THE 456th FIGHTER INTERCEPTOR SQUADRON

THE PROTECTORS OF  S. A. C.

 

Click on Picture to enlarge

 

The Convair XFY-1 "Pogo"

+ Larger Font | - Smaller Font

Originally published in Air & Space/Smithsonian Magazine, Oct/Nov 96.

By Stephan Wilkinson

 

Click on Picture to enlarge

Convair XFY-1 Pogo

One was the riskiest military airplane Lockheed ever built, by the company's own admission. The other "coulda been a contender," in the opinion of the one pilot who successfully flew it. One school holds that neither airplane operated long enough to prove either statement. Another holds that these strange craft flew just long enough to save the U.S. Navy a great deal of money by proving that the concept upon which they operated was terminally flawed.

They were the Tail Sitters--the Convair XFY-1 "Pogo" and the Lockheed XFV-1 "Salmon"--and in the mid-1950s their half-lives flickered, flared, and faded in a matter of months. They were prototype point-defense interceptors intended for the Navy, and their sole virtue was that they didn't need a runway. The XFY-1 and XFV-1 were designed to perch on their tails, like malevolent lawn darts, and take off straight up, obedient to the howling thrust of enormous contra-rotating propellers.

Helicopters do much the same thing. Unlike helicopters, however, the Tail Sitters eschewed the complications and performance limitations of rotor blades, which must hinge, twist, and flex to simultaneously act as lifting and thrusting surfaces in forward flight. The Tail Sitters transitioned from helicopter to airplane by simply pushing over from the vertical ascent to conventional horizontal flight.

Then their stubby wings came into play, and the contra-rotating paddle blades went to work purely as huge thrusters, powering the Pogo (and theoretically the XFV-1) to-well, not F-104 speeds, but at least 575 mph. These airplanes were never intended to be air-superiority dogfighters but bomber killers, rising like angry wasps to protect their ships. Rather than range, loiter time, or supersonic speed, they needed--and ostensibly had--the ability to report for duty with the alacrity and accuracy of a well-aimed five-inch cannon round.

All well and good, but now we're humming along in a Tail Sitter in level flight, mission accomplished. The target is history, the guns are empty, the fuel tanks are reaching that state, and it's time to land--in a Tail Sitter, the procedure that separated the men from the boys. A Tail Sitter returning to base had to again "go vertical"--translate from high-speed horizontal flight to a nose-up hover--and then reverse course, backing down to a landing. This required the pilot to judge his attitude, altitude, and position over the ground while lying on his back and looking over his shoulder as he worked the throttle and flight controls to set up a controlled descent to what in real life might well be a rolling, pitching, crowded ship's deck.

"Takeoff was very easy," recalls James F. "Skeets" Coleman, an ex-Marine fighter and dive-bomber pilot who was the XFY-1 project test pilot. "You can trim up an airplane fast on takeoff." We were sitting in the shade of a dusty hangar on Brown Field, on the Mexican border south of San Diego, very near the concrete ramp where Coleman had first flown the Pogo through its entire routine. Once a Navy auxiliary field, today Brown is home to sun-bleached Cessnas, tired Pipers, and the Experimental Aircraft Association chapter for whom on that Saturday Coleman and his girlfriend had volunteered to make lasagna.

Click on Picture to enlarge

Coleman, now 72, has the worn face of a long-ago prizefighter, but he is a charming and gentle man with an easy laugh. He smiled as he looked back 40-some years to a time when his Marine Reserve greens still fit snug, when he was a test pilot with an aeronautical engineering degree and dreams of someday building and marketing his own flying automobile. "But landing-," he shook his head. "When you came in and pulled it up into the vertical, you were faced with three different configuration changes at the same time, all the time trying to figure out when to add power since you didn't want to zoom up too high, because you had a hell of a time backing down.

"When you pulled up, you had to rotate your seat--it moved from the normal in-cruise position to a setting that put it about 20 degrees up from the horizontal when the airplane was straight up. So you have a seat rotation change, a trim change, and a power change, and at the same time your attention goes from your instrument panel to looking down back over your shoulder, because you can't fly the thing and follow the instruments. Jeez, I still have a stiff neck from that," Coleman says with a laugh, shrugging his shoulders like a wrestler working out a kink.

