REFLECTOR: Cowl flaps better oil temps

John Dibble aminetech at bluefrog.com
Thu Feb 23 10:01:05 CST 2006


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
>
>    ----------------------------------------------------------------
> _______________________________________________
> To change your email address, visit
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives:
> http://www.tvbf.org/archives/velocity/maillist.html
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20060223/78cc45a4/attachment.htm


More information about the Reflector mailing list