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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.

Two Schweizer 2-32s (67-15345 and 67-15346) from the U.S. Naval Test Pilot School X-26 Program (USNTPS) were modified to QT-2 configuration (QT for Quiet Thruster) by the Lockheed Missiles & Space Co. (LMSC) and civil registered as N2471W and N2472W.
In 1967 the aircraft were modified by adding a Continental O-200 engine, V-Belt RPM reduction system, four-bladed fixed pitch wood (Fahlin) propeller, and airframe upgrades. The QT-2 first flew in August 1967.
After demonstrating quiet flight, the aircraft were again modified to military QT-2PC configuration, known only as Tail Numbers "1" and "2", with GFE avionics and camouflage for night operation. They were successfully evaluated in Southeast Asia (Prize Crew OpEval) for covert ("stealth") tactical airborne observation in the spring of 1968 (during Têt). 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 CrewII) 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”.
QT-2PC #1 in the Soc Trang, RVN Army Airfield Hangar in 1968
The two QT-2PCs were returned to USNTPS in 1969 and re-designated X-26Bs.
The #1 QT-2PC was re-designated "67-15345" and the #2 aircraft was used for spare parts.
The #1 ship is now at USAAM at Ft. Rucker, AL. The #2 ship QT-2PC N2472W was retro-verted 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 unattainable 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
Crew: 2


Engine: 1 × Continental O-200, 100 hp (75 kW)
Propeller: Ole Fahlin four-blade, 8 inch chord, fixed-pitch 100 inch diameter
Wingspan: 57 ft 1.5 in (17.37 m)
Wing area: 185 ft² (16.7 m²)
Wing aspect ratio: 18
Length: 30 ft 9 in (9.33 m)
Height: 9 ft 3 in (2.74 m)
Loaded weight: 2,500 lb (kg)
Fuel Capacity: 20 gallons (nominal)
Service ceiling: 13,000 ft (m)
Rate of climb: 200 ft/min (m/s)
Quiet cruise speed: 70 - 80 mph
Wing loading: kg/m² (lb/ft²)
Flight endurance: Planned = 4+ hours; demonstrated = 6.7+ hours
Crew: two




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