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Terminal velocity is so called because it is usually fatal. It also happens to
be the velocity reached by a falling body in air, at which air resistance
balances gravity.
For an unladen human in a face-to-earth position, terminal velocity is
about 120mph. For any randomly-shaped lump of stuff
with a lower
density than a human, terminal velocity will be less.
Formula 1 cars are cunningly designed in such a way that crashes at speeds
exceeding 100mph are often survivable. Even regular cars, with crumple-
zones and airbags, often permit survival of 80mph+ collisions. And, in
both these cases, the structure that has to absorb the impact is quite small
- there is maybe a metre and half of energy-absorbing structure between
you and the thing you've just driven into.
So.
Rather than attaching parachutes, escape pods or automatic rosary beads
to large passenger aircraft, why not just make a regular crash survivable?
First, we want to replace all the seats in the plane with lightweight,
easily-breakable replacements that won't hurt anyone.
In the event of an impending crash, and after advising passengers to don
oxygen masks, simply flood the entire cabin and cargo hold (quite quickly)
with fast-curing (and preferably non-flammable) medium-density
polyurethane foam. As long as there are a few metres of this foam
between the passenger and the fuselage (in the direction of impact), the
foam would absorb impacts at up to a couple of hundred mph, saving the
lives of the majority of the passengers.
Of course, extracting the passengers would be tricky, especially if they
have hair, but hey. And, if it all goes very wrong, the bodies are at least
protected from looting, fire, bears etc.
better than expanding foam, utility fog!
http://en.wikipedia.org/wiki/Utility_fog
[mitxela, Jul 27 2014]
Piper PA-28
http://en.wikipedia.org/wiki/Pa-28
Neat [8th of 7, Jul 28 2014]
Supermarine Spitfire
http://www.telegrap...kes-to-the-air.html
[pocmloc, Jul 29 2014]
...and this too:
http://www.supermarineaircraft.com/
[hippo, Jul 29 2014]
[link]
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//medium-density polyurethane foam//. |
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Have you used fast-curing urethane foam? I have, and I have the burn scars to prove it. Presumably you're going to equip all passengers with asbestos-and-aerogel insulating clothing as well? |
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//I have the burn scars to prove it// |
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I like this idea but I'm not sure the premise is correct. An airliner in an uncontrolled dive will have a terminal velocity significantly higher than that of a skydiver or even an F1 car at full tilt. Impact energy goes with the square of velocity so the comparison with automotive crumple zones may be misleading. |
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Well, it depends. Think of all the ways a plane
can crash. |
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(1) Falling short of a runway, overshooting, or
power failure on take-off: vertical speed is
probably very slow. Horizontal speed is
substantial (typically 100-200mph), but unless
there's a mountain in the way that speed will be
bled off over a few seconds as the aircraft grinds,
cartwheels and breaks up. |
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(2) Failure of power or control at altitude. Plane
will usually settle into a glide. Similar to (1), but
with possibly higher forward speed at time of
ground contact. |
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(3) Bomb or missile. Aircraft breaks up. If
substantial chunks of fuselage remain intact, their
freefall speed will be on the order of 100-200mph
vertically. |
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(4) Dead stall (as in that Air France one). Vertical
speed probably less than 20mph, horizontal speed
less than 150mph. |
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(5) Failure to see a mountain. Vertical speed
negligible, but horizontal speed alarming. |
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(6) Wingover (wingtip into ground) and cartwheel.
Speeds on the order of 100-200mph. |
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I would contend that all but (5) would be
somewhat survivable if you were encased in foam
and more than a few metres away from the
aircraft skin in the direction of travel. |
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I don't know of any cases where an airliner has
entered an uncontrolled dive, though I expect
there are a few. |
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Main point: in most crashes, the mass-mean
deceleration is less than 20G (actually less than
10G), meaning that the centre of mass of the
aircraft (or wreckage) is less than 20G. People die
because the aircraft structure is not built to
withstand anything like 10G, hence, either: |
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(a) the structure of the aircraft collapses around
them, crushing them or |
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(b) they freefall through the aircraft structure
until they hit the terrain (or, rather, the parts of
the aircraft in contact with the terrain),
experiencing much higher G's. |
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//automatic rosary beads // Where is this idea? I must bun it. |
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What about the weight of the passengers behind you?
You just became their crumple zone. |
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Huge airbags on the outside, provide cushioning and reduce (virtually) the overall density of the plane and so it's descent speed... |
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Done cunningly, no need to have an inflation system, just let them be filled from the air rushing past.... |
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Admittedly triggering them by mistake during flight would not be good thing. |
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PS just realised I must have gone on a Malaysian Airline plane, as we went Japan->UK with a layover in Kuala Lumpur...aghh |
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Radio control aircraft have similar trade-offs.
