Igor Sikorsky with his VS-300A, Stratford, Connecticut, 6 May 1941. (Sikorsky Archives)
6 May 1941: At Stratford, Connecticut, Igor Sikorsky piloted his Vought-Sikorsky VS-300 helicopter to a new world’s record for endurance. He flew for 1 hour, 32 minutes, 26 seconds. ¹ The previous record—1 hour, 20 minutes, 49 seconds—had been set by Ewald Rohlfs with the Focke-Wulf Fw 61 tandem-rotor helicopter, 25 June 1937. ²
During its development, the VS-300 went through at least 18 changes in its rotor configuration. This photograph, taken after the record-setting flight, shows an intermediate version, with one main rotor for lift and three auxiliary rotors for anti-torque and directional control.
Igor Ivanovich Sikorsky 1888–1970. Sikorsky Archives)
In the final configuration, Sikorsky arrived at what we now recognize as a helicopter, with the main rotor providing lift, thrust and roll control through variable collective and cyclic pitch, and a single tail rotor for anti-torque and yaw control.
The VS-300 had a welded tubular steel airframe and used a 28-foot (5.34 meters) diameter, fully-articulated, three-bladed main rotor, which turned clockwise (as seen from above) at 260 r.p.m. (The advancing blade was on the left. This would later be reversed.) The main rotor had collective pitch control for vertical control, but cyclic pitch (Sikorsky referred to this as “sectional control”) for directional control would not be developed for another several months.
The tail “propellers” (what we now consider to be rotors—one vertical and two horizontal) each had two blades with a diameter of 7 feet, 8 inches (2.337 meters) and turned approximately 1,300 r.p.m. The vertical rotor provided “torque compensation” (anti-torque) and the blade pitch was fully reversible. The horizontal rotors were mounted on 10-foot (3.048 meters) outriggers at the aft end of the fuselage. For lateral control, the pitch on one rotor was increased and the other decreased. For longitudinal control, the pitch of both rotors was increased or decreased together.
The VS-300 was originally equipped with an air-cooled, normally-aspirated 144.489-cubic-inch-displacement (2.368 liter) Lycoming O-145C-3 four-cylinder horizontally-opposed engine which was rated at 75 horsepower at 3,100 r.p.m. According to Mr. Sikorsky, “early in 1941,” the Lycoming engine was replaced by an air-cooled, normally-aspirated 198.608 cubic inch (3.255 liter) Franklin 4AC-199-E, a four-cylinder horizontally-opposed overhead valve (OHV) direct-drive engine with a compression ratio of 7:1, rated at 90 horsepower at 2,500 r.p.m. It is not known if this change was made prior to 6 May.
¹ During World War II, only a very few ballooning and gliding world records were certified by the Fédération Aéronautique Internationale. Although Sikorsky’s flight duration exceeded that of Rohlfs, it is not listed as an official world record.
Republic XP-47B 40-3051 prototype in flight. (Republic Aircraft Corporation)
6 May 1941: Just eight months after a prototype for a new single-engine fighter was ordered by the U.S. Army Air Forces, test pilot Lowery Lawson Brabham took off from the Republic Aviation Corporation factory airfield at Farmingdale, New York, and flew the prototype XP-47B Thunderbolt, serial number 40-3051, to Mitchel Field, New York.
During the flight, oil which had collected in the exhaust duct began burning. There was so much smoke that Brabham considered bailing out. He stayed with the prototype, though, and when he arrived at Mitchel Field, he exclaimed, “I think we’ve hit the jackpot!”
Alexander Kartveli
The prototype was designed by Alexander Kartveli, a Georgian immigrant and former chief engineer for the Seversky Aircraft Corporation, which became the Republic Aviation Corporation in 1939.
Alexander Kartveli (née Kartvelishvili, ალექსანდრე ქართველი) was born in Tbilisi, in the Kutais Governorate of the Russian Empire, (what is now, Georgia). After World War I, during which he was wounded, Kartvelishvili was sent to study at the Paris Aviation Higher College of Engineering in France by the government of the Democratic Republic of Georgia. He graduated in 1922. Kartvelishvili did not return to his country, which had fallen to the Red Army in the Soviet-Georgian War. He worked for Blériot Aéronautique S.A. until 1928, when he was employed by the Fokker American Company (also known as Atlantic Aircraft, or Atlantic-Fokker) which was headquartered at Passaic, New Jersey, in the United States. In 1931, he became chief engineer for the Seversky Aircraft Company in Farmingdale.
