Coming of age

WILLIAM ROBINSON / BRISTOL

Bristol University aeronautical engineering student William Robinson's winning essay in the Flight International /Rolls-Royce Centennial Future of Flight competition argues that what we learned from Concorde is more important than what we lost with its demise

I am writing this essay, which looks at the prospects for global air travel in the coming decades, at a time that the aerospace community was widely perceived to have taken a step backwards in technology with the axing of Concorde. Is that unfortunate? I admit that the patriotic aeronautical engineer in me is saddened by Concorde's passing, but I believe that any societal step backwards - which is what many hardened aerospace professionals would have us believe it is - is merely a perception. By any sane or sustainable measure, society will be no worse off without Concorde, but what a way to show what we are capable of achieving! However, I do not believe that aircraft design will never depart from the tubular fuselage and plank-wings configuration that has hitherto served us so well. Concorde's demise merely represents the coming of age of civil aviation.

Daunted though I am at the prospect of individuals of unrivalled experience in their fields reading this piece, I am going to attempt to set out the future of civil air transport as I see it.

"Speed means business" was the rallying cry during Concorde's initiation. To a large extent, this was, and remains, true, but it was a flawed assertion in the context of Concorde. Nations around the world were not enamoured with the idea of sonic booms, rendering supersonic overland operation impossible for all practical purposes. Security concerns have increased check-in times and contributed to the already absurd idea of spending half the total travel time covering 100km (60 miles) to and from the airport and the other half covering 5,000km. The upshot of these and other factors (not least of which is cost) is that Concorde and with it, supersonic travel, is grounded - at least in its traditional form.

Meanwhile, back in "the real world", Airbus is busily cutting metal - sorry, GLARE (glassfibre reinforced aluminium) - on the first leviathan A380 (let us not forget that we would not have Airbus were it not for Concorde). Boeing, after a period of apparent indecision, has set its sights on launching the 7E7, whose "E" sums up the three key parameters dominating civil jet development: economy, efficiency and the environment. Scratch the surface of the glitzy marketing campaign for the 7E7 and the extravagant interior visions for the A380, however, and first-glance departures from the "norm" appear few and far between.

Indeed, the A380 is a full-length double-decker and the 7E7 has had cosmetic surgery in the nasal region and some refinements to its posterior, but the underlying concepts remain largely unchanged. The advances that really take these aircraft to the head of their respective packs are at a subsystem level. Weight savings due to new materials such as GLARE used in the A380 and Boeing's bold step of designing an almost all-composite structure result in reduced operating costs. Engine improvements are numerous and include the "more-electric engine" and the introduction of contra-rotating shafts to improve flow matching between stages. However, all these developments are incremental and, while they will offer substantial savings to operators, they are not going to change the face of air travel beyond recognition. So whatever happened to the grand ideas of blended wing body (BWB) and joined-wing airliner designs?

Almost all manufacturers of civil aircraft have, at some point, explored these possibilities and found that from a certain point of view - usually aerodynamics - the new configuration would be appreciably more efficient than conventional designs. Unfortunately, most of these new designs have an Achilles heel (and often more than one). BWB designs make a lot of sense in principle. Blurring the distinction between wing and fuselage may result in a less aerodynamically efficient shape because of increased wing thickness but with active boundary layer control, major improvements are said to be possible.

Greater compactness

BWB designs also give large payload-carrying capacity and greater compactness, which are increasingly important in a world of capacity-nudging airports. Research into the BWB configuration has suggested that it would be suitable only for medium-to-large aircraft (7E7/A380). Due to high programme risk, its debut market is likely to be towards the lower end of that size bracket, taking advantage of the likely larger number of units sold to offset high development costs. Added to these development costs and the level of risk are issues such as passenger acceptance of windowless cabins and proof to the regulatory bodies that this new configuration is safe.

After all, the "60ft" (18m) rule governing the maximum distance between exits in conventional designs would be inappropriate in the context of a BWB design. Such a design would therefore require wholesale rewriting of such regulations accompanied by exhaustive testing. With the introduction of the 7E7, however, any BWB appears to be several decades away. In addition, recent events have clearly demonstrated the fragility of demand for civil transport. A BWB programme is currently far too risky for either of the big manufacturers, who are aware of the airlines' tendency to run for the hills in times of crisis and revert to the conventional.

More likely as a medium-term alternative to conventional designs is the joined (or box) wing. It retains a largely conventional fuselage layout and broad commonality in design with a conventional wing, but offers significant structural weight savings due to the bracing effect of the upper wing, which reduces the bending moment reaction requirements at the wing roots. These designs also generate improvements in aerodynamic efficiency due to the lower wing profile and the possibilities for higher aspect ratio.

One significant selling point of the joined-wing design is that it would take up considerably less terminal ramp space than a conventional airliner. Challenges still exist in this solution but do not appear to be as hard to stomach as with the BWB - an important factor in a very conservative industry. Location of powerplants is not intuitively obvious and providing services such as catering vehicles and passenger air bridges will require some ingenuity. Due to reduced wing volume, it is unlikely that as much of the required fuel could be carried in the wings as with existing airliners and there would therefore be increased reliance on fuselage tanks with potential - though not insurmountable - implications for safety.

After all this, is there really a market for supersonic travel? Seizing on the fact that most Concorde passengers paid substantially more than the price of an equivalent first-class ticket, French manufacturer Dassault has identified a market for supersonic business jets. Dassault is striving to keep the performance of its new business jet at an achievable level. Its current design is to have a range of 7,400km (4,000nm) and the aircraft will cruise at Mach 1.8. While this is clearly slower than Concorde's M2, this lower speed drastically reduces aerodynamic heating effects, removing the need for far more exotic and expensive materials.

Dassault vision

Dassault predicts that although the aircraft will not have transpacific range, it will still be capable of knocking 6h off the Los Angeles to Sydney route (including a fuel stop) compared with today's subsonic business jets. Door-to-door from London to New York, however, the supersonic business jet is likely to be as quick as Concorde, since less time would be spent at airports which would be smaller and closer to the city centre.

With a range only slightly greater than Concorde, however, what will stop Dassault's vision grinding to a halt? This concept appears to be in a far healthier position than Concorde was, given that the strength of the sonic boom increases with aircraft size. Dassault's sonic boom may be acceptable, therefore permitting overland flight. In addition, its engines will be quieter as it is Dassault's intention to avoid the use of afterburners.

The scope of the challenges facing the industry extends far beyond technical developments. In Britain and other parts of the world where land for airports is at a premium and usually in the heart of built-up areas, growth is doubtless constrained, but efforts can be made to mitigate any adverse consequences. A little more joined-up thinking where surface access - particularly high-speed rail links - is concerned, would improve matters greatly. It would prevent valuable runway slots being taken up by innumerable small aircraft, which take up as much space on approach, landing and taxiing as an aircraft of several times the size. Aviation needs to be mindful also of its impact on the environment and in particular of its impact at altitude, which is not well understood.

Although far from exhaustive, this vision of the challenges of civil air travel has tried to encapsulate some of the key developments. From my standpoint - months from graduating - I see exciting times ahead. n

Source: Flight International