HL-10
General information
Type	Lifting bodytechnology demonstrator
Manufacturer	Northrop
Designer	Langley Research Center
Status	On display, NASA Armstrong Flight Research Center
Primary user	NASA
Number built	1
History
First flight	22 December 1966
Retired	17 July 1970

TheNorthrop HL-10 is one of five US heavyweightlifting body designs flown atNASA's Flight Research Center (FRC—laterDryden Flight Research Center) inEdwards, California, from July1966 to November1975 to study and validate the concept of safely maneuvering and landing a lowlift-over-drag vehicle designed for reentry from space.^[1] It was a NASA design and was built to evaluate "inverted airfoil" lifting body anddeltaplanform. It currently is on display at the entrance to theArmstrong Flight Research Center atEdwards Air Force Base.

Northrop Corporation built the HL-10 andNorthrop M2-F2, the first two of the fleet of "heavy" lifting bodies flown by the NASA Flight Research Center. The contract for construction of the HL-10 and the M2-F2 was $1.8 million. "HL" stands for horizontal landing, and "10" refers to the tenth design studied by engineers at NASA'sLangley Research Center,Hampton, Virginia. Main gear was a modifiedT-38 system retracted manually,^[1] and lowered by nitrogen pressure. Nose gear was a modifiedT-39 unit, retracted manually and lowered with nitrogen pressure. Pilot Ejection System was a modifiedF-106 system.Silver zinc batteries provided electrical power for the control system, flight instruments, radios, cockpit heat, and stability augmentation system. To assist in pre-landing flare, four throttleablehydrogen peroxide rockets provided up to 400 lbf (1.8 kN) of thrust.

After delivery to NASA in January 1966, the HL-10 made its first flight on December 22, 1966, with research pilotBruce Peterson in the cockpit. Although the XLR-11 rocket engine (same type used in theBell X-1) was installed, the first 11drops from theB-52 launch aircraft were unpowered glide flights to assess handling qualities, stability, and control. In the end, the HL-10 was judged to be the best handling of the three original heavy-weight lifting bodies (M2-F2/F3, HL-10,X-24A).^[1]

The HL-10 was flown 37 times during the lifting body research program and logged the highest altitude and fastest speed in thelifting body program. On February 18, 1970, Air Force test pilot Peter Hoag piloted the HL-10 toMach 1.86 (1,228 mph or 1,976 km/h). Nine days later, NASA pilotWilliam H. "Bill" Dana flew the vehicle to 90,030 feet (27,440 m), which became the highest altitude reached in the program.^[1]

During a typical lifting body flight, the B-52—with the research vehicle attached to the pylon mount on the right wing between the fuselage and inboard engine pod—flew to a height of about 45,000 feet (14,000 m) and a launch speed of about 450 mph (720 km/h).^[1]

Moments after being dropped, the XLR-11 was lit by the pilot. Speed and altitude increased until the engine was shut down by choice or fuel exhaustion, depending upon the individual mission profile. The lifting bodies normally carried enough fuel for about 100 seconds of powered flight and routinely reached from 50,000 to 80,000 feet (15,000 to 24,000 m) and speeds above Mach 1.^[1]

Following engine shutdown, the pilot maneuvered the vehicle through a simulated return-from-space corridor into a pre-planned approach for a landing on one of the lakebed runways onRogers Dry Lake at Edwards. A circular approach was used to lose altitude during the landing phase. On the final approach leg, the pilot increased his rate of descent to build up energy. At about 100 feet (30 m) altitude, a "flare out" maneuver dropped air speed to about 200 mph (320 km/h) for the landing.^[1]

Unusual and valuable lessons were learned through the successful flight testing of the HL-10. During the early phases of theSpace Shuttle development program, lifting bodies patterned on the HL-10 shape were one of three major types of proposals. These were later rejected as it proved difficult to fit cylindrical fuel tanks into the always-curving fuselage, and from then on most designs focused on more conventionaldelta wing craft.

