Bryan R. Swopes grew up in Southern California in the 1950s–60s, near the center of America's aerospace industry. He has had a life-long interest in aviation and space flight. Bryan is a retired commercial helicopter pilot and flight instructor.
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Captain Milburn Grant Apt, United States Air Force, with a Bell X-2. (U. S. Air Force)
27 September 1956: Captain Milburn G. (“Mel”) Apt, United States Air Force, was an experimental test pilot assigned to the Air Force Flight Test Center at Edwards Air Force Base, California. After Frank Everest and Iven Kincheloe had made twelve powered flights in the Bell X-2 supersonic research aircraft, Mel Apt was the next test pilot to fly it.
The X-2 was a joint project of the U.S. Air Force and NACA (the National Advisory Committee on Aeronautics, the predecessor of NASA). The rocketplane was designed and built by Bell Aircraft Corporation of Buffalo, New York, to explore supersonic flight at speeds beyond the capabilities of the earlier Bell X-1 and Douglas D-558-II Skyrocket.
In addition to the aerodynamic effects of speeds in the Mach 2.0–Mach 3.0 range, engineers knew that the high temperatures created by aerodynamic friction would be a problem, so the aircraft was built from stainless steel and K-Monel, a copper-nickel alloy.
The Bell Aircraft Corporation X-2 was 37 feet, 10 inches (11.532 meters) long with a wingspan of 32 feet, 3 inches (9.830 meters) and height of 11 feet, 10 inches (3.607 meters). Its empty weight was 12,375 pounds (5,613 kilograms) and loaded weight was 24,910 pounds (11,299 kilograms).
The second of two Bell X-2 supersonic research rocketplanes, 46-675, on its transportation dolly at Edwards Air Force Base, California, 1952. On 12 May 1953 this X-2 exploded during a captive test flight, killing Bell’s test pilot Jean L. “Skip” Ziegler. (NASA)
The X-2 was powered by a throttleable two-chamber Curtiss-Wright XLR25-CW-1 rocket engine that produced 2,500–15,000 pounds of thrust (11.12–66.72 kilonewtons)
Rather than use its limited fuel capacity to take off and climb to altitude, the X-2 was dropped from a modified heavy bomber as had been the earlier rocketplanes. A four-engine Boeing B-50D-95-BO Superfortress bomber, serial number 48-096, was modified as the drop ship and redesignated EB-50D.
The launch altitude was 30,000 feet (9,144 meters). After the fuel was exhausted, the X-2 glided to a touchdown on Rogers Dry Lake at Edwards Air Force Base.
Bell X-2 46-674 after drop from Boeing EB-50D Superfortress 48-096. (U.S. Air Force)
With Mel Apt in the cockpit on his first rocketplane flight, the B-50 carried the X-2 to 31,800 feet (9,693 meters). After it was dropped from the bomber, Apt ignited the rocket engine and began to accelerate. He passed Mach 1 at 44,000 feet (13,411 meters) and continued to climb. Apt flew an “extraordinarily precise profile” to reach 72,200 feet (22,007 meters) where he put the X-2 into a dive. The rocket engine burned 12.5 seconds longer than planned, and at 65,589 feet (19,992 meters) the X-2 reached Mach 3.196 (2,094 miles per hour, 3,377 kilometers per hour).
Milburn Apt was the first pilot to exceed Mach 3. He was The Fastest Man Alive.
Bell X-2 46-674 in flight over Southern California, 1955–56. Note the supersonic diamond-shaped shock waves in the rocket engine’s exhaust. (Bell Aircraft Corporation)
It was known that the X-2 could be unstable in high speed maneuvers. The flight plan called for Apt to slow to Mach 2.4 before beginning a gradual turn back toward Rogers Dry Lake where he was to land, but he began the turn while still at Mach 3. Twenty seconds after engine burn out, the X-2 began to oscillate in all axes and departed controlled flight. His last radio transmission was, “There she goes.” ¹
Mel Apt was subjected to acceleration forces of ± 6 Gs. It is believed that he was momentarily unconscious. Out of control, the X-2 fell through 40,000 feet (12,192 meters) in an inverted spin. Apt initiated the escape capsule separation, in which the entire nose of the X-2 was released from the airframe. It pitched down violently and Mel Apt was knocked unconscious again. He regained consciousness a second time and tried to parachute from the escape capsule, but was still inside when it hit the desert floor at several hundred miles per hour. Mel Apt was killed instantly.
