Convair XFY-1 Pogo

The Convair XFY-1 Pogo is one of many attempts made after World War II to devise a practical Vertical Take-Off and Landing (VTOL) combat aircraft. The British finally succeeded with the Hawker-Siddeley Harrier, but before this aircraft arrived, firms around the United States experimented with various VTOL configurations. Wartime experiences had revealed how vulnerable fixed land bases could be to enemy assault from land or air. Aircraft carriers were also vulnerable as demonstrated by Allied experiences with the Japanese kamikaze threat. The U. S. Navy depended on aircraft carriers for many things, including fleet defense, but to assign a carrier task force to protect every convoy or cover every naval operation was impossible. After the U. S. Army Air Forces and the Navy demonstrated practical helicopters during World War II, naval strategists began considering the feasibility of stationing VTOL interceptors aboard non-aircraft carrier hulls.

In 1947, the U. S. Air Force and the Navy conducted design studies under Project Hummingbird. With these data and captured German material from the Focke-Wulf Triebflugel (thrust-wing) program, the Navy launched a formal VTOL fighter study in 1948. The aim was to develop an aircraft that could take off and land vertically on destroyers, LSTs (Landing Ships, Tank), fleet oilers, transports, and larger ships not otherwise equipped to handle conventional aircraft. In theory, a VTOL fighter could protect the mother ship or join other VTOL fighters to defend a task force or convoy.

After four years of study, the Navy awarded contracts to Convair and Lockheed to design, build, and fly experimental VTOL fighters in May 1951. Each company agreed to build two prototypes but in the end, they built only one Lockheed XFV-1 and one Convair XFY-1 Pogo. The XFV-1 never made a vertical takeoff and landing primarily because the Navy gave to Convair the only powerplant rated for both vertical and horizontal flight. The XFY-1 could not only take off and landing vertically, it could also transition to horizontal flight and back and did so many times. A number of interesting design features contributed to this prototype's success.

Both airplanes flew behind the same powerful Allison YT-40 turboprop engine. Allison created the YT-40 by mounting two smaller T-38 powerplants side-by-side and feeding their output into a single, massive gearbox. This brute pumped 5,850 shaft horsepower into two, 4.8 m (16 ft) diameter, counter-rotating propellers.

At rest, Pogo sat atop the trailing edges of its two wings and dorsal and ventral fins. Convair fitted a small, castering wheel onto the end of a strut several feet long and mounted four of these to form an improvised landing gear at the tips of the wings and fins. At touchdown, the struts compressed several feet, like a child's pogostick, to dampen impact forces. There were no brakes and the wheels rolled freely so flying under no-wind conditions was important. This was tolerable on a prototype but the Fleet could not have accepted a production VTOL fighter without brakes on the landing gear.

Because it launched and landed vertically but cruised horizontally, the pilot's seat had to rotate for safety and comfort in both flight regimes. Convair provided about 7.6 m (25 ft) of rope tied inside the cockpit so the pilot could dismount safely in case of off-field or emergency vertical landing. Although weapons were not tested, one proposed armament configuration consisted of either 48 folding-fin aerial rockets or up to four 20mm cannon mounted in the wing tips.

By February 1954, Convair had tested the engine in a vertical stand at Lindbergh Field, San Diego. It performed without problems and the company joined the engine to the airframe a month later. In April, Convair moved the project to Naval Air Station Moffett Field near Sunnyvale, California, for a series of tethered flight tests. It ran these experiments in the old Airship Hangar Number One built in the early 1930s to house the dirigible USS Macon.

On April 29, 1954, James F. "Skeets" Coleman, a lieutenant colonel in the Marine Reserve and a Convair engineering test pilot, made the first tethered flight in the Pogo. The XFY-1 was very much experimental. No other propeller-driven aircraft with similar size, weight, and engine power had ever attempted to take off and land vertically. The Pogo required safety lines to protect the pilot and the aircraft. Convair removed the propeller spinner and rigged a tether to a fitting in the nose. The tether streamed from a motorized reel controlled by Convair flight test engineer, Bob McGreary. McGreary could wind-up the reel and snatch the Pogo upright if Coleman lost control. Four more lines steadied each wingtip.

