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Air Midwest Flight 5481 only had a COG shifted aft by 5%, but that was enough to stall and crash the plane, killing everyone on board and one on the ground, when combined with incorrectly adjusted elevator cables. That's the thing about air accidents, they are usually a combination of factors. So, you don't knowingly make the situation even slightly worse to avoid damage that poses minimal risk to passengers because that increases the likelihood that some other edge case will bite you.
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Oct 20, 2016 17:58
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vessbot posted:I don't see what rear engines have to do with CG sensitivity. Of course the CG is further back relative to the fuselage, but in the end the CG is where the CG is, and the main gear and wing are placed accordingly. I suppose what I mean is moment of inertia (I think that's the right term) is much more sensitive with all the mass hanging so far from the center of gravity, to the point of a 50kg person walking to the back of the cabin is enough to start the plane rotating. You don't have that risk with aircraft with engines under the wings. The envelope there is much greater due to the mass being centralized.
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Oct 20, 2016 18:26
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vessbot posted:You're still not getting it. The crux of this issue has nothing to do with the feasibility of moving the CG aft of the limit. Not with how easy it is to convince the pax to cram in the tail, not with whether they can physically fit back there, not with whether fitting them all there will move the CG enough, not any of that. I think you're all ignoring that he's actually advocating that the passengers, in an emergency landing, to remove their seatbelts, and cram into the back of the plane, possible without proper seating or safety equipment. Great! You saved the props, but all your passengers have horrifying injuries that could have been prevented by being in their seat. Edit: drat Sullenburger! If only he was more concerned with keeping water out of the cabin! Ruined a perfectly good airframe! If he'd have gotten rid of all the 
xergm fucked around with this message at 22:11 on Oct 20, 2016 |
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Oct 20, 2016 22:04
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xergm posted:Edit: If he just got all the passengers to jump in the air at once, think of how much longer the plane could have glided!
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Oct 20, 2016 22:24
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Safety Dance posted:If he just got all the passengers to jump in the air at once, think of how much longer the plane could have glided! Same reason why planes carrying cargoes of live birds never crash!
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Oct 20, 2016 22:38
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Yes, it's like a lava lamp.
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xergm posted:If he'd have gotten rid of all the I'm not actually sure it would have glided any further, just slower. Less stored energy if there are no passengers. In gliders we often carry up to 200 liters of water ballast, especially during competition flights. The theory is that the plane will glide the same distance, but you can glide at faster speed.
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Oct 21, 2016 00:33
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Saukkis posted:I'm not actually sure it would have glided any further, just slower. Less stored energy if there are no passengers. It's a tradeoff of glide speed (and potentially losing less energy to turbulence and stuff) versus ability to climb in a thermal, no?
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Oct 21, 2016 00:35
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Ignoring kinetic energy, the optimum glide angle of any given design is unaffected by weight.
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Oct 21, 2016 01:20
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TheFluff posted:In RC aircraft modelling the saying goes "a nose heavy plane flies poorly, a tail heavy one flies once". I've flown a lot of tail heavy r/c planes. It's.. exciting. More importantly, I"ve landed them, successfully.
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Oct 21, 2016 03:56
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This is your yearly reminder to always dip your tanks if there's any doubt how much fuel you have. https://www.youtube.com/watch?v=4z3gkq_gWL4
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Oct 21, 2016 04:51
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I'm pretty sure the deer's CG has been adjusted:
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Oct 21, 2016 05:00
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 I am surprised there isn't a huge pool of blood on the ground though even if it died almost instantly.
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Oct 21, 2016 05:02
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There's a spray of blood on the right wing. I think that the plane hit the deer somewhere else, and they dragged the halves over to it for the picture.
