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A Little Gear That Could Reshape the Jet Engine

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Re: A Little Gear That Could Reshape the Jet Engine

#61

Post by jcoby »

ars wrote: post #55
hinkley wrote: post #51

Earlier quoted context omitted.

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.

I think you are off by 3 orders of magnitude unless you are planning on putting 1000 motors on each wing. I said 15000 kW. That's 15 MW. 300v @ 50A is only 15000 W or roughly 20 HP (actually a bit less when you consider the power factor).

Re: A Little Gear That Could Reshape the Jet Engine

#62

Post by nether »

Gibbon1 wrote: post #52
dexterdog wrote: post #42

Earlier quoted context omitted.

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.

Yeah, it's a fair question. Most are unused to weight optimization. It's why everything in a commercial jet down to the forks served with meals is purpose designed for aviation.

Re: A Little Gear That Could Reshape the Jet Engine

#63

Post by nether »

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.”

Well, that's what you get with age discrimination. There are probably all manner of worthwhile problems that older people understand better due to experience in long-haul, delayed gratification efforts (raising kids to adulthood, financing a house, chronic illnesses) rather than scrambling for the latest gastropub or gallery opening.

Re: A Little Gear That Could Reshape the Jet Engine

#64

Post by hinkley »

hyperbovine wrote: post #59
hinkley wrote: post #48

Earlier quoted context omitted.

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 engineeri…

You can't compare a giant pipe bomb with passengers on one end to an airplane either, but I'm the one who opened that door without a suitable qualifier, so that's on me.

What I meant to convey is that I expect someone to do to commercial aviation what Musk is trying to do to rocketry, and what I expect that to look like is for more effort to be placed into reducing single points of failure by designing complementary systems instead of just putting three of everything on the vehicle and then adding two more layers of stuff to manage it. And also for them to act like progress in software development processes actually applies to them now instead of in thirty years. We got no end of grief for refusing to do pure waterfall, and they were conspicuously silent when we're were able to fix fundamental up front design flaws in 3-8 weeks, and without doing a reenactment of Macbeth starring William Shatner, set in a rehab clinic.

Then again, I expect something to happen to improve the caliber of software developers out there as well, so we'll see how that goes. Often when I expound on the qualities of my profession I am intentionally and consciously imagining that the 30% of my peers that are responsible for 70% of our problems either don't exist, or are off doing something that's not important.

Re: A Little Gear That Could Reshape the Jet Engine

#65

Post by BuffaloBagel »

ckozlowski wrote: post #33
PhantomGremlin wrote: post #21

Earlier quoted context omitted.

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…

You're exactly right. But as you suspect, there's reasons why you wouldn't want to do that in all cases. Turbojets derive all of their thrust from the turbine exhaust. It's a small, compact engine, which means high power-to-weight ratio, and it's great for small jet fighters. Unfortunately, it also consumes a lot of fuel. Turboprops are at the other end, where the turbine drives the propeller at much faster speeds th…

Turboprops are at the other end, where the turbine drives the propeller at much faster speeds than a regular 4-stroke engine would

You're mistaken. Prop speeds are comparable between piston and turbine engines. Bigger, slower moving props are preferable. When prop tip speeds approach the transonic region, on either turbine or piston power plants, efficiency goes south.

Re: A Little Gear That Could Reshape the Jet Engine

#66

Post by BuffaloBagel »

hinkley wrote: post #53
PhantomGremlin wrote: post #21

Earlier quoted context omitted.

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.

https://en.wikipedia.org/wiki/Auxiliary_power_unit

Re: A Little Gear That Could Reshape the Jet Engine

#67

Post by gear54rus »

knodi123 wrote: post #7

> what may be most remarkable about the engines is that they took almost 30 years to develop. That’s about 15 times as long as the gestation period of an elephant Who the hell is running their analogy department?!? "Thirty years! That's a big number! We need some kind of comparison that will instantly give the reader perspective. Of course, in this, as in so many other things, the answer lies in pachydermian pregnanc…

Well the editor (or whoever else) is obviously butthurt over the SV and general direction where technology is headed.

Tough luck... he'll have to adapt just like everyone else. Or go on a strike right with those taxi drivers.

Re: A Little Gear That Could Reshape the Jet Engine

#68

Post by vxNsr »

jws wrote: post #36
knodi123 wrote: post #7

> what may be most remarkable about the engines is that they took almost 30 years to develop. That’s about 15 times as long as the gestation period of an elephant Who the hell is running their analogy department?!? "Thirty years! That's a big number! We need some kind of comparison that will instantly give the reader perspective. Of course, in this, as in so many other things, the answer lies in pachydermian pregnanc…

As long as we are ripping on their numbers… "75% less noise" almost certainly means 75% less power in the noise which means about 6 decibels quieter. That's noticeable, but not huge.

Maybe it means 75% fewer decibels, which would be quite the accomplishment.

Re: A Little Gear That Could Reshape the Jet Engine

#69

Post by fancyketchup »

iammaxus wrote: post #45
Animats wrote: post #19

There's a long negative history of high-speed gearing. Jet engines have one big rotating unit, and that basic simplicity is good for reliability. Turboprops have a gearbox, and fragile, high-maintenance gearboxes are a long-standing problem with turboprops. Adding a gearbox without reducing reliability is a major achievement.

High-speed gearing is indeed very difficult, but jet engines already typically have two separate, concentric rotating units (spools: https://en.wikipedia.org/wiki/Turbofan#Basic_two_spool ). Also, as the article mentions, turboprops (essentially jet engines connected to a propeller) already commonly use gearing. I guess you can think of it as a turboprop with a duct. The reality is probably just that this is a solvab…

> High-speed gearing is indeed very difficult, but jet engines already typically have two separate, concentric rotating units [...]

Yes, everyone knows that, but the spools are not connected by a set of gears as they are in the P&W's new engine.

> Also, as the article mentions, turboprops (essentially jet engines connected to a propeller) already commonly use gearing. I guess you can think of it as a turboprop with a duct.

The new engine is ALSO unlike most installations of turboprop engines in that the fan is driven by the power spool, not a free turbine. The free turbine (in turboprops that have them), which powers the reduction gears for the propeller, runs at a much lower speed than the power turbine.

Re: A Little Gear That Could Reshape the Jet Engine

#70

Post by pbowyer »

GauntletWizard wrote: post #3
JSeymourATL wrote: post #2

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

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.

> I'm certain that were human life so cheap, Pratt and Whitney would have a much shorter dev cycle, too.

I read a book recently about the history of Supermarine, and what jumped out was the attrition rate of their test pilots. Ditto for the post-war British jet industry.

There is a trade-off point between safety and fast development, but I'm glad we've moved to the side of safety.

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