Republic XP-47B Thunderbolt prototype 40-3051 at Farmingdale, New York, 1941. The pilot standing in front of the airplane gives a scale reference. (Republic Aviation Corporation)
Kartveli submitted his design proposal for the XP-47B to the U.S. Army Air Corps, 12 June 1940. The prototype was ordered 6 September, and a week later, 13 September 161 production P47Bs and 602 P-47Cs were ordered. The contract was for $56,499,924. The company named the new fighter “Thunderbolt,” which had been suggested by C. Hart Miller, director of the military contracts division of Republic Aviation.
The XP-47B was the largest single-engine fighter that had yet been built. The production P-47B was 34 feet, 10 inches (10.617 meters) long with a wingspan of 40 feet, 9-5/16 inches (12.429 meters), and height of 12 feet, 8 inches (3.861 meters).¹ The wing area was 300 square feet (27.9 square meters). At a gross weight of 12,086 pounds (5,482 kilograms), it was nearly twice as heavy as any of its contemporaries.
Republic XP-47B Thunderbolt 40-3051 at Wright Field, Dayton, Ohio.(Ray Wagner Collection, San Diego Air & Space Museum Archives )
The XP-47B was powered by an air-cooled, supercharged and turbocharged, 2,804.4-cubic-inch-displacement (45.956 liter) Pratt & Whitney R-2800-21 (Double Wasp TSB1-G) two-row, 18-cylinder radial with a compression ratio of 6.65:1 had a normal power rating of 1,625 horsepower at 2,550 r.p.m., to an altitude of 25,000 feet (7,620 meters), and a takeoff/military power rating of 2,000 horsepower at 2,700 r.p.m. at 25,000 feet (7,620 meters). The engine drove a 12-foot, 2 inch (3.708 meter) diameter, four-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction. The R-2800-21 was 4 feet, 4.50 inches (1.340 meters) in diameter and 6 feet, 3.72 inches (1.923 meters) long. The engine weighed 2,265 pounds (1,027 kilograms). Approximately 80% of these engines were produced by the Ford Motor Company. It was also used as a commercial aircraft engine, with optional propeller gear reduction ratios.
A large General Electric turbosupercharger was mounted in the rear of the fuselage. Internal ducts carried exhaust gases from the engine to drive the turbocharger. This supercharged air was then carried forward through an intercooler and then on to the carburetor to supply the engine. The engine’s mechanical supercharger further pressurized the air-fuel charge.
Republic XP-47B 40-3051. The pilot enters the cockpit through a hinged canopy segment. (Ray Wagner Collection Catalog, San Diego Air and Space Museum)
During flight testing, the XP-47B Thunderbolt demonstrated speeds of 344.5 miles per hour (554.4 kilometers per hour) at 5,425 feet (1,654 meters), and 382 miles per hour (615 kilometers per hour) at 15,600 feet (4,745 meters). Its maximum speed was 412 miles per hour (663 kilometers per hour) at 25,800 feet (7,864 meters). The test pilot reported that the engine was unable to produce full power during these tests. It was determined that it had a cracked cylinder head, resulting in a loss of 2.5–4% of its maximum rated power. Also, the XP-47B was painted in camouflage, resulting in a slight loss of speed.
It could climb to 15,000 feet (4,572 meters) in just five minutes.
The Thunderbolt was armed with eight Browning AN-M2 .50-caliber machine guns, four in each wing, with 3,400 rounds of ammunition. It could also carry external fuel tanks, rockets and bombs. The structure of the P-47 could be described as “robust” and it was heavily armored. The amount of damage that the airplane could absorb and still return was remarkable.
Republic XP-47B Thunderbolt 40-3051, 4 May 1941. (Republic Aviation Corporation)
During a test flight, 4 August 1942, the XP-47B’s tail wheel was left down. The extreme heat of the turbocharger’s exhaust set fire to the tire, which then spread to the airplane’s fabric-covered control surfaces. Unable to control the airplane, test pilot Filmore L. Gilmer bailed out. The prototype Thunderbolt crashed into Long Island Sound and was destroyed.
The third production Republic P-47B Thunderbolt, 41-5897, at Langley Field, Virginia, 24 March 1942. The door-hinged canopy of the XP-47B has been replaced by a rearward-sliding canopy, requiring that the radio antenna mast be moved.(NASA)A Republic P-47B Thunderbolt in the NACA Full Scale Tunnel, 31 July 1942. (NASA LMAL 29051)
A total of 15,683 Thunderbolts were built; more than any other U.S. fighter type. In aerial combat, it had a kill-to-loss ratio of 4.6:1. The P-47, though, really made its name as a ground attack fighter, destroying aircraft, locomotives, rail cars, and tanks by the many thousands. It was one of the most successful aircraft of World War II.
