TABLE 2-1 Lightweighting Attributes for Military Aircraft Systems

Capability Aircraft Type Summary
General
Attributes
Specific Attributes Fighters Transports
and
Bombers
Helicopters RPA / UAVs Commercial Transports Aircraft
(Tactical and
Transport)
Performance Speed
Maneuverability
Payload
Range
Effectiveness
Primary
1
Primary
1
Primary
1
Primary
1
Primary
2
Primary
1
Operational Supportability Fuel Consumption
Maintainability
Durability
Reliability
Repairability
Secondary 3 Primary
2
Primary
2
Primary
2
Primary
1
Primary
2
Survivability Ballistic Impact
Explosion
Damage Tolerance
Observability
Primary
2
Secondary
3
Secondary
3
Secondary
3
Secondary
3
Secondary
3

NOTE: RPA, remotely piloted aircraft; UAV, unmanned aerial vehicle.

However, at least two trends are forcing UAVs to become more reliable. When these aircraft begin to fly over populated areas, the potential for damage and injury to personnel on the ground when such aircraft fail in flight will be a concern. Moreover, the suite of sensors they carry is becoming increasingly expensive. UAV designers will need to begin paying as much attention to risk as designers of manned aircraft do. This risk tolerance must be traded off against the performance requirements for vehicles such as high-altitude, long-endurance (HALE) UAVs, where risk increases if design margins are reduced to achieve the lowest possible density, but flight over populated areas drives a desire for reduced risk. Generally speaking, lightweighting of military aircraft will therefore need to be done with an eye to retaining or improving survivability.

2.1.2 Historical and Current Lightweighting

Early work on composite and hybrid material systems in transport aircraft attempted to match their properties and design methods to those of aluminum. The results were nicknamed “black aluminum” structures, which ended up sacrificing many of the favorable characteristics of composites that had led to their adoption in the first place. For example, incorporating composites into structures originally designed for aluminum where transverse and shear stiffnesses had to be maintained meant that the tailored stiffness in bending of the composites could not be put to use.

Rotorcraft have also taken advantage of lightweight materials and structural concepts. Lightweight components for the engine and transmission housings have been studied but are not seeing widespread use today; however, lighter-weight materials and designs are finding their way into the airframe and the rotors of advanced rotorcraft.1 Composites with integral stiffening were examined in the NASA/Army-sponsored Rotary Wing Structures Technol-

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1 J.K. Sen and C.C. Dremann. 1985. “Design Development Tests for Composite Crashworthy Helicopter. Fuselage,” SAMPE Quarterly, Vol. 17, No. 1, October, pp. 29-39.



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