Grumman E-2X Hawkeye

By the 1990s the Grumman E-2 Hawkeye had already been about 30 years old. Also, at the time Grumman had spent considerable research resources into conformal antenna arrays such that the Navy requested that Grumman look into fitting a conformal array to the Hawkeye. Grumman began looking at ways to integrate the conformal array radar while maintaining most of the Hawkeye’s airframe commonality, landing gear and subsystems.

Grumman proposed the E-2X powered by the GE TF-34 turbofan (the same engine that powers the S-3 Viking and A-10). The conformal arrays would be fitted to the leading edges of the wing, fuselage sides, trailing edges and horizontal tail trailing edges. In order to house the array in the horizontal tail dihedral was removed and replaced by the same tail used in the C-2 Greyhound.

Removing the rotodome also had some effects to flying qualities when compared to the original E-2. longitudinal stability in the pitch axis necessitated a wing glove that also had additional fuel (which would make up for the fuel volume lost in the wings from antenna accommodation). The other major challenge in the E-2X was how to accommodate the TF-34 engines with changing the E-2C landing gear:

General Electric TF-34 Turbofan powers both the S-3 Viking and A-10 Warthog.
General Electric TF-34 Turbofan powers both the S-3 Viking and A-10 Warthog.

The solution was to “wrap” the TF-34 engine intake and exhaust ducts around the landing gear utilizing a split fan exhaust system…”

TF-34 cutaway drawing.
TF-34 cutaway drawing.

The resulting drag penalty would be overcome by using a slightly more powerful version of the TF-34.

Placement of the conformal array posed some unique problems. There were some problems with aircraft volume and weight distribution. The proposed number of transmitters posed weight and cooling problems resulting in additional complexity and therefore weight. Not to mention resulting changes to the flight control system based on the constraints of operating from an aircraft carrier.

Grumman's display model of the E-2X Hawkeye.
Grumman’s display model of the E-2X Hawkeye.

The E-2X was presented to the Navy and the E-2X program was shelved.

Source: The Aircraft Designers: A Grumman Historical Perspective.