• HL-10 pilots
  • John A. Manke — 10 flights, 7 powered flights
  • William H. Dana — 9 flights, 8 powered flights
  • Jerauld R. Gentry — 9 flights, 2 powered flights
  • Peter C. Hoag — 8 flights, 7 powered flights
  • Bruce Peterson — 1 flight, 0 powered flights

According to the book "Wingless Flight", by project engineerR. Dale Reed, the HL-10 was considered to fly into space in the early to mid-1970s. Following the cancellation of the Apollo moon project, Reed realized that there would be substantial Apollo hardware left over, including several flight-rated command service modules (CSM) andSaturn V rockets.^[2]

The proposal was to add an ablative heat shield, reaction controls, and other additional subsystems needed for crewed spaceflight to the HL-10. The now space-rated vehicle would have then been launched in the space for theLunar Module on a Saturn V launch vehicle with an Apollo CSM. Once in Earth orbit, it was planned that a robotic extraction arm would remove the HL-10 from the rocket's third stage and place it adjacent to the crewed Apollo CSM spacecraft. One of the astronauts would then spacewalk from the Apollo and board the lifting body to perform a pre-reentry check on its systems.^[2]

It was planned that there would be two flights in this program. In the first, the lifting body pilot would return to the Apollo and send the HL-10 back to earth uncrewed. If this flight was successful, the second launch would be involve a piloted landing at Edwards AFB. Reportedly,Wernher von Braun was enthusiastic about the mission, offering to prepare two Saturn Vs and Apollo Command Service Modules. However, he was overridden by the Flight Research Center director, and nothing came of the proposal.^[2] Launching a Saturn V to low Earth orbit with a light payload would not be an efficient use of capability, and theApollo program was ended mainly on cost grounds.^{[citation needed]}

• Northrop HL-10 — NASA 804, 37 flights

The HL-10 is currently on display at the entrance of Armstrong Flight Research Center at Edwards, CA.

• Crew: one pilot
• Length: 21 ft 2 in (6.45 m)
• Wingspan: 13 ft 7 in (4.15 m)
• Height: 9 ft 7 in (2.92 m)
• Wing area: 160 ft² (14.9 m²)
• Empty: 5,285 lb (2,397 kg)
• Loaded: 6,000 lb (2,721 kg)
• Maximum takeoff: 10,009 lb (4,540 kg) (propellant wt 3,536 lb - 1,604 kg)
• Powerplant: 1 xReaction Motors XLR-11 four-chamber rocket engine. 8,000 lbf (35.7 kN) thrust

• Maximum speed: 1,228 mph (1,976 km/h)
• Range: 45 miles (72 km)
• Service ceiling: 90,303 ft (27,524 m)
• Rate of climb: ft/min ( m/min)
• Wing loading: 62.5 lb/ft² (304.7 kg/m²)
• Thrust-to-weight: 1:0.99

In the pilot movie, and an episode ofThe Six Million Dollar Man series, titled "The Deadly Replay", the HL-10 serial number 804 is identified as the aircraft flown by Col.Steve Austin when he crashed, leading to his transformation into a bionic man, and the HL-10 is also featured in this episode.^[3] Other episodes andMartin Caidin's original novel,Cyborg, contradict this, however, by identifying Austin's aircraft as a fictional cousin of the HL-10, the M3-F5.^[4] Further confusion is added by the fact that both the HL-10 and the M2-F2 are featured in the opening credits of the television show.

• HL-20 Personnel Launch System
• X-plane

Aircraft of comparable role, configuration, and era

• Martin Marietta X-24
• NASA M2-F1
• Northrop M2-F2
• Northrop M2-F3
• X-38 Crew Return Vehicle

Related lists

• List of experimental aircraft

Wikimedia Commons has media related toNorthrop HL-10.

• NASA Dryden HL-10 Photo Collection
• Developing and Flight Testing the HL-10 Lifting Body - NASA 1994 (PDF)
• Current display location

• Lifting bodies
• 1960s United States experimental aircraft
• Gliding in the United States
• Rocket-powered aircraft
• Northrop aircraft
• Aircraft first flown in 1966

• Articles with short description
• Short description is different from Wikidata
• All articles with unsourced statements
• Articles with unsourced statements from June 2019
• Commons category link from Wikidata