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Oct 21, 2016 05:14
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I suspect the huge blood stain is about 30 feet back. Still, 
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Oct 21, 2016 05:26
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Speaking of Sully, Major Kong did a pretty decent take on the ditching: http://www.dailykos.com/stories/2016/10/14/1577211/-The-A320-and-the-Hudson "The Captain and F/O famously checked the plane to make sure everybody got out. Something us box-haulers don’t have to worry about. If I go back there it’s because I’m looking for any boxes labeled 'ACME Inflatable Boat Company.'" BIG HEADLINE fucked around with this message at 07:19 on Oct 21, 2016 |
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Oct 21, 2016 07:12
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BIG HEADLINE posted:Speaking of Sully, Major Kong did a pretty decent take on the ditching: http://www.dailykos.com/stories/2016/10/14/1577211/-The-A320-and-the-Hudson  the first item on the dual engine-out checklist is "LAND ASAP".Somebody else beat me to asking about the dual-engine-out procedure for the BUFF -- Kong's answer was "wake me up if we lose a couple more." Now I'm wondering if the B-52 has an option to eject the backseaters independently of the pilots (or is it every man for himself, and they all leave when the pilot gives the order/they decide not to ride it in with the pilot)? Pretty sure some fighters have the latter setup -- the pilot has a switch with the option of "both seats' ejection handles fire both seats" or "GIB can only fire his own, but pilot's fires both," both with their advantages: the first, either one could be incapacitated and the other get them both out, the second, maybe you don't trust the RIO/WSO to trust you or maybe you want to ride it in to protect civilians but he can save himself. Edit: Sort of like how WWII bomber crews would toss their not-immediately-mortally wounded comrades out the dooron static lines (basically tie the ripcord to the airframe, 'chute opens as soon as it's clear, it's what the paratroopers use), hoping that somebody would find them and take pity on them, because waking up as a POW in hospital is (usually) better than bleeding out before getting home. Chillbro Baggins fucked around with this message at 13:15 on Oct 21, 2016 |
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Oct 21, 2016 13:09
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Bad Angus! Bad!
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Finger Prince posted:I suppose what I mean is moment of inertia (I think that's the right term) is much more sensitive with all the mass hanging so far from the center of gravity, to the point of a 50kg person walking to the back of the cabin is enough to start the plane rotating. You don't have that risk with aircraft with engines under the wings. The envelope there is much greater due to the mass being centralized. With the mass farther away from the center, the moment if inertia is bigger, which would make it more resistant to rotation, i.e., it would be less, not more, sensitive to rotational jolts. But in this case it wouldn't matter either way, because with gradual placements of boxes (or occupants walking back) one by one, it's essentially a static system with changing steady states. All that matters is CG vs. main gear position. If, instead, everyone started jumping in unison, then you'd have to start considering resistance to rotation.
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Oct 21, 2016 13:12
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Delivery McGee posted:Pretty sure some fighters have the latter setup -- the pilot has a switch with the option of "both seats' ejection handles fire both seats" or "GIB can only fire his own, but pilot's fires both," both with their advantages: the first, either one could be incapacitated and the other get them both out, the second, maybe you don't trust the RIO/WSO to trust you or maybe you want to ride it in to protect civilians but he can save himself. This is definitely true in at least one fighter. An F-14 pilot was giving an orientation flight for a surface warfare officer who would be working with aviation, gave him a heads-up, and rolled inverted. The guy in the backseat reacted instinctively, grabbing for something and holding on. "Something" happened to be a reassuring yellow and black handle. The pilot had a very confusing and presumably loud experience but landed the plane and the backseater was recovered safely. http://www.vfp62.com/f14_rio.html
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Oct 21, 2016 13:24
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vessbot posted:With the mass farther away from the center, the moment if inertia is bigger, which would make it more resistant to rotation, i.e., it would be less, not more, sensitive to rotational jolts. Sounds like I need to retake high school physics. What causes a rear engined aircraft suspended by two jacks placed at the exact center of gravity to be more sensitive to weight change aft of that point, versus an underslung (much larger + more massive, does that factor in?) engined aircraft suspended by two jacks at the same point which isn't or is less sensitive to weight changes at the back of the aircraft?
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Oct 21, 2016 13:31
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I'd expect it's the mass, because the lever arm should be shorter, but when calculating center of gravity you weight the contribution of an object by its weight, so if the plane's half as heavy, the same weight the same distance from the center of gravity should cause twice or roughly twice the shift.
