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Geared Turbofan

July 21st, 2018 at 12:35:03 AM permalink
Pacomartin Member since: Oct 24, 2012 Threads: 1068 Posts: 12569	Can anyone talk about the possibility of developing a geared turbofan with 40,000 to 50,000 lbf in thrust in five years? Geared turbofans greatly reduce stress as the fan blades no longer need to spin at supersonic speeds.

July 21st, 2018 at 3:15:50 AM permalink
odiousgambit Member since: Oct 28, 2012 Threads: 154 Posts: 5097	I'm your man! NOT! sorry for the wisecrack I'm Still Standing, Yeah, Yeah, Yeah [it's an old guy chant for me]

July 21st, 2018 at 7:25:36 AM permalink

Pacomartin

Member since: Oct 24, 2012
Threads: 1068
Posts: 12569

Wikipedia states that for Boeing's NMA a new 50,000 lbf turbofan could be proposed by GE Aviation/CFM International, Pratt & Whitney or Rolls-Royce plc with a bypass ratio of 10:1 or more and an overall pressure ratio over 50:1.

The General Electric GEnx --1B70 had a takeoff thrust of 69,800 lbf and a bypass ratio of 9.0 with a top-of-climb overall pressure ratio of 53.3

It sounds like they have already designed a 70K lbf engine, so how much harder could it be to design a 50K lbf engine. Unless the desire is to have a geared turbofan. AFAIK, no one has designed a geared turbofan with thrust over 33K lbf.

July 21st, 2018 at 8:47:06 AM permalink

Dalex64

Member since: Mar 8, 2014
Threads: 3
Posts: 3687

Well, I can think of a few potential challenges, which may or may not be what is holding them back.

Strength of the reduction gear assembly. It has some limit, which would be weaker than a fixed shaft.

Can fix that by making it physically larger - either a greater diameter so all of the parts are larger and stronger, or larger longitudinally to spread the load over a larger area. Or both. The problem with that is it will increase the power losses due to friction, and increase weight, and if it has to be too big, block the center airflow requiring a larger cowling and a sort of a half-duct/reduction cone.

Then, speaking of friction, there is the problem of lubrication and cooling, if it needs it, and how much.

Still, I don't think power loss is their concern, as it will probably still be quieter and more efficient than a traditional engine.

"Everyone is entitled to his own opinion, but not to his own facts." Daniel Patrick Moynihan

July 21st, 2018 at 3:19:21 PM permalink
Fleastiff Member since: Oct 27, 2012 Threads: 62 Posts: 7831	What about a fluid gear reduction? A bunch of lubricated ball bearings as a reduction drive?

July 21st, 2018 at 7:11:45 PM permalink
Dalex64 Member since: Mar 8, 2014 Threads: 3 Posts: 3687	I am not familiar with one of those, but a turbine-based one, like a torque converter, also has more limited torque capacity than reduction gears, and would require external cooling, having higher heat losses. "Everyone is entitled to his own opinion, but not to his own facts." Daniel Patrick Moynihan

July 22nd, 2018 at 7:42:43 AM permalink

Pacomartin

Member since: Oct 24, 2012
Threads: 1068
Posts: 12569

Airbus Americas president Barry Eccleston feels that arguing about configuration of the NMA is pointless because there are no geared turbofan engines above 33,000 lbf that is used on the A321LR.

Quote: Airbus Americas president Barry Eccleston

“Suppose Boeing or we decide to make a new Middle of the Market airplane. If we could actually agree on what that is, it is probably going to need an engine that is 50,000 lbs thrust. Don’t tell me 45, because the airplane is only going to grow, it’s going to need more thrust. It’s going to need 50 on day one anyway and probably more than that to grow over the life of the program,” said Eccleston.

“How many proven 50,000 lb thrust turbo fan or unducted fan engines are there right now? Do you think there will be by 2025, given the engine business today?

“A 50,000 lb engine with a gear box in the middle of it is a lot of shaft horsepower and a lot of heat. That’s an engineering challenge of a magnitude beyond producing a 30,000 lb engine. I think 2025 is probably a little aggressive to me. Twenty 27 is probably still a little aggressive. Twenty 30 maybe, but by then maybe you have an unducted fan anyway.
“The point is, none of have an engine to build an airplane around even if you could figure out what the airplane is.”
https://leehamnews.com/2016/10/12/airbus-boeing-agree-nma-now/

But all the larger jets do not use gears in their engines. I am trying to understand why he thinks that a geared turbofan engine is a requirement for the NMA. The NMA is supposed to cost only a little more than a single aisle jet, and that is the requirement for saying the market is 5000 jets

Quote: CFM not ruling out geared turbofan for Boeing NMA 18 JUNE, 2017

CFM International executives are not ruling out a geared turbofan concept as they consider architectures for an engine to power a new Boeing aircraft.

The GE-Snecma joint venture is evaluating "multiple" architectures and technologies for engines for Boeing's new midsized aircraft, a proposed concept for a family of 200-270 seat airliners with 5,000nm range that would enter service in the middle of the next decade.

"We're not ruling out an architecture," says Francois Bastin, executive vice-president and general manager of the CFM programme. "We've done a geared engine. We have no religion against the gear. For [the Leap engine programme], the gear was just not the right architecture."
In the late 1970s, GE participated in NASA's quiet clean short-haul experimental engine (QCSEE) programme, which led to testing of a geared turbofan. In the '80s, the manufacturer experimented with open-rotor engines featuring a power gearbox.

But Pratt & Whitney is asserting broad intellectual property ownership of geared turbofan technology. In late May, P&W president Bob Leduc promised to "enforce our rights" if another competitor, Rolls-Royce, proposed a geared turbofan for Boeing's NMA concept.

P&W's rivals in the engine industry, however, have not conceded the technology. To be sure, CFM has not said it is planning to propose a geared turbofan for Boeing's NMA, but is keeping its options open, at least publicly.

"The gear is itself not an [intellectual property]," Bastin says.