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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

#71

Post by jimbrusstar »

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.”

It's easy to dismiss Silicon Valley companies as trivial, but if nothing else, SV stands for a culture of experimentation. This, by contrast, sounds like an engineer's nightmare:

> “In other years we hid him [McCune] behind the curtain and slipped him some sandwiches so management wouldn’t know what the investment was,” he jokes.

Maybe a decades-long attention span wouldn't have been required in the first place if the company in question gave their engineers better support.

Re: A Little Gear That Could Reshape the Jet Engine

#72

Post by onion2k »

ams6110 wrote: post #56
onion2k wrote: post #5

Earlier quoted context omitted.

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.

A software test is equivalent to a testing small part in an engine design. The cost of failure is low. The cost of a full production test in an engine design is clear, but it's the equivalent of a product handover and acceptance testing in software. The cost of failing that test could well run to millions of dollars.

The only difference for a SaaS startup is that they're their own customer for product development (in the sense that they build and test in-house rather than someone else paying them to build a product). The cost of failure is still there, it's not measured.

Re: A Little Gear That Could Reshape the Jet Engine

#73

Post by ars »

jcoby wrote: post #61
ars wrote: post #55

Earlier quoted context omitted.

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).

Yes, I misread kW for W :( :(

They'll actually need some very high voltages to make this work. That's going to be an enormous challenge - even simple motor windings, what will you insulate them with?

15MW? That's some serious power, are you sure about that number?

Re: A Little Gear That Could Reshape the Jet Engine

#74

Post by iSnow »

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.

High-Tc superconducting cables?

Re: A Little Gear That Could Reshape the Jet Engine

#75

Post by iSnow »

BuffaloBagel wrote: post #65
ckozlowski wrote: post #33

Earlier quoted context omitted.

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.

Is this why on the Antonov-70 and the military Airbus, they have those strange curved multi-blade props?

Re: A Little Gear That Could Reshape the Jet Engine

#76

Post by ckozlowski »

iSnow wrote: post #75
BuffaloBagel wrote: post #65

Earlier quoted context omitted.

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.

Is this why on the Antonov-70 and the military Airbus, they have those strange curved multi-blade props?

The curving of the blades I don't think is intended to support faster blade speeds at all, but rather scoop air more efficiently. Computer modeling has enabled designers to develop much more advanced blade designs.

And BuffloBagel is right, I got that part wrong. I think what I was trying to say is that a turboprop supports faster aircraft speeds than a traditional engine. But yes, the propeller remains subsonic.

Unless you're experimenting with madness: https://en.wikipedia.org/wiki/Republic_XF-84H

Edit: So apparently the Tu-95 does have supersonic turboprops. But I think it's the only production aircraft with them. Also, it's loud as hell. https://en.wikipedia.org/wiki/Tupolev_Tu-95

Re: A Little Gear That Could Reshape the Jet Engine

#77

Post by dognotdog »

rm445 wrote: post #24
dognotdog wrote: post #12

It'd be interesting to know what exactly they are doing in the gearbox, apart from the flexible mount to absorb excess torque. New materials? Surface treatments? Special lubrication?

This article has much more detail: http://theflyingengineer.com/flightdeck/pw1100g-gtf/ The gearbox is described as the epicyclic type with the compressor driving the sun gear and the carrier of the five planet gears driving the fan. The article doesn't seem to identify any extra special sauce. It points out that geared turbofans have been used on an airliner in the past, and identifies some design trade-offs. "there…

Thanks, that article was indeed much better to understand what's going on. Still, as mentioned, high-speed gearing of the kind does offer some design challenges, but apparently its all secret sauce.

Re: A Little Gear That Could Reshape the Jet Engine

#78

Post by hvidgaard »

vxNsr wrote: post #68
jws wrote: post #36

Earlier quoted context omitted.

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.

Quite the accomplishment is a major understatement, if it is true.

Re: A Little Gear That Could Reshape the Jet Engine

#79

Post by pjc50 »

readams wrote: post #28

So basically this seems to be a extra-high-bypass turbofan achieved by gearing down the fan. But delayed hugely because giant megacorps move very very slowly.

"Move fast" certainly applies to jet engines, but "break things" results in lots of expensive high-velocity shrapnel.

Re: A Little Gear That Could Reshape the Jet Engine

#80

Post by jcoby »

ars wrote: post #73
jcoby wrote: post #61

Earlier quoted context omitted.

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).

Yes, I misread kW for W :( :( They'll actually need some very high voltages to make this work. That's going to be an enormous challenge - even simple motor windings, what will you insulate them with? 15MW? That's some serious power, are you sure about that number?

There really isn't a good way to rate turbines to hp. I did find this article [1] that says a 747 uses some 87000 hp in cruise across all 4 engines. That's approx 20000 hp per. It also says that's only 1/4 of the rated thrust it's capable of. I have no idea if you can say each of those engines is capable of 87000 hp or not since it's entirely dependent on speed.

If you watch agentjayz on YouTube he rebuilds turbojets that have been converted to become gas generators for power plants and some of those are easily capable of generating 30000 hp using tech from the 60s.

It really is phenomenal how much power turbine engines can make. There is a thread on the Concorde [2] that goes through a q&a session with the people who operated it. In that thread it says that the engines at idle consumed some 5 metric tons of fuel per hour per engine.

1: http://www.aerospaceweb.org/question/propulsion/q0195.shtml

2: http://www.pprune.org/tech-log/423988-concorde-question.html

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