¹ Data from Pilot’s Flight Operating Instructions, Technical Order No. 01-65BC-1, 20 January 1943
Airship D-LZ129 Hindenburg moored at New Jersey at the end of a previous voyage.
6 May 1937: After a three-day Trans-Atlantic crossing from Frankfurt, Germany, the rigid airship Hindenburg (D-LZ129) arrived at Lakehurst, New Jersey, with 36 passengers and 61 crewmembers.
Airship LZ-129 Hindenburg burning, 1925 hours, 6 May 1937, at Lakehurst, New Jersey.
At 7:25 p.m., while the airship was being moored, it suddenly caught fire. The fabric covering burned first, but then the hydrogen gas contained in the buoyancy tanks exploded and burned. Hindenburg settled to the ground and was completely destroyed within 30 seconds.
Water ballast rains down as Hindenburg burns at the mooring mast 1925 hours, 6 May 1937, at Lakehurst, New Jersey. SFA003016395Hindenburg NY Daily NewsHindenburg settles to the ground. (Arthur Cofod, Jr./USAF 12293 A.C.)
Of those on board, 13 passengers and 22 crewmembers died. One member of the ground crew was also killed.
Surprisingly, though there were many survivors and witnesses—as well as newsreel footage of the accident—the cause has never been determined.
This dramatic accident ended the airship passenger industry.
Airship LZ-129 Hindenburg burning, 1925 hours, 6 May 1937, at Lakehurst, New Jersey.Hindenburg burningWreckage of Hindenburg, photographed the following day.
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
6 May 1935: At Buffalo, New York, the prototype Curtiss-Wright Model 75, X17Y, serial number 11923, made its first flight.
Donovan Reese Berlin. (Niagara Aerospace Museum)
Designed by Donovan Reese Berlin, the airplane was a modern design of all metal construction, with fabric covered control surfaces. The Model 75 was a single-seat, single-engine low-wing monoplane with retractable landing gear.
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
In its original configuration, the Model 75 was powered by an air-cooled, supercharged 1,666.860 cubic inch displacement (27.315 liter) Wright Aeronautical Division GR1670A1 two-row 14-cylinder radial engine. The GR1670A1 was a developmental engine with a compression ratio of 6.75:1. It was rated at 775 horsepower at 2,400 r.p.m. at Sea Level, and 830 horsepower at 2,600 r.p.m. for takeoff, burning 87-octane gasoline. The engine was 3 feet, 9 inches (1.143 meters) in diameter, 4 feet, 4–25/32 inches (1.341 meters) long, and weighed 1,160 pounds (526 kilograms). The GR1670A1 drove a three-bladed Curtiss Electric constant-speed propeller through a 16:11 gear reduction.
The GR1670A1 was also used in the Seversky SEV-S1, NR18Y, a record-setting experimental variant of the rival Seversky P-35.
The United States Department of Commerce, Bureau of Air Commerce, registered X17Y to the Curtiss-Wright Corporation, Kenmore & Vulcan Street, Buffalo, New York, on issued 1 June 1936. This registration was cancelled 26 April 1937.
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
The Curtiss-Wright Model 75 would be developed into the P-36 Hawk fighter for the U.S. Army Air Corps. France ordered it as the H75A-1, and in British service, it was known as the Mohawk Mk.I.
The tenth production P-36 was modified with a liquid-cooled Allison V-1710 V-12 engine to become the prototype XP-40.
1st Lieutenant Benjamin Scovill Kelsey in the cockpit of a Curtiss-Wright P-36A Hawk, circa 1938. (U.S. Air Force)1st Lieutenant Benjamin Scovill Kelsey, Air Corps, United States Army, with a Curtiss Wright P-36A Hawk, Air Corps serial number 38-2, at Wright Field, Ohio, circa 1938. (Ray Wagner Collection/San Diego Air & Space Museum Archives)Curtiss-Wright P-36B 38-020. (U.S. Air Force)Curtiss-Wright P-36B 38-020. (U.S. Air Force)Curtiss-Wright P-36C camouflage test, Maxwell Field, 1940. (Ray Wagner Collection, San Diego Air & Space Museum Archives)Curtiss-Wright P-40 Warhawk, 55th Pursuit Squadron, Oakland, CA, 1941 (IWM FRE11437)
Mercury-Redstone 3 lifts off from LC-5, 10:34:13 EDT, 5 May 1961. (NASA)Alan Bartlett Shepard Jr., Astronaut. (NASA)
At 10:34:13.48 a.m., Eastern Daylight Time ¹ (13:34:13.48 UTC), 5 May 1961, Mercury-Redstone 3 lifted off from Launch Complex 5 at the Cape Canaveral Air Force Station, Cape Canaveral, Florida. On board was a NASA Astronaut, Commander Alan Bartlett Shepard, Jr., United States Navy. Shepard had named his spacecraft Freedom 7.
