The problem with airplanes is that they need runways, and in wartime, the average runway might as well have the words "Bomb Here" painted on it in big block letters. Runways are among the first targets bombed when a war starts, so over the years people have hatched various schemes to build combat airplanes that don't need a vulnerable stretch of pavement.
Seaplanes substitute water for concrete, but when the Jet Age came along, seaplanes proved ill-suited to the higher speeds. The Navy's Convair Sea Dart, essentially a jet fighter on water skis, experienced such severe vibration on takeoff that the testing program was scrapped after only five of the model had been built.
Vertical-takeoff-and-landing aircraft like the turboprop-powered Lockheed XFV-1, Convair XFY-1 "Pogo," and pure-jet Ryan X-13 Vertijet were all designed to operate without runways. But the turboprop "tail sitters" were not popular with their pilots, who had to look over their shoulders to make the necessary tail-first, feel-your-way-down landings. The X-13 had the same problem, and none of the three went beyond the experimental stage.
In the 1950s the ultimate solution appeared on the conceptual horizon: the portable runway. The idea arose in the minds of planners to put rocket-boosted jet fighters on the decks of flatbed trailers. By adding a solid rocket booster powerful enough to catapult the airplane to flying speed, they could reduce the runway to a short ramp that could be hidden until it was needed, or towed around so its position was constantly changing. Then, when the time came, the crew could simply stop the truck, set up the launcher, and fire the airplane.
For all its apparent craziness, the plan had significant advantages. It gave Air Force planners unprecedented freedom and mobility: The aircraft weren't tied to a known location. For another, the concept promised total immunity from the "Bomb Here" problem posed by a fixed runway. You didn't even need a road; you could drive the trailer into a wheat field, desert, or cow pasture, raise the airplane's nose to its firing angle, light the engine, afterburner, and rocket, and off you'd go. Theoretically, you could also park the truck in a garage, barn, or mountainside cave and launch the airplane from inside the enclosure. The aircraft would be fully airborne even before clearing the hangar doors.
As odd as these ideas seem today, they were all developed and tested with real, full-size, fully loaded fighters. And they worked perfectly, time and again, though the whole concept ignored one question: After a jet was launched, where would it land? As it would turn out, the ultimate mission for truck-launched airplanes rendered the question irrelevant.
The Air Force's jets-on-trucks concept had its roots in the early days of aviation, when a few forward-looking aeronauts first mated rockets and gliders. In Germany, first Friedrich Stamer (in 1928), Julius Hatry, and finally Fritz von Opel (both in 1929) flew gliders that were boosted aloft by solid-propellant rockets--the earliest known examples of jet-assisted takeoff. The first flight of a conventional aircraft boosted by JATO was made in 1929, when an overloaded Junkers W33 seaplane took off from the Elbe River near Dessau, Germany, with the aid of six black-powder rockets. In 1941, Homer A. Boushey, a U.S. Army Air Corps pilot, achieved a milestone when he took off in a two-seat Ercoupe solely on the power of a rocket.
Boushey, a Stanford graduate and former airmail pilot, had been so gung-ho about rocketry that in 1939 he'd written to Robert Goddard at his Roswell, New Mexico testing location and later traveled to the site to visit the pioneering rocket scientist. While he was stationed at Wright Field in Ohio, Boushey was assigned to the aircraft lab to investigate rocket propulsion. Meanwhile, at the California Institute of Technology, Theodor von Karman and his staff had, after several failures, managed to produce small rockets reliable enough to be attached to a light aircraft. Boushey came up with the idea of putting them on the Ercoupe.
"The idea was we wanted to get as light a plane as we could," Boushey remembers. "The Ercoupe belonged to the Army Air Corps. I flew it out from Wright Field to March Field in California, where we made the test." The tests, conducted in August 1941, were highly successful: three solid-propellant rockets were strapped under each wing of the airplane, and the Ercoupe took off in about half the length of runway it normally used.
At the end of the tests, Boushey recalls, "von Karman said, 'Just for history, let's unscrew the propeller and be the first to fly an airplane with rocket power alone.' "
To be sure of getting off the ground, they doubled the number of rockets and started the airplane rolling by towing it with a rope attached to a truck. Boushey left the cockpit canopy open and held the end of the rope in one hand. Thus was born the little-known and short-lived concept of Rocket-'n'-Rope-Assist.
"I guess I must have gotten 30 or 40 miles an hour before the tension got too great for me to hold onto," Boushey says. "Then we lit the rockets--we put 12 on instead of six--and it took off in a hurry."
