Stealth Pilot wrote in
:

On Sat, 12 Jul 2008 08:45:36 -0700 (PDT), More_Flaps
wrote:

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
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 it 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 what 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
leading 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 often 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?


not a myth at all. it was a well documented problem on one of the
early fibreglass canards. the addition of a decorative tape stripe on
the top of the canard resulted in the aircraft not being able to
takeoff. removal of the stripe fixed the problem.


Yeah, I remember that. On the flip side of that the additin of a turbulator
strip in the right place will enhance lift..

http://www.standardcirrus.org/Turbulators.html


Bertie