Bell 525 Relentless N525TA makes its first flight, 1 July 2015. (Bell Helicopter)
1 July 2015: Bell Helicopter’s new medium transport helicopter, the Model 525 Relentless, N525TA, made its first flight at Bell’s assembly plant in Amarillo, Texas. Test pilots Troy Caudill and Jeff Greenwood were in the cockpit.
The Bell 525 is the first helicopter to use fly-by-wire flight controls. Side stick controllers replace the customary cyclic and collective controls. For the first time for Bell, the 525 uses a five blade main rotor and four blade tail rotor.
Bell 525 Relentless prototype, N525TA.
The helicopter is designed to be operated by two pilots and carry up to 18 passengers. It is powered by two General Electric CT7-2F1 turboshaft engines, each rated at 1,714 shaft horsepower, maximum continuous power, and 1,979 shaft horsepower for takeoff.
N525TA during a test flight.
The Model 525 is the largest helicopter built by Bell. It has an overall length of 64.81 feet (19.75 meters) with rotors turning. The fully-articulated main rotor has a diameter of 54.50 feet (16.62 meters) and rotates counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) The mast tilts forward 5°. The four bladed tail rotor is mounted on the left side of a pylon and rotates clockwise when viewed from the helicopter’s left side. (The advancing blade is below the axis of rotation.) It has a diameter of 10 feet (3.05 meters). The pylon is canted to the left at 15°. The 525 Relentless has a maximum gross weight of 20,000 pounds (9,072 kilograms).
The Model 525 has a maximum cruise speed of 160 knots (184 miles per hour/296 kilometers per hour), and maximum range of 580 nautical miles (1,074 kilometers). At its maximum gross weight the helicopter can hover in ground effect (HIGE) at 10,700 feet (3,261 meters), and out of ground effect (HOGE) at 8,100 feet (2,469 meters).
The prototype Bell 525 Relentless, N525TA, in cruise flight. (Bell Helicopter)
N525TA was destroyed during a test flight approximately 30 miles south of Arlington, Texas, 11:48 a.m., 6 July 2016. While conducting a test to determine never exceed speed (VNE) for single-engine flight, the 525 was flying 185 knots (213 miles per hour/343 kilometers per hour) at 1,975 feet (602 meters), the main rotor blades “departed their normal plane of rotation” and struck the nose and tail. The two test pilots on board, Jason Cori Grogan and Erik Allan Boyce, were killed. Both were majors in the United States Marine Corps Reserve, assigned to HMLA 773. Each pilot was a graduate of the U.S. Naval Test Pilot School.
The National Transportation Safety Board (NTSB) determined that the Probable Cause was:
A severe vibration of the helicopter that led to the crew’s inability to maintain sufficient rotor rotation speed (Nr), leading to excessive main rotor blade flapping, subsequent main rotor blade contact with the tail boom, and the resultant in-flight breakup. Contributing to the severity and sustainment of the vibration, which was not predicted during development, were (1) the collective biomechanical feedback and (2) the attitude and heading reference system response, both of which occurred due to the lack of protections in the flight control laws against the sustainment and growth of adverse feedback loops when the 6-hertz airframe vibration initiated. Contributing to the crew’s inability to maintain sufficient Nr in the severe vibration environment were (1) the lack of an automated safeguard in the modified one-engine-inoperative software used during flight testing to exit at a critical Nr threshold and (2) the lack of distinct and unambiguous cues for low Nr.
There are currently three 525s undergoing flight testing. The Federal Aviation Administration certified the Bell 525’s CT7 engines in March 2019.
The number three Bell 525 Relentless prototype, N525BN, first flew 22 April 2016.
The prototype Lockheed C-5A Galaxy, 66-8303, at Marietta, Georgia, 30 June 1968. (Bettmann/CORBIS)Lockheed test pilot Leo J. Sullivan. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)
30 June 1968: At 7:47 a.m., Eastern Daylight Time, the first Lockheed C-5A Galaxy transport, serial number 66-8303, took off on its maiden flight at Marietta, Georgia. Chief Engineering Test Pilot Leo J. Sullivan and test pilot Walter E. Hensleigh, flight engineer Jerome H. Edwards, and E. Mittendorf, flight test engineer, made up the flight crew. U.S. Air Force test pilot Lieutenant Colonel Joseph S. Schiele was also on board.
