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.

in an allied situation a friend complained of a sudden 45 knot
reduction in the speed of his RV6. it really put the wind up him.
a cursory inspection and I could see that the heavyweight polyurethane
protective tape he'd applied to the prop had destroyed the aerofoil
shape. he removed it at my suggestion and immediately had his 45 knots
back.

remember being told to remove frost from the wings before flight?
more than one aircraft has crashed because they didnt.

same effect.

Stealth Pilot