Hi Terry,
A very interesting comparison. But why doesn't everyone have this problem ?
I never noticed high temperatures, and then how can your case reach melting
point of stainless steel. And my affected area is very specific with no
scorching anywhere else.
I still have this theory about an electrical discharge between aluminum duct
and engine above. The duct, including radiators, is electrically isolated. I
assume that coolant and oil are not very good conductors.
Cheers,
Karl
>From: "Terry Seaver (terrys)" <terrys@cisco.com>
>Reply-To: europa-list@matronics.com
>To: <europa-list@matronics.com>
>Subject: RE: Europa-List: Melting silencer
>Date: Mon, 7 May 2007 09:58:20 -0700
>
><terrys@cisco.com>
>
>Hi Karl,
>
>We have a 912S powered XS and had problems with very high temperatures
>under the cowl, near the muffler, hot enough to melt nylon tie wraps
>(about 450 deg F melting point) and take the temper out of exhaust
>retaining springs. We spent many months working on getting this under
>control, doing many test flights with data logging of multiple in-cowl
>temperatures. What we found was that air would stagnate around the
>muffler, creating very high localized temperatures. Many things were
>tried (some similar to what you have tried) until we finally found a
>solution. We opened up the exit area for the engine compartment, closed
>off the gills in the top cowl because they were letting cooling air
>escape without cooling anything, and finally installed a baffle between
>the foot wells to keep cooling air from just going around the back of
>the engine without cooling much. These three mods forced the air to go
>around the cylinders and then around both sides of the muffler.
>This mod solved our in-cowl temperature problems and lowered our oil
>temperatures about 20 deg F in the climb.
>
>A write up of what we did can be found at;
>
>http://terryseaver.home.comcast.net/N135TD_mods.htm
>
>
>Look at the section titled: Engine compartment cooling
>
>Regards,
>Terry Seaver
>A135/N135TD
>
>
>-----Original Message-----
>From: owner-europa-list-server@matronics.com
>[mailto:owner-europa-list-server@matronics.com] On Behalf Of Karl Heindl
>Sent: Monday, May 07, 2007 6:18 AM
>To: europa-list@matronics.com
>Subject: Europa-List: Melting silencer
>
>
>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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