The C-5A weighed 497,000 pounds (225,435 kilograms) at takeoff. After a 3,800 foot (1,158 meters) takeoff roll, it lifted off at 123 knots (142 miles per hour/228 kilometers per hour). It remained in takeoff configuration while it climbed to 10,000 feet (3,048 meters) at 140 knots (161 miles per hour/259 kilometers per hour). The flight lasted 1 hour, 34 minutes. On landing, the Galaxy’s touchdown speed was 116 knots (133 miles per hour/215 kilometers per hour).
Lockheed C-5A Galaxy 66-8303 during its first flight. (Code One Magazine)
The Lockheed C-5A Galaxy (Lockheed Model L-500) is a long-range, heavy lift military transport with high, “shoulder-mounted” wings and a “T-tail.” It has a flight crew of two pilots, two flight engineers and three load masters. The airplane’s cargo compartment can be accessed by a ramp at the rear of the fuselage, and the nose can be raised to allow cargo to be loaded from the front. The wings’ leading edges are swept to 25°. Four turbofan engines are mounted on pylons beneath the wings. The landing gear has 28 wheels in five units, and can “kneel” to bring the cargo deck closer to the ground for loading and unloading.
The C-5 is a truly giant aircraft. It is 247 feet, 10 inches (75.540 meters) long with a wingspan of 222 feet, 9 inches (67.894 meters) and overall height of 65 feet, 1 inch (19.837 meters). The cargo compartment has a height of 13 feet, 6 inches (4.115 meters) and width of 19 feet (5.791 meters). It is 143 feet, 9 inches (43.825 meters) long. The C-5A has a maximum takeoff weight of 840,000 pounds (381,018 kilograms) and a maximum cargo weight of 270,000 pounds (122,470 kilograms).
A McDonnell Douglas KC-10 Extender refuels a Lockheed C-5A Galaxy. (U.S. Air Force)
The C-5A, C-5B and C-5C are powered by four General Electric TF-39 high-bypass turbofan engines, rated at 43,000 pounds of thrust, each. The C-5M uses four General Electric F138 engines rated at 51,250 pounds of thrust, each.
The Galaxy has a cruise speed of 0.77 Mach and maximum speed of 0.79 Mach. Its service ceiling is 35,700 feet (10,881 meters) and its unrefueled range is 2,400 nautical miles (3,862 kilometers).
Lockheed C-5A Galaxy 66-8304, the second airplane, during a test flight near Edwards Air Force Base, California. (U.S. Air Force)
Lockheed produced 81 C-5A Galaxy transports for the U.S. Air Force between 1969 and 1973. These were followed by 50 C-5Bs. Two C-5As were modified to C-5Cs to carry larger “space cargo.” Remaining C-5s in the fleet are being modified to an improved C-5M Super Galaxy variant.
The first prototype C-5A, 66-8303, was destroyed by and explosion and fire after being defueled at Dobbins Air Force Base, 17 October 1970. One person was killed.
An M1A1 Abrams Main Battle Tank being loaded on the forward cargo ramp of a Lockheed C-5M Super Galaxy. The transport’s nose has been raised to provide loading access from the front of the airplane. The tank weighs 139,081 pounds (63,086 kilograms). (Roland Balik/U.S. Air Force)
North American Aviation Engineering Test Pilot Louis Wait with a wind tunnel model of the NA-73X. (North American Aviation, Inc.)
28 June 1940: A ¼–scale mahogany model of the North American Aviation NA-73X, prototype of the Royal Air Force Mustang Mk.1, was tested in the Ten-Foot Wind Tunnel at the Guggenheim Aeronautical Laboratory of the California Institute of Technology (GALCIT) in Pasadena, California, from 28 June to 26 July 1940.
The Ten-Foot Tunnel was funded by a $300,000 grant from the Daniel Guggenheim Foundation. Construction of the Laboratory began in 1927 and the wind tunnel became operational in November 1929. A 15 foot (4.572 meter) diameter fan was capable of producing air speeds up to 200 miles per hour (322 kilometers per hour). The first complete scale model airplane to be tested was the Northrop Alpha.