This was the very first time that an American astronaut had been carried into space aboard a rocket and came 23 days after Soviet Union Cosmonaut Yuri Alekseyevich Gagarin had completed one orbit of the Earth.
During the launch, acceleration reached 6.3 gs. The Redstone’s engine shut down at T+02:21.3, with the rocket having reached a velocity of 7,388 feet per second (2,251.9 meters per second). 10 seconds later, the Mercury spacecraft separated from the Redstone booster. The spacecraft’s maximum speed was 5,134 miles per hour (8,262.4 kilometers per hour). For the next 5 minutes, 4 seconds, Alan Shepard was “weightless.” Freedom 7 reached a peak altitude of 101.2 nautical miles (116.46 statute miles/187.42 kilometers), 0.9 nautical miles (1.7 kilometers) higher than planned.
Alan B. Shepard, Jr., seated in the cockpit of Freedom 7 before launch, 5 May 1961. (NASA)
Alan Shepard’s flight was suborbital. The rocket launched the capsule on a ballistic trajectory. During the flight, Shepard demonstrated the use of manually controlled thrusters to orient the Mercury capsule in three axes.
Freedom 7 began reentry to the atmosphere at T+07:38. Deceleration forces reached 11.0 gs. Shepard manually controlled the vehicle’s attitude, and once correctly oriented for reentry, reverted to automatic control. With the blunt (bottom) end of the spacecraft forward, aerodynamic drag slowed the capsule. A spherical-segment ablative Beryllium heat shield protected the space ship and its passenger.
On reaching the lower atmosphere, the capsule’s speed was reduced by a 63-foot (19.2 meter) diameter ring-sail parachute, and a “landing bag” deployed from the base of the spacecraft to provide an impact cushion. The landing, or “splash down,” took place in the Atlantic Ocean, 263.1 nautical miles (302.8 statute miles/487.3 kilometers) down range, 6.8 nautical miles (7.8 miles/12.6 kilometers) farther than planned. (N. 75° 53′, W. 27° 13.7′)
The total duration of Alan Shepard’s flight was 15 minutes, 28 seconds. All mission objectives were accomplished and no malfunctions occurred.
Alan B. Shepard, Jr., being hoisted aboard the Sikorsky HUS-1 Seahorse helicopter, N. 75° 53′, W. 27° 13.7′, in the Atlantic Ocean, 5 May 1961. (NASA)
Eleven minutes after splash down, Commander Shepard was hoisted from the capsule to a hovering U.S. Marine Corps HUS-1 Sea Horse (Sikorsky S-58) helicopter of Marine Helicopter Transport Squadron (Light) 262 (HMR(L)-262).² The helicopter then lifted the Mercury capsule and flew to the nearby U.S. Navy Ticonderoga-class anti-submarine aircraft carrier, USS Lake Champlain (CVS-39). The Mercury capsule was returned to Cape Canaveral for inspection and found to be in excellent condition.
U.S. Marine Corps HUS-1 Seahorse (Sikorsky S-58) Bu. No. 148767 of HMR(L)-262 hovers while hoisting Alan Shepard from Freedom 7 after his sub-orbital flight, 5 May 1961. The Mercury capsule will also be lifted from the ocean by the helicopter and carried to USS Lake Champlain (CVS-39). (NASA)USS Lake Champlain (CVS-39), 1 July 1960. (U.S. Navy)
Freedom 7 was the seventh of twenty Mercury capsules built by McDonnell Aircraft Corporation at St. Louis, Missouri, which would also build the follow-on, two-place Gemini spacecraft. It was delivered to Cape Canaveral 9 December 1960.
The space capsule was truncated cone with sides angled 20° from the longitudinal axis. It was 6 feet, 10 inches (2.083 meters) long and had a maximum diameter of 6 feet, 2.50 inches (1.892 meters). The total height of the spacecraft, from the tip of the aero spike to the booster adapter, was 26 feet, 1.26 inches (7.957 meters). At launch, Freedom 7 weighed 4,040.28 pounds (1,832.64 kilograms).
