Prop Strikes

wrote in message
oups.com...
Anyone else here ever experience one?

I had one while returning to Boulder City about 3 years
ago. It was early in the afternoon in late May & the winds
were out of the south at about 15 knots. The ride was smooth,
so I didn't expect gusts (big mistake). Landing on the 3 degree
downhill runway 15 with a 7 knot right crosswind was pretty standard,
but during the roll-out while braking hard the wind shifted and
lifted up the left wing. I thought at first I must have scraped the
right wing, but what actually happened is that the plane (182) rotated
about the right main/nose wheel axis sufficiently for the prop tip
to touch the tarmac. Clearing the runway, the automated unicom
was reporting winds as 090@20 with wind shear. The insurance
company (USAIG) were very nice about it & handled the tear-down
& new prop to the tune of about $15K, and without increasing my
premium subsequent years. During the tear-down, discovered
problems with the crank shaft (which may have been caused by
the strike) and some AD's which hadn't been complied with on
the counterweights.

Here's what I learned from that.

1) If it's hot in the desert southwest, always expect wind shear.
Be prepared to adjust the ailerons as necessary & don't just
throw the yoke over to whatever side you think the crosswind
is coming from.

2) Maintain back pressure when on the roll-out especially when
braking hard.

3) Bring up the flaps (they were at 40 degrees) during the
roll-out to make yourself a smaller target for the wind.

On Fri, 28 Jan 2005 02:37:48 GMT, "Tony Cox" wrote in
. net::


Here's what I learned from that.

1) If it's hot in the desert southwest, always expect wind shear.
Be prepared to adjust the ailerons as necessary & don't just
throw the yoke over to whatever side you think the crosswind
is coming from.

Actually, it is more appropriate to "steer" with the wind rather than
into it to minimize its effect. That is, if the aircraft is for
example experiencing wind from the right rear, one would push the
yoke/stick forward and to the left. This lowers the elevator and
right aileron, so that the wind can't get under them as easily.

2) Maintain back pressure when on the roll-out especially when
braking hard.

That's what the POH recommend, IINM.

3) Bring up the flaps (they were at 40 degrees) during the
roll-out to make yourself a smaller target for the wind.

It also puts more weight on the main gear tires to increase brake
effectiveness.

It's a Cub, but it can still kill people when that
"field-repaired" prop throws a chunk of blade and tears the engine off
its mounts. Or later, when that almost-certainly cracked crank fails.
As I said in another post, the small Continentals are prone to crank
cracking after prop strikes. Anything violent enough to bend a prop
warrants investigation.

Dan

"Larry Dighera" wrote in message
...
On Fri, 28 Jan 2005 02:37:48 GMT, "Tony Cox" wrote in
. net::


Here's what I learned from that.

1) If it's hot in the desert southwest, always expect wind shear.
Be prepared to adjust the ailerons as necessary & don't just
throw the yoke over to whatever side you think the crosswind
is coming from.

Actually, it is more appropriate to "steer" with the wind rather than
into it to minimize its effect. That is, if the aircraft is for
example experiencing wind from the right rear, one would push the
yoke/stick forward and to the left. This lowers the elevator and
right aileron, so that the wind can't get under them as easily.

The problem, of course, is how do you *know* the wind is
coming from the right rear? I was taught to throw the yoke
over when on the ground, but that presupposes that the
wind is still coming from the same direction as when you
were coming down final. I certainly didn't expect the wind
to go from a 30 degree right x-wind to a 90 degree left
x-wind in the time it takes me to roll out! Live and learn,
eh?


2) Maintain back pressure when on the roll-out especially when
braking hard.

That's what the POH recommend, IINM.

Indeed. And I've replaced my previous limp-wristed gentle
tug with something more akin to reigning in a panicked horse!
As I say, live and learn.


3) Bring up the flaps (they were at 40 degrees) during the
roll-out to make yourself a smaller target for the wind.

It also puts more weight on the main gear tires to increase brake
effectiveness.

I've always been nervous touching the flaps on landing. Mainly
because of flight instructors who have cautioned against
unnecessary distractions until clear of the runway and others
who think it establishes a bad habit which may come back to
bite if landing in a retractable (confusing flaps with gear). Not
so nervous now...

Dive both ways?
--
Gene Seibel
Hangar 131 - http://pad39a.com/gene/plane.html
Because I fly, I envy no one.

"Blueskies" wrote in message
om...

"Gene Seibel" wrote in message
oups.com...
I was pretty much right at the point where the wind went from tail to
head. Elevator control was something that simply wasn't instinctive to
me, and it happened in a split second.
--
Gene Seibel
Gene & Sue's Aeroplanes - http://pad39a.com/gene/planes.html
Because I fly, I envy no one.


Tricycle gear while taxiing; always dive into the wind or dive away from
it...

Bank into a quartering headwind, neutral elevator; dive away from a
quartering tailwind .

"Sam O'Nella" wrote in message You guys are freaking me out. I think
I'll go buy an LA-4.

LA-4s suffer prop strikes too. The prop strikes the upper fuselage skin.

D.

Capt.Doug wrote:
"Sam O'Nella" wrote in message You guys are freaking me out. I
think I'll go buy an LA-4.

LA-4s suffer prop strikes too. The prop strikes the upper fuselage
skin.

Under what circumstances does this happen?

Incidentally, what's a "stress riser?"

A stress riser is any flaw in a structural piece that concentrates
the stresses through that area to the point that failure might occur. A
common example is cutting glass. The "cutter" doesn't cut; its small
roller causes a shallow crack in the glass that will allow you to break
the glass cleanly when it's bent. On a propeller a nick intereferes
with the lines of force in the blade, causing them to have to bend
around the nick and so concentrating them below the damage. Their
concentration can start the propeller cracking. The blade undergoes
huge G forces outward, thrust forces forward, and drag forces
chordwise; a prop is often the most heavily stressed part on the whole
airplane, and I often see chewed-up props on otherwise cared-for
airplanes.
Owners don't understand the risks. A prop that throws a foot or so
of blade is liable to tear the engine out of the mounts before the
pilot can get it stopped, and guess what happens to the CG when about
300 pounds of engine and prop leave a 172? The airplane can't even
glide.
I demonstrate the stress riser phenomenon to my class using
strips of light aluminum flashing. The students try (unsuccessfully) to
tear a piece of the flashing. Then I file a tiny nick in the edge, and
it tears easily. A second piece with a nick dressed out becomes
impossible to tear.

Dan

a prop is often the most heavily stressed part on the whole
airplane,

From an engineering standpoint -

A light plane propeller, whether wood or aluminum, is about 1/8 inch
larger in diameter at cruise than when standing still due to
centrifugal acceleration. Consider also that a prop is an essential
non-redundant monolithic structure, which if aluminum, is made of a
material (2024-T3) that has good tensile, but mediocre fracture
toughness properties. In operation it is subject to very high-cycle
bending fatigue due to torsional resonances.

Fracture toughness is a measure of the crack propagation resistance of
a material. As a fracture toughness example, compare the tensile
strength of cellophane vs shrinkwrap with and without a tiny transverse
slot cut into it.
Props are highly stressed and must not be treated casually.