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  #1  
Old 11-07-2014, 07:14 PM
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RVTrumpet RVTrumpet is offline
 
Join Date: Jun 2012
Location: Hillsboro, OR
Posts: 63
Default Tighten Your Tie-Wraps!

Last Saturday we were out at the hangar to inspect the 12 for a small coolant leak. After pulling both the top and bottom cowls off, the following was noticed:



The black tie-wrap had apparently been installed at the last annual to hold the oil line in position that passes under the crankcase and over the muffler. It had been installed around the oil line and the rubber coolant hose that joins the elbow coming from the cylinder to the elbow coming from the coolant pump. Apparently the tie-wrap was not installed quite tight enough. Sometime in the last ~40 hours of operation the tie-wrap slipped forward off the rubber coolant tube and came to rest on the aluminum elbow coming from the cylinder head. Because the OD of the aluminum tube is much less than the OD of the rubber tube, the tie-wrap was very loose and freely vibrated against the elbow. (The tie-wrap was moved aft for the picture).

As shown in the picture, the result of the tie-wrap vibrating against the elbow was a chafed groove in the aluminum approximately .020 deep. The decision was made to ground the aircraft until the elbow could be replaced. Thankfully the elbow is fairly inexpensive and the repair will not be too extensive. However it is scary to think what could have happened if the tie-wrap had ground its way through the entire tube wall.

The lesson here is that the plastic components we use in our aircraft are harder than the aluminum ones. Plastic wiring connectors, tie-wraps, and even wire insulation will slowly chafe aluminum components if not properly restrained, resulting in possible electrical systems failure and compromising the strength of the aluminum component it chafes against.
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  #2  
Old 11-07-2014, 09:16 PM
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stinson pilot stinson pilot is offline
 
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Default

Zip ties don't really belong in the engine compartment.

The only place they're used on big airplanes is in the pressurized areas. The hot/cold cycles make them brittle and never in a high vibration area.

Glad it's an easy fix.
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  #3  
Old 11-07-2014, 09:39 PM
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ColoRv ColoRv is offline
 
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Don't use tie wraps. I am shocked your DAR signed off on that plan. Mine told me long before he ever saw my plane, a single tie wrap firewall forward and you fail the inspection.
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  #4  
Old 11-07-2014, 09:47 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by ColoRv View Post
Don't use tie wraps. I am shocked your DAR signed off on that plan. Mine told me long before he ever saw my plane, a single tie wrap firewall forward and you fail the inspection.
Oh lord - another guy making up his own rules! I have seen more certified airplanes with tie-wraps forward of the firewall than I can count. Let's not start folks off with old wives tails and false doctrine. Tie wraps come in many different types and temperature ranges, and I have seen them in some pretty awful environments. You just have to use the right ones, and use them appropriately.
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  #5  
Old 11-07-2014, 10:11 PM
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Greg Arehart Greg Arehart is offline
 
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And there are some stainless zip ties as well, although those might cause chafing or other issues if not installed properly. As Paul said, depends on the job whether they can be utilized safely.
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  #6  
Old 11-07-2014, 11:39 PM
aerovin aerovin is offline
 
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Interesting to me how many tie wraps Lycoming sent with a brand new engine as part of the hardware kit to secure the spark plug cables. You'd think they know...
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  #7  
Old 11-08-2014, 06:23 AM
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Weasel Weasel is offline
 
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Quote:
Originally Posted by ColoRv View Post
Don't use tie wraps. I am shocked your DAR signed off on that plan.
Question: Since when does the DAR have the authority to decide if an experiment can be conducted?
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  #8  
Old 11-08-2014, 08:03 AM
johnfurey johnfurey is offline
 
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A friends $3,500,000 TBM 850 came from the factory with tie wraps all over the engine compartment. I think Paul said it best.
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  #9  
Old 11-08-2014, 09:03 AM
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ColoRv ColoRv is offline
 
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The inspectors at Oshkosh said the same thing while inspecting my engine compartment. No tie wraps. They said they will do the same thing to your engine mount as the photo above did to the aluminum pipe. I dunno if it's true or not of course, as I followed my DAR's directive and everything is done with adel clamps. Considering how easy it is to clamp everything and use sparkplug wire separators on the sparkplug wires, I can't say I was ever tempted to argue it out with the DAR, unlike the ridiculous wet compass requirement.

I can't think of any good reason to use zip ties firewall forward. I used a few hundred of them for initial wire bundling in the fuselage but once complete used the tie methods called out in the bible (Ac43). The great thing about these planes though is we get to do what we want (as long as your DAR isn't the pain in the butt mine was). Obviously there are tie wraps out there that will work firewall forward. There are far more that will do what the photo above did. We each spend our money and make our own decisions. How many of those 3.5M TBM's came with Lycoming vibration generators?
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Last edited by ColoRv : 11-08-2014 at 09:18 AM.
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  #10  
Old 11-08-2014, 09:32 AM
evogelman evogelman is offline
 
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Default mt props

check out the hub on an mtv 7 c prop.
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