Project Mercury spacecraft under construction at McDonnell Aircraft Corporation, St. Louis, Missouri. (NASA)
During flight outside the atmosphere, the Mercury spacecraft could be controlled in its pitch, roll and yaw axes by hydrogen peroxide-fueled reaction control thrusters. Both manual and automatic attitude control were available. It could not accelerate or decelerate (except for reentry), so it could not change its orbit.
The spacecraft cabin was pressurized to 5.5 psi (0.38 Bar) with 100% oxygen. The astronaut wore a B.F. Goodrich Mark IV Model 3 Type I full-pressure suit and flight helmet for protection in the event that cabin pressure was lost.
Mercury-Redstone Launch Vehicle with dimensions. (NASA)
The Redstone MRLV rocket was a redesigned, “man rated” version of the Chrysler Corporation Missile Division-built United States Army M8 Redstone nuclear-armed medium range ballistic missile (MRBM). It was lengthened to provide greater fuel capacity, a pressurized instrumentation section was added, the control systems were simplified for greater reliability, and an inflight abort sensing system was installed. The rocket fuel was changed from hydrazine to ethyl alcohol.
The cylindrical booster was 59.00 feet (17.983 meters) long and 5 feet, 10 inches (1.778 meters) in diameter. The rocket had four guidance fins with rudders mounted at the tail section. (Interestingly, the Redstone stood freely on the launch pad. No hold-downs were used. The guidance fins supported the entire weight of the vehicle.)
Compare the U.S. Army M8 Redstone medium-range ballistic missile in this photograph to the Mercury-Redstone launch vehicle in the photograph above. This rocket, CC-1002, was the first Block 1 tactical rocket, photographed at Cape Canaveral Air Force Station, 16 May 1958. (NASA)
The Redstone MRLV was powered by a single liquid-fueled NAA 75-110-A7 rocket engine built by the Rocketdyne Division of North American Aviation, Inc., at Canoga Park, California. The MR-3 A7 produced 78,860 pounds of thrust (350.79 kilonewtons) at Sea Level, and approximately 89,000 pounds (395.89 kilonewtons) in vacuum, burning ethyl alcohol with liquid oxygen.
The total vehicle height of Mercury-Redstone 3, including the booster, adapter, capsule and escape tower, was 83.38 feet (25.414 meters). The total MR-3 vehicle launch weight was 66,098 pounds (29,982 kilograms).
Alan B. Shepard, Jr. is credited with two Fédération Aéronautique Internationale (FAI) World Records for this flight:
FAI Record File Num #9519 [Direct Link]
Status: ratified – current record
Region: World
Class: K (Space records)
Sub-Class: K-1 (Suborbital missions)
Category: Spacecraft with one astronaut
Group: General category
Type of record: Altitude
Performance: 186.307 km
Date: 1961-05-05
Course/Location: Cape Canaveral, FL (USA)
Claimant Alan B. Shepard, Jr (USA)
Spacecraft: NASA Mercury Redstone MR-7 / Capsule Mercury Spacecraft n°7
FAI Record File Num #9520 [Direct Link]
Status: ratified – current record
Region: World
Class: K (Space records)
Sub-Class: K-1 (Suborbital missions)
Category: Spacecraft with one astronaut
Group: General category
Type of record: Greatest mass lifted to altitude
Performance: 1 832.51 kg
Date: 1961-05-05
Course/Location: Cape Canaveral, FL (USA)
Claimant Alan B. Shepard, Jr (USA)
Spacecraft: NASA Mercury Redstone MR-7 / Capsule Mercury Spacecraft n°7
The flight of Freedom 7 was the first manned spaceflight in the 50-year history of the NASA program.³ Alan Shepard would later command Apollo 14, the third successful manned lunar landing mission, in 1971.
Alan Shepard’s Mercury spacecraft, Freedom 7, is on display at the John F. Kennedy Presidential Library and Museum, Boston, Massachusetts.
Alan Shepard’s Freedom 7 on display at the John F. Kennedy Presidential Library and Museum, Boston, Massachusetts.
¹ In 1961, Daylight Saving Time in the United States began on 30 April, just six days before Shepard’s flight. Contemporary newspaper articles about the flight frequently give the time of the launch in both standard time and daylight saving time.
² Sikorsky HUS-1 Sea Horse, Bu. No. 148767, modex ET-44. Sikorsky serial number 581318.
³ From the liftoff of Mercury-Redstone 3 until wheel stop of Space Shuttle Discovery (STS-135), the era of NASA’s Manned Spaceflight Programs lasted 50 years, 2 months, 15 days, 20 hours, 23 minutes, 41 seconds.