Since 1950, Milburn G. Apt was the thirteenth test pilot killed at Edwards Air Force Base.
Wreckage of the Bell X-2, 46-674, in the Kramer Hills, east of Edwards Air Force Base. (U.S. Air Force)Wreckage of the Bell X-2, 46-674. (NASM 9A08208)
Milburn Grant Apt was born at Buffalo, Kansas, 8 April 1924. He was the third child of Oley Glen Apt, a farmer, and Ada Willoughby Apt.
“Mel” Apt enlisted as a private in the Air Corps Enlisted Reserve, United States Army, 9 November 1942. On 23 June 1943, Private Apt was appointed an Aviation Cadet. After completing flight training, Cadet Apt was commissioned a Second Lieutenant, Army of the United States (A.U.S.). He was promoted to First Lieutenant, A.U.S., 4 September 1945. Apt was released from active duty on 11 August 1946. On 10 October 1947, he was reclassified as a Second Lieutenant, Air Corps, United States Army, with date of rank 8 April 1945.
In February 1950, Lieutenant Apt, then stationed at Williams Air Force Base, Arizona, married Miss Faye Lorrie Baker of Phoenix. They would have two children.
Mel Apt earned a Bachelor of Science degree from the University of Kansas, Lawrence, Kansas, in 1951, and a second bachelor’s degree in aeronautical engineering from the Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio. He then attended the U.S. Air Force Experimental Test Pilot School at Edwards Air Force Base, California, graduating in September 1954. Apt was assigned to the Fighter Operations Branch, Air Force Flight Test Center, as a test pilot.
On 22 December 1954, Captain Apt was flying a chase plane during a test at Edwards. The test aircraft crash-landed on the dry lake and caught fire with its pilot trapped inside. Mel Apt, with his bare hands, rescued the other test pilot, saving his life. For this courageous act, he was awarded the Soldier’s Medal.
Captain Apt was posthumously awarded the Distinguished Flying Cross for his flight in the X-2. The medal was presented to his widow in a ceremony at Edwards in March 1957.
Captain Milburn Grant Apt, United States Air Force, was 32 years old at the time of his death. His remains were buried at the Buffalo Cemetery, Buffalo, Kansas.
Captain Iven Carl Kincheloe and Captain Milburn Grant Apt (seated in cockpit) with the Bell X-2 at Edwards Air Force Base, 1956. (Jet Pilot Overseas)
¹ Recommended: Coupling Dynamics in Aircraft: A Historical Perspective, by Richard E. Day, Dryden Flight Research Center, Edwards AFB, California NASA Special Publications 532, 1997.
27 September 1946: Geoffrey Raoul de Havilland, Jr., O.B.E., Chief Test Pilot of the de Havilland Aircraft Co., Ltd., and the son of the firm’s founder, was killed during a test flight of a prototype DH.108 Swallow, TG306.
Geoffrey de Havilland, Jr., in the cockpit of the second DH.108 Swallow prototype, TG306. (FLIGHT)
De Havilland had taken off from the company airfield at Hatfield at 5:26 p.m. for a planned 45 minute flight. Flying over the Thames Estuary, east of London, England, de Havilland put the swept-wing jet into a high-speed dive from 10,000 feet (3,048 meters). As it approached 5,000 feet (1,524 meters) at 0.88 Mach, (658 miles per hour, 1,060 kilometers per hour), the shock waves building up along the wings’ leading edges disrupted the air flow over the wings, causing them to stall. TG306 pitched violently downward. A NASA report called this “. . . an undamped violently divergent longitudinal pitching oscillation at Mach 0.875. . . .” The extreme aerodynamic loads cracked the main spar and both wings failed. The DH.108 crashed into Egypt Bay, Gravesend, Kent.
The wreck was located the following day. The body of Geoffrey de Havilland was found ten days later. He had suffered a broken neck and fractured skull as a result of his head striking the canopy during the violent oscillations of the aircraft.
(Grace’s Guide)
FLIGHT reported:
Geoffrey de Havilland was one of the outstanding test pilots in the country, and his work has played a vital part in the perfecting of such noteworthy types as the Mosquito, Hornet, Vampire and 108. His death is a serious blow not only to the company but to the country, for in the exploration of the unknown threshold of sonic flight, a combination of skill and cool courage are qualities demanding the utmost of test pilots. Geoffrey de Havilland had these qualities in a very high degree.
