DARPA's Morphing Program

While there is no concrete quantitative definition of the term "Morphing", The Defense Advanced Research Projects Agency DARPA defines Morphing Structures, for its applications as

Adaptable, time variant airframes, whose changes in geometry influence aerodynamic performance

DARPA's concept of a Morphing aircraft is a multirole aircraft that

NextGen Aeronautics and Lockheed Martin are working (and have produced initial prototypes of) the aircraft models. The NextGen version has sliding skin type of design like that of a chinese fan (shown in the below picture), which can extend to complete span and as well as contract to a smaller size producing a significant shape change.


Nextgen Aeronautics' Design of the Morphing Wing, Source: NewScientist

On the other hand, Lockheed Martin has a version that can flod itslef to a much smaller area. Hence this is the foldable wing type design of morphing. This particular design is inspired from a sea gull as it allows wing folding out of the plane of the span, putting a part of it in to the fuselage. They are right now, addressing the problem of exposing the joints to the air flow.


Lockheed Martin's Design of the Morphing Wing, Source: NewScientist

DARPA is using the cutting edge materials technology in developing the morphing technologies. Piezoelectric actuators (Compact Hybrid Actuators Program), having very good capacities operating at low frequencies for operation over periods of several seconds or even minutes to move the wing to a new configuration are being researched. These piezoelectric actuators can are also efficient at high frequencies.

About the SMAs, I quote Dr.Weisshaar from the interview (cited below) " There are new materials called Shape Memory polymers. The primary SMAs we use today are alloys like Nitinol, which have the stiffness of steel and relatively large strains of may be five percent, as well as responding to heat. But they have a lower modulus. So they are not good candidates for carrying large loads,they are good carrying low loads". Hence DARPA is planning to use them to make certain portions of the airframe out of these alloys. In case of morphing wing where we have large shape changes, they plan to use them as sealants to close open gaps.

More information can be had from NewScientist's interview with Dr.Terry Weisshaar

DARPA's efforts towards morphing program were motivated from its success in the "Smart Wing Program", an effort towards development of hingeless control with the aid of active materials.


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