Wingless Flight in the M2-F1
Sometimes, the most interesting aircraft are the experimental ones that barely made it off the ground. Sometimes the most intriguing stories come out of things I don’t understand.
I was thinking about hybrid airships and I was struggling to understand the concept of a lifting body. My attempt to understand how a wingless vehicle could possibly fly led me to the NASA research. Once I saw the sci-fi looking M2-F1 being towed by a Pontiac convertible, I was hooked.
The concept of a lifting body has been discussed since the mid 1950s, with a series of possible shapes. My struggle to understand how the body could provide lift says more about my lack of physics understanding than anything else. However, I’m a bit relieved to see that in the 1960s, I was in good company: there were plenty of engineers at NASA who felt the same as I did.
The idea of an aircraft without wings met with skepticism among engineers. R. Dale Reed of the NASA Flight Research Center – now the Dryden Flight Research Center – was the exception. Reed was excited about the concept and began testing a series of small balsa wood and tissue-paper lifting bodies, which he flew down the hallways of the center’s main office building and off its roof.
A lifting body is effectively a fuselage with little or no conventional wing. A fixed-wing aircraft is kept in the air by the forward motion of the wings. Helicopters have wing-shaped rotors (or rotor blades or rotary wings) which revolve around a mast. The flying wing maximises cruise efficiency at subsonic speeds by eliminating non-lifting surfaces. A dynastat, a type of hybrid airship, has both fixed wings and a lifting body and excels at long-endurance flights.
The key point is that a lifting body is inefficient at low airspeeds but the shape means that there’s very little drag, which has clear potential for subsonic, supersonic and hypersonic flight. NASA were particularly interested in its potential for spacecraft re-entry with a view to developing a lightweight manned spacecraft with a minimal amount of drag. Well, when I say NASA, initially, it was just Reed.
The engineer had more than a working knowledge of aviation: he was a general aviation pilot and he enjoyed building model aircraft. He became intrigued by the idea of the lifting body as a means to land a spacecraft horizontally after atmospheric re-entry.
“Lifting” reentry is achieved by flying from space to a conventional horizontal landing, using a blunt half-cone body, a wingless body, or a vehicle with a delta platform (like the shape of the current Space Shuttle), taking advantage of any of these configurations ability to generate body lift and, thus, fly. We could not put conventional straight or even swept wings on these vehicles because they would burn off during reentry–although a delta platform with a large leading-edge radius might work. These vehicles, or lifting bodies as we called them, would have significant glide capability down-range (the direction of their orbital tracks and/or cross-range (the direction across their orbital tracks) due to the aerodynamic lift they could produce during reentry.
Putting his model aircraft experience to good use, Reed worked on the idea at home. He created a small model to illustrate the concept. His wife filmed the flights on their 8-mm home camera and Reed took the footage to work to present the concept.
It worked, sort of. NASA offered Reed $30,000 in funding, “about the cost of a Cessna,” to build a lightweight lifting-body prototype which would take less damage on atmospheric re-entry.
Reed recruited NASA craftsman Ernie Lowder for the project, who had worked on Howard Hughes’ Spruce Goose. Then he went to the local airfield to recruit Gus Briegleb, a glider manufacturer who was selling kits of a high-performance wooden sailplane that he had designed.
Once we had the initial team, we needed a place to work. We sectioned off a corner of the fabrication shop with a canvas curtain, labeling it the “Wright Bicycle Shop.” Indeed, we felt very much like the Wright Brothers in those days, working at the very edge between the known and unknown in fight innovation.
Together, they built the M2-F1, basically a mahogany plywood shell placed over a tubular steel frame. The tail, pushrod controls and the landing gear were taken from a Cessna 150. M stood for manned and F for flight version, so in this case, the first flight version of the lifting body prototype. The NASA website describes it as looking like a bathtub sitting on a tricycle.
That’s where the Pontiac comes in. The prototype was unpowered so they needed a tow vehicle. A hot-rod enthusiast who worked at the Flight Research Center purchased a 1963 Pontiac Bonneville convertible for the job. But the Pontiac still wasn’t powerful enough to lift the M2-F1 off the ground so he took it to “Bill Straup’s renowned hot-rod shop near Long Beach” where the car was “hot-rodded” with racing slicks and a special gear box until it was able to reach 110 miles per hour (180 km/h) while towing the M2-F1. They also added radios and a rollbar and turned the front passenger bucket seat around so that a passenger could watch the M2-F1 being towed behind. The souped-up engine got about four miles to the gallon.
Of course, the Pontiac had to have government plates and the NASA logo on both sides. And just so no one would be encouraged to think the car was someone’s personal toy paid for with government funds, the hood and the trunk of the Pontiac were spray-painted high-visibility yellow, so that the convertible looked just like any other flight-line vehicle.
