A Little Gear That Could Reshape the Jet Engine • Hacker News Board

Re: A Little Gear That Could Reshape the Jet Engine

#51

Post by hinkley » Tue, Oct 20, 2015, 1:36 AM UTC

jcoby wrote: post #44

mhandley wrote: post #15

I wonder if instead of gearing a single large fan, you could just remove the fan from the turbine altogether, add a much larger alternator, and power several large electric external fans from each turbine? That would give you more fan area than you can get with a geared turbofan, optimal fan speed for efficiency, redundancy in case one of the fans suffered damage, allow cross-routing of power between turbines if one…

I think the issue would be weight. You'd need an alternator capable of absorbing some 20000+ HP (~15000 kW). And then the electric motors and associated fans and housings and mount points. And then the cabling to handle distributing the current. And if you're going to cross route you'd need the switches and associated stuff to drive it.

Not to mention the wiring. How much wire and shielding do you need to keep that sort of current safely contained? Especially since the gas tanks are in the wings too?

Re: A Little Gear That Could Reshape the Jet Engine

#52

Post by Gibbon1 » Tue, Oct 20, 2015, 1:41 AM UTC

dexterdog wrote: post #42

WalterBright wrote: post #31

Earlier quoted context omitted.

Re-engining an airframe is a big deal. A lot of engineering has to go into it.

Why can't they just have a standard mount like an LCD panel?

I upvoted cause not dumb question. Yes they do to an extent. One of the major reasons the engines are mounted on pylons is exactly to make maintenance and replacement easy.

Re: A Little Gear That Could Reshape the Jet Engine

#53

Post by hinkley » Tue, Oct 20, 2015, 1:42 AM UTC

PhantomGremlin wrote: post #21

mhandley wrote: post #15

I wonder if instead of gearing a single large fan, you could just remove the fan from the turbine altogether, add a much larger alternator, and power several large electric external fans from each turbine? That would give you more fan area than you can get with a geared turbofan, optimal fan speed for efficiency, redundancy in case one of the fans suffered damage, allow cross-routing of power between turbines if one…

just remove the fan from the turbine altogether I don't think you can. The large volume of airflow surrounding the turbine is what makes it a turbofan[1]. Without, it is a turbojet[2]. The airflow from the turbofan surrounds the hot exhaust gas and it is much quieter than the turbojet. But, other than noise, the rest of your comment makes a lot of sense to me. But I know very little about this stuff. [1] https://en.w…

I can't rattle off the model numbers, but some commercial jets have a turbine in the tail section for auxiliary power. If there's something that looks like an exhaust pipe in the tail, it probably is.

Re: A Little Gear That Could Reshape the Jet Engine

#54

Post by TeMPOraL » Tue, Oct 20, 2015, 1:58 AM UTC

PeterWhittaker wrote: post #46

Love this: “It’s the antithesis of a Silicon Valley innovation,” says Alan Epstein, a retired MIT professor who is the company’s vice president for technology and the environment. “The Silicon Valley guys seem to have the attention span of 3-year-olds.”

I suppose the world is big enough for both. Sadly, media follows the kids more often than the adults.

Re: A Little Gear That Could Reshape the Jet Engine

#55

Post by ars » Tue, Oct 20, 2015, 2:19 AM UTC

hinkley wrote: post #51

jcoby wrote: post #44

Earlier quoted context omitted.

I think the issue would be weight. You'd need an alternator capable of absorbing some 20000+ HP (~15000 kW). And then the electric motors and associated fans and housings and mount points. And then the cabling to handle distributing the current. And if you're going to cross route you'd need the switches and associated stuff to drive it.

Not to mention the wiring. How much wire and shielding do you need to keep that sort of current safely contained? Especially since the gas tanks are in the wings too?

It's not that bad. Use 300 volts and it's only 50amp. That kind of amperage is routinely used by oven/stove/ranges.

And 300 volts is not considered high voltage.

If they upped the voltage to 1,500v (which is the limit before you need much more complicated stuff) it's only 10amp - a simple thin wire would do it.

Re: A Little Gear That Could Reshape the Jet Engine

#56

Post by ams6110 » Tue, Oct 20, 2015, 2:22 AM UTC

onion2k wrote: post #5

GauntletWizard wrote: post #3

Earlier quoted context omitted.

