Lockheed QT-2 / Q-Star
Faced with the military requirement for a quiet observation aircraft, Lockheed Missiles & Space Co. (LMSC) developed the "Q" Series Aircraft: QT-1 (conceived, but not constructed), QT-2 (N2471W and N2472W) later modified to QT-2PC configuration (#1 and #2), and Q-Star. Note: "QT: for Quiet Thruster.
The Q-Star Aircraft was LMSC's "House Aircraft" for evaluating "quiet recon" concepts. Eighteen propeller/reduction systems and other items were evaluated. It flew early versions "Black Crow" Sensors and was the first aircraft to use a rotary combustion chamber (Wankel) engine for primary power.
The QT-2 first flew in August 1967. Both were later converted to military aircraft for the Prize Crew OpEval in Southeast Asia. Arriving in South Vietnam just before the 1968 TET Offensive, they accumulated approximately 600 hours flying exclusively tactical night missions during the first three-month deployment. They continued to operate in Vietnam during most of 1968 (Prize Crew II) and were then transferred to the Navy (NTPS Pax. R.) as X-26Bs in 1969. The QT-2PCs were the first military aircraft to use "Starlight Scopes”.
The #1 ship is now at USAAM at Ft. Rucker, AL. The #2 ship was retroverted to SGS 2-32 configuration and is operated by Mile High Gliders in CO.
Lockheed Aircraft Corp. offered the rotating combustion engine its first chance to fly. Under a Navy contract, Lockheed was experimenting with ultra-quiet aircraft for undetected low altitude reconnaissance. Several air-frame configurations, were developed culminating in the QT-3. Basically the QT-3 (QT for quiet thruster) consisted of a highly modified Schweizer 2-32 sailplane equipped with art amidship mounted Continental 100 horsepower engine turning a large slow-turning propeller through a reduction drive and long overhead propeller shaft. The QT-3 yielded airframe and propellor noise so low that the most noticeable remaining sound was valve action in the engine. Endeavoring to eliminate valve noise, Lockheed's engineers seized upon the RC engine since it has no valves, only ports.
Replacing the air-cooled Continen-tal with an RC 2-60 U5 liquid cooled engine required extensive reengineering. A Corvette aluminum radiator was grafted to the nose and redesigned reduction gearing was required. A 5.34/1, two-stage 'V' belt reduction system reduced 6,000 rpm at the en-gine down to 500 propeller rpm. Only 185 horsepower was used in the Q Star due to carburetor limitations. Nevertheless, power was increased by 85% with only a 6% increase in airframe weight. A three blade 90-100in constant speed propeller converted power to thrust. Laminated birch was used for blade material but at least one propeller had a balsa wood core covered with glass fibre.
Throughout the QT project, Lockheed tested five 4-blade, two 6-blade, and two 3-blade props.
Flight testing revealed previously un-attainable levels of quiet flight. Compound muffling culminated in a discharge pipe pointing straight up. Residual noise was thereby directed away from the ground. As a test a Cessna 182 and the Q Star, both loaded to 2,600 pounds gross weight, were flown over the airport at 800 feet. The 182 was easily detectable by engine and propeller noise; Q Star was almost impossible to detect. Even at 400 feet the Q Star sounded only like leaves rustling in a light wind. In the cockpit, engine noise is similar to the hum of an electric motor and even then, most noise in the cockpit seemed to be aerodynamically originated.
Potential of the QT-2 / Q-Star was such that Lockheed produced a refined version for the US Army: The YO-3A.
Engine: 1 x Cont. IO-360, 154kW
Wingspan: 17.4 m / 57 ft 1 in
Length: 9.2 m / 30 ft 2 in
Wing area: 17.0 sq.m / 182.99 sq ft