Modular, morphing and reconfigurable aircraft
Each of these themes has the connecting idea that the aircraft need not be confined to a single design standard for its entire life. Modular aircraft design seeks to achieve this by connecting different modules together in a flexible and changeable way. Morphing aircraft achieve similar changes to configuration by reversible changes to the structural units in-situ. Re-configurable aircraft are effectively a sub-set of modular aircraft and have changes made by exercising one of a pre-planned series of possible changes to give a limited number of variants of the original design.
The potential mechanisms for achieving these changes are numerous. Modular aircraft (and their re-c0nfigurable sub-set) can be based on relatively changes to equipment loaded into pre-prepared bays in the aircraft. These may have profound importance to the aircraft mission systems but have relatively little effect on the aircraft flight characteristics.
More fundamental changes to the aircraft have been envisaged. These include pods that may be attached to provide different uses for the aircraft, power-plant change routines, individual passenger enclosures or personal seat units, and wing sets for different duties.
Each of these modular changes seeks to achieve a similar end – to provide the aircraft with more flexibility of use, to reduce its use in sub-optimum configurations, to increase its service deployment time or to reduce its load and unload times.
The degree to which they achieve these ends depends upon several factors:
- Is the aircraft type going to be used (mainly) in a single role?
- Is the "modularity overhead" (the excess of weight to achieve the modular changes) going to outweigh the advantages?
- Is the safety of the aircraft compromised?
- Is the cost going to be excessive?
Where the answer to these questions is negative the feature, at least potentially, will be successful.
Modularity concerns different usage for the aircraft. For many conventional airliners in European or US service this seems to have limited appeal since their operations are, for the most part, entirely uniform. Certainly the aircraft have varying load patterns and sometimes have large numbers of unfilled seats. The airlines constantly seek ways to improve their load factors. Those airlines with very focused routes, like budget airlines, generally have better load factors than general service airlines but in both cases the argument for a modular approach seems to be uncertain.
The concept is more relevant to aircraft with varying demands – operating from isolated strips and having to meet a number of different calls. Or aircraft operating throughout the year with demands for snow, land and sea operation – as might apply in parts of Canada, for example. This has been the philosophy that has prompted the design of the Gevers Genesis9 which is designed to operate selectively on all three surfaces. Other change versions might be for an optional cargo/passenger layout or proportion, or an optional passenger/fuel/ water layout, or a long/short range aircraft choice. Each of these has implications for the optimum design of aircraft and modular approaches might well be economical if presenting these choices would obviate the need for another aircraft to be purchased.
Keeping the weight and cost overhead of modularity as low as possible is clearly a challenge. This overhead arises from the provision of additional fixings and strong points that, on an integrated design, would be redundant.
The removal of engine modules (for their replacement by a more role-suitable engine) would be relatively straightforward but the exchange of load carrying sections would be more difficult. An extreme suggestion was to modularise the passenger space down to either single- or a few passengers. The conceptual benefits of this would perhaps lie in loading time and in tailoring the capacity to the number of passengers.
Such passenger pods would need to be attached to the main airframe in a way that maintained aircraft structural integrity that would in practice probably, although theoretically not necessarily, have the main load paths running around the pod constructed zone. This would leave the pods to provide for their own structural security and would also imply that services for passengers – heating, ventilation, pressurisation, in-flight services etc. would need to be connectable to the aircraft either via each pod individually or through a number of pods.
One of the benefits foreseen for passenger pods is that they could be used to transport passengers and their baggage from a remote point – often the home – directly to the aircraft assembly point. This would imply a possible transformation of the airport operating structure and might save very large sums as a result. From an aircraft operating perspective, however, the integrity of these pods would need to be assured in respect of key parameters.
These might concern the fixing points, service connections, outer skin, pressurisation safety margins and so on. This argues against individual or distributed ownership except by agencies able to maintain the pods correctly.
At a lower scale an example of modular design concepts is the personal seat idea. This imagines a seat unit that provides for the standard support of a passenger – connections to in-flight services etc – a luggage container and in-flight ready access supplies. The seat thus becomes the travelling support module for the passenger and can be transported by different means and transferred from one to the other and then to the aircraft where it would clip into a prepared docking station in the passenger compartment. In the aircraft it would require to be plugged into the supply system for entertainment etc but would obviate all other check-in processes because the seat and its contents would be checked-in and security cleared as a unit.
Morphing is an entirely different concept but having somewhat similar purposes. It envisages the use of flexible, moveable or adjustable elements of the structure to change the configuration of the air vehicle in flight. Among the simplest expressions of this idea are the several "swing-wing" aircraft that are in service. But more sophisticated means are also possible. DARPA has a number of projects concerned with aircraft structures and envisages a mixture of mechanical linkages and flexible skin structural elements to achieve much more adaptation than simple wing sweep-back changes. The Gevers Genesis incorporates an extendable wing in its concept that would allow cruise to take place with a more suitable wing form than the extended wing more suitable for landing and take-off. Various forms of adaptable and flexible materials are being researched. To date no morphing designs for large commercial aircraft have been flown.
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