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The vernatherm works the opposite as you
might think. When it is cold, it opens the shortcut passage inside the
vernatherm that causes the oil to bypass the cooler and go back to the engine.
The passage to the cooler is still open but the oil takes the path of least
resistance and flows into the engine. When the oil is hot, this shortcut
passage is blocked off forcing the oil to go to the cooler.
Most high oil temp problems are caused by
insufficient airflow through the cooler. This is due to insufficient pressure
differential across the cooler. You can have plenty of blast air hitting
the face of an oil cooler but if the hot, expanded exit air can’t depart
the other side free of any obstructions or slightly increased lower cowl
pressure then the cooler won’t function well. If you have an air duct
& hose on the back side of the cooler it needs to be 3x the diameter of the
feed hose to accommodate the 3x volume of hot expanded air.
A balloon makes a good illustration, especially
in winter. Blow one up then put it outside and watch it shrink. The best
mounting for an oil cooler is such that the exit air dumps directly overboard
to a low pressure area. The P51 Mustang is a good example. The Glasair III mounted
to the side of the lower cowl has proven to work well also.
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Sky2high@aol.com
Sent: Thursday, March 12, 2009
7:30 PM
To: lml@lancaironline.net
Subject: [LML] Re: oil
cooling/Vernatherm
Oh, I forgot. I also replaced the
Vernatherm, but I don't remember technical details of the testing (a long story
involving a flash fire - best told in a bar). I believe the chamber
that the Vernatherm operates in is such that, when cold, allows oil to
bypass being sent to the cooler. When hot, the extension of the device
shuts the bypass opening. Thus, if the Vernatherm does not fully extend
when hot, the bypass is not sealed and uncooled oil would be returned to the
system.
In a message dated 3/12/2009 9:35:08 A.M.
Central Daylight Time, randylsnarr@yahoo.com writes:
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Scott,
I was thinking the same thing and am making plans to "redo" my oil
cooler to cowl connection and make it nice and smooth. That will happen after
I verify the vernatherm is doing what is supposed to...
I pulled out the vernatherm the other day and put it in boiling water to see
what it would do.
I admit I really do not understand how it works but the spring loaded end got
about 1/8" longer when going from room temp to 212 F.
Does that mean it is working?
If anyone knows if this is good or bad, please pipe in...
Thanks for the feedback!
Randy Snarr
--- On Tue, 3/10/09, Sky2high@aol.com <Sky2high@aol.com>
wrote:
From: Sky2high@aol.com <Sky2high@aol.com>
Subject: [LML] Re: oil cooling
To: lml@lancaironline.net
Date: Tuesday, March 10, 2009, 8:36 PM
My large sharp
edged NACA duct is poorly placed on the left rearward side of
cowling. It enters a short flexible 3" smooth rubber sleeve
(plumber's sleeve) and then to a plenum above the small SW oil cooler mounted
to the fire wall. The bottom is open to the lower cowl. I climb
at about 135 KIAS and see cylinders occasional reach 400 degrees on a hot day
while the oil stays at 180. In cruise in 30-40F temps, I must at least
partially close the door between the NACA and the cooler. Recently, in
10C temps, I had to completely close the door to keep the oil temps about
180. In the pattern at 100 KIAS I will see the oil go 190F or even 200F on
hot days because of lack of air thru the cooler.
It wasn't always that
way.
When I had high oil
temps, I tried a special cooler air exit to assist, no help..
Another was to try
exiting thru shark gills on the side of the cowl, no help.
I temporarily attached
a scoop to force more air in the duct, no help.
I finally discovered
that the air was backed up in the NACA duct plenum (or chamber), thus cutting
off air flow. I used Micro to smoothly shape the chamber, thus
directing the air into its 3" outlet (no more dead corners) with the
results detailed above.
Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)
In a message dated
3/9/2009 12:41:32 P.M. Central Daylight Time, marv@lancair.net writes:
Posted
for randy snarr <randylsnarr@yahoo.com>:
All,
Thanks for the good suggestions on the oil cooler.
I flew again today and my oil temps are at 208 F flying in 35 f air.
They will be 215 or 220 this summer.
I will try a few solutions that do not need to cut the cowl. I will
most
likely make a duct to carry the exhaust air from the oil cooler down to the
lower aft part of the cowl. I have also heard that the aft vertical edge of
the naca opening should be shaped like an air foil. Mine is flat and fairly
sharp. The easiest way to test will to be construct a piece to give it a
little airfoil made from balsa or foam taped in place and flight tested. If
that does not work, I will make a duct from the cooler to the low pressure
area on the bottom of the cowl and lastly would be a small lip on the bottom
of the cowl aft.
every producton airplane I have seen with an opening on the bottom of
the
cowl has 45 deg lip to create a low pressure area. I should have done that
before I painted....
I will post my findings when I get them.
Randy Snarr
N694RS
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