More_Flaps wrote in
:

On Jul 13, 12:53*am, wrote:
On Jul 12, 8:37*am, Stealth Pilot
wrote:



On Fri, 11 Jul 2008 06:00:22 -0700 (PDT), wrote:
On Jul 11, 7:09*am, Stealth Pilot
wrote:
On Fri, 11 Jul 2008 08:57:13 +0000 (UTC), Bertie the Bunyip
T...@ld
.you
wrote:

sid wrote in
news:702f8b8d-b77e-452c-904c-
:

On older planes, does the angle of attack change ? Does the
prop
angle
relax like a motorboat prop does after 1 or 2 decades of
constant use ? (fixed pitch of course)

There are some older warriors on the field (20 - 25) years,
and i
t
seems that there props don't have the bite that the new
warrior (
10
years old) does.

No, but years of wear and dressing the prop because of nicks
and wh
at not
doesn't do them any good at all.

Bertie

I have a fibreglass covered wooden prop which makes it
reasonably resilient in light rain. I paint it.
when the aforesaid light rain has eroded the paint *near the
leadi
ng
edge I lose 5 knots in cruise speed.

also If I alter the shape with a poor paint coat I lose cruise
speed
.

the other factor with some commercial aircraft is that there are
oft
en
3 props approved for them. a climb, a utility and a cruise prop.
on little cessnas they are each 2 inches of pitch apart.
memories of cruise with a cruise prop would make cruise on a
climb prop seem quite anaemic.

....and what bertie wrote.

Stealth Pilot

I can understand why a poor -- as in not smooth -- paint job would
alter the prop's efficiency, but never would have guessed having a
fractional mm of paint ablated from the leading edge of the prop
would affect it that much. Tongue in cheek question -- did the
natural color of the prop clash with that color and scare the air,
or something?

On a serious note, have you any thoughts as to why such a minor
change in shape would have such a remarkable change in efficiency?
A 5 knot change in airspeed is like reducing the manifold an inch
or so, isn't it? That's huge! It also suggests there may be very
minor changes in prop that could improve performance too.

l

the prop had a fairly average sheath put on it. average
workmanship. I use the paint layers to fair the surface to a
smoother shape. the face I see is painted matte black to make it
invisible. the leading edge is blue, the rest varnish.
chipped paint just creates a turbulator which seems to affect this
blade section. (clark Y, aka naca 44xx series)

I got 5 extra knots in cruise for nothing when I cleaned up the
prop and got the shape right the first time. the damaged leading
edge paint just drops me back to the original slower cruise.

Stealth Pilot

Five knots is a huge gain. I remember reading some years ago of a
homebuilt getting a new paint job, and the color change on the wings
led to a paint 'bump' or seam near the leading edge which so altered
the airflow the airplane could not fly (probably changed the
stagnation line).

Sounds like a myth to me. How thick is a paint line?

Still, that big a change in cruise speed seems
remarkable.

I'd say unlikely.

Not in an airplane like the Tailwind. A small change in somethign like a
Cherokee might not get you much, though a series of changes will get you
quite a lot evn in one of those, but something that acts more of a whole
like a talwind or a Midget mustang can be hugely affected by one single
ingredient being out.


Bertie