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10.11 Summary

This chapter has focused on the upstream and downstream influences on architecture, which the architect must interpret and condense in order to reduce ambiguity. The architect must always be prepared to declare a current valid information set so that others can work, understanding that it might be corrected and updated. The influences presented in this chapter include:

An understanding of corporate strategy, so that the guidance on investment of resources is known to the architect, and the development can be aligned with major initiatives of the enterprise.
Close cooperation with marketing, so that stakeholders can be mutually appreciated, markets defined and segmented, and competition understood.
An understanding of the current regulation, a prediction of the anticipated regulation, and an approach to other pseudo-regulatory sources from standards and liability.
A thorough knowledge not only of the technology available and its readiness, but also of the process of infusing it into the system and the value it will create.
A working partnership with the implementation experts in the enterprise, so that they can be drawn in early, help formulate make/buy decisions, and engage suppliers when appropriate.
An understanding of the operational environment, including the nominal, off-nominal, commissioning, and decommissioning operation of the system.
A clear view of the evolution of the product, and of the relationship of the product to the platforms or other products with common sub-systems.
Application of the iterative Architecture Business Case Decision (ABCD) framework, a tool to integrate many of the key ambiguous upstream flows of information into one decision process, the Product Case.

The other major approach to reducing ambiguity is engagement with stakeholders, which is the subject of Chapter 11.

Box 10.4 Case Study: Architecture and Platforms: B-52 and B-2

As an example of architectural decisions related to legacy, product evolution, and product platforms, we discuss the architectural decisions in Figure 10.11, which shows a B-52 bomber and a B-2 bomber. There are many differences between the two aircraft, but which differences were decided early in their development? Which differences have the greatest impact on their performance envelopes?

Figure 10.11 Left: A B-52 bomber. Right: A B-2 bomber. What are the architectural differences? (Source: U.S. Air Force photo)

A major difference is the presence, on the B-52, of a tail, specifically horizontal and vertical control surfaces separated by a significant distance from the main lifting surface, the wing. The B-2 does not have any horizontal or vertical control surfaces other than those on its main wing; this has significant consequences for its stability in pitch (nose up and down) and yaw (nose left and right).

A second difference between these two aircraft is in engine placement. The B-2’s design uses concealed engines, which are helpful for reducing the radar signature of the aircraft, whereas the B-52 has under-wing engines. The B-2 engine placement is much more integral, whereas the B-52 visually suggests modularity. In fact, the B-52 has received several engine upgrades, because the clockspeed of engine technology has progressed faster than the structure of the aircraft.

The B-52 architecture is called a “tube-and-wing” architecture, whereas the B-2 architecture has been referred to as a “flying wing.” How do these two architectures compare in terms of their ability to scale to different sizes? Pictured in Figure 10.12 are two civil aircraft families, based on the two architectures.

It is a common practice for tube-and-wing aircraft to be designed in product families with a variety of seating capacities, often with the explicit intent of platforming (sharing components). The concept is that the wing is sized for the longest (and heaviest) variant; the wing produces the lift and therefore supports the weight of the aircraft in flight. The fuselage (the “tube”) is lengthened or shortened as needed. Because wings are expensive to optimize, they are frequently shared across the family with minor changes, the net result being that the wing is “overdesigned” for the smallest family member; it can produce more lift than that aircraft needs.

On the other hand, the family concept shown on the right in Figure 10.12 proposes a different scaling scheme. The flying wing is split in half along the centerline, with middle sections (shown in light gray) added to increase the seating capacity.

What, then, were the downstream influences on the product family in these two architectures? The architectural implications are significant. Figure 10.13 shows the lift distribution for the two aircraft, in dark gray. For the tube-and-wing architecture, the fuselage does not produce much lift. To lengthen the fuselage and add seating capacity, the wing must be enlarged to support the additional weight, which is why tube-and-wing aircraft families size the wing for the largest variant. To add seating capacity to the flying wing, a center section is added, but (crucially) that center section is also part of the wing, so it produces lift. The flying-wing architecture can more closely optimize the wing to the desired performance for each of its variants, whereas the tube-and-wing architecture will always struggle with overdesigned wings that are less than optimal for the smallest variant of the product family.

Figure 10.12 Left: The A350 product family. Right: A proposed “flying wing” civil transport family, more specifically referred to as a Blended Wing Body

(Source: (a) Copyright Airbus (b) Liebeck, Robert H., “Design of the Blended Wing Body Subsonic Transport,” Journal of Aircraft 41, no. 1 (2004): 10–25, reprinted by permission of the American Institute of Aeronautics and Astronautics, Inc. [14])

Figure 10.13 Lift distribution dark gray on a tube-and-wing architecture and a flying-wing architecture, showing that the wings of tube-and-wing aircraft must be sized for the heaviest variant, whereas for a flying-wing architecture, the lift scales with the size of the aircraft variant.

(Source: Robert H. Liebeck, “Design of the Blended Wing Body Subsonic Transport,” Journal of Aircraft 41, no. 1 (2004): 10–25)

Figure 10.13 Full Alternative Text

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Table of Contents for 10.11 Summary

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Table of Contents for
10.11 Summary