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Not to speak for Gary, but the pusher/puller configuration has what's called
"centerline thrust" - i.e. if you lose an engine, the thrust vector stays on
the centerline - theoretically making the engine-out procedure easier to
handle (ditto for a single-engine, though the engine-out procedure is a lot
more cut-and-dried...  ;-)).

Wing-mounted twins have a more-complicated engine-out procedure - not only
identifying the dead engine, securing/feathering it (also true of
centerline-mounted engine configs), but also maintaining a slight bank angle
to compensate for the thrust imbalance caused by the dead engine.

http://en.wikipedia.org/wiki/Critical_engine

Not sure if the Vmc (minimum-controllable velocity) restrictions would apply
to A/C with centerline-mounted engines, that's probably a question for Gary.

--
GregR


----- Original Message ----- 
From: "Greg Rudzinski" 
To: "NavList" 
Sent: Sunday, August 02, 2009 12:16 PM
Subject: [NavList 9297] Re: Bygrave and Chichester



Gary,

How would the Cessna 336/337 perform if one engine fails? Is there an
advantage to a pusher puller configuration over a single or wing
mounted twins?

Greg

On Aug 2, 11:18 am, Gary LaPook  wrote:
> Well, I would agree with you Douglas, as judged from our perspective in
> 2009, that Chichester may have been "reckless." But as judged from the
> standards of aviation pioneers almost 80 years ago, I prefer the word
> "bold." If you look at early pioneering efforts, Lindberg, Perry, Sir
> John Franklin, Columbus etc., they all appear reckless as viewed through
> our prism of time. But that is what pioneering is all about, taking
chances.
>
> Regarding you preference for twin engine flying, the accident statistics
> show that they are more dangerous than singles, pretty
> counter-intuitive. Flying a twin when both engines are operating is just
> like flying a single, it only gets interesting when one quits. Then the
> pilot must deal with a greatly reduced performance envelope and
> asymmetric thrust causing control difficulties. If the pilot doesn't do
> everything exactly right he ends up crashing and the crash happens at a
> higher speed than would have occurred in a single. By US certification
> standards (I expect they are similar in Britain) a single must have a
> stall speed below 60 knots while a twin can have a much higher speed.
> This means that a pilot trying to crash land a twin must fly above the
> stall speed resulting in a higher impact speed and much more kinetic
> energy to dissipate (varies with velocity squared), can we say "torn
> aluminum" and "mangled bodies?" I've litigated airplane crashes for the
> last twenty years and I have seen my share of bent aluminum and autopsy
> photos. (BTW, a Cessna 310 Twin fits in a box on a standard pallet,
> about five feet square and three feet deep after it impacts the dirt.
> Airplanes are mostly air surrounded by an aluminum skin, just like an
> empty beer can and they squish just like a beer can..)
>
> After the loss of one engine the airplane has little or no climb
> capability. It will only climb or maintain altitude if the pilot does
> everything right. If he doesn't get rid or the drag form the flaps, the
> landing gear and the windmilling propeller immediately then he is going
> down.
>
> I'll give you some examples. About seven years ago a Cessna 310 was
> taking off from Laverne airport just northeast of Los Angeles on July
> 4, 2002, Independence Day. One engine quit right after takeoff and the
> pilot did not do everything right and the plane crashed on top of a
> bunch of picnickers celebrating Independence Day in the park near the
> airport resulting in the deaths of the two occupants of the plane, two
> deaths of the picnickers and severe injuries for nine other people on
> the ground. See the accident report at:
http://www.ntsb.gov/ntsb/GenPDF.asp?id=LAX01FA152&rpt=fa
>
> The left propeller control was found "one inch aft." In order to feather
> the propeller it is necessary to pull the prop control all the way aft,
> about eight inches. Since the pilot did not move the prop control all
> the way aft the prop did not feather and the plane could not maintain
> altitude with the left engine windmilling creating a lot of drag. It
> turned out that the pilot had done exactly as he had been instructed.
> His instructor's technique for practicing engine out emergencies called
> for the student pilot to just pull the prop control back one inch to
> demonstrate that he had identified the failed engine and that he would
> have feathered the prop in a real emergency. But in a high stress
> situation people do what they have practiced so four dead people,
> including two little children, and nine serous injuries.
>
> Another case I worked on involved a Piper Navaho hauling sight seers
> around Hawaii. One engine packed it in and because the mechanic had not
> used the proper method to adjust the wastegate controller on the other
> engine, the remaining engine was not developing full power so the
> airplane could not maintain altitude on the one engine. So even though
> the pilot was doing everything right he still had to ditch in the sea
> near Hilo and one little old lady, celebrating her fortieth wedding
> anniversary, rode the plane to the bottom of the sea. See report
> at:http://www.ntsb.gov/ntsb/GenPDF.asp?id=LAX00FA310&rpt=fa
>
> Another case I worked on involved a Twin Otter powered by two Pratt &
> Whitney turboprop engines. The underground fuel tank from which the
> airplane had just been refueled was contaminated with water (it looked
