What are cowl flaps?

On 26 Oct 2006 15:05:08 -0700, "swag" wrote:

They absolutely cause a 10knot difference in performance in a Skymaster
P337.
And if I recall they caused about 7 knots degradation in my 73 F33a Bo

In my old Deb which has a number of speed mods and big engine they are
good for at least 10 knots.

Jon Kraus wrote:
5 or 10 knots? What are they freakn' barn doors or something? :-)
Sure your not fibbing?

It's not the flaps creating the drag. It's the air the let in around
the engine and out the bottom that adds the extra "cooling" drag.




Ron Natalie wrote:

In my plane, I can get another five to ten knots when
I close them.
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Roger (K8RI) wrote:
On 26 Oct 2006 15:05:08 -0700, "swag" wrote:

They absolutely cause a 10knot difference in performance in a Skymaster
P337.
And if I recall they caused about 7 knots degradation in my 73 F33a Bo

In my old Deb which has a number of speed mods and big engine they are
good for at least 10 knots.

Jon Kraus wrote:
5 or 10 knots? What are they freakn' barn doors or something? :-)
Sure your not fibbing?

It's not the flaps creating the drag. It's the air the let in around
the engine and out the bottom that adds the extra "cooling" drag.


The air that goes into the cowling for cooling is air that isn't
used for thrust anymore, and when there's less thrust there's less
speed. With the cowl flaps closed, most of the air can't get into the
cowl openings and goes around instead, contributing to thrust.
There were some airplanes with well-designed cooling systems that
were able to recapture the lost thrust through the heating and
expansion of the cooling air. There was a discussion on one of these
groups several years ago about it. I think the P-51 was one of them.
The light airplanes we fly have cooling systems that are crude by
comparison.

Dan