A dozen years later, JATO technology had improved to the point that the Air Force wanted to demonstrate the concept of zero-length launch. After all, early cruise missiles were routinely launched from short ramps; why couldn't ordinary aircraft, appropriately souped-up with the latest in rocket boosters, do the same? As for the landing run, you could shorten that too, by equipping the airplane with a tailhook that would engage an arresting cable, allowing the airplane to slow abruptly and settle onto a huge (80- by 400-foot, 30-inch-high) inflatable rubber pad. The theory was that the jet would descend gear up, snag the cable, whomp onto the slick surface (which had been lubricated with something suitably slippery), and slide to a stop on its belly.
It was the kind of scheme that only a rocket booster manufacturer intent on opening up a vast market could love. Clearly, the whole system--which came to be known by the acronym ZELMAL (zero-length launch and mat landing)--would have to be tested. Testing began at California's Edwards Air Force Base in December 1953, with rocket-assisted Republic F-84G Thunderjets flying from a trailer-mounted aircraft launcher. The takeoffs were uniformly successful. "The airplane was completely under control and the pilot was flying the airplane from X minus zero," recounted a declassified secret report on the project. "There was nothing to it," says George Rodney, who flew some of the launches. "It was a very nice takeoff."
The mat landings were another story. The underlying rationale was simple enough: The object was to land very short. This could have been accomplished with aircraft carrier-type arresting cables alone, but that would have required strengthening the airplane's landing gear so it could survive the tremendous G-forces and impact produced by the arrests and recoveries. The purpose of the mat, with its rubber air cells, was to absorb the shock of sudden deceleration and thereby eliminate the need for landing gear altogether. In return, the airplane would be able to carry another 500 pounds of bombs or fuel.
"You didn't have to design the plane for the huge Gs that you get in a carrier airplane," says Rodney. "Any Navy airplane has a very distinct weight penalty because of all the beef that has to be put into the landing gear. What the mat did was allow you to take a typical Air Force design--a standard fighter--and make an arrested landing with it.
"The other issue is that you can carry the inflatable mat; you just dump it onto an unprepared field," he adds. "The whole mat was truckable. It all fit on a couple of trailer trucks."
In practice, though, this miracle appliance didn't work out too well. The mat leaked the first time it was set up, and several of the rubber air cells had to be sent back for repair to the Goodyear Tire and Rubber Company, which had manufactured them. As for the landings themselves, "The initial mat landing was performed on 2 June 1954 but it was unsuccessful," according to the declassified report. "The F-84G test aircraft, USAF S/N 51-1225, piloted by Robert Turner, Glenn L. Martin test pilot, was wrecked beyond economical repair. Turner received back injuries which grounded him for several months." (He later recovered but died in 1969 while testing a Martin-built B-57.)
Turner's tailhook missed the arresting cables and tore through the surface of the mat, puncturing three air cells. The mat was again repaired by Goodyear and readied for another attempt. Two more test landings met with better results. Still, during the second landing the pilot suffered a strained neck--"due to the high pitching rate (62 deg/sec) when the hook engaged the arresting cable." On the third try the aircraft behaved the way you'd expect of a 15,000-pound object smacking into a pneumatic tube at 144 mph: "The airplane hit 10 degrees nose down, bounced level, and then pitched 11 degrees nose down again."
But that was how it was supposed to work. "That was more or less the way the thing was designed," says Rodney. "The plane would hit and bounce up and pitch a little bit, and then come to a halt. When you hit the cable, it essentially brought you to a halt in mid-air. Then it pitched you into the mat, and the mat of course was resilient, and it threw you back up in the air again. Not very far. Four or five feet, I would guess."
The one thing the mat did not do, however, was bring the pilot's head to a safe and gentle halt. "We tied ourselves into the seat real well, so we wouldn't pitch forward into the control column and into the instrument panel, but unfortunately your head, it goes through a big arc and comes down on your chest," says Rodney. "Your head came forward like a shot, and I ended up with a gimpy neck. Even right now I have a little after-effect from that--one of the few [bad] things that ever happened to me in flying."
Originally, 30 mat landings had been planned, but the program was canceled after just three attempts. "Sufficient data had been obtained on the two successful landings for the evaluation team to complete their report," said an official summary of the tests. And at that point, after a total of 28 launches, 25 conventional landings, and three mat landings, the ZELMAL project was considered closed.
"It needed some more work, that was for damn sure," says Rodney. "At the end, the Air Force had no interest in it whatsoever."
The zero-length-launch concept, though, survived. Military planners could not let go of the idea of dispersed, mobile, A-bomb-equipped jet fighters instantly launchable from roadside rest stops. The mat landing was easily dispensed with. The point of the exercise was to present a credible deterrent to an enemy's first strike, and for that all you needed was a flock of nukes headed off toward Moscow. The whole question of landing--a question nobody seemed to ask--was simply irrelevant.