—FLIGHT and AIRCRAFT ENGINEER, No.1971, Vol. 1, Thursday, 3 October 1946, at page 364
De Havilland DH.108 TG306. (Unattributed)
The DH.108 was a single-seat, single-engine jet fighter prototype with swept wings and no conventional tail. It was similar in configuration to the Messerschmitt Me-163 rocket-powered interceptor. The first two prototypes, TG283 and TG306, were built using production English Electric DH.106 Vampire F.I fuselages. TG283 had a 43° sweep to the wings’ leading edge, while TG306 had a 45° sweep. The airplane was powered by a de Havilland Goblin 3 centrifugal-flow turbojet engine (a development of the Halford H.1) which produced 3,350 pounds of thrust (14.90 kilonewtons).
The first and third DH.108s also crashed. VW120 was destroyed on 15 February 1950 when it crashed after a dive. The left wing had separated and the pilot, Squadron Leader Stuart Muller-Rowland, also suffered a broken neck as a result of the airplane’s violent oscillations. On 1 May 1950, while conducting low-speed tests, TG283 went into an inverted spin. Squadron Leader George E.C. Genders, AFC, DFM, bailed out but his parachute did not open before he hit the ground and he was killed.
Geoffrey de Havilland, Jr., OBE, exits the cockpit of a DH.108 Swallow prototype. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)
Yves Rossy over the English Channel, 26 September 2008. (Times Online)
26 September 2008: Yves Rossy flew across the English Channel, 22 miles (35 kilometers) in 13 minutes, using his jet-powered wing. At 8,000 feet (2,440 meters) over Calais he jumped from an airplane and aimed for the cliffs of Dover. His only means of steering was by moving his head. After flying at speeds of 120 miles per hour (193 kilometers per hour), he parachuted to the ground at Dover.
“David Hempleman-Adams, left, with Saint John resident Jim Rogers on Sept. 26, 2003, just before the balloon launch.” (Kings County Record)
26 September 2003: At 2:38 a.m., Friday, David Kim Hempleman-Adams, O.B.E., lifted off from the athletic field of Sussex Elementary School, Sussex, New Brunswick, Canada, in his Rozière balloon on a four-day transatlantic flight. Hempleman-Adams was in an open 7 feet × 3 feet (2.1 × 0.9 meters) wicker basket.
Hempleman-Adam’s Cameron R-90 being prepared for takeoff on a previous transatlantic attempt, 27 June 2003, at Mount Pleasant, Pennsylvania. (AP Photo/Gene J. Puskar)
The balloon was built by Cameron Balloons, Ltd., Bristol, in 2000. It was a Cameron R-90, serial number 4751. The balloon was first registered 31 March 2000, as G-BYZX.
The R-90 is a Rozière balloon, which has separate chambers for helium and heated air. This allows the aeronaut to control the balloon’s buoyancy, but the hybrid type uses much less fuel than a hot-air balloon. The type is named after its inventor, Jean-François Pilâtre de Rozier. The Fédération Aéronautique Internationale places the Cameron R-90 in the free balloon sub-class AM-08, for mixed balloons with a volume of 2,200–3,000 cubic meters (77,692–105,944 cubic feet).
G-BYZX had a maximum takeoff weight of 2,654 kilograms (5,851 pounds).
Hempleman Adams had previously flown G-BYZX, then named Britannic Challenge, to the North Pole, on 3 June 2000. Following his transatlantic flight, he would use it to set a FAI World Record for Altitude of 12,557 meters (41,198 feet), 23 March 2004.
During the first day, Hempleman-Adams’ balloon gradually rose to an altitude of 8,000 feet (2,438 meters) as it drifted eastward. On the second day he was at 10,000 feet (3,048 meters), and on Day 3 he reached a peak of 14,000 feet (4,267 meters).
The weather was very cold, with rain and snow. Hempleman-Adams said that the average temperature during the flight was -12 °C. (10.4 °F.). Ice built up on the balloon’s envelope, increasing its weight. It became heavy enough that the balloon began to descend. Hempleman-Adams was unable to prevent the descent by using the propane burners to heat the air and increase buoyancy, and was forced to lighten the balloon by jettisoning six propane cylinders.
During the third day, the balloon was hit by the shock waves of a Concorde supersonic airliner as it passed overhead at 30,000 feet (9,144 meters). Hempleman-Adams felt a very abrupt, but fortunately, brief, descent as a result.
G-BYZX reached the southwestern tip of Ireland at 8:30 a.m., BST, on 29 September, completing the transatlantic phase of his flight. The balloon continued to drift eastward, and at 6 p.m. on 30 September, came to rest near Hambleton, Lancashire, England. The total duration of the flight was 83 hours, 14 minutes, 35 seconds.
