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Date: Sun, 23 Mar 2014 15:12:26 -0400
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From: Bill Bradburry <bbradburry@bellsouth.net>
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Subject: Re: [LML] Prime suspect
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I bet that would have been beautiful at night!

B2
On 3/16/2014 8:41 AM, adam@validationpartners.com wrote:
> During January's cold snap I had to attempt an engine start after the 
> plane had been sitting outside in 20degF weather for 4 hours. After 
> many minutes of cranking, priming, and more cranking I had to throw in 
> the towel and cancel the flight. I had the FBO move my plane to their 
> heated hangar. When I was finally able to retrieve it 4 days later I 
> noticed significant heat damage on belly just aft of the right exhaust 
> pipe. I don't know how long the damage was there but I strongly 
> suspect it was from raw fuel spitting out the exhaust and catching fire.
>
> You can see pictures of the damage and repair here:
> https://plus.google.com/photos/102798913343718743387/albums/5991210570436247697?authkey=CIK38uXuxNOOJg 
>
>
> I believe this ties in with recent discussions about vibration 
> isolation for exhaust systems. The header pipe attaches to the 
> tailpipe with a ball joint which allows about 3" of movement in any 
> direction. A stiff rubber strap bolts to the firewall and extends down 
> to support the tailpipe and attaches with a clamp.
>
> The problem is that the rubber strap allows too much movement. I set 
> the strap length so that the tailpipe is angled slightly down. But if 
> I push the tailpipe up so it's parallel to the fuselage or even angled 
> up slightly it stays there after I let go. The stiffness of the rubber 
> strap can't overcome the friction in the ball joint.
>
> I'm not sure about the solution yet. Certainly changing from stock 
> baloney-slice tip to a turn-down tip would help. Changing from a 
> rubber strap to a metal bar would also help, but I'm only just 
> starting to think about the geometry and required freedom-of-movement 
> issues.
>
> On the bright side, the plane is still in primer so at least I didn't 
> ruin a nice paint job!
>
> -Adam Molny
> Legacy N181AM 220 hours
>
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