Airships, airplanes, and structures (bridges, buildings) were tested in the tunnel. According to Caltech, the Douglas Aircraft Company used the facility more than any other manufacturer.
During World War II, a staff of sixty worked three shifts, seven days a week. A technician who worked there later said, “We had a tighter schedule than the tightest schedule anyone ever had.”
The wind tunnel’s test equipment was damaged by the Whittier Narrows Earthquake. It was closed in 1997 to be replaced by a new facility.
Model builders working on a scale model wing for use in NACA’s wind tunnels. (NASA)
26 June 1942: The Grumman XF6F-1, Bureau of Aeronautics serial number (Bu. No.) 02981, prototype for the Navy and Marine Corps F6F Hellcat fighter, with Grumman’s Chief Engineer and Test Pilot Robert Leicester Hall flying, made a 25-minute first flight at the Grumman Aircraft Engineering Corporation plant, Bethpage, Long Island, New York.
The first Hellcat was powered by an air-cooled, supercharged, 2,603.737-cubic-inch-displacement (42.688 liters) Wright Aeronautical Division Twin Cyclone GR2600B676 (R-2600-10) two-row, 14-cylinder radial engine. This engine had a compression ratio of 6.9:1 and required 100-octane aviation gasoline. The R-2600-10 was rated at 1,500 horsepower at 2,400 r.p.m. at Sea Level, and 1,700 horsepower at 2,600 r.p.m. for takeoff. It turned a three-bladed Curtiss Electric propeller through a 0.5625:1 gear reduction. The R-2600-10 was 4 feet, 6.26 inches (1.378 meters) in diameter and 6 feet, 2.91 inches (1.903 meters) long. It weighed 2,115 pounds (959 kilograms).
Beginning with the second prototype, Bu. No. 02982, the Pratt & Whitney Double Wasp SSB2-G (R-2800-10) 18-cylinder engine became the standard powerplant. The R-2800-10 was an air-cooled, supercharged, 2,804.4-cubic-inch-displacement (45.956 liter), twin-row 18-cylinder radial engine with water injection. The engine had a compression ratio of 6.65:1 and was rated at 1,550 horsepower at 2,550 r.p.m. at 21,500 feet (6,553 meters), and 2,000 horsepower at 2,700 r.p.m. for takeoff, burning 100-octane gasoline. The engine drove a three-bladed Hamilton Standard Hydromatic constant-speed propeller with a diameter of 13 feet, 1 inch (3.988 meters) through a 2:1 gear reduction. The R-2800-10 was 4 feet, 4.50 inches (1.334 meters) in diameter, 7 feet, 4.47 inches (2.247 meters) long, and weighed 2,480 pounds (1,125 kilograms), each. The engine weighed 2,480 pounds (1,125 kilograms).
Grumman XF6F-1 Hellcat Bu. No. 02981 in flight. (Northrop Grumman)
The first prototype was quickly re-engined to the Pratt & Whitney radial and redesignated XF6F-3. Bob Hall flew it with the new engine on 30 July 1942. A few weeks later, 17 August, the Hellcat’s new engine failed and Hall crash-landed at Crane’s Farm. The airplane was moderately damaged and Hall was seriously injured.
Grumman XF6F-3 Bu. No. 02981 after crash landing in a field at Crane’s Farm, Long Island, New York, 17 August 1942. (Northrop Grumman)
The airplane was rebuilt and continued in the test program. It was eventually converted to the XF6F-4 with a two-speed turbocharged Pratt & Whitney Double Wasp 2SB-G (R-2800-27) which produced 2,000 horsepower at 2,700 r.p.m. It was armed with four 20 mm cannon.
The first prototype Hellcat was converted to the XF6F-4 configuration, seen here at NACA, Langley Field, Virginia in 1944. (NASA)
The Grumman F6F-3 Hellcat is single-place, single-engine fighter designed early in World War II to operate from the U.S. Navy’s aircraft carriers. It is a low wing monoplane monoplane of all metal construction. The wings can be folded against the sides of the fuselage for storage aboard the carriers. Landing gear is conventional, retractable, and includes an arresting hook.
