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
Subscription Required
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
1 Comment
Posted on January 3, 2017 by Scott Hamilton
Airbus, ATR, Boeing, Bombardier, CFM, Comac, CSeries, E-Jet, Embraer, Etihad Airways, Farnborough Air Show, GE Aviation, Irkut, Leeham News and Comment, Middle of the Market, Mitsubishi, Pratt & Whitney, Premium, Rolls-Royce, Sukhoi
Airbus, Boeing, Bombardier, CFM, Comac, Embraer, GE Aviation, Irkut, Mitsubishi, Pratt & Whitney, Rolls-Royce, Sukhoi
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
5 Comments
Posted on December 16, 2016 by Bjorn Fehrm
Bjorn's Corner, CFM, GE Aviation, Pratt & Whitney, Rolls-Royce
CFM, CFM56, GE Aviation, Geared Turbo Fan, IAE, Pratt&Whitney, Rolls-Royce
The Boom SST engine problem, Part 4
By Bjorn Fehrm
Subscription required
Introduction
December 15, 2016, ©. Leeham Co: In our article series around the engine for a Boom SST, we established the thrust requirements for the engines in Part 3.
To fulfill these requirements, we have now designed four different engines. Three are of the type that Boom says it is considering, an engine that is based on an existing core.
Figure 1. Boom Technologies Boom Mach 2.2 45 seat airliner. Source: Boom.
We based these around a military core with the right characteristics for a low-to-medium bypass SST engine. The fourth engine is a custom-designed straight turbojet, very similar to the engine that propelled the only operational SST, the Concorde.
We will use the reference turbojet to understand the difference to a turbofan in this application and why the selection of an engine for a SST follows different rules than for a normal airliner.
Summary:
Read more
4 Comments
Posted on December 15, 2016 by Bjorn Fehrm
Future aircraft, Rolls-Royce
Boom, EJ200, Rolls-Royce, SST
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
6 Comments
Posted on December 9, 2016 by Bjorn Fehrm
Airbus, Bjorn's Corner, CFM, GE Aviation, Pratt & Whitney, Rolls-Royce
CFM, CFM56, GE Aviation, Rolls-Royce, Trent XWB
The Boom SST engine problem, Part 3
By Bjorn Fehrm
Subscription required
Introduction
December 08, 2016, ©. Leeham Co: Boom Technology and Virgin Atlantic plan to offer supersonic business class passenger traffic over the Atlantic. We covered the type of challenges that this poses in previous articles. The most difficult challenge is finding a suitable engine.
Figure 1. Boom Technologies Boom Mach 2.2 airliner with 45 seater. Source: Boom.
We described what type of engine will be required in Part 2 of the series. We will now investigate what thrust this engine must deliver at different parts of the flight envelope.
How “draggy” is supersonic flight? Why did Concorde and the Tu-144 need afterburners for the acceleration to cruise speed?
Summary:
Read more
1 Comment
Posted on December 8, 2016 by Bjorn Fehrm
Boeing, Future aircraft, Rolls-Royce
Boom SST, Concorde, Rolls-Royce, SST
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
13 Comments
Posted on December 2, 2016 by Bjorn Fehrm
Airbus, Bjorn's Corner, Boeing, CFM, GE Aviation, Pratt & Whitney, Rolls-Royce
Airbus, Boeing, CFM, CFM56-5, GEnx-1B, GEnx-2B, Rolls-Royce
The Boom SST engine problem, Part 2
By Bjorn Fehrm
Subscription required
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:
Read more
2 Comments
Posted on December 1, 2016 by Bjorn Fehrm
Future aircraft, GE Aviation, Pratt & Whitney, Rolls-Royce
Boom SST, CFM, GE Aviation, GEnx-1B, GTF, LEAP, Pratt & Whitney
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:
Read more
6 Comments
Posted on November 28, 2016 by Bjorn Fehrm
Future aircraft, GE Aviation, Rolls-Royce
Boom SST, EJ200, GE Aviation, GEnx-1B, Rolls-Royce, SST engine
Resurgence for ERJ-145
Note: Nov. 24 and 25 are Thanksgiving Holidays in the US. Our next post will be Monday.
Subscription Required
Introduction
Nov. 23, 2016, © Leeham Co.: The 50-seat regional jet market is dead.
That’s the conventional wisdom.
Well, not quite.
Embraer ERJ-145 is finding new life with regional airlines.
Piedmont Airlines, a unit of American Airlines, is adding the 50-seat Embraer ERJ-145 to its fleet. Eleven joined so far and next year the company plans to add 24 more.
CommutAir, an operator for United Airlines, is adding the same aircraft type to its fleet. Forty of them.
Why the mini-resurgence?
Low fuel prices and cheap airplanes.
Summary
Read more
1 Comment
Posted on November 23, 2016 by Scott Hamilton
Airlines, American Airlines, Bombardier, Embraer, Premium, Rolls-Royce, United Airlines
American Airlines, Aviation Specialists, Bombardier, CommutAir, CRJ-100, CRJ-200, Embraer, ERJ-145, Joel Hussey, Piedmont Airlines, Rolls-Royce, Tradewind Capital, United Airlines
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
15 Comments
Posted on November 18, 2016 by Bjorn Fehrm
Bjorn's Corner, CFM, GE Aviation, International Aero Engines, Pratt & Whitney, Rolls-Royce
CFM, GE Aviation, Pratt & Whitney, Rolls-Royce, Safran, Silvercrest, Turbofan
Email Subscription
Associations
Aviation News-Commercial
Commentaries
Companies-Commercial
Companies-Defense
Engines
Resources
YouTube
Archives