Whatever else they might have done, I don’t believe for a moment that the Pontiac ever looked like any other flight-line vehicle.
The problem now was that the prototype was designed as a full-scale model. The team had not been authorised to flight test the M2-F1.
The test pilot, Milt Thompson, argued that it wouldn’t really count as flying if they just lifted it off the lake-bed a couple of inches. And so, on the 1st of March 1963, they took the prototype out for a spin. Milt Thompson sat in the back as the Pontiac dragged it along Rogers Dry Lake. They initially drove at slower speeds, working their way up to the nose lift-off speeds over the course of the month. Eventually, they reached 86 miles per hour and Thompson carefully lifted the nose off the ground for the first time!
Slowly Milt brought the nose of the lifting body up until the M2-F1 got light on its wheels. Then something totally unexpected happened. The M2-F1 began bouncing back and forth from right to left. Milt stopped the bounce by lowering the nose, putting weight back on the wheels. Several times he again brought the nose up until the M2-F1 was light on its wheels, and each time the vehicle reacted the same way, Milt ending the bounce by lowering the nose as he had the first time.
He called a halt to the test and the team reviewed the movies taken of the attempt in an attempt to understand what made the M2-F1 bounce on the main landing gear, as there was no physical reason why the lifting body should oscillate. In the filmed footage, it became clear that the rudders were making small movements to the left and right which caused the vehicle to become unstable. But it wasn’t the test pilot; the slop and inertial weights in the rudder system were causing the rudders to move.
The next attempt was more successful: Thompson managed to lift off and remain airborne for a short time, still connected to the Pontiac.
The prototype was taken to Ames Research Center for Wind Tunnel Testing and to stabilise the control system. These tests were equally unorthodox.
Reed described it in his book…
The inside of the wind tunnel was an awesome sight, especially at night. One night, as the M2-F1 team was preparing for a test, I took my family on a tour of the tunnel. We boarded an open-cage elevator on the ground floor, then rose through a darkness of steel beams and unlit open spaces to the floor of the dimly lit test section. The tunnel was a huge closed-circuit system in the shape of a race track, it’s entire length being about half a mile. Soot from engines stained the walls, making the interior of the tunnel dark and dingy, adding an eeriness to the atmosphere. My wife, Donna, said that the tunnel would be a wonderful place to make an Alfred Hitchcock movie.
The M2-F1 didn’t have some of the more exciting features of research vehicles, like remote controls. So they convinced the wind-tunnel crew to let one person sit in the cockpit during the tests so that they could see the effects of the control settings. Otherwise, they would need to stop the test every time they wanted to change a pilot control; this way the wind tunnel could keep running.
Reed now admits that the tests were probably unsafe and would not be allowed at NASA these days. His descriptions of the tests are most evocative.
I found it scary sitting there over 20 feet off the ground inside a plywood barrel-like vehicle perched atop three spindly poles inside a dark cavern, shaking around as a windstorm screamed past at 135 miles per hour. I then decided that the best use of my time would be directing the tests in the safe confines of the wind tunnel control room. With the wind-tunnel operators and I peering at the wind-tunnel pilots through thick windows in the tunnel walls, they felt like some kind of biological laboratory specimens under scrutiny.
Thompson the test pilot, on the other hand, loved every minute of it. He asked them to attach a rope to the M2-F1 and let him lift off in the tunnel for a test flight but the wind-tunnel crew refused, worried that the tow line could break and “plaster the spacecraft and its pilot against the turning vanes.”
The vehicle underwent two weeks of wind tunnel testing. On the 16th of August 1963, the M2-F1 was authorised for flight. Thompson was now officially allowed to lift off of the lake bed. The team towed the M2-F1 at faster speeds reaching higher altitudes, until the final flight where Thomson managed to stay aloft for four miles. It was time to try to fly.
The Pontiac wouldn’t do for free flight, of course. Instead the plan was to use NASA’s R4D Skytrain, a Douglas C-47 (military transport plane based on the DC-3) utility aircraft which was mostly used for transport and to shuttle people to and fro.
The R4D Skytrain was one of the work horses for NACA and NASA at Edwards AFB spanning a time from 1952 to 1984. Designated R4D by the Navy the aircraft was called C-47 by the Army, DC-3 by Douglas Aircraft and “Gooney Bird” by all others.
There was a problem: the World War II plane didn’t have a glider tow hook. They eventually found one is a surplus yard in Los Angeles and attached it.
Now that the flight of the prototype was becoming a reality, the team needed to overcome a series of objections. They had to install an ejection seat, which added 250 pounds to the M2-F1 although the fact that the seat and pilot were in the center, the added weight didn’t unbalance the lifting body. However, it did mean they needed higher airspeeds to fly. They added small rockets in the tail, which could be used to extend the landing flare for a few seconds if needed. And finally, they added a placard to the interior which stated No Aerobatic Roll Maneuvers.
