wrote in
:

On Jul 12, 9:44*am, Stealth Pilot
wrote:
On Sat, 12 Jul 2008 05:53:59 -0700 (PDT), 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...@l
d.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
constan
t
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 w
hat 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
lead
ing
edge I lose 5 knots in cruise speed.

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

the other factor with some commercial aircraft is that there
are of
ten
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 woul
d
affect it that much. Tongue in cheek question -- did the natural
colo
r
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
chang
e
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). Still, that big a change in cruise speed seems
remarkable.

In that I fly behind controllable pitch props it's nothing I'd have
noticed, but still, if TLC *gains that kind of speed advantage it
should be standard of care for propellers.

I repainted the prop (and rebalanced it) and replaced the windscreen
plastic and saw an 11knot increase in cruise speed.
this is after an extensive period of taping up seams and other toying
that saw absolutely no improvement at all.

it took my aero engineer friend about a month to work out what I'd
accidently done.

it was ...put back all the windscreen bolts.

this removed some blasts of air into the low pressure zone over the
windscreen.
the blasts of air were doing two things my aero engineer friend
deduced.
reducing the depression in pressure over the wing which reduced the
lift and required a slight increase in angle of attack which
increased induced drag.
increased the thickness of the boundary layer which increased drag.

the jump in performance on the first flight was just stunning to
behold. where before I could just make 120 knots balls to the wall in
a flypast I can now easily achieve 145 knots at max rpm after a dive.

your controllable prop gives you so much of an advantage.

Stealth Pilot

There are a lot of differences between the Mooney Executive and the
201, but the two that made the real difference in speed was a
redesigned windscreen and a redesigned cowling. Everything else was
pretty much lipstick but it was NOT lipstick on a pig, most agree the
Mooney 201 was a pretty airplane in its day. I don't think the Mooney
brothers overlooked much, but I'll take a close look to be sure things
are still smooth where they should be.


mooney brothers?

Al had a brother?


Bertie