Sir David Kim Hempleman-Adams, K.C.V.O., O.B.E., K.St.J., D.L., is an interesting guy. He is the first person to have completed the True Adventurer’s Grand Slam, by reaching the North and South Poles, the North and South Magnetic Poles, and to have climbed the highest mountains on each of the seven continents. The Fédération Aéronautique Internationale online database currently credits him with 49 world aviation records.
David Hempleman-Adams waves at the camera after landing in England, 30 September 2003.
by Captain Sean M. Cross, United States Coast Guard (Retired)
During the Vietnam conflict from 1967–1972, eleven U.S. Coast Guard Aviators voluntarily served with high honor and distinction with the U.S. Air Force Aerospace Rescue and Recovery forces in Southeast Asia in the dual role of aircraft commanders and instructor pilots. They regularly risked their lives flying into harm’s way to save airmen in peril of death or capture. Their significant contributions and exceptional performance were highly commended by the Air Force with the award of four Silver Stars, sixteen Distinguished Flying Crosses, and eighty-six Air Medals, in addition to many other recognitions. The previous accolades did not come without cost—designated Coast Guard Aviator #997, Lieutenant Jack Columbus Rittichier was killed in action while attempting to rescue a downed Marine airman in hostile territory on June 9th, 1968. These Aviators carried out their noble mission with heroism and a focus on duty, honor, country and the Coast Guard. Their actions brought honor on themselves, the United States of America, the U.S. Air Force and the U.S. Coast Guard.
A U.S. Air Force Sikorsky HH-53C Super Jolly Green Giant. (National Archives at College Park)
26 September 1971: A Sikorsky HH-53C Super Jolly Green Giant, crewed by Coast Guard Lieutenant Commander Joseph Lawrence (“Jay”) Crowe, Jr., CGA ‘62 (Pilot), Xxxxxx Hampton (Copilot), William Simm (Flight Engineer), Daniel G. Manion (Pararescue Jumper) and Richard L. Steed (Pararescue Jumper), rescued the crew of a North American Aviation OV-10A Bronco (call sign “RUSTIC 07″), Lieutenant Lansford Elmer Trapp, Jr., and Cambodian observer, Sergeant Chap Khorn, after they ejected from their 12.7mm-damaged aircraft, about 10 miles (16 kilometers) northwest of Kampong Cham, Cambodia.
A little more…(much of this content was slightly modified from the book Leave No Man Behind: The Saga of Combat Search and Rescue by George Galdorisi and Thomas Phillips, pages 393 and 394)
To better cover the southern portion of South Vietnam and be closer to the increasing levels of operations in Cambodia, the 37th Aerospace Rescue and Recovery Squadron (ARRS) had for some time maintained a pair of HH-53Cs at Bien Hoa Air Base, about fifteen miles northeast of Saigon. On September 26, 1971, it was Coast Guard exchange pilot Lieutenant Commander Joseph “Jay” Crowe’s turn to stage at the forward operating location (FOL). Standing the alert with his crew, Hampton, Simm, Manion, and Steed, they were scrambled to rescue of the crew of an OV-10A from the 19th TASS who shared the ramp at Bien Hoa.
A U.S. Air Force North American Aviation OV-10A-5-NH Bronco, 67-14605, fires a white phosphorous rocket. (TSGT Bill Thompson, United States Air Force DFST8505744)
The Rustic FAC, the call sign that any FAC [Forward Air Controller] operating in Cambodia used, regardless of squadron, had fallen victim to a “.50-caliber trap” when it was hit at 3,500 feet (1,067 meters) by converging fire from four 12.7mm AA machine guns ringing the perimeter of a small village about ten miles (16 kilometers) northwest of the Mekong River town of Kampong Cham. When grouped as a battery, the 12.7 mm guns, “heavy guns” of the southern air war (where the heavy AA weapons of Laos and North Vietnam had not yet appeared in large numbers), were still quite deadly. The Bronco pilot, 1st Lieutenant Lansford Trapp, and his observer, Cambodian Sgt. Chap Khom, had parachuted down into the apex of the gun formation, and the hostile forces accompanying the AAA gunners were in no rush to go get them.
In an interview with his grandson recorded in 2018, retired General Lansford E. Trapp described the incident:
“When I was a lieutenant, and this would have been in 1971, I was flying an observation aircraft over in Vietnam. I was on a mission over in Cambodia and we were helping ground forces who were fighting against bad guys over there. That ensuing battle that went on as I was flying over head in my airplane, we actually got hit by ground fire and the left wing of the airplane caught on fire.
