REFLECTOR: Cowl flaps better oil temps
Andrew Ellzey
ajlz72756 at yahoo.com
Thu Feb 23 10:47:38 CST 2006
As stated my Textron Lycoming operators manual for O-540 and IO-540 states that Max never exceed red line cyl head temp is 500 deg F (260 C). For maximum service life cylinder head temps should be maintained below 435 deg F (224 C) during high performance cruse operation and below 400 deg F (205 C) for economy cruse.
Also stated in this same manual, Oil pressure normal operation for all models has a max pressure of 95lbs. Minimum of 55lbs. Idling pressure of 25, and start and warm-up of 115lbs.
The maximum permissible oil temperature is 245 F (118C). For maximum engine life, desired oil temperature should be maintained between 165 F (73.8C) and 200 F (93.3C) in level flight cruse.
More food for thought,
Andy Ellzey
----- Original Message -----
From: John Dibble
To: Velocity Aircraft Owners and Builders list
Sent: Thursday, February 23, 2006 10:01 AM
Subject: Re: REFLECTOR: Cowl flaps better oil temps
This raises questions that I was not able to get answers for - Is there an optiumu CHT? Is there a minimum CHT? Seems like these questions need answering before flaps are considered.
John
Andrew Ellzey wrote:
See attached crude example of how cowl flaps could be added to NACA scoops.
Every high performance complex general aviation aircraft that I can think of, has cowl flaps. They are not only important for
summer and winter operation but for high altitude operation.You can actually hurt your engine from to much cooling. The
choke in our cylinders is there for a reason. It is intended to allow the cylinders to become a straight bore when the cylinder
temperature is at the correct operating temperatures. If you are running your engine too cool, you could be prematurely
warring out your rings and cylinders. There is a very easy way that I see that a butterfly type valve could be added to
the NACA scoops. These two butterfly valves could be controlled by a push pull cable located inside of the ceiling fresh air duct,
having a lawn mower type throttle control also mounted in the overhead duct. I flew a 1964 M20E for 15 years that had the
original oversized air intake. I was able to control my oil temp using the cowl flaps very easily. See the attached crude drawing of a
very simple butterfly valve that I have in mind. Remember the Butterfly valve shouldn't completely close off the air, only
provide control over restricting air flow. So the valve in the closed position shouldn't block any more than about 30% of
the air flow (could vary for your engine and cowling configuration). Ground operation and takeoff to cruising altitude should
be full open. After you have leaned for cruse and temps have stabilized, then start closing your cowl flaps watching your
cylinder head temps and oil temp. My Textron Lycoming operators manual for O-540 and IO-540 states that Max never exceed red line
cyl head temp is 500 deg F (260 C). For maximum service life cylinder head temps should be maintained below 435 deg F
(224 C) during high performance cruse operation and below 400 deg F (205 C) for economy cruse. Cowl flaps also help
prevent shock cooling (very destructive) on fast let downs from altitude. How many times has ATC asked you to expedite
your decent? Its happened many times to me. Velocities and Mooneys don't like to slow down when loosing altitude, you
are forced to reduce power to prevent airframe red line . Cowl flaps allow you to reduce power and still keep you cylinder
head temps in the green operating zones even for that slow gear speed. I was cruising at about 6500 feet one beautiful
summer day and his a pocket of clear air turbulence so severe that all the luggage in the luggage compartment hit the
ceiling of the aircraft. If my wife and I hadn't been belted in it probably would have knocked us out, or broke our necks.
Mooneys will easily cruise in the yellow ark on the air speed indicator. When this turbulence occurred my first reaction
was to slow down out of the yellow ark. I pulled off the power two quickly and shock cooled my IO-360 engine and stuck
an exhaust valve. We had enough altitude and enough power on three cylinders to land at FSM airport. As we were taxing
up to the FBO, the stuck valve came loose and the 4th cylinder came back to life. It took about an hour to get my wife back
in the plane to fly the rest of the way home. Just an extreme example of shock cooling your engine. I was lucky this time
that the valve came loose and we weren't stranded with a hefty repair bill.
My thoughts your airplane.
Andy Ellzey
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