The F6F-3 is 33 feet, 7 inches (10.236 meters) long with a wingspan of 42, feet 10 inches (12.842 meters) and overall height of 14 feet, 5 inches (4.394 meters) in three-point position. It has an empty weight of 9,207 pounds (4,176 kilograms) and gross weight of 12,575 pounds (5,704 kilograms).
A Grumman F6F Hellcat ready for takeoff from an Essex-class aircraft carrier, circa 1943. (U.S. Navy)
The F6F-3 Hellcat was powered by a Pratt & Whitney Double Wasp SSB2-G (R-2800-10W) engine with water injection, rated at 2,000 horsepower at 2,700 r.p.m. for takeoff, using 100/130 octane aviation gasoline. The normal power rating was 1,550 horsepower at 2,550 r.p.m. at 22,500 feet (6,858 meters). The engine drove a three-bladed Hamilton Standard Hydromatic constant-speed propeller with a diameter of 13 feet, 1 inch (3.988 meters) through a 2:1 gear reduction. The engine weighed 2,480 pounds (1,125 kilograms).
Two Grumman F6F-3 Hellcat fighters, Summer 1943. (U.S. Navy)
In clean configuration, the F6F-3 had a maximum speed of 321 miles per hour (517 kilometers per hour) at Sea Level, and 384 miles per hour (618 kilometers per hour) at 18,000 feet (5,486 meters). It could climb to 10,000 feet (3,048 meters) in 3.2 minutes, and to 20,000 feet (6,096 meters) in 7.0 minutes. The service service ceiling was 38,800 feet (11,826 meters). It had a combat radius of 335 nautical miles (386 miles/620 kilometers). The maximum ferry range was 1,540 miles (2,478 kilometers).
The Hellcat’s armament consisted of six air-cooled Browning AN-M2 .50-caliber machine guns, mounted three in each wing, with 2,400 rounds of ammunition.
The Grumman Hellcat was the most successful fighter of the Pacific war, with a kill-to-loss ratio of 19:1. It was in production from 1942 to 1945 and remained in service with the United States Navy until 1956. A total of 12,275 were built by Grumman at Bethpage. This was the largest number of any aircraft type produced by a single plant.
High humidity creates visible propeller tip vortices as this Grumman F6F-3 Hellcat prepares to takeoff from USS Yorktown (CV-10), November 1943. (U.S. Navy)
Robert Leicester Hall
Robert Leicester Hall was born at Taunton, Massachussetts, 22 August 1905. He was the son of Bicknell Hall, a mechanical engineer, and Estella Beatrice Lane Hall.
Hall attended the University of Michigan, graduating in 1927 with Bachelor of Science degree in Mechanical Engineering (B.S.M.E.).
In 1929 he went to work for the Fairchild Airplane Manufacturing Company at Farmingdale, New York. While there, Hall met his first wife, Eugenie, a secretary at the plant. They were married in 1930, and lived in a rented home on St. James Avenue, Chicopee City, Massachusetts. Their son, Robert Jr., was born 5 November 1931.
Granville Brothers Gee Bee Model Z, NR77Y, City of Springfield.
Also in 1931, Hall began working for Granville Brothers Aircraft at Springfield, Massachusetts. He designed the Gee Bee Model Z Super Sportster air racer. He left Granville Brothers in 1933 to go to work for the Stinson Aircraft Company in Dayton, Ohio. There he designed the Stinson Reliant.
A Stinson SR-8E Reliant, NACA 94, at the Langley Research Center, 5 August 1936. (NASA)
In 1936, Bob Hall became the Chief Engineer for the Grumman Aircraft Engineering Corporation, Bethpage, Long Island, New York. He designed the F4F Wildcat, F6F Hellcat, F7F Tigercat, and F8F Bearcat fighters, and the TBF Avenger torpedo bomber. As corporate vice president, he supervised the design of the F9F Panther and Cougar jet fighters.
Hall married his second wife, Rhoda C. Halvorsen, 18 January 1939, at New York City, New York.
Hall retired from Grumman in 1970. Two of his sons, Eric and Ben Hall, founded Hall Spars and Rigging of Bristol, Rhode Island.
