Tag Archives: Raleigh Ellsworth Fletcher

27 February 1963

First flight of the Hughes YOH-6A prototype, N9696F, 27 February 1963. (Hughes Tool Company)
Raleigh Ellsworth Fletcher

27 February 1963: Hughes Tool Company, Aircraft Division, test pilots Raleigh Fletcher and James A. Vittitoe made the first flight of the prototype Model 369, serial number 13-0002. The helicopter received F.A.A. registration N9696F on 5 April 1963.

The Hughes Model 369 was built in response to a U.S. Army requirement for a Light Observation Helicopter (“L.O.H.”). It was designated YOH-6A, and the first aircraft received U.S. Army serial number 62-4211. It competed with prototypes from Bell Helicopter Company (YOH-4) and Fairchild-Hiller (YOH-5). All three aircraft were powered by a lightweight Allison Engine Company turboshaft engine. The YOH-6A won the three-way competition and was ordered into production as the OH-6A Cayuse. It was nicknamed “Loach,” an acronym of the initials, “L O H.”

Initially, the prototype had a tail boom with an airfoil-shaped cross section. Though this performed well in forward flight, it limited sideways flight to just 5 miles per hour. When replaced with a symmetrical cross section tail boom, sideways flight increased to 60 miles per hour (97 kilometers per hour).

The first prototype Hughes YOH-6A, N9696F, in final configuration. (Hughes Tool Company, Aircraft Division)

The YOH-6A was a two-place light helicopter, flown by a single pilot. It had a four-bladed, articulated main rotor which turned counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) Stacks of thin stainless steel “straps” fastened the rotor blades to the mast and also allowed for flapping and feathering. Hydraulic dampers controlled lead-lag. Originally, there were blade cuffs around the main rotor blade roots in an attempt to reduce aerodynamic drag, but these were soon discarded. A two-bladed semi-rigid tail rotor was mounted on the left side of the tail boom. Seen from the left, the tail-rotor rotates counter-clockwise. (The advancing blade is on top.)

Overhead photograph of a Hughes YOH-6. Note the blade cuffs. (U.S. Army)

The YOH-6A was powered by a T63-A-5 turboshaft engine (Allison Model 250-C10) mounted behind the cabin at a 45° angle. The engine was rated at 212 shaft horsepower at 52,142 r.p.m. (102% N1) and 693 °C. (1,279 °F.) turbine outlet temperature for maximum continuous power, and 250 shaft horsepower at 738 °C. (1,360 °F.), 5-minute limit, for takeoff. Production OH-6A helicopters used the slightly more powerful T63-A-5A (250-C10A) engine. The T63-A-5A is a 2-spool, reverse-flow, turboshaft engine with a 6-stage axial-flow, 1-stage centrifugal-flow compressor and 4-stage axial-flow turbine. 2 turbine stages (gas generator) drive the compressor section, while the other 2 stages (power turbine) drive the engine’s output shaft through a gear reduction section.

Hughes YOH-6A 62-4211 in its configuration during the three-way LOH competitive testing. (U.S. Army)
The Boeing AH-6 “Little Bird” (formerly McDonnell Douglas Helicopter Company) is a direct development of the Hughes Model 369.

© 2021, Bryan R. Swopes

30 September 1975

AV-02, the second prototype Hughes YAH-64 Advanced Attack Helicopter makes its first free hover at Palomar Airport, California, 30 September 1975. (Boeing)
AV-02, the second prototype Hughes YAH-64 Advanced Attack Helicopter, 74-22248, makes its first free hover at Palomar Airport, California, 30 September 1975. (Boeing)

30 September 1975: At Palomar Airport (CRQ), Carlsbad, California, Hughes Helicopter Company Chief Test Pilot Robert George (“Bob”) Ferry (LTC, USAF, Ret.) and Raleigh Ellsworth (“Bud”) Fletcher made the first flight of the YAH-64 Advanced Attack Helicopter prototype, U.S. Army serial number 74-22248. This aircraft was the second of three prototypes built by Hughes and was identified by the company as AV-02. AV-01 was a ground test prototype, while AV-02 and AV-03 (74-22249) were used for flight testing. The first flight took place one day before the first flight of the rival Bell YAH-63.

Robert G. Ferry, Chieft Test Pilot, Hughes Helicopters.

The YAH-64 was designed as a two-place, twin-engine ground attack helicopter. The pilots sit in tandem configuration like the earlier Bell AH-1G Huey Cobra. The prototype was 57.50 feet (17.526 meters) long, with rotors turning, and the fuselage had a length of 49.42 feet (15.063 meters). The overall height of 12.07 feet (3.679 meters). The four-blade fully-articulated main rotor turns counter-clockwise, as seen from above (the advancing blade is on the right), and has a diameter of 48.00 feet (14.630 meters). It turns at 289 r.p.m., giving the blades’ a tip speed of 726.36 feet per second (211.70 meters per second). The main rotor uses elastomeric lead/lag dampers and the blades are retained by laminated V-shaped stainless steel “strap packs” which are flexible to allow blade flapping and feathering. The main rotor is mounted to a hollow static mast with a concentric drive shaft inside.