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Oct 21, 2016 13:56
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hogmartin posted:This is definitely true in at least one fighter. An F-14 pilot was giving an orientation flight for a surface warfare officer who would be working with aviation, gave him a heads-up, and rolled inverted. The guy in the backseat reacted instinctively, grabbing for something and holding on. "Something" happened to be a reassuring yellow and black handle. That's an awesome read
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Oct 21, 2016 14:18
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hogmartin posted:This is definitely true in at least one fighter. An F-14 pilot was giving an orientation flight for a surface warfare officer who would be working with aviation, gave him a heads-up, and rolled inverted. The guy in the backseat reacted instinctively, grabbing for something and holding on. "Something" happened to be a reassuring yellow and black handle. That's where I remember it from, yeah. The other option is for actual combat with a crew who trust each other and the backseater won't ND his seat (planes used for VIP rides really should have an "only pilot can initiate ejection" option, because of that), but is there any fighter with an option for "pilot leaves, GIB stays"? Maybe the Mudhen, it's got rudimentary flight controls in the back seat, but IIRC all the WSO can do is bombs, only the pilot can fire air-to-air munitions and guns. Though the Mudhen's one air-to-air-kill was by the bombardier -- during Desert Storm, IIRC, they dropped a laser-guided bomb at a Hind on the ground, it took off, but they kept it painted until the chopper was well above ground level and put the 2,000-pound iron bomb into it in midair. Also, Ironically, the Hind has a similar setup -- the gunner can drive if he has to.
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Oct 21, 2016 14:32
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I remember seeing a picture from the back seat of the SR-71 that had a light labeled something like "Pilot Ejected." Was along with some writing about how the GIB could drive via the autopilot, but not much else since there was no visibility or flight controls for the back seat. Don't remember how the ejection was set up, the light may have only been there due to not really sharing a cockpit, but I know it's come up before.
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Oct 21, 2016 16:08
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Delivery McGee posted:Now I'm wondering if the B-52 has an option to eject the backseaters independently of the pilots (or is it every man for himself, and they all leave when the pilot gives the order/they decide not to ride it in with the pilot)? http://www.ejectionsite.com/b-52.htm
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Oct 21, 2016 16:13
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drzrma posted:I remember seeing a picture from the back seat of the SR-71 that had a light labeled something like "Pilot Ejected." Was along with some writing about how the GIB could drive via the autopilot, but not much else since there was no visibility or flight controls for the back seat. Don't remember how the ejection was set up, the light may have only been there due to not really sharing a cockpit, but I know it's come up before. If this doesn't make the friendly reassuring 'deep-doop' flight attendant call button sound I'm very disappointed. 
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Oct 21, 2016 16:17
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hogmartin posted:If this doesn't make the friendly reassuring 'deep-doop' flight attendant call button sound I'm very disappointed. Very cool video about the SR-71 flight controls. There's some really weird stuff in there that you wouldn't see in an airplane that didn't fly the Blackbird's mission -- got instance, the gyroscopic laser projector that shines a stabilized horizon line across the entire instrument panel, so you know which way is up when everything around you is the blackness of space. He goes into the back seat about two thirds of the way through and talks about the ejection system. https://www.youtube.com/watch?v=tj9UwKQKE3A
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Oct 21, 2016 17:43
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Sagebrush posted:Very cool video about the SR-71 flight controls. There's some really weird stuff in there that you wouldn't see in an airplane that didn't fly the Blackbird's mission -- got instance, the gyroscopic laser projector that shines a stabilized horizon line across the entire instrument panel, so you know which way is up when everything around you is the blackness of space. This video is excellent. It never occured to me that you'd only get 16 goes at starting/lighting the afterburner on each engine. I mean, if you're trying to re-light an engine in that thing mid flight you're probably going to get some use of the bailout lights anyway so it's not really an issue, but it seems like another thing that would weigh in the back of the pilot's mind the whole time.
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Oct 21, 2016 19:43
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Sagebrush posted:Very cool video about the SR-71 flight controls. There's some really weird stuff in there that you wouldn't see in an airplane that didn't fly the Blackbird's mission -- got instance, the gyroscopic laser projector that shines a stabilized horizon line across the entire instrument panel, so you know which way is up when everything around you is the blackness of space. That video was great man, thanks for the link.
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Oct 21, 2016 21:32
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jammyozzy posted:This video is excellent. It never occured to me that you'd only get 16 goes at starting/lighting the afterburner on each engine. Wasn't the whole point of carrying all of that starter fuel the fact that the J58 is not an easy engine to keep running?
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Oct 22, 2016 00:10
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Mainly they had to relight the afterburners after tanking but also the engines were prone to unstarts, yes. VVVV Not jet fuel; starter fuel. The SR-71 used triethylborane to light the engines since JP-7 is too hard to light normally. That wasn't replenished by tankers. Mortabis fucked around with this message at 01:42 on Oct 22, 2016 |
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Oct 22, 2016 01:27
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IOwnCalculus posted:Wasn't the whole point of carrying all of that starter fuel the fact that the J58 is not an easy engine to keep running? What? No. They took off nearly empty and had to refuel with a tanker within 20 minute of taking off...
