dimik747 From Greece, joined Nov 2010, 51 posts, RR: 0 Posted (3 years 3 weeks 5 days 3 hours ago) and read 4490 times:
Hello Everybody, this is my first post on airliners.net after following it for more that 5 years, particularly the Tech/Ops forum!
I have tried searcing for a similar post but have failed, if a similar posts exists i apologise in advance
This question has been troubling me for some time, since there are some general aviation planes such as the cirrus aircraft that do have a parachute system that can help safety wise in certain situations, how come commercial airliners, say a 737, dont have them? I read somewhere it was a problem with the weights and forces involved in such big aircraft but since aircraft are held up in the air by the lift provided, and that lift suports the fuselage where the two components meet, would it be possible to place the hold points for a parachute system in the structure that joins the wings and the fuselage? since it caries most of the aircrafts weight anyways?
xero9 From Canada, joined Feb 2007, 150 posts, RR: 0 Reply 3, posted (3 years 3 weeks 4 days 22 hours ago) and read 4387 times:
Quoting Starlionblue (Reply 2): you would be carrying tons of extra weight for something that you will probably never use,
You took the words out of my mouth, that's for sure.
I also can't think of any crashes off the top of my head that could have been saved by such a system. I suppose if a plane had some kind of hydraulic failure and that preventing the crew from controlling the aircraft they could reduce power on the engines, let the plane slow down, then deploy the chute. Aside from that, I'm not sure of any other situations where it could result in a more favorable outcome.
rwessel From United States of America, joined Jan 2007, 2137 posts, RR: 2 Reply 4, posted (3 years 3 weeks 4 days 22 hours ago) and read 4384 times:
Just to put a few numbers on things... It's not impossible as a concept, and chutes in the approximate ballpark of the required size have been used with reasonable success. But the weight and expense would be quite high, and low altitude deployment is probably impossible, since chutes of the required size would need to be deployed in stages.
Back of the envelope calculate is that for a 75t airliner (about a 737-700ER), you'd need a chute of over 125m diameter (assuming a single canopy) to get the landing impacts down to the humans-are-likely-to-survive-without-incapacitating-injuries range - about 8m/s (and 8m/s - 1600f/m - will definitely be a memorable impact). A real chute of that capacity would be a fair bit larger since the above assumes a perfectly dome shaped and solid chute, which is quite unrealistic for anything of that size.
The Shuttle SRBs are a useful point of comparison. The empty SRBs weigh about 91t, the main chutes (there are three), are 41m in diameter, and weigh about 990kg each (note that these are the largest chutes ever deployed). The SRB's recovery system is designed for a 23m/s touchdown, which buys them about a factor of eight reduction in required area compared to a 8m/s touchdown requirement). Basically using a cluster of SRB chutes, you'd need about 20 of them.
However the SRB also requires a drogue chute (16m, over 500kg) to stabilize and slow the SRB to the point where you can deploy the mains. There's also a pilot chute which deploys the drogue, and the drogue actually deploys in three stages, fully reefed at first, then unreefed in two stages (the final unreef happens 12s after the drogue deploys). Then the (reefed) mains are pulled out by the drogue, and again there's a two stage unreef process (17s to the final unreef).
The SRB's speeds are not really higher than an airliner’s during the parachute deployment, the SRBs are subsonic the whole time there are parachutes involved, so the aerodynamic forces are going to be in the same ballpark.
So for our hypothetical 737, we're talking about a system weighing on the order of 25-30t (basically the entire non-fuel useful load), that well over 30 seconds to deploy (which would rather limit its effectiveness at low altitudes), and is half a dozen times bigger than any similar system ever built. Without even getting into the rather more severe design requirements for something rated for human use (the SRBs are unmanned, of course, and NASA has had several incidents where SRBs were damaged because of partial failures of the recovery system - most recently the Ares-I-X test).
rwessel From United States of America, joined Jan 2007, 2137 posts, RR: 2 Reply 5, posted (3 years 3 weeks 4 days 22 hours ago) and read 4383 times:
Quoting xero9 (Reply 3): I also can't think of any crashes off the top of my head that could have been saved by such a system. I suppose if a plane had some kind of hydraulic failure and that preventing the crew from controlling the aircraft they could reduce power on the engines, let the plane slow down, then deploy the chute. Aside from that, I'm not sure of any other situations where it could result in a more favorable outcome.
Can anyone else think of any situations?
Alaska Airlines 261, Japan Airlines Flight 123, and United Airlines 232 immediately come to mind.
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9 Reply 6, posted (3 years 3 weeks 4 days 22 hours ago) and read 4378 times:
So far most people have given technical reason for not having a parachute sysytem on a commercial airliner. I can think of a couple of reason that even if a systen was developed why it would not work:
o Most crashes happen on takeoff/landing where a parachute system would do little or no good!
o You have a problem at 40,000 feet the airframe starts to break-up or all power is lost and the aircraft is uncontrollable and have to deploy the parachute. It gently lowers you to the ground. But all on board died because of lack of oxygen! The amount of supplemental oxygen on board is limited and descending by parachute would be too slow.
rwessel From United States of America, joined Jan 2007, 2137 posts, RR: 2 Reply 7, posted (3 years 3 weeks 4 days 21 hours ago) and read 4365 times:
Quoting 474218 (Reply 6): o You have a problem at 40,000 feet the airframe starts to break-up or all power is lost and the aircraft is uncontrollable and have to deploy the parachute. It gently lowers you to the ground. But all on board died because of lack of oxygen! The amount of supplemental oxygen on board is limited and descending by parachute would be too slow.
