Getting back to the OP, if I was an engineer with sufficient resources, and if I was faced with the seemingly intractable problem of getting a 747 out of my airport with a runway which, by all normal circumstances was too short to expedite normal rotate velocity - well, I’d seriously be considering mounting a temporary steam catapult system as used on the flight decks of Nimitz class Aircraft Carriers.
Now, such a catapult might need extending by 100% in length, and perhaps a once-off temporary mounting point might need to be bolted onto the fuselage behind the front landing wheel assembly - but to be sure, the great thing about steam is that you can build up an awful, AWFUL shitload of it and it travels long distances when it needs to.
I would suggest that a temporary steam catapult could be rigged up to work over 400 meters - and the best part about it is that you’d still have enough runway for the 747 to hit reverse thrust for a preliminary test ot two.
Now, I know, I know - it’s all a bit hypothetical, but certainly, given the premise of the OP, I’d seriously be considering such a solution.
At the very least, I’d be calling in a few Navy Aircraft Carrier engineers, and if we got the go ahead - man I’d get those dudes in the bright Telly Tubby outfits to do all their whirly arm jigs and launch that jumbo straight into the friggin sky!
Airplanes of any size are made to come apart to a much greater degree than you’d expect in order to conduct very thorough periodic inspections. Large portions may be replaced over time. And, remember, the darn thing had to be assembled in the first place. It wouldn’t surprise me at all that you could take it apart and reassemble it into airworthy condition.
As for lightening the load - that, too, is more possible than you might think. In addition to removing all seats, non-structural walls, floors, and ceilings could be removed as well. Even some of the avionics could be removed for the purpose of moving the airplane to a more suitable field.
Whether all that makes economic sense is another question entirely.
You’ve got two big problems with this hypothetical situation. One is the landing. That breaks into two sub-problems: can the runway support the weight, and do you have enough time to stop before sliding off the pavement. Big Boeings are huge and they weigh as much as a small building - the Airport and Facilities Directory, an information guide on airports for pilots, publish runway information on airports that includes the maximum safe weight that can be supported by each runway. You start to realize why runway construction at someplace like ORD or LAX or JFK is so darn expensive - the loading supported by a 747 landing gear is mind-boggling.
If such a plane were to land on, say, my home field (about 5000 feet of runway) the length of the runway would be irrelevant - the 747’s wheels would punch through the pavement because the pavement just isn’t built to hold that much weight. This would, of course, bring the landing gear to a complete halt. Unfortunately, the rest of the airplane would keep moving, shearing off the gear attachments. The jet would then slide down the rest of the pavement on it’s belly or engine nacelle or whatever happens to be lowest. More Bad Things will follow shortly thereafter, most requiring the attention of the fire department.
After all that, whether you could take off or not from the field would be sort of irrelevant.
But, let’s say for the sake of argument, you do have pavement at a short field that can support the jet. OK, wheels are on the ground, you’re rolling - NOW you have to stop this juggernaut. If you don’t get it stopped before you run out of pavement the wheels will punch through the surface of the ground, bringing the landing gear to an abrupt halt while the rest of the airplane proceeds forward — well, we’ve covered that scenario before, haven’t we?
If your sole concern is stopping the airplane and you don’t care about reusing things like brakes afterwards you can stop an airplane in a much shorter distance than usual. The brakes and wheels do have a tendency to catch fire from the friction, or even blow out. You can use the engine thrust reversers. You can use “aerodynamic braking” - that’s using the flight controls on the wings and tail to increase drag and slow the plane further. You can “s-turn” down the runway, if it’s wide enough - it may take a certain distance to stop, but that distance doesn’t have to be on a straight line (although you don’t want to get so enthusiatic you lose directional control and wipe out that way).
And I bet that’s not even without unloading the seats and unneeded interior structures! Wait for a good, steady 20-30 mph wind straight down the runway, or nearly so, and it would be even easier.
As I said, my home runway is 5000 feet - long enough, right? Except the pavement wouldn’t have even a chance of supporting it.
As a general rule, an airplane requires less distance to land than to take off. You can’t assume that if you can land in a spot you can also take off - this has stranded more than one pilot.
OK, there was this really really ugly thing that happened about 2 years and 18 days ago involving Bad People and jets… since then, it’s become a little harder to get info on the operating limits and characteristics of big airplanes.
