Bjorn’s Corner: Aircraft engines in operation

By Bjorn Fehrm

January 20, 2017, ©. Leeham Co: We have now covered the technology around airliner turbofans. Now it’s time for the real stuff: their operational life. Most decisions that an engine designer does is about how the engine shall function in practice.

To understand a typical cycle of an airliner engine and the stresses it endures, we will follow an engine during a typical mission.

Figure 1. A principal picutre of a direct drive turbofan. Source: GasTurb.

We chose a single aisle mission because most flights are with single aisle aircraft and the cycle these fly is the most stressful for an engine. Read more

Boeing 737 MAX 10

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By Bjorn Fehrm

Introduction

January 17, 2017, © Leeham Co.: Boeing has given its sales team the “authority to offer” the 737 MAX 10. The aircraft is a stretched version of the 737 MAX 9, designed to compete more successfully with Airbus A321neo.

Boeing worked on the variant for the last year. It started off as a more ambitious change over the 737 MAX 9, but it turned out too expensive and would have taken too long to get to market. The variant that Boeing now offers to airlines is a simple stretch of the 737 MAX 9.

The backing down to a stretched MAX 9 solves the cost and timing problem, but will it solve the competitiveness problem? We make a first analysis.

Summary:
  • The offered 737 MAX 10 is a longer fuselage MAX 9.
  • The longer fuselage closes the cabin dimensions gap to the A321neo.
  • The 737 MAX 10 is longer and heavier than the MAX 9, affecting performance.
  • To save field performance, a change to the main landing gear was necessary.

Read more

Airbus sets new delivery record for 2016

By Bjorn Fehrm

January 11, 2017, ©. Leeham Co: Airbus Commercial Aircraft presented a new record in yearly deliveries at its Press Briefing in Toulouse today.  The division of an integrated Airbus (therefore Airbus Commercial Aircraft, ACA) delivered 688 aircraft during 2016, thereby beating its target of 650 aircraft for the year.

Airbus A321neo with Pratt&Whitney engines was certified end 2016. Source: Airbus.

Orders were also higher than expectations at 731 net orders, giving a Book to Bill of 1.06. The market, including LNC, widely expected Airbus to fall somewhat short of a 1:1 book:bill.

There were no formal forecasts given for 2017. ACA President Fabrice Bregier stated that he expects it to be over 700 deliveries but full details will given at the Airbus Group’s financial press briefing in February.

Read more

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.

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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
  • Wide-body sales remain weak.
  • Narrow-body backlogs and low oil prices continue to inhibit sales.
  • China, Middle East concerns emerging.
  • United Aircraft MC-21 and COMAC C919 begin flight testing.
  • Airbus A330neo, Boeing 787-10, Embraer E195-E2 and Mitsubishi Aircraft MRJ-70 roll-out and begin flight testing.
  • Airbus A321neo and Boeing 737 MAX 8 EIS.

Read more

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.

Read more

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.

trent-xwb-model-stations_

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

Bjorn’s Corner: Turbofan engine challenges, Part 4

 

By Bjorn Fehrm

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.

gasturb-graph

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

Bjorn’s Corner: Turbofan engine challenges, Part 3

By Bjorn Fehrm

By Bjorn Fehrm

November 12, 2016, ©. Leeham Co: In our trip through a modern turbofan airliner engine and its technologies, we looked last week at the engine intake and the fan. We now continue with the compressor parts.

As compressors and turbines use the same principles (but in opposing ways), we will look at these principles this week and how their roles in the engine create their special characteristics.

trent-xwb-model-stations_

Figure 1. Stylistic cross section of a three-shaft turbofan with section numbers. Source: GasTurb.

As before, to make things concrete, we use a GasTurb simulation of a Rolls-Royce Trent XWB 84k engine to look at practical data when needed. As before, I have no specific knowledge about the engine and will not use any data outside what is public information.

The GasTurb cross section of a three-shaft turbofan is shown in Figure 1. We will examine the sections between station numbers (22) and (3) and (4) and (5) in the general discussion of compressors and turbines. We will then look at some data for common compressors. Read more