Real stats on engine failures?

"Kyler Laird" wrote in message
...
Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

If the only thing that could go wrong with an engine was some sort of
failure of the cylinder, then that would actually be a pretty close
approximation of the truth. And in fact, if you have a six-cylinder engine,
you ARE (about) six times as likely to have a failure *of a cylinder* as you
would with a single-cylinder engine.

In the single vs. twin analysis, you have nearly double the chance of an
engine failure as with a single, all else being equal. If X (a number
between 0 and 1) is the chance of an engine failure for a single engine,
it's not that you have 2 * X chance of an engine failure for two engines.
You actually have 1 - ((1-X) * (1-X)) chance of an engine failure. But when
X is small (as it is in this case), the square of 1-X is pretty close to 1 -
(2 * X).

If all that could fail on an engine was a cylinder, or component related to
a cylinder, then a six-cylinder engine would be 1 - ((1-X) ^ 6) likely to
fail, where X is the chance of failure for a single-cylinder engine. But
just as 1 - ((1-X) ^ 2) is very close to 2 * X for small X, so too 1 -
((1-X) ^ 6) *is* actually very close to 6 * X for small X.

Now, with that essay out of the way, the real reason that six cylinder
engines aren't six times as likely to fail is that a number of failure modes
have nothing to do with the cylinder. They involve one or more other parts,
parts which exist in the same number regardless of the number of cylinders.

Note also that just as having two engines provides a benefit to offset the
very real increased opportunity for failure, having four, six, or more
cylinders provides a benefit to offset the very real increased opportunity
for *cylinder failure*. That is, with a six cylinder engine, if something
that IS specific to a cylinder fails, often the result is simply reduced
power, not a complete power failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Sounds like you've got some good geniuses advising you. Stick with them.

Pete

"Kyler Laird" wrote in message
...
(Captain Wubba) writes:

So what is it? If the engine-failure rate is one failure for every
50,000 flight hours, I'll feel much less reticent about night/IFR
single-engine flying than if it is one in 10,000 hours. Anybody have
any facts or hard data, or have any idea where I might be able to
track some down?

Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Not so, smart ass. You don't have six oil pumps, six crank seals, six fuel
pumps, six alternators, six crankshafts, 12 magnetos, 6 carbs, ect, ect, on
that six cylinder engine, do you?
--
Jim in NC

"Morgans" writes:

Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Not so, smart ass. You don't have six oil pumps, six crank seals, six fuel
pumps, six alternators, six crankshafts, 12 magnetos, 6 carbs, ect, ect, on
that six cylinder engine, do you?

Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

--kyler

"Kyler Laird" wrote in message
...
Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

Such as? Other than fuel exhaustion, I'm at a loss to think of any.

"Peter Duniho" writes:

"Kyler Laird" wrote in message
...
Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

Such as? Other than fuel exhaustion, I'm at a loss to think of any.

Fuel exhaustion certainly accounts for a lot, but there's also
misfueling, fuel contamination, and intake clogging by widespread
particulates. All are as about likely to take out one as they are
several.

BTW, one of the things I like about a twin is the slight
difference in when such a loss is likely to happen. If one
engine runs out of fuel, runs into bad fuel, or gets socked with
ice/ash/..., at least I usually have a few seconds/minutes of power
on the other one before it experiences the same thing. It might
not seem like much, but it can be quite an advantage in sticky
situations. (Yes, yes...and if I decide to be stupid, it also
makes flipping the airplane over even easier - just like stalling a
single upon loss of power.)

--kyler

On 24 Nov 2003 11:31:57 -0800, (Captain Wubba)
wrote:

snip

So what is it? If the engine-failure rate is one failure for every
50,000 flight hours, I'll feel much less reticent about night/IFR
single-engine flying than if it is one in 10,000 hours. Anybody have
any facts or hard data, or have any idea where I might be able to
track some down?

snip

No hard facts, only "remembered" incidents, definitely not scientific,
sorry.

Engine failures/inflight shutdowns that I've "seen" as a licensed
technician in the last 20 years:

Beech "Super" 18-cylinder hold-down stud/crankcase failure x 2.

Beech "Super" 18-connecting rod failure.

Beech "Super" 18-cylinder barrel/head separation.

Beech "Super" 18-intake valve ingestion x 2.

Beech "Super" 18-crankshaft failure/prop departure (on TO, so
technically not an in-flight).

T-arrow-broken non-standard tee fitting to oil pressure (hourmeter)
switch, oil fire.

Archer-fuel bowl bail popped off x 3.

Cherokee 180-accessory gear driving camshaft split in half.

Navajo Chieftain-cam fell off of fresh overhauled single drive (and
cam) "dual" magneto. Pilot/mechanic (not me) that installed it was
driving it when it crapped.

Navajo Chieftain-turbocharger grenaded, oil fire (fresh turbo
overhaul).

Navajo Chieftain-turbo supply line left loose after maintenance (that
one would be my fault).

Navajo Chieftain-cylinder hold-down stud/crankcase failure.

Navajo Chieftain-severe detonation, eventual oil exhaustion.

Cherokee Six-fuel exhaustion.

Warrior-fuel exhaustion.

J-3 Cub-carb ice.

SWAG of total operating hours +-200000.

The Twin Beech figures are due to the extreme age/unknown-high cycle
time of engines/cylinders.

The Chieftain crankcase failure was on a previously repaired
crankcase.

I think of any more, I'll add 'em to the list.

TC