“I had a Cambodian interpreter sitting in my back seat, a Sergeant Chung (Khorn), and it was his seventh ride in an airplane. I didn’t even know that the wing was on fire until one of the other airplanes came by and said “hey your left wing is on fire”. So, I looked out, my wing was on fire, and we decided that I was gonna be able to land at one of the airports that was right there. So, we came in and tried to land, but I lost control of the airplane. So, I pushed the power back in and climbed up over the airfield. Then the left wing burned off, and so we started in a pretty good spiral into the wing that had burned off. We ejected from the airplane.
“Sergeant Corn (Khorn) went out first, and then I went out. The craziest thing was that we used to fly with about 250 to 300 big maps, so we could look at the country as we were trying to figure out where we were. Those all came flying out of the cockpit as we ejected. It looked like confetti outside. As we came down sergeant Corn he got burned pretty bad from the wing fire, and I banged my ankle up pretty badly, but we were OK. We got picked up by friendly forces and I got a nice helicopter ride back to home base that night.”
A gunner looks over a General Electric GAU2/A minigun, while his aircraft flies formation with a Sikorsky HH-53C Super Jolly Green Giant over Southeast Asia. (U.S. Air Force)
Crowe’s Jolly approached at 8,000 feet (2,438 meters), safely above the range of the still-active hostile guns, while the A-1H Sandys of the 1st Special Operations Squadron (SOS) went in low to begin their routine of locating the survivors and the hostile guns. In the flat and relatively open terrain of central Cambodia, penetrating the ring of guns was going to be dicey, there not being the ridges, karsts, and dense vegetation of the 37th’s regular operating area to provide a modicum of masking for the helicopter. By this stage of the war, a low, treetop-hugging approach by the rescue helicopter was a well-known procedure, and the enemy gunners would be waiting for it, scanning the low horizon for the rescue helicopter sure to follow on the heels of the tough Skyraiders. Each gun guarded its quadrant of the circle around the downed airmen, waiting.
A Douglas A-1H Skyraider dive bombing a target during a close air support mission. (U.S. Air Force)
Crowe decided to use a variation of the diving spiral approach he had used June 4th with success, rescuing a Covey FAC crew up in southern Laos. Rather than descending some distance away prior to a low-level run-in, he entered an autorotation from directly overhead, copilot Hampton pulling the throttles of the twin engines back, and Crowe lowering the collective stick. Down the helicopter fell, with the rush of air up through the rotors keeping the blades spinning, while the engines idled (relatively quietly). The blades are unloaded in an autorotative descent, so the characteristic whop-whop is virtually eliminated, and with the engines at idle, there is significantly less of the distinctive noises that normally come from the helicopter.
With the Sandys rumbling around, strafing and bombing and attracting the eye of the gunners, the diminished but still telltale sounds made by the falling Jolly were masked. Crowe kept the helicopter in a steep turn, spiraling down inside the perimeter of the four guns around the downed aircrew, literally behind their backs, careful not to swing out too wide, where he might catch a gunner’s eye. The Jolly would be easily seen should anyone glance straight up, luckily the last place a sane gunner would be looking for a helicopter. They were falling out of the sky at more than five thousand feet per minute. As the Jolly approached the ground, Crowe began to level off, converting vertical speed to speed across the ground, still spiraling, and then raised the nose to decelerate.
HH-53C (VIRIN: DF-ST-83-02388)
At the same time, Hampton slowly and smoothly pushed the engine throttles forward, to accelerate them back into normal speed and gently engage their drive wheels with the spinning gears of the main rotors. The accelerating engines and the rotors digging into the air as Crowe pulled up on the collective and flared into a quick-stop created loud rotor beats, accenting the whine of jet turbines accelerating to maximum power, announcing their arrival to all. But the helicopter was safely down beneath the trees in a hover, and the telltale was too late to help the gunners acquire their target. This tight spiral autorotative descent and recovery to a hover requires a superior feel for the helicopter, and exquisite coordination with the copilot to return the rotors to engine-driven flight smoothly at just the right instant. Done right, the procedure is a dramatic and breathtaking maneuver and a grand entrance. But the room for error is very small, and a botched maneuver is perilous and very unforgiving.
