Civilian Jetliners of Alternate History

May I present....the BAe 146! One of my favourite regional airliners! :D
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As a matter of fact, I've gone on this aircraft type at least a dozen times, all but once with Air BC, shown above in the 1980s colour scheme (the other airline was with Air Nova, which was based out of Halifax, NS), partly because it was used quite a bit on the Edmonton-Vancouver route during the 1990s and the early 2000s.

For a civilian passenger jet aircraft, to have four engines for plane that small sounds like overkill, especially for one which went into production in the early 1980s. It was originally the HS 146, since it was first designed by Hawker-Siddeley before it merged with Vickers to become British Aerospace. But from what I've read, one reason was stricter noise restrictions at many airports which were coming into effect. This meant coming up with four smaller jet engines instead of two larger ones to make less noise overall. The noise level was astoundingly low for a jet aircraft from the outside. Inside the cabin, it was definitely louder but not horribly so - more like inside an Airbus A319/320. I used to live in an apartment only a few km from Edmonton City Centre Airport (Municipal Airport), very close to the one of the flight paths out of that airport. Whereas the 737-200s would actually rattle windows in my apartment (not exaggerating here!), the 146s used there by Air BC were often almost so quiet that you almost didn't notice them! This was especially true when they were landing.

It seems to have had fairly good range compared to other RJs - I know they were used on long domestic routes in Australia such as Darwin-Perth and also routes in North America such as Edmonton-Denver. Later production models were known as the Avro RJ-70/85/100 series.

I've heard it was supposedly designed as a hot-and-high aircraft, or in other words, designed to operate out of high-altitude airports and in very hot weather. However, I've see contradictory reports about this. Even then, it was used extensively in hot countries like Australia. It was even supposed to have been a STOL aircraft, but I don't know - four engines would've made it a little heavy for very short runways.

I find it very odd that British Aerospace never went on to produce a twinjet version of this plane, although BAe did come up with such proposals in the early 1990s known as the NRA series, a model of which is shown below alongside a BAe 146-100. It would've been cool to see BAe/Avro actually put a twinjet version into production.

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But at least, the Ukrainian aircraft design bureau, Antonov, has come up with a twinjet 146 lookalike. That plane is the An-148, first developed in the 1990s and first flown in 2004.

Antonov--148_2.jpg
 
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If no one in the industry had any clue about metal fatigue as such, I guess the problem had to bite whoever first tried to fly under these conditions.

But it isn't clear to me just what was new about the Comet that exposed the problem--except for pressurization!

That is, a jet engine not only can but almost must operate at stratospheric altitudes. There's not a good way to throttle a jet engine back so it's producing less thrust at the same efficiency as when it is going full blast; we might have improved considerably on this with more modern turbojets and turbofans, but first-generation jet engines in particular were quite thirsty enough without operating them far off optimum thrusts, which would be practically the same as full thrust.

Therefore altitude served in two ways; one, the higher you go, the faster you have to go to achieve a given dynamic pressure which in turn is set by the wing area and the optimum lift coefficient for minimum drag; since jet engines produce the same thrust at all speeds (roughly speaking, up to an upper speed limit of course) the higher the cruise speed the better because that minimizes the time during which a given thrust, implying a given fuel consumption rate, would be needed. Second, the thinner air at higher altitudes also does "throttle" the engine; at RPMs for optimum efficiency, the less dense the air is, the less the fuel consumption. Thus thrust does drop with altitude. Make an engine capable of maintaining minimum drag thrust at full throttle at cruise altitude, and you have one that puts out lots more thrust at a lower altitude--but guzzles fuel in proportion, so that higher thrust has to be used to climb fast to cruise altitude.

Thus a passenger jet needs to be pressurized and the stress of holding in that pressure will be a factor.

However the Comet was hardly the first pressurized airliner; Douglas and Boeing and I believe Curtiss were all developing stratospheric piston planes before WWII. They probably didn't climb as high but I'd think if the fatigue problem were one caused by pressure alone, it should have been those planes first stricken.