Bottom line is you can build an aircraft to fly well
or you can build it to crash well. The "fly well"
radio-control aircraft are light-weight and cheap
but are totally destroyed/pulverized by a high-
speed crash. The smaller number of "crash well"
aircraft use durable, shock-absorbing materials
such as corrugated plastic. These tend to be
heavy, expensive, and worse-performing. |
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So, you could build an airliner to withstand crashes
(e.g. include a very strong "shell" around the
passengers plus "cushioning" such as a whole-
aircraft air-bag and set of parachutes) but tickets
would cost roughly 2x to 4x what they do now. |
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Would you pay twice as much to reduce your risk
of dying on a given plane flight from 1 in ~20
million to, say, 1 in ~200 million? |
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//Would you pay twice as much to reduce your risk of dying on a given plane
flight from 1 in ~20 million to, say, 1 in ~200 million?// A lot of people
would... |
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// A lot of people would...// |
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..And that's why lotteries and casinos make so much money. |
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I would have thought that surviving the impact is only part one
of surviving the crash. The next big survival obstacle is the 100+
tonnes of burning kerosene. What if sufficient foam was injected
into the cabin such that it completely filled the void and
generated a hydrostatic pressure that was sufficient to pop the
structure apart prior to impact? i.e. the wings, fuel tanks, tail,
engines etc. are shed, sort of like a moulting insect, leaving a
ballistic lozenge of foam-encapsulated passengers. |
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Jettisoning of mass would help a lot. If a pilot had an
"oh dear it seems to be going horribly wrong" button
which jettisoned fuel, non-functioning engines, the
contents of the cargo hold, the toilets, overhead
bins, the cart with the Johnnie Walker and cartons of
Silk Cut, all the in-flight magazines and the packets of
headphones... the plane would be a lot lighter. Much
lower terminal velocity and stall speed. Crash would
be a lot more survivable. |
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Deaths from falling bottles of Johnnie Walker
however, would increase above the presently low
baseline. |
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// button which jettisoned fuel, non-functioning engines, the contents
of the cargo hold, the toilets, overhead bins, the cart with the Johnnie
Walker and cartons of Silk Cut, all the in-flight magazines and the
packets of headphones... the plane would be a lot lighter.// |
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Fuel, yes. Engines, maybe - would seriously affect the W&B, and
without power to the control surfaces that is a Bad Thing. As to the
rest, why not just jettison everything aft of First Class ? |
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// Deaths from falling bottles of Johnnie Walker however, would
increase above the presently low baseline // |
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Would that be from cranial injuries, or cirrhosis of the liver ? |
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//why not just jettison everything aft of First Class// |
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Actually, you're more likely to die in 1st class. The
place to be is over the wings. Nice strong structure
there. |
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//Would that be from cranial injuries, or cirrhosis of
the liver// |
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A little of both... actually. Working in alcohol
research, you'd be amazed at precisely how little
alcohol does to the liver. Directly at least. |
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// The place to be is over the wings. Nice strong structure there. // |
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Indeed. The Supermarine Spitfire and the PA-28 <link> are both
particularly well proportioned in that area. |
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The C-130, being a high wing, is rather less attractive, but has
sufficient other features to endear it to the canny air traveller.
However in the Cessna 172 it's something of a deficiency... |
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so there's a sound argument for the widespread
adoption of the Supermarine Spitfire as personal
transport from a safety point of view? |
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Got it in one. You get a nice safe seat over
the wing, outstanding agility, considerable
immunity from heat-seeking MANPADS,
ecelllent rate of climb and high top speed,
grass strip capability, optional hardpoints for
stores, and 20mm cannon. |
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On the downside, they are somewhat
maintainance heavy, the cockpit is rather
cramped, and wherever you land you're in
constant danger from other pilots who want
to quietly murder you (nothing personal,
mind) and take your aeroplane. |
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//...nice safe seat over the wing, outstanding agility, ... e[x]celllent rate of climb and high top speed, grass strip capability, optional hardpoints for stores...// |
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I was in the process of posting an idea inspired by this but I found it is baked. <link> |
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[pocmloc] I was about to add a link to the idea you briefly posted, but I'll add it here instead (see link). |
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If, presumably, the plane is travelling forwards, the place to be is in the aft, near the tail cone, behind that several meters of foam and human flesh matrix. |
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//the place to be is in the aft// |
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Depends on the crash. First class passengers do have
a higher death rate, but there are probably a few
compounding factors. 1. They're probably older 2.
The complementary gin provides a baseline
motivation to stay in the aircraft. Conversely, the
economy experience has people trying to leave
perfectly serviceable aircraft. |
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Actually its the strength benefit of the tail section that makes the difference. |
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