Clearly there was some opposition, however the team’s program manager was 100% behind them, to the extent that Reed later wrote that he risked his career to support their project.
The plan was for the R4D Skytrain to tow the lifting-body to 5,200 feet over the lakebed and then let go. Thompson was given clear instructions that if he couldn’t achieve level flight he should simply eject and not try to recover the prototype.
Once in the air, Thompson found that the visibility from the M2-F1 cockpit was very bad. The Skytrain realigned to tow the smaller vehicle about 20 feet above it, so that the pilot could see the aircraft through his nose window.
Thompson released the tow line.
The M2-F1 immediately went into a steep descent of about 3,600 feet per minute. From the ground, it looked like the prototype was simply falling from the sky but this was exactly how it was supposed to work.
Unlike the normal landing of an airplane, landing the M2-F1 was more like pulling out of a dive. A pushover maneuver had to be done at about 1,000 feet to build airspeed up to about 150 miles per hour, followed by a flare at about 200 feet altitude from a 20-degree dive. The flare maneuver would take about 10 seconds, leaving three to five seconds for the pilot to adjust to make the final touchdown. Milt had the option of hitting a switch to fire a rocket motor, giving him five to six more seconds to adjust the sink rate before touchdown.
At 1,000 feet above the ground,Thompson lowered the nose into a 20° dive to increase the speed to 150 miles per hour. He flared at 200 feet and landed exactly on the planned touchdown spot without using the rocket.
It was perfect.
The flying research continued over 1964 and 1965, with the M2-F1 flying twice a week on average, or as quickly as the research team could “digest the data” from one flight and plan the tests for the next one.
The tests generally went well but then one day, it went wrong. Shortly after lift-off, at just 200 feet above the ground, the test pilot (Gentry) made small roll inputs to counteract the movements of the tow plane. But as they continued, he needed to make larger and larger corrections. The team on the ground watched in horror as the M2-F1 rocked side to side in an uncontrollable oscillation.
Travelling at 100 knots airspeed (about 115 mph or 185 km/h) the M2-F1 twisted upside down with the nose high. The test pilot released the tow line.
Normally, the vehicle would be straight and level and stabilised at 120 knots and the pilot would flare at about 300 feet above the ground. There was no strategy for dealing with the vehicle if it became inverted and the probability of recovery was effectively zero. But the test pilot ignored the odds. He continued to descend and then touched down on the lakebed as he completed the barrel roll. There was no time to think: the manoeuvre from releasing the line to landing took nine seconds. The landing gear broke as he touched down but nothing else was damaged, except, as Reed says, the test pilot’s pride.
The M2-F1 continued testing but three years after its first free flight, the M2-F1 rolled again. It was the same test pilot flying and this time he at least knew what to do. He released the tow rope and completed the barrel roll. This time he used the landing rocked to touch down perfectly and there was no damage to the M2-F1. Nevertheless, the management lost faith in the M2-F1 and the first lifting body was retired from flight in 1966.
The next model, the M2-F2, was based on the same design but bigger and heavier. Instead of being towed, the M2-F2 was launched from its mothership, NASA’s Boeing B-52 Stratofortress. It received mainstream attention after a crash in 1967, and the footage of the crash inspired the premise for a popular American television show, The Six Million Dollar Man.
When NASA astronaut Steve Austin is severely injured in the crash of an experimental lifting body aircraft, he is “rebuilt” in an operation that costs six million dollars.
Here are the opening credits:
And here’s footage of the real crash, in which the test pilot lost control on landing. Unfortunately, the only online version I found showing the various angles has been “improved” with music, so I recommend muting the audio before watching.
Note: if you subscribe to the mailing list and cannot see the videos, you may need to click through to the website to view them.
This was the only serious accident which occurred over the years of the lifting-body flight testing.
Research continued on manned lifting bodies, with a focus on metal heavyweight designs. The M2-F2 led the way to the Northrop HL-10 and the US Air Force X-24 programs, leading the way to the space shuttle programme .
The M2-F1 program proved to be the key unlocking the door to further lifting-body programs, including the current Shuttle spacecraft and several other vehicles currently in progress, such as the X-33. Flight tests of the M2-F1 supplied the boost in technical and political confidence needed to develop low lift-to-drag ratio, unpowered, horizontal-landing spacecraft.
The original M2-F1 was restored in the mid 1990s and returned to NASA Dryden. It is now on display at the Air Force Flight Test Museum at Edwards Air Force Base in California.
If you have found this of interest and would like to learn more, then I recommend downloading the book, which NASA have kindly made available as a PDF: Wingless Flight: The Lifting Body Story by R. Dale Reed