> like mud) and one engine stopped right after the nose was raised due to
> ingesting the water. The pilot then did everything wrong and feathered
> the wrong engine, shutting down the one operating engine. This resulted
> in 16 deaths of the occupants.
> See:http://www.ntsb.gov/ntsb/GenPDF.asp?id=LAX93FA149&rpt=fa
>
> Having two engines gives one the sense that he has redundant systems and
> that it is unlikely to have two reliable systems fail at the same time.
> So, if an engine should fail once every 5,000 hours then the chance of
> two such engines failing at the same time should be only once every
> 25,000,000 (5,000 times 5,000) hours. But that assumes that the two
> systems are completely independent from each other which is rarely the
> case. First, obviously, both engines are being operated by the same
> pilot and any error on his part can result in the loss of both engines.
> Both engines received the same fuel so if one tank has contaminated fuel
> they both do. They were refueled at the same time so if the pilot runs
> one out of fuel then the other will follow moments later. The same
> mechanic worked on both engine and if he screwed up one then he probably
> screwed up the other one too. I remember watching a Cessna 310 take off
> from Chicago Midway airport one day. Right after takeoff one engine
> failed and the pilot was able to bring it around and land safely. The
> plane taxied up to my hangar with one prop stopped and my friend Bill
> jumped out and walked right past me. I asked him, as he passed, what had
> happened and he said he couldn't stop to talk as he had to "go and clean
> out his shorts." I don't think he was talking figuratively since he went
> immediately into the men's room. The next day when I saw him I asked
> again and he said he was doing a test flight after the mechanic had
> adjusted the propeller governor and right after takeoff that one
> propeller had gone into feather uncommanded which resulted in the loss
> of power from that engine. As he was bringing the plane around to land
> he said that all he could think about was that the mechanic had just
> adjusted _both_ propeller governors and he was waiting for the other one
> to go into feather too.
>
> In the case of over water ferry flights on which the plane is heavily
> overloaded with fuel, the single engine ceiling may be below sea level.
> This means with such a heavy load that the plane cannot maintain
> altitude if just one engine fails and a ditching is inevitable. In this
> case a twin is quite a bit less safe than a single since with two
> engines you have twice the probability of an engine failure, 2 per 5,000
> hours using my prior example.
>
> gl
>
> douglas.de...@btopenworld.com wrote:
> > My interest in the Bygrave helical slide rule too Gary, was stimulated
when I read Chichester's book 'The Lonely Sea and the Sky' many years ago.
>
> > I have been hoping ever since to find one, perhaps one of them would
turn up in an antique shop or 'car boot sale', but now realise that fond
dream is far from ever becoming a reality.
>
> > It is very strange that they are now so incredibly rare considering they
must have been made in reasonably large numbers from the early 1920's up to
the mid 1930's, and were also an official piece of navigating 'kit' for
aircraft navigators in that period for the RAF, so must have been made in
fairly large numbers rather than just a relatively few for experimental
purposes. They were also available to buy privately. So what happened to
them all? It's most odd.
> > Even the most arcane scientific apparatus and instruments are usually
preserved or survive in private hands to be sold on or given away to others
rather than just binned.
>
> > Are all those RAF Bygrave slide rules still locked away in some old,
musty, forgotten RAF or government store at the back of dusty shelves
awaiting some storekeeper to find them and be told to put them in an auction
of ex-government surplus. (Still dreaming you see !).
>
> > Whilst the skill and amazing endeavour of what Chichester achieved is
not to be denied an any way, (and you have now confirmed by your own
practical flying test in a Tiger Moth); which was immediately apparent to me
when I read of the exploit, and it has continued to amaze me still - with
what he wrote I was also filled with the astonishment and feelings that
Chichester was idiotically reckless in what he did,..(I think) to the point
of insanity.
>
> > Given that he writes in a style which is deliberately meant to make his
story not just interesting but no doubt boost his (Chichester's) reputation,
and sales of the book, and hopefully have the reader clutching the book with
white knuckles in anticipation of events unfolding; nevertheless, he exposes
a devil-may-care attitude of quite serious stupidity and ignores issues of
high importance which any right-thinking person would not consider
reasonable, and certainly not anyone who knows anything about flying and the
consequences involved in flying solo in a single engined aitrcraft with a
'dodgy' engine over large stretches of water.
> > ----------
>
> > I had a personal friend who taught me to fly, he was the Chief Flying
Instructor at Bembridge flying school, and who very nearly lost his life
when the donkey of the Cessna 150 stopped en route, mid - Solent, as he was
flying back to Bembridge from Goodwood, (The Solent is the sea - only four
miles of water between the Isle of Wight and the mainland) -and after
turning downwind towards the mainland to maximise his ground traverse, he
did not make it and was...
>
> read more �



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