Prop Strikes

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.

Someone please remind me again why a complete engine teardown is always
necessary afterwards?

Lyc and TCM require it based on possible damage to the engine from a sudden
stoppage. This has never made sense to me from an engineering standpoint.
When the engine is started it goes from barely turning to suddenly spinning
fast. Why can't it take a faster than normal deceleration from a prop
flailing against pavement or bashing a tow bar?


"Sam O'Nella" wrote in message
...
Someone please remind me again why a complete engine teardown is always
necessary afterwards?

Dan Thompson wrote:
Lyc and TCM require it based on possible damage to the engine from a
sudden stoppage. This has never made sense to me from an engineering
standpoint. When the engine is started it goes from barely turning to
suddenly spinning fast. Why can't it take a faster than normal
deceleration from a prop flailing against pavement or bashing a tow
bar?

I can see how the impulse decelleration of a strike vastly exceeds that of
normal engine operation.

I could see the crank "twisting" especially if it were pressed together from
separate parts (I have no idea if it is). I'd be interested to know what %
of teardowns after prop strikes actually uncover hidden damage, and what
damage that was.

On Thu, 27 Jan 2005 00:12:02 -0500, "Sam O'Nella"
wrote:

Someone please remind me again why a complete engine teardown is always
necessary afterwards?

I have always been told there are several reasons. One is the
possibility of twisting the crankshaft and having it fracture. So when
they tear it down, it gets magna fluxed to make sure there are no
fractures in it. Second reason is more for the insurance. Because of
issues with the engine possibly being harmed, the insurance company
would rather try and place the blame on someone else if something were
to happen later on. So they require a mechanic to do a complete
inspection, so if something does happen to the aircraft after that,
then they possibly have somewhere else to go; like to the mechanics
insurance saying that the mechanic did not do his job properly. This
will ease the pain from the aircrafts insurance.



Scott D

To email remove spamcatcher

Sam O'Nella wrote:

I could see the crank "twisting" especially if it were pressed together from
separate parts (I have no idea if it is).

On every airplane I know about, the crankshaft is a single monolithic steel
forging. Some are hollow to allow for oil passages.

Someone please remind me again why a complete engine teardown is
always necessary afterwards?

During a prop strike, the engine is producing power, yet an external
force is suddenly counteracting it. That leads to conflicting
internal forces that can damage crankshafts, retaining bolts (see a
recent Lycoming AD), probably all sorts of moving things.

- FChE

When the engine is started it goes from barely turning to suddenly spinning
fast. Why can't it take a faster than normal deceleration from a prop
flailing against pavement or bashing a tow bar?

The difference is whether the acceleration or deceleration is constant or
sudden.

Lyman

"George Patterson" wrote in message
...


Corky Scott wrote:

Nothing happened right away, not at idle anyway. The prop missed the
still attached towbar. But when the engine was revved up for the
runnup, the lowered pressure in front of the prop sucked the tow bar
up and I guess caused a sudden stop.

Machado tells the story of a plane spotted taxiing with the towbar still
attached. Someone radioed to stop him from taking off.

He had just landed.

George Patterson
He who marries for money earns every penny of it.

I watched one take start to take off with the tow bar
attached.It dropped off just as the plane left the ground.
No damage as far as I know.

Bob Barker N8749S

On every airplane I know about, the crankshaft is a single monolithic
steel
forging. Some are hollow to allow for oil passages.

Cranks in radials are pressed together from several pieces. The
master rod can't have the usual split feature since it has pin bosses
all around it for the other connecting rods to attach to.
Any propstrike can cause unseen damage inside the case. I had a
crank break due to a propstike sometime in the undocumented past. It
broke between the rearmost rod throw and the one next ahead, a long way
behind the prop. In small Continentals, this is apparently the usual
place to break. Some guys will dial the prop flange to see if it's
bent, but this doesn't tell you how much it bent and then sprang back.
Cracks can form anywhere in the crank due to twisting and bending
forces, rods can bend or pistons crack, rod bolts stretch and crack or
come loose. A propstrike is a MUCH more rapid decelleration than
spooling down or starting up, however brief it might be. Wooden props
will often spare the engine, metal props are unforgiving. A propstrike
could be a bomb waiting to bite someone later on.

Dan