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Gary,
I have changed how my exhaust is supported to stop the cracking. Originally I had no supports. I only had the pipes connected to each other at the tails. I have had one crack where the #4 tube is welded to the wrap around pipe early in my flying about 75 hours if memory serves. I did what the RV guys do and made a support that connects the pipe to the engine just behind the sump using 2 supports. As for inspection, I just put the wrap on last year. I removed it when I did some major work on the engine and there were no cracks. This time, I was so impressed with how well the material performed when I did my experiment, I decided to add several layres on the entire exhaust. I will just unwrap it once each year at annual. If it goes 2 or 3 years with no cracking I may go every other year on the inspection. I would also not make the wrap super tight.
When it is a little loose, it holds the heat in better and it has a natural dampening affect on the pipes. Try to make a pitch fork ring with a sock over it....
What are your head temps running at?
I think there is a flaw in the lower cowl design of the 235/320/360 series Lancairs. If you look on any production airplane. The openings on the bottom of the cowls all have an angled piece or lip angled away from the opening to create a low pressure area. I think that ours should have that as well. I also think we are getting airflow into the slot in the bottom of the cowl where the nose gear travels.
My friend had major head cooling issue on his Zenith 801 and tried everything to get them to cool down to no avail. When he added a lip on the botttom opening of his cowl, shazam! head temps waaay down.
I have been trying to think of a way to test that on my airplane without buggering up my paint as that may be the answer to my oil
cooling issue.
I did a little better job of sealing around the engine baffeling with RTV to get the best affect from the plennum cooler. I also did the exhaust wrap, opened up the exits under each cylinder. I also radiused those exits. All of that changed my head temps from running in the upper 300's and 25 degrees apart to 360 F average with all the heads running within 5 or 10 Degrees of each other. Not sure what did what but I like where I am on that front.
Randy Snarr
--- On Tue, 3/10/09, Gary Edwards <gary21sn@hotmail.com> wrote:
From: Gary Edwards <gary21sn@hotmail.com>
Subject: [LML] Re: oil cooling/ head temps
To: lml@lancaironline.net
Date: Tuesday, March 10, 2009, 8:37 PM
Good information Randy.
On this bird, the cylinder with the highest CHT (#3) has the least
amount of exhaust piping in its vicinity. As you know the exhaust pipes
are routed around the left side. Those side cylinders (#2, #4) have CHT's
lower than #3. Also, the headers are heat coated on
the inside. The engine has been sealed up with RTV at every
opening. That was the first thing I did 10 years ago. The bottom
wrap-under baffling on #3 was opened up then also. I have modified
the rear baffling on #3 head so as to create an air space where there was none
before (the rear of #3 has no cooling fins so the baffling is typically tight
against the head). Removing the 4" exit scat tubing from the oil
coolers did nothing to lower the CHT's or RAISE the oil temps. Bottom cowl
rear exit area (sq. in.) was calculated and is equal to or more than standard
320 and RV cowls.
How do you do visual condition inspections on the headers with the pipe
wrap on them? Of all the repairs I have had to do in the engine
compartment, the most have been to the headers. Multiple cracks to
weld - stainless headers.
Gary
----- Original Message -----
Sent: Monday, March 09, 2009 10:41
AM
Subject: [LML] Re: oil cooling/ head
temps
Gary, One side note on the head temps. I made my plennum
similar to yours.
My head temps run within 6 deg of each other
usually 310-360 F depending on power and temps.
One thing that I
did was to shine a light up through the bottom of engine with the hangar
lights out and found and sealed EVERY gap in the baffeling except where
cooling air needs to go with high temp RTV.
I also opened up the gap
on the bottom of each cyl to 2.6" times the dept of the cooling fins as
I read somewhere NASA had done some testing and determined that was the
optimum opening. I also radiused the baffeling exits inder the cylingers
rather than 90 deg bends on the exits. I understand that helps flow as
well.
I have also come to the conclusion that there is airflow
coming into the cowl through the nose gear slot and bottom exit cowl
area. I see this when I get an oil leak. the oil runs down and then
blows forward. Weird. Ayway, you may need a small 45 deg lip on the
bottom of your cowl exit like I probably do.
One last thing of
note, in my pictures you will see the exhaust wrap, that did make a
difference on head temps and it also evened them up. My exhaust wraps
around the engine like yours does and runs close under the cyinders. I
wrapped those areas with 4 layers of exhaust wrap and 2 or 3 layres
everywhere else and have had good results lowering engine compartment
temps-unmeasured but it appears to be so. I tested the heat wrap on my
heat gun. With 4 loose layres I could hold my hand on a heat gun nozzle
on the high heat setting. That sold me on that
stuff.
FWIW...
Randy Snarr
N694RS
--- On Sat,
3/7/09, Gary Edwards <gary21sn@hotmail.com> wrote:
From:
Gary Edwards <gary21sn@hotmail.com>
Subject: [LML] Re: oil
cooling
To: lml@lancaironline.net
Date: Saturday, March 7, 2009,
6:33 PM
It seems that most temp issues are with oil. Mine are not
with oil, but with CHT's.
As you know (you have seen pictures), I have 2 smaller (6" round)
oil coolers, one on each side (mounted to the engine mount) with naca
ducts and short 4" to 6" long straight 2" inch scat duct to
them. The scat duct is connected via glass enlargers.
On the outlet side, there are glass reducers down to 4" scat duct,
with the duct routed down to near the nose gear front cover on the
firewall. It as close to the lower cowl outlet area that I
could get.
The oil temps. are too low, especially in winter. It is
difficult to get the temp to 180. In summer, the oil temp is
about 190 to 200 climb and cruise. I tried (for winter) closing
off one cooler with duct tape over the cowl inlet to raise the temp
and it didn't make any difference. Tried it on both sides.
I also removed the 4" outlet duct (reducers left on), to let the
outlet flow directly into the rear cowl area, with no change
noticed. In only one case, have I had a high oil temp; in Bend,
Or., giving a friend a ride after a previous flight.
Outside temp in the '70's. Never has happened again.
Now, if I could just get my CHT's down. I have to step
climb with that issue when at gross weight.
Gary Edwards
LNC2
235/320
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