Baffler

I agree that's the naturally intuitive assumption, but actual crash data shows no clear and unmistakeable safety advantage overall.

Realize first that ALL multi-engine aircraft are multi-engine NOT for redundancy but for POWER. Their airframes need the power of multiple engines to achieve their performance aims. Eliminate a significant producer of that power and the airframe's performance capability is seriously crippled. It is NOT simply a matter of continuing the journey a little slower, in some airplanes the original destination may suddenly be out of reach, beyond fuel range (now there's a counterintuitive notion, but it works like this: the dead engine reduces fuel consumption, certainly, but added power is needed on the surviving engine to stay aloft, so fuel consumption is not halved but perhaps reduced by a quarter or a third, but most important is the added drag of asymmetric trim (flying sideways to track straight) kills the MPG. You burn less per hour, but your airspeed is so decayed the number of hours it takes to reach the original destination is more than the remaining gas can provide. If over water, you might have to ditch. Here's an example of a 377 Stratocruiser that lost an engine (1 out of 4) and couldn't reach land as a result

[ame=http://en.wikipedia.org/wiki/Pan_Am_Flight_6]Pan Am Flight 6 - Wikipedia, the free encyclopedia[/ame]


There's a flight regime that's virtually ALL single-engine, a flight regime of very high continuous hazard - heavy, slow, and close to the ground: crop-dusting. Lose an engine in a duster and you're on the ground in seconds, hopefully under control. Now, you'd think adding the power of multiple engines would improve the efficiencies of aerial application - mostly you could carry more and not have to reload as often. But for decades and decades right up to to today the only crop dusters are single engine. Most are turboprop - for obvious safety reasons, and turboprops are also substantially more powerful than recips, but no one has built a twin duster. I'm sure it was tried - but experience keeps that regime single-engine. I haven't studied it but I'd guess the reason is that the advantages of a twin in aerial application are too outweighed by the added risks and increased complexity. Duster pilots can't handle more than stick and throttle - their eyes are outside full time (a friend once asked a duster pilot how fast he crossed the threshhold before flaring & the duster pilot said "hell if I know!")


There are of course many flight scenarios where loss of an engine only reduces the number of airports available for landing but you could still easily make it to an airport and land under control. There are no doubt many incidents where a twin landed safely with one engine caged that, had it been a single engine plane, would never have reached ANY airport. But it's like the endless argument over guns: yes, some gun incidents seem to prove the "safety" of keeping lots of loaded guns at hand. Actual data, on the other hand, suggests the added risks are probably greater than risks deflected.


One last point: our little Cessna has a glide ratio of about 5 to 1. In rough numbers it'll glide a mile for every 1000 feet of altitude. A lot of our flying is flown at about 5000 feet, so if the engine quit, we'd have a circle of earth beneath us 10 miles in diameter to find a place to park. I think it's about 50 square miles. That's a LOT of territory to find something straight only about 500 feet long with perhaps half a mile of relatively unobstructed approach to, especially over the Central Valley. The loss of an engine in our Cessna would very likely be expensive and hugely inconvenient, but not likely to be fatal, or even injurious.

 

Perfectly - and with a lot fewer words I wish I'd said myself

 

1st test flight was this afternoon: 1 hour orbiting the Coliseum at 2500 feet and about 80% power (2500 RPM). Head temps were higher than I expected but after landing I checked & found a small flap of baffle seal not seated right after putting the cowling on, which meant a little ram air leaked into the lower section in flight and reduced the strength of the cooling downdraft. I repositioned it with a pick hook.

But no problems - engine smooth, head temps all within 50F of each other, oil pressure center green, oil temp center green, putting out rated max RPM, oil the right color after landing (still clean, basically, no darkening of blow by). We'll fly it longer tomorrow.

No taxiing for the next 10 hours or so - we'll have to get fueled by truck at the hangar (at $7.50 a gallon!!) and use the closest runway to keep our ground operations to a minimum.

Cylinders are Cermi-Nil by ECI. For those familiar with the O-200 I also put on Real Gasket's modified pushrod housings which make a better oil seal and, most important, can be removed without havng to pull the cylinder. They're a miniature version of the housings on the O-470 & larger Continentals. That mod JUST got FAA certified last week (after, I don't know, FIVE years of process) - which meant I had to pull them off & re-install them with the FAA approved springs they sent me, which is why there was a delay doing the test flight. But I have an STC to stick in the logbook for them, which makes the Form 337 a snap instead of a hassle. Our AI signed the logbooks just before flight today.

We celebrated with french dip sandwichs and tea at Carrows afterward (saving money for fuel).

 

During break-in, yes. The new piston rings are worn into their final shape against the cylinder wall; the reciprocating action literally sands them down a few tens of thousandths of an inch. This occurs when the "sanding" action is rapid, e.g. high RPM. The process mates the rings and cylinder wall to perfectly matched surfaces, creating a seal that prevents oil from seeping past the rings into the combustion chamber (which inhibits combustion, dirties up/fouls valves and spark plugs, and makes the engine consume more oil than it needs to).

If a new engine is run excessively at low RPM, it retards the rate of break-in, and the heat soon cooks a "glaze" of oil on the cylinder wall that no amount of further operation will ever "break". If a glaze forms, the rings are helpless to keep oil out of the combustion chamber.

The cylinder-piston ring interface is a precise, paradoxical configuration. It has to do two things perfectly: stop oil from flowing at the same time that it allows oil to flow. It stops oil from getting into the combustion chamber, yet allows oil to coat the cylinder wall just enough to prevent further wear of the rings and wall after break-in is accomplished.

To create a space for oil to coat the cylinder wall while at the same time leaving a surface that the rings can stop the oil from flowing too far, the cylinder walls are "honed" by abrasive stones with a diagonal cross-hatching of tens of thousands of tiny scratches. If the cylinder wall "glazes" with cooked oil, it covers the scratches, forcing oil onto the wall surface where it can seep past the rings.

That's why no taxiing - every minute at low RPM is a minute that the rings are NOT wearing faster than the oil is "cooking" and too many of those will glaze the cylinder.

 

It does make more sense - IF you have a sufficient reservoir of electrical energy to both drive the motor powerfully enough and long enough to be useful, yet is light enough to carry with you (the only hundred mile extension cord system that's practical is streetcars running a fixed, limited route). We're still not quite there technologically for it to work with airplanes, which have to be really lightweight. We're only just beginning to be there for it to be practical with cars - whose portable battery reservoirs even now still aren't as enduring as a portable 20 gallons of gasoline for a reciprocating engine.

It's true a gasoline engine only turns about 10% of the energy in the gasoline into useful work, but it's been the ONLY way for many years to generate PORTABLE energy powerful enough for transport.

The route to efficiency in light aircraft is the gas turbine, used either as a turbojet or as a turboprop - but has the problem of being absurdly expensive, out of reach of all but large or wealthy operators. It's another paradox - the gas turbine in principle is about as simple as an electric motor, both being shafts that spin with no reciprocating action, but in practice require exotic alloys to survive hot section temperatures and hundreds of high precision blades that drive their cost right into the stratosphere they operate best in. 15 years ago a SINGLE main fan blade on a GE or Rolls Royce or Pratt & Whitney turbofan engine on a Boeing 777 cost $60,000.