The terrible danger, however, was that at a descent rate of greater than 10 feet per second, the airplane would suddenly tumble, totally out of control, most likely at an altitude too low for successful ejection. (It had already happened to a Pogo model in a wind tunnel.) The irresistible temptation was to play it safe: hover, even climb. But the higher you climbed, the more you had to work at backing down. And the farther off the ground you were, the more difficult it became to judge vertical speed and altitude. "Standing still at 500, 600 feet, I lost my depth perception," Coleman says.

Coleman had practiced by flying every helicopter the Navy would provide (he was by that time a civilian with a commercial helicopter rating). "These Navy helicopter guys would tell me they could hover at 500 feet and know whether they were going up or down, so I said, 'Fine, let's mask off your rate-of-climb and altimeter.' And they couldn't do it."

He learned to fly the Pogo in hover inside an enormous blimp hangar at Moffett Field, near San Francisco, while the airplane was tethered to keep it from straying too far. The main cable was attached above the propellers, and a winch operator stood by to jerk all the cables tight, suspending the Pogo like a badminton birdie on a string.

Click on Picture to enlarge

"My call was-'Catch me--catch me,' " Coleman later wrote in a report on those tests, "-and I had to call him a lot." The team eventually realized that the Pogo was being batted around by its own turbulence--a rotating doughnut of downwash, its own prop blast confined and cycled by the hangar walls. Coleman took the airplane outdoors for its first untethered tests.

Still, flying the Pogo in hover required a pat-your-head/rub-your-belly knack. "Here, let me take you for a hovering flight in a Pogo," says William F. Chana, today 75, who had been a Pogo flight test engineer. "Here's your control stick" (Chana hands me a pen) "and put your feet on the rudders. You're in the air, in a vertical hover. Okay, now, if you want to transition forward, what do you do?" I push the stick forward. "Right. Transition aft?" I pull the stick back a bit. "Okay. Transition to the right."

Click on Picture to enlarge

Coleman has already told me that the rudders controlled side-to-side movement when the airplane was vertical, so I step on a make-believe right rudder pedal.

"Okay. To the left. Okay. Now let's get back to neutral. Now let's transition 45 degrees to the left." Baffled, I poke the stick to the 10:30 position. "No, don't tilt the nose, stay in hover-no, you're not going that way-you gotta use some rudder and some forward stick. It's confusing as all hell-. You cannot fly the airplane unless you have 50 hours in the Moffett Field tether."

In the late 1940s Chana and two other Convair engineers had for the fun of it built the WeeBee, a tiny, 30-horsepower miniplane, in an attempt to fly the smallest airplane that could carry a pilot. The media inevitably called it "the world's smallest airplane" (and indeed it was, if you consider weight rather than wingspan). But what particularly interested Chana was that he flew the WeeBee while lying prone on the outside of a flat-topped fuselage, which was the size of a locker room bench. If you could fly a WeeBee while lying on your stomach as though you were doing a belly-whopper on a Flexible Flyer, why couldn't you fly a Pogo the same way?

Click on Picture to enlarge

"Skeets and I put a chair on the hangar floor at the tip of the Pogo's vertical tail," Chana recalls, "and I stood on the chair and just envisioned possibly flying it from that position." Chana saw that a vertical landing with the pilot in what would then be a standing position would be a lot easier than the neck-wrenching dentist-chair job Coleman had until then been doing. "I presented the idea to Convair, but it was too late in the Pogo's development to consider it," Chana says.

"If the program had gone faster, if we had come up with a couple of backup pilots, we would have had a good airplane," Coleman insists. "Because the more I flew it, the more I knew I could have put that thing down on a dime.

"We tried to check out John Knebel, my backup pilot, but he nearly destroyed the airplane. He couldn't help feeding in aileron, and soon he's twisting and turning up there. I finally got him down near the ground and got him to take out some of the cross-pad movement and said, 'Land it, Johnnie, land it!' He knocked a couple of the wheels off. We had to tell him to drop it, because he was over by the Ryan factory [at Lindbergh Field, Convair's San Diego base], and there were a lot of people out there watching him." Knebel, an experienced test pilot, wouldn't have had such problems had he spent 50 hours flying in a tethered rig, as Coleman had, but he hadn't had that chance.

