Introduction to Aircraft Design

INTRODUCTION

The design, manufacture and operation of aircraft are very complex and potentially risky activities. There is a natural tendency towards trusting tried and tested configurations, and adopting an evolutionary approach. There are many cases, however, of revolutionary design changes, such as the advent of the jet engine, or the delta wing. Revolution involves more risk, but can be very rewarding. The history of aircraft design has had many examples of excitingly innovative, not to say weird designs. A minority of these are successful, some marginally successful, but many have been failures, some of them disastrously expensive failures! This chapter will describe a number of different projects and attempt to classify the reasons that led to their difficulties.

On a more positive note, the chapter will conclude by describing a number of innovative designs that might have a great influence on the future of aeronautics – positively or negatively!

AIRCRAFT THAT SUFFERED FROM REQUIREMENTS THAT WERE TOO RESTRICTIVE, TOO AMBITIOUS OR WERE CHANGED DURING DEVELOPMENT

Ward [34] contains many examples of such projects from the depressing record of British aircraft developments since 1945, and several examples will be repeated here, both civil and military. Other sources were used for later aircraft.

The Hawker Siddeley Trident

This aircraft (Fig. 11.1) had many years of successful service in the UK and in China, and was a pioneer in the field of automatic landing, but sales were disappointing. British European Airways (BEA) were initially offered a short-haul jet transport, (the DH121) which would have carried 110 passengers over stage lengths of up to 1800 nmiles. The manufacturers’ projections in 1958 predicted sales of 550 aircraft. According to Ward [34] BEA had been examining market trends that showed a marked slip in 1958–9 and thus considered that the DH121 was too big. They required that the aircraft only have 97 seats over an 800 nmile range. The Trident was designed round this specification, as was the Spey turbo-fan engine. The aircraft satisfied the requirement, but it and the engine had limited development potential. The Boeing 727 design team developed a competing tri-jet to almost the same requirements as for the original DH121.