In any case, it would be just one figure but a range of figures that incorporate factors like wind speed and direction, temperature, humidity, altitude above sea level, weight of the load of the airplane, wing configuration…
Maybe Pilot 141 will wander by and enlighten us - but I think he’s at work right now and may not be back for a day or two.
And Boo Boo Foo - you wouldn’t use a catapault, more likely they’d use a strap-on JATO bottle like the military uses to get cargo and troops out of fields just a little too short for the airplane in question.
I don’t think width would be the problem. Height is. A 747 is something like 5 or 6 stories high. There are lots of bridges that are over 20 feet wide, but very few on the roads that I drive on that are 6 stories high.
During overhauls planes are completely disassembled; even the fuselage is stripped, and for example, I´ve seen pictures of a 747 being overhauled, one showed the fuselage bulkheads set aside for X-ray inspection… so, yep, the thing can be brought to rather handy pieces. However I´m not so sure about the wings, AFAIK the wings remain more or less in one piece, because the fuel tanks are integral with it´s structure; during overhauls a poor wretch has to crawl into the tanks to inspect them, claustrophobics abstain.
Nah, too complicated. One word: JATO. Jet Assisted Take Off. Strap a few rockets to the fuselage and it will take off in a hurry. This is commonly done on military transports.
In the early days of JATO, they even tried strapping a whole bunch of rockets to planes to get them off in a real hurry. It was called zero-length launch, and it worked.
Large jets are generally VERY good gliders, with glide ratios much better than your typical general aviation airplane like a Cessna. The reason is because they are designed to fly at very high altitudes, with fairly low indicated airspeeds. As a result, they generally have very long, thin, high aspect ratio wings. Have a look at a glider sometime - they also have long, thin wings.
High aspect ratio wings create less induced drag at slower speeds, and so the airplane is more efficient.
Also, jets are very aerodynamically clean. There’s not a lot of crap hanging out in the breeze. So they have low parasitic drag as well.
The end result is that some big jets can easily approach 20:1 glide ratios. That means for every mile up a jet is, it can glide 20 miles. And since these jets are cruising 6-8 miles up, they can glide a LONG way. And if they happen to be getting a good tailwind, they can stretch that another 10% or so.
If I recall correctly, the Gimli Glider glided about 80 miles to its touchdown spot.
Does anyone remember the dead-stick landing by a DC-10 (I think it was) on the Azores about 3 years ago?
My recollection of the incident was that the pilots accidentally dumped fuel from both wings, thinking they were doing it from only one wing which had an engine problem. The jet ran dry and the pilot did a perfect dead stick glide in from some 50 miles out onto the runway on the Azores Islands - which, in reality are but a miniscule dot in the Atlantic.
I’m sorry if that’s the “Gimli Glider” story you’re talking about.
My understanding is that “dead stick” landings with passengers on board has only been done two or three times in history.
I think the skin of the 747 is assembled with rivets. To disassemble you would have to grind off the developed rivet head. I know that the main structural members probably have an assortment of connections, but lots of metal airplane skins are attached with aluminum rivets.
This sounds like a bitch. Of course, reading and posting on the boards has given a fair amount of respect for others knowledge. That is what I’m asking for here.
And hey, DS, the observation about big wings for me came on a flight years ago on a 727. Upon landing, with landing flaps extended and spoiners up, one could see that the entire wing aft of the spar was fairly transparent! Great stuff.
Heavy iron is not “overhauled” in the sense that small planes are - it would be a never-ending task to dis-assemble a 747, inspect/repair/replace everything as needed, then re-assemble.
They are on what is known as a “progressive maintenance” program - specific checks of the various systems are performed in certain sequences at specified times.
Depending on the plane, some of these REQUIRED procedures can render a plane economically unviable - the wing-pull test on old DC-3’s come to mind.
Removal and replacement of aircraft skins is not unusual - hell, I’ve got rivet removal tools - as to whether or not any given plane is routinely re-skinned, I don’t know that any are, but would not be surprised if they were - those planes are designed (and priced) to last a long time - quite possible longer that a section of skin is intented to last.
p.s. - the factory head of aircraft riviets have centered dimples in them - to remove them, you use an automatic center punch to enlarge the dimple, then drill out the rivet shaft.
I’t s worse than you remember. It was an Air Transat A330, on a flight from Toronto to Libson, Portugal. They were 85 nautical miles out at 32,000 feet when they ran out of fuel. They landed very fast and very hard, blowing out most of the tires (which is, of course, much better than coming in too slow and coming up short).