Robert Leicester Hall died at Newport, Rhode Island, 25 February 1991, at the age of 85 years.
Grumman F6F-3 Hellcat, Bu. No. 4778, Long Island, New York, circa 1942. (Rudy Arnold Collection/NASM)
Grumman F6F-3 Hellcat Bu. No. 26108, Long Island, New York, circa 1943. (Rudy Arnold Collection/NASM)
Northrop XB-35 taking off at Northrop Field, Hawthorne, California. (U.S. Air Force)Max R. Stanley (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers))
25 June 1946: Northrop Aircraft, Inc., experimental test pilot Max R. Stanley, flight test engineer Dale Schroeder and Orva H Douglas, Jr., flight engineer, made the first flight of the Northrop XB-35 “Flying Wing,” serial number 42-13603. They took off from the factory’s airfield at Hawthorne, California, and flew the prototype bomber to Muroc Army Air Field (now, Edwards Air Force Base). The initial flight lasted 55 minutes.
The Los Angeles Times reported:
Gigantic Flying Wing Triumphs in First Flight
Northrop 110,000-Pound Superbomber Soars 44 Minutes, makes Perfect Landing
Unleashed into the future, a huge and spectral devilfish bellowed up from the earth yesterday and soared eastward toward the morning sun—Northrop’s malevolent Flying Wing superbomber on her maiden test flight, Forty-four minutes later the ship made a perfect landing at Muroc Army Airfield.
Eerie, almost supernatural, she trundled to the west end of Northrop’s mile-long Hawthorne runway as the sun burned away the morning mists.
Thundering Take-off
For 45 minutes she stood motionless, a 172-foot knife blade, while her four 3000 h.p. engines turned eight coaxial pusher propellers into life.Then at 10:29 a.m. her whirling blades fused into blurred disks. Her thunder enveloped the field.
Interminably she seemed to hug the ground as Test Pilot Max Stanley held her charging 110,000 pounds down past the hangars, past the flight line, past the midfield control tower.
Monster Leaves Ground
For 30 thudding heartbeats—and as many seconds—the fantastic silver monster strained at the shackles of earth, hurtling at more than 100 m.p.h. toward the end of the runway.
Then at 3000 feet Stanley eased back the yoke. Sunlight skipped beneath the spinning wheels and the Wing lifted into her element under perfect control.
Vanishes Into Haze
In another 60 seconds she vanished into the haze, her wheels still down as Stanley gently tested her sinews. Below, and to the right of his bubble canopy, Co-pilot Fred C. Bretcher stared ahead through plexiglas in the leading edge, and just aft of the pilot, Engineer O. H. Douglas watched her pulse in the needles of scores of instruments.
In an easy climb, Stanley took the superbomber to 10,000 feet over the flat lands between the San Gabriel Mountains and the sea and then banked her slowly north and inland toward Muroc.
Settles to Runway
At the Muroc test field, the strip was cleared and ready. Spectators watched the incredible ship circle once and then gently settle to the runway as gently as a tuft of cotton and roll to stop in 3000 feet.”She handled beautifully,” grinned Stanley.
The outgrowth of years of engineering, she followed the secret testing of a parade of small wings, and her designer, John K. Northrop, is confident she’ll carry more bombs farther and faster than any other airplane ever built.
Fourteen more of the giants will be built under Northrop’s contract with the Army.
—Los Angeles Times, Vol. LXV, Wednesday Morning, 26 June 1946, Page 1, Columns 5 and 6
The Los Angeles Daily News reported:
Flying wing passes tests
Everybody who had anything to do with it was happy today over the 44-minute maiden flight of Northrop’s flying wing.
The bat-like plane, a 104-ton monster bomber, met all expectations during the 85-mile flight from Northrop Field to Muroc Army Air Base.
“The wing handled just as I expected it would,” veteran test pilot Max Stanley declared after landing the giant ship. “We were delighted with its performance and the plane fully came up to our expectations.”
Officials of Northrop Aircraft, who witnessed the initial take-off, said the flight had justified their confidence in the wing.
The ship, a tailess airplane with a bat-like appearance, is the latest in a series of 15 Northrop designed flying wings and was built at a cost of $13,000,000 for the army.
