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There's nothing wrong with unstable airframes. Military craft have required computer assisted flight for decades. What's problematic with 737 MAX is that the s
by fsloth 8y ago
There's nothing wrong with unstable airframes. Military craft have required computer assisted flight for decades.
What's problematic with 737 MAX is that the stability assist was obviously installed as an after thought, and even worse, it's dependent on instrumentation that does not have several layers of fault tolerance as would be the case if it was actually built with the care that planes actually require to be as dependable as they are.
So the instability is not a problem. That boeing tried to get around it with a cheap patch of jury rigged software that is depending on input from non-fault-safe instrumentation, is.
- deleted 8y ago[deleted]
- qrbLPHiKpiux 8y ago> There's nothing wrong with unstable airframes. For military purposes, I agree. There is an end objective to fighter jet development. To own the sky at all costs. With civilian aircraft, there is too much to lose. You can't have an unstable air frame for civilian commercial mass purposes.
- pps43 8y agoHelicopters are inherently unstable at low speeds, yet there are civilian models.
- macintux 8y agoAnd if they carried 500 people we’d think that was a bad idea.
- qrbLPHiKpiux 8y agoHelicopters scare the hell out of me because they resemble nothing that's natural.
- dreamcompiler 8y agoI guess you've never seen a maple seed then. https://duckduckgo.com/?q=maple+seed&t=ffab&iax=images&ia=images https://duckduckgo.com/?q=maple+seed&t=ffab&iax=images&ia=im...
- Drdrdrq 8y agoMaple tree seeds?
- serf 8y ago(to other repliers) maple tree seeds resemble auto-rotation in a helicoptor, not powered flight. It's a nice mental model as to why you won't fall out of the sky necessarily with a loss of power in a heli, though.
- CydeWeys 8y agoWhy does that matter? There are plenty of natural things that are scary as hell, and plenty of unnatural things that aren't. The reason you don't see it in nature is that macroscopic organisms never evolved a continuously rotating joint. It's a hard problem for evolution to solve; how would blood vessels cross that boundary? But of course machines have no such constraints, and the wheel and axle is hardly a new (or scary) invention.
- thaumasiotes 8y agoYour shoulder comes close, on a ball-and-socket model rather than wheel-and-axle.
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- CydeWeys 8y agoIt doesn't continuously rotate, and it's nowhere close to allowing so.
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- rujuladanh 8y agoWhat? Of course there is somethig wrong with unstable airframes. This is not a figther jet where it may make sense to maximize maneuverability, it is a bloody airliner, where stability and reliability should have been the design goals.
- brianberns 8y agoInherent instability in a commercial aircraft seems like a very bad idea. Safety has to the top priority. The military has very different priorities.
- InclinedPlane 8y agoI disagree that "instability is not a problem". In military aircraft that are unstable it's common for everyone in the plane to be in an ejector seat or to have a parachute. Can you provide statistics on how many (or what proportion of) military planes with inherent instabilities routinely carry passengers without parachutes?
- ceejayoz 8y agoI suspect military planes have ejection seats not because of built-in instability, but because they have a tendency to get shot at.
- InclinedPlane 8y agoIt doesn't matter why they have them, the fact that they are there changes the overall risk equation for the aircraft. Many military planes have bailout procedures because everyone has ejection seats or parachutes. Civilian planes universally do not. What is an acceptable risk in one circumstance is not necessarily acceptable in another.
- ceejayoz 8y agoIt does matter why they have them, if you're using their having them as evidence that something else is a problem. Swap out "instability" for "drab paint jobs" and see: > I disagree that "drab paint jobs are not a problem". In military aircraft that have drab paint jobs it's common for everyone in the plane to be in an ejector seat or to have a parachute. Can you provide statistics on how many (or what proportion of) military planes with inherent drab paint jobs routinely carry passengers without parachutes?
- yarrel 8y agoYes we can make an argument incoherent by swapping words in and out. In this case the argument is not that a is evidence of b, it is that a ameliorates b. And that the risk of b is therefore priced differently where a is also present. So where a is not present, we must price the risk differently. How that assertion relates to the historical record may be of interest.
- TecoAndJix 8y agoAs an unrelated side note, I have always said “jerry rigged” and wanted to know which of us have been saying it wrong. Turns out it’s both! https://www.merriam-webster.com/words-at-play/jerry-built-vs-jury-rigged-vs-jerry-rigged-usage-history https://www.merriam-webster.com/words-at-play/jerry-built-vs...
- war1025 8y agoOr the rather less tasteful version starting with N that was common with many of the older people while I was growing up.
- qaq 8y agoYou can eject from most of those mil aircraft
- VBprogrammer 8y agoThat's a huge stretch. The fix was to work around a certification requirement that the control forces shouldn't decrease as the aircraft approaches the stall. This is a long way away from the aircraft being inherently unstable.
- kraig 8y ago"Fehrm said Boeing must have added this system on the MAX because when the angle of attack is high this model is less stable compared to prior 737 variants. That’s because the MAX has bigger, heavier engines that are also cantilevered further forward on the wing to provide more ground clearance. That changes the center of gravity." Fehrm, a former jet-fighter pilot and an aeronautical engineer: https://www.seattletimes.com/business/boeing-aerospace/faa-evaluates-a-potential-design-flaw-on-boeings-737-max-after-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faa-e...
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- VBprogrammer 8y agoIt seems like you think that contradicts what I said. The system by design adds a little trim in very specific circumstances. That's not the same as being needed because the aircraft is aerodynamically unstable. That is a term which has an actual definition. That said there are airliners out there which are unstable in the longitudinal axis and require a yaw damper to prevent Dutch roll.
- fsloth 8y agoThanks, you are quite right. My intention was not to claim 737 MAX had the same aerodynamic nature as, say, F-16, but in the scope of the discussion point out that fixing instabilities with flight software can be made to work reliably. The main argument was that it was inherently a bad idea to require computer assist to maintain stability and decades of military planes demonstrate that you can engineers such systems to be more or less fault safe.
- usrusr 8y agoA combat aircraft can trade reliability for superiority, you increase one kind of risk to lower another. This trade-off simply does not exist in civilian aviation.
- abfan1127 8y agois that the case? The Osprey certainly tried and failed that trade off, at least in the beginning. https://en.wikipedia.org/wiki/Accidents_and_incidents_involving_the_V-22_Osprey https://en.wikipedia.org/wiki/Accidents_and_incidents_involv...