It's a bit easier to be blasé about testing when your worst-case-scenario is that somebody misses a ride, vs when you kill ~150 people. The rapid cycle of innovation is a tradeoff that SV is able to make (and finds amazingly beneficial) because we're working with soft tools and have backups of our data. I'm certain that were human life so cheap, Pratt and Whitney would have a much shorter dev cycle, too.

Shorter project sprints came about to try to fix the problem of project failure. Failure to create a loop that feeds discoveries in to a project's knowledge, and to communicate knowledge between teams is exactly what makes projects come to catastrophic ends, and that's what the shorter cycle time attempts to correct. The fact the product benefits from faster innovation is a function of more efficiently sharing knowle…

Yes it is intrinsically software-only. When a software test fails you fix the bug and run it again. When a jet engine test fails you just blew up a $10M prototype.

Re: A Little Gear That Could Reshape the Jet Engine

#57

Post by gilgoomesh » Tue, Oct 20, 2015, 2:54 AM UTC

TeMPOraL wrote: post #54

PeterWhittaker wrote: post #46

Love this: “It’s the antithesis of a Silicon Valley innovation,” says Alan Epstein, a retired MIT professor who is the company’s vice president for technology and the environment. “The Silicon Valley guys seem to have the attention span of 3-year-olds.”

I suppose the world is big enough for both. Sadly, media follows the kids more often than the adults.

Yeah, there are definitely people in Silicon Valley who are working on the same problems they were working on 20 years ago – it's just not very interesting to outsiders so you don't hear about it (until they have a breakthrough).

Re: A Little Gear That Could Reshape the Jet Engine

#58

Post by joncp » Tue, Oct 20, 2015, 3:03 AM UTC

> "At times, the extent of the operation had to be protected from bean-counting Pratt executives"

Yep, that's how UTC operates. It's amazing they make any money at all.

Re: A Little Gear That Could Reshape the Jet Engine

#59

Post by hyperbovine » Tue, Oct 20, 2015, 3:05 AM UTC

hinkley wrote: post #48

JSeymourATL wrote: post #2

“The Silicon Valley guys seem to have the attention span of 3-year-olds.”

Yeah I don't think this is an argument the aerospace industry can win. To whatever degree SV lacks patience, the airplane industry has the opposite problem. Tolerance of needless complexity leads to expensive systems that aren't necessarily any better for it. There's a real sense that design has absolutely no place and every problem can be engineered around, even if it takes two more layers of parts to achieve it. No…

> That is I believe Musk's premise with his rocketry division.

One hull loss per nineteen attempts is not an acceptable failure rate for "the airplane industry", is it? It's difficult for me to put into words the level of respect and admiration I have for the risk-averse, plodding, and methodical aerospace culture that has created modern aviation. (Seriously, have you ever considered the absolute miracle of engineering that is a modern jetliner?) To lump that profession under the same rubric of engineering as the one where a bunch of overcaffeinated "disruptors" write software to get people to click on ads seems... unjust, to put it mildly.

Re: A Little Gear That Could Reshape the Jet Engine

#60

Post by nether » Tue, Oct 20, 2015, 3:10 AM UTC

dexterdog wrote: post #42

WalterBright wrote: post #31

Earlier quoted context omitted.

Re-engining an airframe is a big deal. A lot of engineering has to go into it.

Why can't they just have a standard mount like an LCD panel?

You actually could. It would take a very strong, very heavy airframe that could handle any stresses generated by the intended selection of engines. It would just be overbuilt and get terribly fuel hungry for most engines, while being optimum for one. This isn't financially acceptable for an industry where operating costs are razor thin (all driven by the fact that a $10 difference in airfare can mean losing a passenger).

Aircraft safety margins are 1.5 (built to handle 1.5x the maximum expected load), while bridges are 5+. The latter aren't constrained by weight, so you might as well go to town with a cheap, heavy design. A lower safety margin is only acceptable though when the expected loading is extremely well defined with very low uncertainty. This takes extensive testing (years for an aircraft), basically reducing the sigma by increasing the sample size.