bhill
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Eject! Eject!

Mon Feb 01, 2016 4:00 pm

Carpe Pices
 
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DocLightning
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RE: Eject! Eject!

Mon Feb 01, 2016 9:38 pm

1) Few catastrophic failures happen at sufficient altitude to warrant this mechanism. And those catastrophic failures usually affect the fuselage. Most crashes happen either on landing or takeoff, when this mechanism would be useless.

2) The additional mechanisms would be heavy.

3) Ejecting the cabin would catastrophically upset the weight and balance of the remaining aircraft and would basically be suicide for the pilots. Hard call to make in the heat of the moment.
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copter808
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RE: Eject! Eject!

Mon Feb 01, 2016 11:10 pm

I should think that a ballistic recovery system for the entire aircraft would be far simpler and save everyone, including the pilots.

Still, since most accidents happen at low altitudes, not sure a BRS would bee all that useful in the long run. Quite frankly, I can't think of any recent accidents where either of these systems would useful.
 
rwessel
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RE: Eject! Eject!

Tue Feb 02, 2016 12:36 am

Quoting copter808 (Reply 2):
I should think that a ballistic recovery system for the entire aircraft would be far simpler and save everyone, including the pilots.

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, although they are working for some larger ones for use on Mars). 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 takes 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).
 
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Scooter01
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RE: Eject! Eject!

Tue Feb 02, 2016 7:24 am

Some of you "techies" should read the "Civ,AV" forum a bit more often......

Dropping And Parachuting The Passenger Cabin... (by flyingturtle Jan 14 2016 in Civil Aviation)

Scooter01   
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Starlionblue
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RE: Eject! Eject!

Tue Feb 02, 2016 12:04 pm

The mainstream press regularly comes out with "in the future in aviation" stuff that is nowhere near plausible. As far as I can tell, they've been doing this since the 19th century with lighter than air stuff.

This is just the latest example. Sounds like a great idea to someone not in the industry. If you have some inside knowledge, not so much. And of course if you tell people on FB, YouTube or other such platform why it is a silly idea you get told that you "lack imagination", and "how do you know?" which is why I avoid such platforms.

But I'm not bitter...

Quoting rwessel (Reply 3):
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 takes 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).

Quite.

Quoting Scooter01 (Reply 4):
Some of you "techies" should read the "Civ,AV" forum a bit more often....

There's reason we don't?  
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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flyingturtle
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RE: Eject! Eject!

Tue Feb 02, 2016 2:29 pm

Quoting bhill (Thread starter):

Hehe, I knew I started an earlier thread about it in Civ Av...  
Quoting Starlionblue (Reply 5):
The mainstream press regularly comes out with "in the future in aviation" stuff that is nowhere near plausible. As far as I can tell, they've been doing this since the 19th century with lighter than air stuff.

Mainly because it's a cheap kind of journalism. You get to present the newest and latest in tecknulogy resurch, you can say how much safer aviation is becoming, you have handy promotional websites (and blogs) covering it... but rarely is the question asked: Is our journalists learning?

Gone are the days when journalism came with a basic understanding of the topic one covers, or a knowledge of which people to ask for a comment.


David
Reading accident reports is what calms me down
 
bhill
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RE: Eject! Eject!

Wed Feb 03, 2016 4:43 pm

Yeah, I kinda chuckled when I saw where the "engineer" that thought this up is from....
Carpe Pices
 
roseflyer
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RE: Eject! Eject!

Wed Feb 03, 2016 6:59 pm

All the "engineer" who invented this is did is make a cool animated video. The idea is ridiculous and terrible.

The engineer obviously does not understand how the loads in an airplane are carried through the fuselage. Airplanes are not boats with a keel that holds the ship together. The fuselage itself provides the structural support from the wings to tail to flight deck. You can't eject the fuselage and have anything still in tact. What that means is he essentially created a system that ejects the wings and empennage from the airplane. The idea of detatcheable wings in flight is about the worst idea I have heard. Let's design in a failure mode so that the wing can fall off in flight???? That certainly will not improve safety. We want the wings to stay on the airplane.
If you have never designed an airplane part before, let the real designers do the work!
 
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TWA772LR
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RE: Eject! Eject!

Sat Feb 06, 2016 2:52 am

Ejection seats for the pilots. There. Everybody wins.
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