: ASpruce shows PTFE that has an operating range up to 500F. https://www.aircraftspruce.com/catalog/elpages/spiralwrap.php?gclid=EAIaIQobChMIr7D5lq3h4gIVFoGzCh2SdweFEAYYAiABEgL3ZPD_BwE Thanks! I will order this from Spruce and just get it over with. Perfect. I also now know it something to check at oil changes. Quote Link to comment Share on other sites More sharing options...
Shadrach Posted June 11, 2019 Report Share Posted June 11, 2019 (edited) On 6/7/2019 at 11:21 AM, DaV8or said: OK, I will wrap the oil drain line and maybe squeeze the tube, but it'll take a lot of squeezing. I was mistaken about the cold air source and hadn't thought about muffler cooling. Thanks for the help! Question answered. This is not an uncommon problem. I have seen tubes sleeved with what appears to be MIL6000 rubber tube. It offers chafe protection and offers an oil tight seal over any chafed areas. My number 2 drain had a deep enough chafe in it to warrant replacement. One of the fasteners on the lower rods that tie the baffle together failed causing it to rub the return line. Certainly not unique to your cowl design. Edited June 12, 2019 by Shadrach Quote Link to comment Share on other sites More sharing options...
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