While superficially similar to the later F-117, the "Have Blue" prototypes were smaller aircraft, about one quarter the weight of the F-117, with a wing sweep of 72.5° and inward-canted vertical tails (inverse V-tail). Radar-absorbent material (RAM), developed in a Lockheed laboratory, was applied to the aircraft's flat surfaces – for the windscreen, special coatings were applied to give them metallic characteristics. The aircraft's gross weight of 9,200–12,500 lb (4,173–5,669 kg) enabled the aircraft to use the landing gear from the Northrop F-5 fighter. The aircraft's powerplants were two General Electric J85-GE-4As from the T-2C Buckeye. Because stealth took precedence above all else, the aircraft was inherently unstable. As a result, a quadruple redundant fly-by-wire (FBW) flight control system was integrated into the aircraft to give it normal flying characteristics. The flight control system was borrowed from the F-16. The overwing engine inlet was covered by a low-RCS grid; during takeoffs, when more air is needed, blow-in doors were constructed at the upper fuselage to admit additional airflow.