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Oct 22, 2016 01:34
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We got a Big'un a few days ago: https://www.youtube.com/watch?v=m0r7jZYcRpI
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Oct 22, 2016 01:52
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 I hope they exchanged insurance information. also: don't look now but I think someone's following you: http://i.imgur.com/irK05EQ.mp4 Duke Chin fucked around with this message at 02:26 on Oct 22, 2016 |
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Oct 22, 2016 02:16
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SeaborneClink posted:What? No. They took off nearly empty and had to refuel with a tanker within 20 minute of taking off... IIRC, the fuel tank sealed as they gain altitude, so on the ground, they were leaking. So they filled up the tank, took off asap and refueled at FL300 where the tank was a little more tight, then again blast off to climb to the final altitude were they could finally hold the fuel inside.
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Oct 22, 2016 16:16
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Jonathan Demers posted:IIRC, the fuel tank sealed as they gain altitude, so on the ground, they were leaking. So they filled up the tank, took off asap and refueled at FL300 where the tank was a little more tight, then again blast off to climb to the final altitude were they could finally hold the fuel inside.
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Oct 22, 2016 17:12
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Jonathan Demers posted:IIRC, the fuel tank sealed as they gain altitude, so on the ground, they were leaking. So they filled up the tank, took off asap and refueled at FL300 where the tank was a little more tight, then again blast off to climb to the final altitude were they could finally hold the fuel inside. No. That is one of the biggest misconceptions about the SR-71; yes the tanks leaked fuel on the ground, but it was a very small amount. The reason why they took off light on fuel and tanked right away was solely to improve takeoff performance. A typical takeoff in an SR-71 has a rotation speed of 180 knots and a liftoff speed of 210, which is quite a bit higher than your average fighter aircraft to begin with. Additionally, even with the drogue chute, the SR-71's braking performance was not great - six little brakes on a heavy aircraft means that quickly becomes the limiting factor on takeoff performance.
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Oct 22, 2016 17:18
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^^^ yes, to be clear, it's a small amount of fuel. The engines burn 20,000 pounds per hour, so obviously if it was losing a significant amount of fuel to leakage there would be a flood around every Blackbird all the time. it's true that the leaks don't stop until the correct speed is reached though That's generally correct but it's airspeed, not altitude, that seals the tanks. At full speed, the plane's skin heats up several hundred degrees. If the panels were built to fit flush on the ground, they would buckle after they expanded from the heat. So instead they're built with gaps between them at ambient temperature, and after thermal expansion they fit flush. The fuel runs directly under the skin of the plane because that way you can both preheat the fuel and cool the skin, and you gain additional range that would be lost if you had to make a separate sealed internal fuel tank. But that means that the fuel drips out of all the gaps until the plane is sealed. So primarily because you're using the fuel as coolant, and secondarily because you know it's going to drip out all over the runway, you have to use something with a very high flashpoint for safety. Hence the development of JP-8 and the chemical igniters to actually get it to light off. Sagebrush fucked around with this message at 17:22 on Oct 22, 2016 |
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Oct 22, 2016 17:19
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MrChips posted:No. Dang, beat me to it. Yeah, the "leaky fuel tanks" is often vastly overstated; it was described as a slow drip in the books I've read on it. Not enough to have a serious impact on fuel consumption.
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Oct 22, 2016 17:25
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drzrma posted:I remember seeing a picture from the back seat of the SR-71 that had a light labeled something like "Pilot Ejected." Was along with some writing about how the GIB could drive via the autopilot, but not much else since there was no visibility or flight controls for the back seat. Don't remember how the ejection was set up, the light may have only been there due to not really sharing a cockpit, but I know it's come up before. I recall one of the stories I've seen reposted a few times involved the light coming on erroneously, followed by a very concerned back seater asking over the intercom whether the pilot was still there.
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Oct 22, 2016 17:41
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Sagebrush posted:^^^ yes, to be clear, it's a small amount of fuel. The engines burn 20,000 pounds per hour, so obviously if it was losing a significant amount of fuel to leakage there would be a flood around every Blackbird all the time. it's true that the leaks don't stop until the correct speed is reached though After all that accurate information, you typo JP-7. SMH
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Oct 22, 2016 17:47
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