Originally Posted by
WHBM
The different aerodynamic relationship between the back of the upper deck (original 747 length) and the wing leading edge was "discovered" to give an unexpected benefit, and led to the 747-300 and -400 having the upper deck extended to get the same benefit. I always thought Boeing were pretty good with aerodynamics, and can't quite relate to them suddenly discovering this after the event,
Boeing originally didn't intend for the upper deck to be used for passenger seating - so if was faired in as soon as practical after providing room for the flight deck, crew rest, lav, and a few seats for cargo handler types for the freighter version.
When they shortened the fuselage for the SP, they pleasantly discovered that the upper deck 'fairing' provided favorable 'area ruling' as the upper deck now merged into the wing - which provided better transonic drag characteristics. When the 747 was originally designed (mid 1960s), the area rule concept was still quite new and novel, and so wasn't considered in the original design. I think the B-1 design was the first aircraft (early 1970s) that really took advantage of area ruling.
The 747SP gives a good example of how the large commercial aircraft business has changed. Back then, production runs of a particular aircraft design were quite a bit smaller than what's typical today - so when Boeing sold an aircraft, the price was set such that about 50% went to actually building it, and the other ~50% covered the development costs and cert, and hopefully left a bit over for profit. As a result, although the 747SP wasn't exactly a cash cow, it reportedly at least paid for itself, and aircraft like the 727 (~1,800 produced) were real cash cows.
Today, the development and cert costs have soared (despite all that went wrong with the 737 MAX cert, it's far more difficult and costly to certify a new design that in was even 30 years ago), and the pricing pressures mean that the built price is a much higher percentage of the overall sales price. As a result, in order to pay back all the development and cert costs - and have some profit left over, you need to sell a
lot of that aircraft design.
As an example, Boeing didn't make any money on the 777-200LR (61 delivered). However, the -200LR paved the way for the 777F, which shares much of the design, and the 777F has been a commercial success (over 260 delivered and more than 50 unfilled orders).