Leeham News and Analysis
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Bjorn’s Corner: Turbofan developments in 2017
By Bjorn Fehrm
January 06, 2017, ©. Leeham Co: Before we finish of our series on airliner turbofan technology, let’s spend this Corner on what will happen on the airliner engine front during 2017.
While there is no totally new engine that comes into the market during 2017 there are a number of new variants of existing engine families that will be introduced.
Figure 1. GasTurb principal representation of a three shaft turbofan like our reference Rolls-Royce Trent XWB. Source: GasTurb.
If we start with the engines for regional/single aisle aircraft and then climb the thrust scale, we will cover the engines in climbing thrust class.
Bjorn’s Corner; Turbofan engine challenges, Part 7
By Bjorn Fehrm
December 16, 2016, ©. Leeham Co: After the turbine comes the engine’s exhaust system. This is where the thrust characteristics of the engine are formed. It is also the environment that defines the back pressure for the fan and turbines. It’s therefore more high-tech than one thinks.
For the very high bypass airliner engines of tomorrow, the common fixed bypass exhaust of today (Station 18 in Figure 1) will not be acceptable. Variable exhaust areas will have to be introduced.
Figure 1. GasTurb principal representation of a three shaft turbofan like our reference Rolls-Royce Trent XWB. Source: GasTurb.
On engines that function in high supersonic speed, it gets really complex. Not only is the exhaust area variable, it must have a dual variation exhaust, a so-called Con-Di nozzle.
Bjorn’s Corner; Turbofan engine challenges; Part 6
By Bjorn Fehrm
December 08, 2016, ©. Leeham Co: We have now come to the turbine in our trip through a modern turbofan. The turbines make up the rear of the engine, before the propelling nozzle.
The turbines are the workhorses in the engine. They take the energy released by the fuel in the combustion chamber and convert it to shaft hp to drive the fan or compressors.
Figure 1. GasTurb principal representation of a three-shaft turbofan like our reference Rolls-Royce Trent XWB. Source: GasTurb.
The hotter they can operate, the better. They can then generate more hp on a smaller size turbine. The temperature of the gas entering the high pressure compressor is one of the key parameters of a gas turbine. It dictates the power efficiency of the core and how much work it can perform to drive the fan and the compressors. Read more
Bjorn’s Corner: Turbofan engine challenges, Part 5
By Bjorn Fehrm
December 02, 2016, ©. Leeham Co: We will now look at the combustor area in our series on modern turbofan engines. There is a lot of activity in this area, as it sets the level of pollution for the air transportation industry for some important combustion products.
We will also finish off the compressor part of our series by looking at the bleeding of cooling air for the engine and for servicing the aircraft with air conditioning and deicing air.
Figure 1. GasTurb principal representation of a three-shaft turbofan like our reference Rolls-Royce Trent XWB. Source: GasTurb.
The amount of air which is tapped from compressor stages for cooling and other purposes can exceed 20% of the core flow (some of the flow paths are shown in Figure 1). At that level, it has a marked influence on the performance of the engine. Read more
The Boom SST engine problem, Part 2
By Bjorn Fehrm
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Introduction
December 01, 2016, ©. Leeham Co: Boom Technology and Virgin Atlantic plan to offer supersonic business class passenger traffic over the Atlantic. We covered the number of challenges that this poses in recent articles. The most difficult challenge is finding a suitable engine.
We started the investigation into a suitable engine in the last article. A Supersonic Transport Aircraft (SST) needs an engine which is very different from the latest crop of high-performance airliner engines.
Figure 1. Boom Technologies Boom Mach 2.2 airliner with 45-seater. Source: Boom
The air entering the engine intake at Mach 2.2 is taken from standing still to a speed of 450m/s within a fraction of a meter. This raises the air pressure and temperature more than the combined intake/fan/low compressor does for a modern turbofan. The result is that the core’s high pressure compressor must adapt; it can’t have a high compression ratio (then things get too hot).
Add to that, that the engine must be slender. It can’t have a wide fan and therefore high by-pass ratio because the supersonic drag of such large engines would be too high.
Summary:
- The SST engine must be based on a core with a low pressure ratio.
- Such cores are no longer available in modern airliner engines.
- One must use cores from the military field of supersonic engines.
- We check what kind of engine can be constructed around such a core.
- Is the Boom SST mission then possible with an engine done with an existing core?
