Hacker News Reader

Comment by rurounijones | Hacker News Reader

Gearboxes in the Engines... I cannot quite figure out how that works since they are not driving an axle or anything... are they?

Any aerospace engineers in the house?

On plus side, if they work, more power to them. On the downside, sounds like a maintenance / reliability nightmare in the making.

[EDIT] May be of use: http://en.wikipedia.org/wiki/Geared_turbofan

View on HN

I know this article is focused on noise, but the most important part about this engine is the efficiency. The fuel savings alone from having the high pressure section running at peak RPM in any situation is incredible. Billions and billions of dollars in fuel savings for a modern fleet.

Think of it as an orbital reduction gear more than a transmission that allows two different sections of the same axel to spin at differen speeds.

Checkout fuel burn vs. other engines. [1] The maintenance cost ratios across an entire fleet versus the fuel savings make it an absolute no brainer for regional fleets.

Source: My father a DER at MTU Aero Engines who developed the geared turbofan with Pratt & Whitney. DERs develop and sign off repairs in accordance with FAA regulations. He was also certified is EASA repairs.

1- http://en.m.wikipedia.org/wiki/Pratt_&_Whitney_PW1000G

Edit: Double the

In this context, I think "DER" means Designated Engineering Representative (http://www.faa.gov/other_visit/aviation_industry/designees_d...). I had no idea, so I had to look it up.

That is correct. The short story here is the FAA simply can't keep up with the innovation so they certify a group of people that can certify a repair as safe, and effective. It can than be used, while the FAA eventually full approves the change. The DER assumes full responsibility for the repair, and it's safeness. There have been stressful Christmas eves when approving the duct taping of a loose part of a V2500 so a plane full of troops can make it home for Christmas. Don't worry, it was a single flight one direction approval (but it happens all the time)

they are not driving an axle or anything... are they?

They sure are, just not in the way internal combustion engines do. A turbofan is a turbine hooked up to a fan. The turbine does work by rotating a shaft, and the fan pushes extra air around it.

All engines have the potential to be maintenance / reliability nightmares. Over time we've learned how to make engines more efficient and more complex without failing often. This is just the next step - in a couple of decades, most passenger jets will have gearboxes.

The engine core (hot part) works best at a different speed than the fan part - fast and hot, vs slow and cool. hence they have a gearbox. But it's not like a cars gearbox, it has a single gear.

No, they don't have a gearbox (yet).

What the current generation of engines have is two or three co-axial shafts rotating at different speeds.

The difference in shaft speeds is achieved by varying the size, shape and placement of the turbine blades connected to the shaft, not with a gearbox.

(And a single gear in isolation would be pointless. By definition, the purpose of a gear is to mesh with another gear.)

Here's an informative video: http://www.youtube.com/watch?v=zy4A-z2WKhw

I think the counter-spin turbine is really innovative idea. I wonder if it makes a big deal in terms of efficiency.

http://youtu.be/zy4A-z2WKhw?t=7m3s

Aren't we talking about geared turbofans, as described in the article and http://en.wikipedia.org/wiki/Geared_turbofan ? Geared turbofans, unlike the ungeared GEnx, presumably have gears in gearboxes.

The person I replied to implied that all turbofan engines have gearboxes, that gearing was necessary to have the fan rotate at a slower speed than the "main engine". In reality, the vast majority of the turbofan engines currently used in commercial aviation do not have gearboxes. The engines referred to in the wikipedia article you cite are still in development or just entering production.

The wikipedia article explains the deets, but basically yes, the turbine at the back of the engine is connected to the fan at the front of the engine, and the compressor and whatnot, and the gearbox somewhat decouples the speed of the former and the latter. It would be a bit of a shame if said gearbox fails in flight, of course.

Without knowing a lot about geared turbofans, it would be cool to have a gearbox bypass such that if the gearbox fails, the engine could stop, engage the bypass, and restart in an emergency mode that's less efficient but gets thrust.

i know nothing about turbofans, geared or not, but i would guess that any kind of 'failure' of a gearing system at jet engine speeds means the entire thing is exploding, not just failing over to a backup system.

jet engine model made on a 3D printer: https://www.youtube.com/watch?v=6rX4xv5-NvE

Reply on news.ycombinator.com