The four-bladed tail rotor is unusual in that, rather than the blades being evenly spaced at 90° intervals, the blades are spaced at 55° and 125° angles. This allows for significant reductions in noise. The tail rotor is mounted on the left side of a pylon in a pusher configuration, and rotates clockwise as seen from the helicopter’s left (the advancing blade is below the axis of rotation). It has a diameter of 8.33 feet (2.539 meters) and turns 1,411 r.p.m. (tip speed, 727.09 feet per second/221.62 meters per second).

A stub wing provides additional lift in forward flight and can carry various combinations of guided missiles and rockets. It has a span of 16.33 feet (14.977 meters).

Dimensions diagram for Hughes YAH-64 Advanced Attack Helicopter prototype. (U.S. Army Aviation Engineering Flight Activity)
Dimensions diagram for Hughes YAH-64 Advanced Attack Helicopter prototype, Development Test 1 configuration. (Hughes Helicopter Company)

In the original configuration, the YAH-64 had a “T-tail” with the horizontal stabilizer attached to the top of the tail rotor pylon. This caused undesirable changes in pitch attitude during flight testing and was changed with the follow-on YAH-64A pre-production prototypes.

Hughes Helicopters YAH-64 prototype, 74-22248. (Vertical Flight Society)

The YAH-64 was powered by two prototype General Electric YT700-GE-700 turboshaft engines. These were rated at 1,536 shaft horsepower at 20,000 r.p.m., at Sea Level on a Standard Day. The helicopter carried fuel in two internal tanks with a total capacity of 353 gallons (1,336.25 liters). This gave the two prototypes a mission endurance of 2 hours, 42 minutes.

The two flight test aircraft, 74-22248 and its sister ship 74-22249, were the subject of extensive flight testing during the summer of 1976. At that time, the YAH-64 had an empty weight of 10,495 pounds (4,760 kilograms), loaded weight of 12,242 pounds (5,553 kilograms) and a maximum gross weight 17,900 pounds (8,119 kilograms).

The two YAH-64s were tested at Edwards Air Force Base and the nearby Naval Ordnance Test Station Chine Lake. Additional testing was conducted at Bishop, California (elevation 4,120 feet/1,256 meters) and Coyote Flats (9,500 feet/2,896 meters).

A pre-production YAH-64A Apache in flight, circa 1982. (U.S. Army)
A pre-production YAH-64A Apache in flight, circa 1982. (U.S. Army)

The helicopter could hover out of ground effect (HOGE) at its maximum gross weight at and altitude of 5,350 feet (1,631 meters) with an ambient temperature of 95 °F. (35 °C.) From an out of ground effect hover at 4,000 feet, it could climb vertically at 184 feet per second (56.1 meters per second). At maximum continuous power its cruise speed in level flight was 141 knots, slightly less than required by the Army. With one engine inoperative, the helicopter’s ceiling was 4,750 feet (1,448 meters). There was a 100 foot difference in altitude with the left and right engines.

The 30 mm Hughes XM 230 Chain Gun automatic cannon was installed on the YAH-64 with 90 rounds. The gun’s rate of fire was adjustable and it was set to 535 rounds per minute on the prototype.

The AH-64A Apache was approved for full production in 1982. In 1984, the Hughes Helicopter Company was purchased by McDonnell Douglas and renamed McDonnell Douglas Helicopter Company. A facility to produce the Apache attack helicopters, as well as other civil and military helicopters, was opened in Mesa, Arizona. In 1997, MDHC was acquired by Boeing.

937 AH-64A attack helicopters were built between 1984 and 1997, when the improved AH-64D Apache Longbow entered production. Many AH-64As were remanufactured to the AH-64D configuration. More that 2,000 Apaches have been built. While most were for the U.S. Army, they fly for at least 14 other countries.

The Hughes YAH-64, 74-22248, is in the collection of the U.S. Army Aviation Museum, Ozark, Alabama.

An AH-64 Apache Longbow 99-05097 over Iraq, 2005. This aircraft was originally AH-6A A Apache 84-24287, before being remanufactured at Mesa, Arizona to the Longbow configuration, (TSGT Andy Dunaway/U.S. Army)
AH-64D Apache Longbow 99-05097 over Iraq, 2005. This aircraft was originally AH-6A Apache 84-24287, before being remanufactured to the Longbow configuration at Mesa, Arizona. (TSGT Andy Dunaway/U.S. Army)

© 2016, Bryan R. Swopes