The ZEL project was revived in 1957, the idea now being to launch the airplanes from roving trailer trucks and have the pilots, once their missions were accomplished, eject. "You may not find any place to land, [so] you just punch out when you get back to friendly territory," says Al Blackburn, who flew this second series of tests. "You hope you get back to friendly territory, but what happens to an airplane after you drop nuclear weapons is of very small consequence."
It's not surprising that Blackburn remains unruffled by the thought of a one-way flight. A preternaturally calm test pilot, Blackburn had acquired the reputation of being a little on the overly relaxed side. He recalls that during ground school, "I would always nod off, and the sergeant--or whoever was doing the instruction--would be yelling at me, and after a while he'd say, 'Okay Lieutenant Blackburn, you stand up. If you can't stay awake sitting down, you remain standing.' And then the whole class would get absorbed because I would fall asleep standing up too, and I'd start falling over, and people would wonder if I was going to catch myself." Which he always did. But then there was the time he fell asleep in flight.
"I was up in a Corsair putting in my two hours of night time--you know, just to fill up my logbook--and I was up there droning around, and it was kind of dull, and I fell sound asleep." He woke up after a period he estimates was "no more than 30 seconds."
Blackburn graduated from the Naval Academy as a Marine, fought at Okinawa, returned to the States, and became a carrier-based fighter pilot. After leaving the service in 1949, he got a master's degree in aeronautical engineering from the Massachusetts Institute of Technology, then was recalled during the Korean war and spent a couple of years test flying for the Navy at the Naval Air Test Center at Patuxent River, Maryland. In 1954, he became an engineering test pilot for North American Aviation in Los Angeles. At the company's Palmdale flight test facility, he earned the title of Glider King when, within one two-week period, he experienced unrelightable flame-outs in three successive F-86 Sabrejet flights and managed to land all three craft. By 1957, when he was asked to participate in the resurrected zero-length-launch project, he was ready for just about anything.
"I thought it was interesting," he says. "It sounded like a neat idea."
Although the F-84 tests had demonstrated the general feasibility of zero-length launch, a whole new generation of jet fighters had arrived on the scene. This time around, the workhorse would be the North American F-100 Super Sabre, the world's first supersonic jet fighter. At 35,000 pounds, the F-100 was more than twice as heavy as the F-84. Could the heavier fighter, equipped with a nuclear warhead (the so-called T-63 store), still be fired off a flatbed truck?
The first thing Blackburn did was have a talk with Bob Turner, who'd flown the first F-84 tests. Turner had a no-sweat attitude about the whole thing, comparing the takeoff to a conventional catapult launch from an aircraft carrier. He did have one suggestion for his successor: Make sure you are in sole control of the moment of firing; that way, you can brace yourself for the blast.
The blast would indeed be something to prepare for. The Rocketdyne solid-propellant booster would generate 130,000 pounds of thrust for four seconds, and at burnout the F-100 would be at an altitude of 400 feet and traveling at 275 mph. Supposedly, it would be airborne after a total takeoff run of three-eighths of an inch, the actual length of the ramp that guided the airplane during the initial instant of its launch. During launch, the pilot would experience a maximum force of 3.5 to almost 4 Gs.
Blackburn went back to Patuxent River for some catapult work, and later took a few rides in the centrifuge at the University of Southern California, some producing as much as 13 Gs--all of which left him pretty much unfazed. Of more concern to him was the matter of booster alignment. It was essential that the booster's center of thrust pass through the airplane's center of gravity, or else some rather stellar nose-up or nose-down effects would result. Well before they tested a real F-100, engineers ran a series of launches using a steel-and-concrete dummy called an iron bird. During one test launch, an iron bird did a backward somersault and a few other uncontrolled aerial maneuvers, so everyone knew the booster's thrust line was critical.
But the first manned shot went perfectly. "It was exhilarating! It was just as predicted--no surprises," says Blackburn. "A great feeling of acceleration, like you get on a roller coaster. It's better than any ride you can find at Disneyland."
Not until the next flight did a problem emerge, when the rocket booster wouldn't separate after burnout. This was a cause for concern because there was no way to land the jet with an empty rocket bottle dangling from it like some kind of malignancy. Blackburn flew around for an hour and a half trying various tricks to nudge the thing loose, but nothing worked. He finally ejected, somersaulted, and made a rough landing in a 35-mph wind. The F-100 augered in nearby.