There's another factor, besides the jet planes wanting to go even higher and being able to--as I said, they ought to climb very fast too, to save on fuel and to use the thrust that high fuel consumption at low altitude tends to generate. So the rate of pressure change as well as the levels it ultimately reaches may be the real culprit here and it could well be none of the earlier piston planes, even high performance, big pressurized planes like the B-29, came close. Metal fatigue, after all, is the result of flexing metal by alternating between stress and relaxation; any pressurized plane would experience some of this but one that rises higher and faster would clearly have a much worse problem.

Against this, the fact that DeHavilland went with square windows ultimately, even if he did begin planning on round ones, suggests to me that his team really did not have a deep appreciation of what pressurized flight was all about, and that rival designers perhaps did and avoided disaster by respecting problems DeHavilland did not properly estimate.

I really like DeHavilland and the Comet was a bold and noble venture; I don't like to think it failed merely due to shortsighted design that could have been avoided. But I think that having them adopt enough improvements in advance to prevent the metal fatigue from destroying the planes is too much to have happen by luck alone; someone has to be putting these improvements and no others on the design because they have an inkling what they are protecting against. Someone would have to know about metal fatigue (say from an even earlier airliner attempt like the Avro Canada one, or from military projects) or make an intuitive guess that it might become a problem, then either way come up with design changes that work.

It seems odd to me that OTL there wasn't already a lot of insight about metal fatigue due to rapid pressure changes derived from military bomber development. Maybe there was and it was kept classified, with only bomber builders--like oh say, Boeing, for instance--in the "need to know." But DeHavilland did make a V-bomber didn't they? (No! They didn't!) DeHaviland did make the Vampire and its successor types series of jet fighters and these should have shown some of the same problems as the cockpit of a jet fighter is pressurized. DeHavilland was also involved in cutting-edge supersonic flight research, again putting a premium on flying in very thin air.

Since I believe they were a competent bunch at DeHavilland, I suppose this means that what wrecked the Comets was not a problem that could be readily extrapolated from experience with smaller planes, not even ones that flew faster and higher, nor from older planes that were passenger-plane sized but flew lower and slower. If that's true, there's no reason other than ASB luck that designers would take measures against a threat no one anticipated.

I'm afraid this implies there was only one way to find out, and that was for someone to get there first to market and have their plane fail. Either we wish someone else could scoop even deHavilland (like say, Avro Canada) and they take the fall, or we wish deHavilland had been forced to take it more slowly, and it is Boeing or Vickers or some French firm that suffers.
 
There still remains a lot to learn. Skin thickness is a weight factor in cost per seat/mile. Convairs had thicker skins and they left the business.

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May I present....the BAe 146! One of my favourite regional airliners! :D

One of my favourites as well. A very good regional jet. Pity it was one of the last grander British airliner projects. The various island nations in the northern Atlantic and several Himalayan countries could speak volumes about the usefulness of this nimble little STOL jet. If I ever operated a regional European airline, I'd definitely buy one of these if I had the opportunity.
 
:confused:You're telling me that you burn the same amount of fuel going mach 1.8 as going mach .9? I'd have to see some figures to believe that.


the Olympus 593 and it's intake pack allowed Concorde to supercruise at mach 2

successful supercruise is the key to making any supersonic plane (except a fighter which only needs to supersonic dash)work effectively
 
I don't know why any company (air, auto, whatever) wastes so much on a concept it has no intention on developing. Remember Boeing's sonic cruiser?
Well, in Boeing's case, they really were trying to sell it, it's just that all the airlines said 'we don't want fast, we want cheap'.

As for those future planes, they've got to be looking at what's feasible, and what's going to be required for Stage 5,6 and 7 noise restrictions, plus CO2 and NOx, plus airline demand for economical fuel consumption. So, if they WEREN'T playing with those models now, they'd be at a nasty disadvantage when the other guy formally announced his design.
 
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