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
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
_________________________________________________________________
MSN Hotmail is evolving - check out the new Windows Live Hotmail
http://get.live.com/betas/mail_betas
|