By the 1960s the conquest of space is the new goal of the super-powers. In search of an aircraft that will fly into orbit and land back on earth the M2 shape emerges. This and other lifting body designs will change the shape of aviation forever; leading to the birth of the space shuttle.
The Apollo program fulfilled the challenge put forth by President Kennedy; to put a man on the moon by the end of the 60’s. With this grand gesture the
The Apollo program taught us much but the capsule was not the answer for the future. During hypersonic acceleration and reentry aircraft with sharp protruding wings and fins would be burnt-up. However, blunt bodies like conical capsules are very efficient; deflecting shock waves and heat away from the vehicle due to the detached bow shock wave. During the early 1950’s researchers started testing half cone shapes called lifting bodies with rounded bottoms and flat tops acting much like a wing. The body of the aircraft produced its own lift. In 1962 a Pontiac Catalina became a familiar sight at the dry lake at Edwards Air Force Base. In tow was one of the strangest looking aircraft ever seen. This “flying bathtub” was the M2-F1.
Without official sanction and with little money a group of NASA scientists independently built the plywood glider to see if a lifting body could be successfully flown. After getting a feel for the aircraft behind the
By 1966 with the success of the M2-F1; NASA and the Air Force sanctioned a rocket-powered lifting body. The Northrop M2-F2 was to be launched mid-air from a B-52. Jerry Gentry was to fly the M2-F2 for the Air Force.
Test Pilot Jerry Gentry:“ . . . you get a marvelous view. Maybe you can understand what a bomb might feel like being carried aloft if a bomb had any feelings but that’s exactly what you are. The only thing that is different in our case was that we could get off anytime we wanted. It was a long ride; about 45 minutes to 45,000 feet so you had a lot of time to think about it and mentally prepare yourself for the flight.”
As they reached 45,000 feet at 450 miles per hour the little aircraft dropped away. Pilots found the experience of flight without wings only a little disturbing at first.
Test Pilot Jerry Gentry:“Once you get past the fact that it doesn’t have any wings; you know it’s going to lift. Anything will lift; barn doors will lift if you can figure out how to control them and that’s essentially with the control surfaces and fins on the lifting body we felt that we could control it. The question was how stable it was going to be and how easy it was going to be to fly.”
Control and stability was a problem on the very first flight in July of 1966 when Milt Thompson encountered the same instability he had experienced in the M2-F1 but the flight ended in a successful landing. However on M2-F2 flight number 16 NASA pilot Bruce Peterson wasn’t so lucky. The same problem cropped up again and Peterson struggled to control the rolling aircraft. He succeeded but after dodging a chase helicopter he had no time to fully extend the landing gear. The result: a catastrophe. After hitting the dry lake at 217 miles per hour his aircraft rolled six times ripping itself a part. Although badly injured Bruce Peterson survived to fly again as did the M2. Using new data it was rebuilt. Test pilot Bill Dana took the first flight in the M2-F3.
Test Pilot Bill Dana:“I had the reward of flying the next flight after we rebuilt it with a modified aileron system that no longer had this lateral instability. That probably was my most challenging flight because it followed immediately a stark disaster.
The best testing facilities of NASA and other agencies have proved essential for successful research flight. A model of the HL-10; a lifting body stable-mate of the M2-F2 was being evaluated for different landing methods. Effort was even expended on tests for a water landing. Wind tunnel analysis was essential for any new aircraft and exotic shapes like the HL-10 got a great deal of attention before flight tests. Full scale test models were expensive but proved invaluable in discovering problems not evident in the smaller scale models.
Rolled out in 1966; the HL-10’s first glide flight exposed a desperate need for modifications. One and a half years later it was back in the air. The Northrop HL-10 was basically the M2 shape but turned up-side-down. Instead of a curved bottom and flat top; it had a flat bottom and cured top. In October 1968 the HL-10 became the first lifting body to be flown under power. It would go on to make the first lifting body super-sonic flight; eventually reaching 1,290 miles per hour and an altitude of over 90,302 feet. The unlikely looking HL-10 would remain the fastest and highest flying of all the lifting bodies. The Northrop HL-10 and the M2 were true pioneers of the lifting body concept. NASA’s Bill Dana flew them both.
Test Pilot Bill Dana:“(They) probably got less attention because they weren’t X-airplanes but I considered them equally contributory to the lifting body technology and to the development of the steep power-off approach and landing techniques that were developed for the Space Shuttle.
Recovery was important because although ASSET transmitted data it also carried on-board recording instruments. Of the 4 out of 6 vehicles that were planned to be recovered; failure prevented the recovery of all but one of the craft. The recovered vehicle vividly showed the extremes of heat encountered during reentry and acceleration. Materials able to withstand such thermal punishment proved difficult to find.
