Could an NMA be made good enough, Part 3?

By Bjorn Fehrm

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Introduction

April 6, 2017, © Leeham Co.: After sizing the cabin of the NMA, the time has now come to size the fuselage. Can a fuselage be designed that gives an NMA “dual aisle comfort with single aisle economics”?

Figure 1. The NMA takes more and more the shape of a 767 replacement (A United 767-200). Source: United

We will investigate the dimensions, the drag and the weight of an NMA fuselage. It will be based on the cabin and design techniques we described in Part 2. We then compare the efficiency of the result with the fuselages of the Airbus A321LR and Boeing 767. This will show if the necessary efficiency can be achieved.

Summary:

  • It’s possible to design a dual aisle fuselage with the same perimeter per seat abreast as a single aisle fuselage.
  • This will make the central, cylindrical, section have competitive weight and drag characteristics.
  • The larger diameter of the dual aisle fuselage will increase the size of the tapered front and rear sections however.
  • It’s still possible for an NMA fuselage to be as weight-efficient as a single aisle fuselage, measured per transported passenger.

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Could an NMA be made good enough, Part 2?

By Bjorn Fehrm

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Introduction

April 3, 2017, © Leeham Co.: In the first part of our investigation on how good an NMA can be, we explored low weight and drag fuselage design. We will now continue with the design consequences for the fuselage construction and the cabin.

What drives whether one goes for an Aluminum or CFRP (Carbon Fiber Reinforced Polymer) fuselage?

Figure 1. The NMA takes more and more the shape of a 767 replacement (A United 767-200 pictured). Source: United.

What will be the typical dimensions for an NMA fuselage and what will be passenger capacities?

Summary:

  • An elliptical fuselage will force a CFRP design.
  • The fuselage door configuration will be critical for cabin capacity and flexibility.

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The Boom SST engine problem, Part 4

By Bjorn Fehrm

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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:

  • Supersonic flight requires engines with low frontal areas and low mass flows.
  • Should the engine be designed as for a normal airliner, the inlet drag would be prohibitive.
  • The engine also must have a low pressure ratio core; otherwise the energy of the fuel is wasted on non-productive work.

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The Boom SST engine problem, Part 3

By Bjorn Fehrm

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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:

  • Supersonic drag forces slender aircraft designs to minimize supersonic drag.
  • An SST needs to use a special climb technique to hold this and other drag factors low.
  • Passing the sound barrier and supersonic climb is demanding flight phases
  • Can a non-afterburning turbofan operate efficiently to master these phases and combat the supersonic drag?

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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.

airplane-1

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?

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The Boom SST engine problem

By Bjorn Fehrm

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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.

airplane-1

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.

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Will Boom succeed where Concorde failed?

By Bjorn Fehrm

November 17, 2016, ©. Leeham Co: Boom Technology plans to do a 45-seat airliner for supersonic passenger traffic with service entry by 2023. Richard Branson’s Virgin Atlantic has already placed an optional order for 10 units of the aircraft.

The idea is to fly 45 business class passengers between New York and London in 3 hours and 25 minutes. This means the Boom Super Sonic Transport shall be 10% faster than the Aerospatiale/BAC Concorde.

airplane-1

Figure 1. Boom Technologies Boom Mach 2.2 airliner with 45 seaters. Source: Boom.

What makes the Boom SST succeed where the Concorde failed?

We will look at the challenges that Concorde had and see how Boom SST plans to attack them. We will also discuss what the chances are that Boom SST can master these challenges. Read more

Russian-Chinese wide-body: The aircraft, Part 4

By Bjorn Fehrm

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Introduction

September 15, 2016, ©. Leeham Co: In Part 3 of this series, we identified the type and size of wing we would have on a new Russian-Chinese wide-body. It’s now time to go through all the considerations around the engines for the aircraft.

Russian-Chinese widebody

Figure 1. Concept for new widebody airliner. Source: United Aircraft.

The aircraft would enter the market around 2025. We would have to decide on what size engine that would be needed, what engines would be available at the time and could this project motivate any new engine developments.

Summary:

  • The Russian-Chinese wide-body as outlined would require engines in the size class of the Boeing 787-9/10.
  • GE and Rolls-Royce have been mentioned as engine suppliers. The question would be: will they offer updated 787 engines or new designs and will Russia compete with its announced engine project for the aircraft?

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Russian-Chinese wide-body: The aircraft, Part 2

By Bjorn Fehrm

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Introduction

September 01, 2016, ©. Leeham Co: In Part 1, we concluded that the existing Il-96 fuselage cross section would be suitable for a new Russian-Chinese wide-body. This means that a lot of experience and existing designs for fuselage sections can be re-used.

Russian-Chinese widebody

Figure 1. Concept for new wide-body airliner. Source: United Aircraft.

Most importantly, it means that mock-ups and cabin sections can be made early in the project to start work on new and better cabin equipment. This is an area where the partners really lag their western competitors.

We will now look at what aircraft capacities can be conceived with the existing Il-96-300 and -400 fuselages and what changes will be necessary to achieve the targeted sizes that Russia’s United Aircraft Corporation (UAC) and Commercial Aircraft Corporation of China (COMAC) have communicated.

Summary:

  • The IL-96 fuselage can be re-used for a Russian-Chinese wide-body.
  • The existing IL96-300 cabin is on the small side whereas the Il-96-400 cabin is a bit larger than needed.
  • The project will likely choose an intermediate size fuselage to reach the targeted 250 to 280 passenger capacity.

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Russian-Chinese wide-body: The aircraft

By Bjorn Fehrm

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Introduction

August29, 2016, ©. Leeham Co: We have now covered the capabilities of the joint venture partners for a Russian-Chinese wide-body and its possible market. Now we will look at what kind of aircraft such a cooperation can create, given technology and other constraints.

Russian-Chinese widebody

Figure 1. Concept for new wide-body airliner. Source: United Aircraft.

There have been bits and pieces leaked to media from Russia’s United Aircraft Corporation (UAC) and Commercial Aircraft Corporation of China (COMAC).

We will look at what has been said and combine that with our knowledge of existing and future technological capabilities of the parties to make predictions for what aircraft the project can produce.

Summary:

  • The Russian-Chinese wide-bodywill be made to cover the “small wide-body”market.
  • Initial size will be a 250-280 passenger wide-body
  • The aircraft will be a twin with engines from either GE or Rolls-Royce.
  • Range with 280 passengers will be 6,500nm.

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