It was not a gambit to be repeated very often; if the gunners had detected the helicopter, Crowe and company would have found themselves in a deadly crossfire. But this day it was brilliant: a tactical surprise, completely unexpected, and therefore completely effective. The Jolly crew snatched the two men quickly and escaped out of the circle with a low-level departure. A climbing spiral back up from the center of the guns, with the gunners now alerted, was clearly out of the question. The helicopter received only sporadic fire as it left the scene in the typical low-level escape, while taking no casualties.
Epilogue
Lieutenant Commander Joseph Lawrence Crowe, Jr., U.S. Coast Guard. (Sean M. Cross Collection)
After graduation from high school in Weston, Massachusetts in 1958, Jay received an appointment to the U.S. Coast Guard Academy, New London, Connecticut. Commissioned an Ensign in 1962, he served a tour at sea and then was assigned to naval flight training. Receiving his wings in 1965, he served at Coast Guard Air Stations San Francisco, California, Barbers Point, Hawaii; Cape Cod, Massachusetts; Port Angeles, Washington; Annette Island Alaska, and Sitka, Alaska.
He served during the Vietnam War on an exchange tour with the U.S. Air Force as a Combat Rescue Crew commander with the 37th ARRS Jolly Green Giants in Da Nang AB, RVN.
Jay was a 1981 graduate of the Air War College. He served as Commanding Officer Coast Guard Air Station Port Angeles, Washington, and Coast Guard Air Station Cape Cod, Massachusetts. His final assignment before retirement was as Chief, Operations Division, 11th Coast Guard District, Long Beach, California.
During Jay’s distinguished career he was awarded a Legion of Merit, three Distinguished Flying Cross Medals, nine Air Medals, two Meritorious Service Medals. Three Coast Guard Commendation Medals, a Coast Guard Achievement Medal, and a Meritorious Unit Commendation. Hangar 3172 at Air Station Cape Cod, Massachusetts, was named in his honor.
Captain Crowe flew west crossing the bar February 22, 2003. His family was at his side.
Aircraft
Sikorsky HH-53C Super Jolly Green Giant three-view illustration with dimensions. (Sikorsky Historical Archives)
The MH-53M Pave Low IV is a variant of Sikorsky’s S-65 heavy-lift military transport helicopter series. The MH-53M is a single main rotor, single tail rotor, twin-engine helicopter. It has a crew of six: 2 pilots, 2 flight engineers and 2 gunners. The Pave Low IV is equipped with Terrain-Following Radar and Forward Looking Infrared (FLIR) for low-level operations in darkness and low visibility.
The MH-53M fuselage is 67 feet, 2.4 inches (20.483 meters) long, and the helicopter has a maximum length of 91 feet, 11.34 inches (28.025 meters) with rotors turning and the refueling boom extended. The height to the top of the main rotor pylon is 17 feet, 1.68 inches (5.224 meters). The maximum height (rotors turning) is 24 feet, 10.88 inches (7.592 meters).
The fully-articulated 6-blade main rotor has a diameter of 72 feet, 2.7 inches (22.014 meters). The main rotor turns counter-clockwise at 185 r.p.m. (100% Nr), as seen from above. (The advancing blade is on the helicopter’s right.) The main rotor blades are built with titanium spars and have -16° of twist. The semi-articulated four-blade tail rotor has a diameter of 16 feet, 0 inches (4.877 meters) and is positioned on the left side of the tail pylon. It turns clockwise at 792 r.p.m., as seen from the helicopter’s left side. (The advancing blade is below the axis of rotation.) The gap between rotor arcs is just 4.437 inches (11.270 centimeters).
Empty, the MH-53M weighs 32,000 pounds (14,515 kilograms). Its maximum takeoff weight is 46,000 pounds (20,865 kilograms).
Its two General Electric T64-GE-100 axial-flow turboshaft engines have a Normal Continuous Power rating of 3,810 shaft horsepower at 85 °F. (30 °C.), Military Power rating of 4,090 shaft horsepower, and a Maximum Power rating of 4,330 shaft horsepower. The T64-GE-100 is 79 inches (2.007 meters) long, 20 inches (0.508 meters) in diameter and weighs 720 pounds (327 kilograms). Output (100% N2) is 13,600 r.p.m.
The MH-53M has a maximum speed of 196 miles per hour (315 kilometers per hour) and a service ceiling of 16,000 feet (4877 meters). It carries two 450-gallon (1,703 liter) jettisonable fuel tanks under each sponson.
The MH-53M is armed with two M134 7.62mm miniguns and a GAU-18/A .50 caliber machine gun.