Pontifications: A fresh perspective at Boeing Commercial is sorely needed
By Scott Hamilton
Nov. 28, 2016, © Leeham Co.: Boeing last week named an outsider, Kevin McAllister, as the chief executive officer of Boeing Commercial Aircraft (BCA).
I think this has the potential to be an invigorating move.
McAllister comes to BCA from his position as CEO of GE Aviation Services.
I don’t know McAllister and have no opinion whether he will be good, bad or mediocre. But I do like the idea of bringing an outsider in to run BCA. (My insider favorites were Stan Deal and Beverly Wyse.)
Here’s why.
The Boom SST engine problem
By Bjorn Fehrm
Subscription required
Introduction
November 28, 2016, ©. Leeham Co: We covered Boom Technology’s and Virgin Atlantic’s plans to offer supersonic business class passenger traffic over the Atlantic in recent articles. In the first article, we focused on the problem areas that Boom technology must master.
The most difficult area is to find a suitable engine for the aircraft. Engines for long-range supersonic flight are quite different animals than the normal subsonic airliner engine. We will go through why the engines are different and give an example of how such an engine could look.
Figure 1. Boom Technologies Boom Mach 2.2 airliner with 45 seaters. Source: Boom.
By creating a concrete example of an SST engine for an aircraft the class of the Boom SST, it will be possible to understand if Boom’s claim that suitable cores are available holds water, and how realistic is it to make an SST engine from these.
Summary:
- An SST engine is very different from a modern engine for a long-range airliner.
- A high-performing long-range engine for a normal airliner has a high bypass and pressure ratio.
- A high-perfoming long-range SST engine for a supersonic airliner has a low bypass and pressure ratio.
- Intakes and exhausts on subsonic engine nacelles are simple.
- Intakes and exhausts on supersonic engine nacelles are not simple.
- Considering all these factors, we will design an engine system for the Boom SST to get a deeper understanding of the challenges involved.
Boeing’s Conner steps down, successor named from GE Aviation
Kevin McAllister, the new president and CEO of Boeing Commercial Airplanes. Boeing photo.
Nov. 21, 2016: Boeing today announced that Ray Conner will retire as CEO of Boeing Commercial Airplanes well ahead of his Dec. 31, 2017, contract date.
Kevin McAllister of GE Aviation Services was named as his successor.
Boeing said Stan Deal was named president and CEO of Boeing Global Services, a new business unit “to be formed from the customer services groups within the company’s existing commercial airplanes and defense, space and security business units.”
Conner’s message to employees is below.
Bjorn’s Corner: Turbofan engine challenges, Part 4
By Bjorn Fehrm
November 18, 2016, ©. Leeham Co: In our series on modern turbofan airliner engines, we will now go deeper into the compressor part. Last week, we covered the fundamentals of compressors. As compressors and turbines use the same principles, we also covered the fundamental working principles of turbines.
We also described that compressors are temperamental parts, which can protest to wrong handling with violent “burps” (burst stalls with the combustion gases going out the front of the engine) or end up in a rotating stall where it simply stops working.
Figure 1. Stylistic cross section of a two shaft turbofan with both axial and radial compressor. Source: GasTurb.
Turbines, on the other hand, are your robust companions. Aerodynamically they just work, albeit more or less efficiently dependent on what one asks them to do (mechanically it can be very different; we recently saw a turbine disintegrate with large consequences on an American Airlines Boeing 767 in Chicago). More on the turbines later.
In the GasTurb cross section of a two shaft turbofan in Figure 1, the engine has both an axial and a radial compressor. We will consider why engine designers combine these two for certain engine types. Read more
2017: the year ahead
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Introduction
Jan. 3, 2017, © Leeham Co.: The New Year is here and it doesn’t look like a good one for commercial aerospace, if measured against previous outstanding years.
There are some troubling signs ahead, piling on to a slowdown in orders from last year that didn’t even reach a 1:1 book:bill.
This year looks to be worse than last. Airbus and Boeing will give their 2017 guidance on the earnings calls this month and next. Bombardier and Embraer earnings calls are a ways off, when each will provide its guidance.
But LNC believes the Big Two in particular will be hard pressed to hit a 1:1 book:bill this year and may even struggle to match 2016 sales.
Boeing’s year-end order tally comes Thursday. Airbus’ comes on Jan. 11.
Summary
Read more
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Posted on January 3, 2017 by Scott Hamilton
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Airbus, Boeing, Bombardier, CFM, Comac, Embraer, GE Aviation, Irkut, Mitsubishi, Pratt & Whitney, Rolls-Royce, Sukhoi