Test Pilot Jerry Gentry:“ . . . but that was in the 60’s and there was a lot of metals that have been developed since then that people in those days were calling unobtainium because there just weren’t any.
Another X-20 support program was the PRIME or X-23. Using a similar system to ASSET; PRIME was designed to extend studies into wingless flight control during reentry and test new kinds of shielding and manuverablity. Researchers developed a material that during extreme temperatures would “ablate” or char and peal off taking the heat with it. The X-23 also tested a new lifting body shape that was set to make its debut as a manned aircraft.
The Martin Marietta X-24A would begin where the X-23 left off; exploring the lower regions of the return from space. Rolled out in July of 1967 it became a true ugly duckling story for later in its life it would go through a startling transformation. The X-24A’s appearance seemed almost comical but its shape had purpose. Jerry Gentry was the first to fly the X-24A. It called for skill and discipline.
Test Pilot Jerry Gentry:“People called it the flying football and it did look a little bit like a football that was sort of partially deflated. But the object was to have a curved smooth bottom because you would be reentering bottom first and therefore that’s where you would have your ablative material that would have to stand the heat of reentry. Each mission or flight test as we called it was thourhlly rehearsed and practiced. In other words I liken it to pretty much like a dance routine that somebody would do on a stage because from the moment you’d launch you are going through a set of procedures.”
A series of unpowered glide flights began on April 17th, 1969 with Gentry at the controls. This was common procedure with these air-launched X-planes; giving the pilot a chance to get familiar with the aircraft’s basic handling qualities. Powered flights were initiated a year later in March; again Gentry was the pilot. Like its predecessors the X-24A was powered by an XLR-11 rocket engine which had a rather distinguished background.
Test Pilot Jerry Gentry:“The rocket engine was the same one that was used in the X-1 when Chuck Yeager broke the speed of sound. It was slightly upgraded in thrust but other then that it was identical.”
After launch at 45,000 feet the X-24A would fly at rocket power for about 2 and a half minutes. Then it would nose-over for a steep 5 minute gliding descent. The pilot could almost just point the nose at the spot he wanted to touch down on as the angle of approach was so steep. After the fast acting landing gear literally snapped into position it would be traveling around 200 miles per hour. In an emergency to give extra air speed or to cushion the landing; small hydrogen peroxide rockets could be used. In over 3 years of flight testing no major problem were encountered by the X-24A during these steep power off landings. The method seemed to be a safe and economic way of bringing a space shuttle back to earth without costly and heavy retractable landing engines that were being considered.
Researchers saw other uses; large commercial passenger aircraft use great amounts of fuel and create air and noise pollution using conventional landing patterns. The lifting body team offered a solution. To demonstrate a B-52 was readied for landing by bringing engines to idle and raising the large air brakes on top of the wings, dropping the flaps and making an approach with landing gear fully extended. The effect was to cause greater drag so the bomber would come in steep and quietly; effectively making a landing at a very low power setting and therefore becoming economical. Demonstrations were carried out for commercial aviation authorities using NASA’s Convair 990 airliner with some modification to its flaps. Although these spin-offs from the lifting body research program showed this was a viable, safe and economical way to land commercial aircraft; the team came across no one willing to give it a try.
The X-24A was to fly 28 times; reach a maximum altitude of over 71,400 feet and caulk up a speed of 1036 miles per hour. It was flown for the final time by NASA’s John Manke on June 4th, 1971 but the story of this peculiar looking aircraft didn’t end there because the X-24A would be re-born. NASA and the Air Force were eager to test another shape that they felt could provide greater performance. Budgets were tight; to build a brand new aircraft would cost at least five million dollars. For one million they could re-configure the X-24A.
The already proven systems were retained but a brand new body was fitted over the original airframe. The transformation took 10 months; the result was the sleek new X-24B. The new double delta flat iron shape was a stark contrast to the A model and pilots that flew it noticed its controllability and maneuverability was vastly improved. In 36 flights over 2 years the X-24B provided a huge amount of valuable data. This sleek futuristic design is seen as the final step in the evolutionary trail to the space shuttle. The shuttles ability to return to earth in a long steep glide and touch down safely on a conventional runway is beholden to a family of the strangest shapes ever to become airborne: the lifting bodies.
The X-24A’s strange shape can still be seen at the Air Force Museum in Dayton, Ohio impersonated by its jet-powered brother; the never flown SV-5J. It’s a touch of irony but a fitting tribute to the lifting body that had a face-lift. The lifting bodies belay their strange appearance; for they proved vital to the continuation of aerospace advancements.
Test Pilot Jerry Gentry:“We were able to prove in the lifting body program that you could land these vehicles very, very accurately. Our touch-down dispersion seldom measured more then plus or minus 500 feet from an intended spot and we always named our landing spot before we landed.”
The lifting bodies were a breed a part; radical shapes showing the way for future spaceflights; silently gliding home and landing safely.