There is a lot in common. They are both Canadian airlines, based in Montreal. The planes were wide-body twin-engine. The flights departed from airports that were within a few hundred miles of each other. The pilots were Canadian. How they came to be out of fuel was different.
Well, I´ll be damned if I can´t find a cite with Google, I based my assertion on a magazine article I saw some years ago; I distinctly remember the fuselage bulkheads leaning against a wall and the label saying how they were ready for X-ray analysis to look for metal fatigue. So if the bulkheads are lying around on their own is because all the panneling has been removed.
Having said that I´m quite sure that 747 was not going through a normal overhaul; as far as I remember it was a major one. I´ll see if I can dig out that magazine from the file.
My guess would be that it was a destructive analysis. Maybe one of the big birds was screwed up from some untoward event and taken apart to look at the cumulative effect of wear at different structural points. Them critical Griffith cracks am a bitch.
I don´t think so; the plane was intended to fly again, as as far as I remember it was a scheduled overhaul.
Hmmm… it was an Aerolineas Argentinas 747. Oh rats!, now I´ll HAVE to get that magazine.
OOOK… so I browsed through this two PILES of magazines looking for my cite. I found it on the fifth magazine… before finishing the second pile :smack: The ARTICLE is quite short, and doesn´t have mush depth; it doesn´t say that the whole airframe is disassambled, however it has this PICTURE showing the formers set aside for inspection as I affirmed some posts above (the old brain cell still stands) Now, I retract that during overhauls the fuselage is stripped, that´s not true for most overhauls, and AFAIK in any case the whole thing is not brought down to the last rivet. But the fact is that the picture shows the bare formers; so… this broughts back what I´ve read some years ago (I hope you´ll understand that I don´t feel like looking for further cites right now ) that because of the pear shape of the 747 front fuselage crossection, the formers in that area suffered more metal fatigue due to concentrated tensions from the pressurization; my guess then is that during a major overhaul of a 747 those formers in the front (as the ones in the picture are, the shape is quite tale-telling) are stripped and checked in search of metal fatigue. Talking about fatigue, I´m off to bed, good night.
Wow…look at all the airframe experts that showed up. Impressive!
I’ll leave the “take it apart” discussion to the experts. I’ll try to address the “fly it out” aspect.
The common perception is that if an airplane can fly into an airport, it can fly out. While this is true most of the time, there are (as always) exceptions. After Broomstick’s explanation of runway strength, let’s assume that the only limiting factor is runway length.
Now, for most large jets the single biggest variable concerning runway used for takeoff and landing is weight. A heavy airplane takes more runway, a light airplane takes less. Now factor in normal planning: a typical airline flight lands with MUCH less fuel than it departed with, making it’s gross weight much lower. In the question of the OP, the airplane actually ran out of fuel. With no (or very little) fuel on board most airplanes can stop in very short distances. The decreased weight allows for a slower approach speed, which allows for a slower touchdown, and the brakes have less mass to slow down. Combine these and you have the makings for a short rollout.
Now, when taking off an airplane is fueled for the duration of it’s trip. On something small like a DC-9 this could mean 15,000 lbs of fuel. On something large like a 777 it could mean 300,000 lbs of fuel. This makes a HUGE difference in the amount of runway needed for takeoff. The airframe and engines are designed to perform at the limits - ie maximum gross weight. Anything less than that, and you reap a performance bonus. It also stands to reason that the airplanes with the largest possible variance in their weights (ie the widebodies) would get the largest performance gain at low gross weights. The fuel for widebodies can account for up to 35% of the gross weight, while for narrowbodies it’s more like 20%.
So, take a 777 with a 20% fuel load and a DC-9 with a 20% fuel load, and the 777 will have a better relative performance than the DC-9, everything else being equal. Pull out the seats, put on just enough fuel to get to the next airport and those monster motors on a 777 will just about pull the thing straight off the runway. On a narrowbody, however, the relative performance gains will be smaller, because the weights are still fairly close to normal operations.
So, bottom line: if you plan on landing an airliner on a short runway and want to fly it out again, try to make it a widebody or long range jet. This may explain why the 707s (not a widebody, but with the fuel capacity of one) have been able to fly out, but the 727 and 737s have had to be disassembled and trucked out.