Coleman completed many tethered flights in the hangar, more than sixty hours of flying time, but it was dangerous work. The 4.8 m (16 ft) diameter propellers thrashed up a tremendous airflow that turned extremely turbulent as it washed against the inside of the hanger. Several times, Coleman called McGreary to "catch me, catch me" and the engineer slapped a button, spinning the reel to tighten the tether and steady the teetering Pogo.

By August, it was time to move outdoors. Coleman completed his first free flights on August 1st. He rose 6 m (20 ft) on the initial attempt but soared to 45 m (150 ft) on the second try. A short time later, Convair moved the aircraft to Naval Auxiliary Air Station Brown Field, California, to continue testing, including transition from vertical to horizontal flight. Coleman flew more than 70 additional takeoff-hover-landing flights in keeping with his conservative, safety-first approach to the XFY-1. He gained valuable experience with every flight. On November 2, 1954, Coleman finally transitioned and flew horizontally for 21 minutes. The test pilot spent seven minutes hovering. Just two days later, the aircraft made its public debut. Coleman launched and transitioned about 15 m (50 ft) above ground, thanks to tremendous engine power and a low-drag, streamlined airframe. The Pogo was fast too. Even with the throttle set at minimum power, the XFY-1 knifed through the air at well over 483 kph (300 mph). The airplane had no speed brakes or spoilers to help control airspeed and Coleman often outpaced the chase aircraft assigned to monitor him.

Trouble controlling low-speed velocity only aggravated the problems encountered during landing. Coleman's technique was interesting. He approached the field low with the engine set at flight-idle. At mid-field, he popped the control stick back into his stomach and pitched the airplane's nose straight up. The speed fell sharply but just as he reached the peak of his climb, Coleman applied power and stopped the Pogo in mid-air. With practice, the testpilot could stop the climb in a hover, reduce power and "back" down to a nice landing.

His descents often began higher than 300 m (1,000 ft). The aircraft was not stable and maintaining a hover required constant corrective action on the flight controls. Close above ground, the Pogo descended through its own, turbulent propwash, and Coleman fought the controls to get through it. With great skill and huge control inputs (stick and rudder pedal deflections), the test pilot brought this flying experiment back to earth safely, every time.

Yet another problem for the pilot made landings the most challenging part of flying the Pogo. When descending for touchdown from a high hover, Coleman found it almost impossible to judge rate-of-descent accurately with eyeballs alone. The Ryan Aeronautical Company developed a compact radar altimeter and mounted it in the left wingtip pod. Signals from the altimeter activated three lights: green signaled a stable hover or ascent, amber meant the rate of descent was safe, and red signaled an unsafe dive toward the ground at more than 10 feet per second.

Coleman climbed the airplane to 3,000 m (10,000 ft) on February 5, 1955. At this altitude during winter, temperatures can drop to freezing, yet he never closed the canopy once, during the entire time he flew the XFY-1. Convair installed an ejection seat but everyone thought it unreliable and technicians disarmed it. If serious trouble occurred in flight, Coleman's only option was to "step over the side" but it was considerably easier to leave the airplane if the canopy was already open.

No other pilot flew the airplane until May 19, 1955. John Knebel attempted to fly without tethered rig experience and the flight nearly ended in disaster. The Navy moved the tether rig from Moffett Field to Brown, and two other pilots began training in May 1956 but the end was already near. The giant gearbox had begun to wear and bits of metal were appearing in the lubricating oil. It was time for a major overhaul but the Navy was becoming enthusiastic about flying fixed-wing jets from aircraft carriers. Coleman had made his last flight on June 16, 1955. Interest in the program, and the funding, was disappearing and on August 1, 1956, the Navy closed the books on the XFY-1.

The Pogo proved that the VTOL fighter concept was theoretically possible but that much work remained to make the idea operationally practical. As it stood, flying the XFY-1 required above-average piloting skills and special training. It remained near San Diego for several more years until the Navy shipped it to Naval Air Station Norfolk, Virginia, and the Pogo sat "gate guard" there for a number of years. In 1973, the Navy transferred the aircraft to the National Air and Space Museum.