—Daily News, Wednesday, 26 June 1946, Page 3, Column 1
The flight test crew of the Northrop XB-35 at Northrop Field, Hawthorne, California, 1946. Left to right, Dale Schroeder, flight test engineer; Orva H Douglas, Jr., flight engineer; and Max Stanley, test pilot. (Unattributed)
The XB-35 was designed as an aerodynamically efficient heavy bomber. It had a very unusual configuration for an aircraft of that time. There was no fuselage or tail control surfaces. The crew compartment, engines, fuel, landing gear and armament was contained within the wing. It was 53 feet, 1 inch (16.180 meters) long, with a wingspan of 172 feet (52.426 meters) and overall height of 20 feet, 1 inch (6.121 meters). The prototype weighed 89,560 pounds (40,624 kilograms) empty, with a gross weight of 180,000 pounds (81,647 kilograms).
The Wing defined the airplane. It had an aspect ratio of 7.4:1. The wing’s root chord was 37 feet, 6 inches (11.430 meters). The wing was 7 feet, 1.5 inches (2.172 meters) thick at the root. The tip chord was 9 feet, 4 inches (2.844 meters). There was 0° angle of incidence at the root, with -4° of twist, and 0° 53′ dihedral. The leading edge was swept aft 26° 57′ 48″, and the trailing edge, 10° 15′ 22″. The wing’s total area was 4,000 square feet (371.6 square meters).
This view of the first prototype Northrop XB-35, 42-13603, the “Flying Wing,” on the ramp at Muroc Air Force Base shows the pusher arrangement of four-bladed contra-rotating propellers. In the background, a turbojet-powered Northrop YB-49 is in a steep bank. (U.S. Air Force)
The XB-35 was powered by four air-cooled, supercharged and turbocharged 4,362.49 cubic-inch-displacement (71.49 liter) Pratt & Whitney Wasp Major TSB1P-RGD (R-4360-17 or -21) four-row 28-cylinder radial engines with a compression ratio of 7:1. The R-4360-17 was rated at 2,500 horsepower at 2,550 r.p.m at 40,000 feet (12,192 meters), and 3,000 horsepower at 2,700 r.p.m., for takeoff. It could maintain the takeoff rating to an altitude of 40,000 feet (12,192 meters) for Military Power. The engines were mounted completely inside the wing and were connected to a remote propeller drive unit by drive shafts. The engines were direct drive, while the propeller gear boxes had a 0.381:1 reduction ratio. The R-4360-17 was 5 feet, 7.00 inches (1.702 meters) long, 4 feet, 4.50 inches (1.334 meters) in diameter, and weighed 3,306 pounds (1,499.6 kilograms).
Northrop XB-35 42-13603 in flight with early contra-rotating propellers. (U.S. Air Force)
The propellers were dual three-bladed contra-rotating assemblies located in pusher configuration at the wing’s trailing edge. (These were quickly changed to four-bladed propellers, which were smoother in operation and more efficient.)
Northrop XB-35 42-13603. (U.S. Air Force)
The XB-35 had a cruising speed of 183 miles per hour (295 kilometers per hour) at 39,700 feet (12,100 meters) and maximum speed was 391 miles per hour (629 kilometers per hour) at 35,000 feet (10,668 meters). With a crew of nine, and another six relief crewmembers, the bomber had a range of 8,150 miles (13,116 kilometers).
The production Northrop B-35 would have been armed with twenty .50-caliber machine guns for defense and a maximum bomb load of 51,200 pounds (23,223 kilograms).
Underside of a Northrop XB-35. (U.S. Air Force)
The XB-35 was plagued by unresolved problems with the propeller gear boxes which eventually forced Jack Northrop to ground the aircraft until the engine and propeller manufacturers could come up with a solution, which was to change from piston to turbojet engines. That version became the YB-49. Because of the continuing problems, though, 42-13603 was grounded after only 19 flights, and with its sister ship, XB-35 42-38323, was scrapped in August 1949.
1 July 2015: Bell Helicopter’s new medium transport helicopter, the Model 525 Relentless, N525TA, made its first flight at Bell’s assembly plant in Amarillo, Texas. Test pilots Troy Caudill and Jeff Greenwood were in the cockpit.
