Black boxes in autos?

He's probably talking about an L-1011, and more than that he's probably talking about Eastern Airlines' famous incident where the O-rings were left off the oil drain plugs on all 3 engines.

Reply to
Steve
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In the first place, that's hardly an exhaustive list. Just pick a month on

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and start reading, it won't be terribly long before you hit a structural failure. In the second place, 5 is a large number compared to 0, which is how many automobiles typically undergo structural failure.

That's not what happened to either of the air-tankers. Yes, they were levelling off after a retardant run, but they were well within the (presumed) limits of the airframe.

No, airplanes in general are a fair comparison. Many small private planes are now pressurized.

Except for the fuel injection, multiple turbochargers (in some cases), ceramic piston coatings, solid-lubricant piston side and valve stem coatings, etc. etc. etc. etc. etc. The turbines are the ones with single-crystal turbine blades, but since more and more general aviation aircraft use turbines, its a fair comparison.

. They

And doing it any other way would not only be counter-productive, but stupid in that running a 4-valve per cylinder 7000 RPM engine to drive an air-screw that has to turn at 2000 RPM offers no advantages and countless liabilities. Fortunately aircraft engineering is not driven nearly so much by what is "trendy" as auto engineering (you don't see articles in magazines calling a brand new engine "archaic" just because it uses pushrods).

SOME models (for the very large replacement market) are indeed that way. But the new designs for new-production airplanes are pretty much on a part with automobiles, and in some ways very much ahead from the purely MECHANICAL side of things, even if you limit yourself just to Lycoming and Continental piston engines. And besides, the real comparison IS the turbine, because everyone knows that the piston engine's role in aviation is never going to increase again in the future.

Reply to
Steve

The O'Hare accident (after which not ONE more DC-10 was ever sold!) happened way before Sioux City. Again, you could argue it was "human error" because American Airlines was hanging engines on the pylons with a forklift, which over-stressed one of the 3 bolts that held the engine, which in turn led to structural failure of the pylon months (or maybe years) down the road. But it WAS a structural failure, and you can abuse most systems on a car much worse than that without causing a failure.

The point of the debate is that airframes are always stressed much closer to their ultimate limits than cars are because they just can't carry any excess weight, and that's just a simple fact.

However, it did have at least one major design flaw that

True. But the DC-10 had a hell of a lot more problems than just that one system. It was a maintenance pig, and the MD-11 was worse. Those two airplanes killed Douglas, no question. Even the wild success of the DC9-80 (aka MD-80) couldn't help the company dig out of the hole the DC-10/MD-11 fiascos created.

Reply to
Steve

Nope - I was referring to the McDonnell Douglas DC-10, one of which was an American Airlines plane that crashed on attempted takeoff out of O'Hare from - engione pylon bulkhead-to-wing failure due to maintenance procedure shortcut not authorized by McDonnel Douglas though they suffered financial devastation over the affair.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

That is hilarious. I've experienced structural failure in an automobile and witnessed several structural failures. The difference is that nearly any significant failure of an airplane makes the national news, whereas rarely does an automobile accident make the national news. The fact that you aren't aware of structural failures of cars, doesn't mean they don't exist.

Did the tankers have FDRs onboard?

Must be your definition of many is the same as your definition of much. Very few small private planes are pressurized. The P210 is one, but very few of those were built. There are a few piston twins that are pressurized, but again, not many of those are privately owned, unless you consider a small business to be a private owner. Maybe you consider bizjets to be small private planes.

Well, I don't consider bizjets to be a reasonable comparison to passenger cars as few are truly privately owned and operated. Most are owned and operated by businesses.

It is only counter productive if the reduction unit weight offsets the performance and efficiency gain from a high RPM engine. A number of WWII airplanes used higher RPM engines with reduction drives. They are also becoming more popular in the homebuilt market. I suspect it is only a matter of time before Honda or Toyota introduce a high performance, high RPM piston engine with a decent reduction drive. Then again, the piston engine market is so miniscule that they may never do so, especially after the Porsche/Mooney experience.

Except that the turbine has almost no role yet in small airplanes. A number of 4-6 pax jets are on the drawing board or flying as proof of concept prototypes, but even the cheapest of those are far out of reach of the average GA pilot. And turbine efficiency below 25,000 feet is pretty poor.

Matt

Reply to
Matt Whiting

A high-RPM engine is not necessarily efficient. In fact its harder to make a high-RPM engine as efficient as a slower-turning engine with relatively low compression and a fair amount of turbocharger boost.

You mean "high RPM" as in a Rolls Royce Merlin that ran a whopping 3000 RPM and had a reduction gear so it could swing a 14-foot prop? Or "high RPM" as in a Napier Sabre that ran maybe 4500 (and was so unreliable that not a single running example remains)? If 4000 RPM is "high" then I agree with you- but that's nowhere near the point that 4 valves per cylinder makes sense.

It'll never happen. The aircraft reciprocating engine has been through a very, very long evolutionary cycle, and everything except air-cooled / low RPM engines has ultimately proven to be a failure in that environment except for niche applications. Nothing's going to change that.

Reply to
Steve

Most aircraft piston engines are redlined at or near 2,700 rpm for reasons having to do with the prop more than the engine. Of course a constant speed prop is more efficient because you can choose between a faster prop speed (with the engine developing more power) for takeoff/go-around situations and a lower speed for efficient (and quieter) cruise settings. According to the guys at Lycoming, 2,700 is too slow for the engine to develop its potential max power, but it is a compromise for the prop efficiency, load, and noise.

A reduction gear allows both engine and prop to operate at their most efficient speeds simultaneously, but it presents several challenges. First it adds expense and weight, and both are very undesirable--particularly weight. The cowling would likely need to be extended, changing the W&B. It also is another complication in a design where simplicity is greatly favored. Finally, a sharp reduction in power (e.g. pulling the black or even blue handle back sharply) can cause problems with the reduction gear system and engine counterweights. In World War II, engineers found that reduction gears and very high performance engines were a very desirable combination that was favored over its drawbacks, but they are fairly rare on today's designs.

On the other hand, reduction gears are certainly used for turboprop engines.

Reply to
Greg Houston
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Yeah, but that's a COMPLETELY different loading profile than a piston engine. With a turbine, there's no torque pulsation as the cylinders fire, and far less "reverse" torque when power is reduced. Big piston engines routinely beat the tar out of their reduction gears- even the ones with planetary reduction gears like the big radials use.

Reply to
Steve

All true, and more importantly turbines tend to operate at speeds that would be considered exotic for recips, such as 30,000 rpm. Needless to say, it would be very problematic to have a propeller operate at these speeds, and even if you could design one to withstand the force, efficiency would be terrible and the noise prohibitive. Hence the need for a reduction gear to a more respectable

2,200 rpm. :)
Reply to
Greg Houston

Most of what you suggest is far too sensible to ever be implemented...

DAS

Reply to
Dori A Schmetterling

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