A postmortem revealed that the booster had gotten hung up on the attachment bolts, which were supposed to shear off but hadn't. Blackburn's next airplane was equipped with a redesigned booster attachment system featuring explosive bolts that could be detonated on command. After that, there were no problems of any consequence. Between March and October of 1958, North American performed 14 successful launches, often making one flight per week. The whole procedure became so routine that when Air Force pilot Bob Titus flew a public demonstration of the concept at Nevada's Nellis Air Force Base, he executed a roll after burnout. ("I did it as I came off the launcher," he recalls. "It was a four-second rocket burn, and when the rocket fell off I did a roll. It's only every now and then that you get to shine in front of a crowd.")
At this point the feasibility of zero-length launch was, if anything, overproven. With a properly modified airplane, the whole procedure was trivial: You could set up for launch in about five minutes. "Probably you could do it in less if you were on really high alert," says Blackburn.
But just when all of it had been proven beyond reasonable doubt, serious misgivings arose about the whole idea. Europeans were growing wary of schemes in which nuclear exchanges took place above their towns, and the prospect of live nuclear bombs roaming around the Continent was becoming an increasingly sensitive issue. Then there were security aspects to think about: sabotage, accidents, visions of stray F-100s ending up on someone's front lawn.
But there was an alternative: You could hide the things away, store them in "hard sites"--bomb-proof bunkers that could be scattered along the perimeter of air bases, deep in forests, or off in tunnels. The airplane would fly from the same trailer, but it would be an "indoor" launch as opposed to an "outdoor" one.
On August 19, 1959, Blackburn made the world's first indoor takeoff from New Mexico's Holloman Air Force Base. He loved it. "A smooth, slick, easy way to go," he says.
At that point, he recalls, "We said the only thing we haven't done, other than launch in a blinding blizzard, is to do one at night. So I did that too."
And finally there was nothing more to prove.
Later that year, Blackburn went around the country giving briefings to various Air Force higher-ups. He made a tour of Europe, presenting the ZEL story to the military commanders of England, Denmark, the Netherlands, Germany, France, and Italy. Everyone agreed that this was a great notion, entirely workable, with no show-stoppers in sight. More than a hundred F-100s incorporating provisions for zero-length launch were actually built, and then...
Every few years after the second cancellation of the ZEL program, Blackburn would be called to the Pentagon to tell them all about it once again. People would listen politely, nod their heads, and say it was all very interesting. And still nothing would happen.
In the early 1960s, the concept was trotted out and tested yet again, this time with Lockheed F-104 Starfighters, which began lifting off smartly from launchers just as the F-84s and F-100s had done. These new tests were sponsored by the Luftwaffe, which had a bunch of F-104Gs on hand. But once again no hard sites were built and no nuke-laden fighters were driven hither and yon around the countryside.
Everyone involved has a theory about why the whole thing fizzled. Bob Titus says, "I'm sure the commander in Europe said, 'Look, there's no way I can provide security for these aircraft if we stick them out in the woods. And maintaining them--and maintaining my training schedule--that can't be satisfied with planes in hard sites.' "
"The issue was whether it was really needed," says George Rodney, "especially when you have a modern extended-range fighter with drop tanks, which can go quite a distance. And it was fairly expensive--it took a rather large bottle, the solid rocket motor. Anyway, the tactical need for it never materialized."
Al Blackburn says, "The security requirements for it--to have enough security personnel, plus all the cooks and bakers that you'd need to feed them--that took more people than they had in Germany. That's what killed the concept."
Whatever the reason, the zero-length launch was abandoned until the Marines solved the runway problem with an airplane called the Harrier. The now famous vertical-takeoff "jump jet" even eliminates the need for the rocket booster and the flatbed trailer.
George Rodney is retired in Florida. Bob Titus spends much of his time skiing at Snowmass, Colorado. Al Blackburn runs an aviation consulting firm, flies sailplanes, and has plans for a nonstop flight around the world--solo. This would top Voyager's nonstop flight with two souls aboard. And the Voyager had a lift-to-drag ratio of something like 28 to 1; Blackburn has a glider with a ratio of 57 to 1. His current idea is to glue two of them together, put an extremely fuel-efficient engine on the result, and head east.
"I could go around the world in five days and burn 1,500 pounds of fuel," he says. "I'm serious. You're going to have the best meteorological people in the world, you're going to fly at the right altitude, you're going to go from west to east, not the other way, you're going with the high winds. They guarantee me a 100-knot tailwind all the way."
A world record. Easy. Nothing to it. "It's going to be on autopilot, for God's sake," says Blackburn. "All you got to do is sit there and sleep."