Karl
stainless steel melts around 1550 deg C so it's highly unlikely you have
melting.
Karl Heindl wrote:
>
>
>
> The mod 72 has one good side benefit, it gives us the chance for a real
> close inspection of the back of the engine and underneath. I had to
> remove the silencer for better access to the firewall and two bottom
> frame bolts. Here is what I discovered :
> The bottom of the silencer , starboard side, an oval area of 30x90mm was
> badly pitted with strong signs of having melted. The aluminum duct
> directly underneath is similarly affected. I tapped the affected area
> with a hammer to look for any weakness, but it appears to be still okay.
> The aluminum is paper thin and needs to be patched.
>
> My installation is a standard 912S fwf kit with stainless exhaust system
> and Singleton firewall. I never experienced any temperatures (according
> to the EIS) above the permissable ranges. The EGT probes are on the
> exhaust stubs of cylinders 3 and 4. I never noticed anything unusual.
> There is no other heat damage. The coolant pipe directly behind it to
> the radiator shows no sign of anything unusual.
>
> My questions are:
>
> Has anyone ever experienced or heard of anything like this before ? What
> could be the possible cause ? What is the melting point of stainless
> steel ?
>
> There is no direct fresh air to the bottom of the engine. Some time ago
> I had taped off the starboard NACA duct, as it was supposedly designed
> for the 914. There was no detrimental effect to the engine temperatures.
> I have now opened up the precut flap in the starboard side of the alu
> duct, which will divert some fresh air to the silencer. (I believe this
> flap was also designed for the 914).
>
> One very long shot : Could there be any electrical sparking between the
> two surfaces, acting like a capacitor ? I just don't see how those high
> temperatures could come from the exhaust gases without also burning the
> outside of the fuselage etc.
>
> I wonder if anyone knows. And any help greatly appreciated.
>
> Karl
>
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--
Graham Singleton
Tel: +441629820187
Mob: +447739582005
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