That, at least, would not be an issue in any real system. Initial descent would be far more rapid than the final landing speed. The chutes would initially be deployed reefed, and between the thin air, and significantly reduced effective size, would significantly increase the descent rate at the beginning. And you'd probably have at least a two stage system for anything that large (so the initially opened chute would be a small fraction of the final canopy size). Consider the recovery system on the SRBs I described above. The drogue chute (16m) is less than a twentieth the final total canopy size (41m, times three), and is initially deployed reefed, which probably cuts its effective area (edit: was "size") down by another factor of four or five. Toss in the air density at 40000ft being a fifth of sea level, and it just isn't going to be a problem to achieve any reasonable descent rate needed to stay within the capabilities of the oxygen system.
Obviously an automated system would control the deployment sequence and timing.
Of course this is pretty impractical for a host of other reasons - just not this one.
bohica From United States of America, joined Feb 2004, 2562 posts, RR: 0 Reply 8, posted (3 years 3 weeks 4 days 19 hours ago) and read 4332 times:
Even if there was a feasable parachute system, there is no guarantee that the point of touchdown would be the best location for the safety of those aboard. There is a chance it may float gently into a clearing on soft ground. Otherwise it will be a very rough landing with very serious and fatal injuries.
Wingscrubber From UK - England, joined Sep 2001, 842 posts, RR: 0 Reply 10, posted (3 years 2 weeks 2 days 2 hours ago) and read 3856 times:
What about engineering the cabin into segmented 'escape pods' which can jettison fron the rest of the aircraft structure, and therefore use much smaller parachutes? That would be economically a bit more viable, still entails a large parasite mass to lug around, burning extra fuel.
Starlionblue From Greenland, joined Feb 2004, 16357 posts, RR: 66 Reply 13, posted (3 years 2 weeks 20 hours ago) and read 3703 times:
Quoting Whappeh (Reply 12): Quoting Starlionblue (Reply 9):
Having skydived with a parachute a few times, I can tell you it's not really that gentle. I certainly wouldn't want to do it on broken ground.
Given the alternative, I'd take that chance.
Fair point. However I'd rather invest in making other things better than implementing an iffy and heavy parachute system.
Quoting dl767captain (Reply 11): I say just eject the roof and eject the seats in a machine gun style one after the other each with their own parachute! That's easy to do right?
Well, in an anime it is doable. In the real world....
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
tsugambler From United States of America, joined Jul 2010, 302 posts, RR: 0 Reply 15, posted (3 years 1 week 6 days 3 hours ago) and read 3554 times:
I was always under the impression that one of the leading causes of death in airplane crashes was fire. I have heard about many accidents where the crash itself was relatively survivable, but the passengers died from the resulting fire. If a parachute system is too heavy/inefficient to be practical, is there instead any possible kind of fire-suppression system that could be put into play for a crash?
Starlionblue From Greenland, joined Feb 2004, 16357 posts, RR: 66 Reply 16, posted (3 years 1 week 6 days ago) and read 3521 times:
Quoting tsugambler (Reply 15): I was always under the impression that one of the leading causes of death in airplane crashes was fire. I have heard about many accidents where the crash itself was relatively survivable, but the passengers died from the resulting fire. If a parachute system is too heavy/inefficient to be practical, is there instead any possible kind of fire-suppression system that could be put into play for a crash?
You raise a good point, in that there are other things that should be addressed before mounting a parachute.
I guess you could carry tons of flame retardant, but we run into weight issues. The fuel is of course flammable, but if it isn't flammable that would sort of defeat the purpose.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
rwessel From United States of America, joined Jan 2007, 2137 posts, RR: 2 Reply 17, posted (3 years 1 week 5 days 16 hours ago) and read 3492 times:
Quoting Wingscrubber (Reply 14): Since we're considering the concept, does anybody know the rough weight of a martin-baker ejection seat and parachute?
Just wondering how much weight that would add to the average economy cabin
Various seats range from about 130 to 200lbs. The western seats tend to be towards the lighter end of the range, Russian seats towards the heavier.
So something approximating the weight of the passengers.
But that doesn't include things like the blowable hatches (a short rocket flight into the ceiling would presumably be less than useful), which will have considerable structural implications, as well as fixing the cabin configuration (the seats obviously have to stay directly under the hatches). The hatch now needs a surrounding structure that can bear all of the load (it would be really embarrassing if you blew all the hatches, and the aircraft collapsed), plus the hatch is more door-like, plus whatever opening mechanism you now need. Plus you could never put the seats as close together as most coach seats are (of course since we're better than halving the passenger load of the aircraft, maybe that works out).
And the idea of blowing the whole roof is very problematic, again, you have huge structural issues, plus the need to quickly an reliable detach a *very* large piece of the aircraft.
And passengers are likely to suffer horrifically if they weren't wearing proper five point harnesses, even with eject seats that were a lot more gentle than those on military aircraft. Anyone slouching in their seat would just be begging for a broken pine, for example. And then there's the question of how you can eject a few hundred people in a relatively short time and not have collisions of various sorts.
And then there's the question of what you do with the double-deckers...