The problem with airplanes is that they need runways, and in wartime, 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.
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.
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.
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 inflatable rubber pad. The theory was that the jet would descend gear up, snag the cable, whomp onto the slick surface and slide to a stop on its belly.
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 was to absorb the shock of sudden deceleration and thereby eliminate the need for landing gear altogether.
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."
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. "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.
The zero-length-launch concept survived through at least two more experiments with F-100s and F-104s. But, in the end, logistics and the Harrier finally put the concept to rest.
The photo below is a frame from the Air & Space video. The video shows a test conducted of one such launch, and may be viewed using QuickTime viewer (required, available for download from the Air & Space web site) by going to the Air & Space F-84 Zero Length Launch page. For the complete story, order a copy of Runways of Fire from the Air&Space Website Market. The article from the October/November 1995 issue is also available online.
Frame from Air & Space video showing F-84E during Zero Length Launch.