Click on Picture to enlarge

XFV-1

Lockheed's Tail Sitter, the XFV-1, flew a lot more but accomplished somewhat less than Convair's, which ended up making six un-tethered flights for a total of two hours and 21 minutes. The XFV-1 never took off or landed vertically, instead flying its 23-hour flight test program from conventional runways, trundling along on stalky temporary landing gear that looked as though it had been borrowed from a biplane, complete with 1930s wire cross bracing. "We were able to do a lot of flying without putting the pilot in that jeopardy," says Ernest Joiner, today 78 but then, when he was the XFV-1's head flight test engineer, "just a kid."

Because of the Convair's deep ventral fin, "they couldn't do what we did--attach a somewhat conventional gear and put the airplane in the air--so we got a lot of information on the engine installation, how the airplane flew, and how all the systems worked," Joiner says. "I always felt the concept was flawed. To expect a pilot to be able to look down back over his shoulder and maneuver and land that thing confidently-it was a dumb idea."

The XFV-1 was something of an embarrassment to Clarence "Kelly" Johnson, the legendary Lockheed engineer who ran the company's experimental Skunk Works. Johnson is said to have once given a speech in which he enthused about the Tail Sitters as the first generation of an ever more capable vertical-takeoff-and-landing class of aircraft to come. The next iteration, he predicted, would not only land vertically in forest clearings but would then lower itself to a horizontal position and crawl into hiding among the shrubbery.

Click on Picture to enlarge

Johnson eventually recanted. "We did excellent in terms of cost and weight," Jay Miller quoted him in the authorized company history Lockheed's Skunk Works, "but this aircraft was a failure-because we had a bad powerplant, and we couldn't look back over our shoulder when flying the thing and judge height. We could practice [landing] on clouds all day, but this is the only airplane we ever built which we were afraid to fly ourselves in the final tests."

Both Convair's XFY-1 and the XFV-1 used the the new Allison T40 turboprop engine (two relatively proven T38s driving one contra-rotating propeller shaft through an admittedly unproven gearbox), and Skeets Coleman had been able to judge height well enough to land numerous times. But Coleman hadn't much liked the engine either, and it didn't help that Convair was simultaneously testing a large flying boat, the R3Y Tradewind, that used four T40 engines--or, to put it another way, eight paired T38s. "I heard from the test crew that on one flight of the R3Y they lost seven out of the eight," Coleman says. "That was worrisome, because on the Pogo, you'd have had no choice then but to blast out" if you lost even one.

Click on Picture to enlarge

Lockheed was initially encouraged by research that the National Advisory Committee on Aeronautics had conducted on a one-quarter-scale radio-controlled vertical-takeoff-and-landing model, but of course nobody needs to look back over their shoulder when landing a radio-controlled model. In the real world, however, the XFV-1 evinced a trait that didn't seem to bother the Convair Pogo, perhaps because the Pogo had large, highly swept delta wings while the Lockheed prototype had what were essentially stubby F-104 straight wings: When transitioning from horizontal to vertical flight, the XFY-1 was unstable.

Lockheed's test pilot for the project was Herman Salmon (stuck for life with the inevitable nickname Fish). He was a handsome, mustachioed, freewheeling Errol Flynn look-alike, not an engineer but a former barnstormer.

In an interview published in Steve Ginter's Naval Fighters: Lockheed XFV-1 VTOL Fighter, Salmon said, "[A] shallow transition was considerably different than the easy process of going vertical from a zoom climb. As you would slow down and pull up-about the time you hit 30 degrees and 60 mph, she'd want to start to roll and be quite unmanageable. At that point the prop wash was being deflected [due to the extreme angle of attack] and you weren't flying on the wing anymore, and the airplane was really stalled. Things would get progressively worse until you came to about 80 degrees, almost vertical, and then it would become quite easy to handle again."

Click on Picture to enlarge

Salmon was widely admired in the test pilot community, but he was never allowed to master the XFV-1. "We finally concluded that it was just foolish to risk the pilot's life with the lack of reliability that the engine/propeller combination had shown us," Joiner says today. "I had to write the letter to the Navy saying 'Dear Navy: We'd like to quit this program.' No, we didn't say 'Hey, Navy, this whole idea is too stupid to continue,' but I thought it was a flawed concept." In at least one sense, Salmon, who died in 1980 in the crash of his Super Constellation, made out better than Coleman. "Fish Salmon got a big bonus, and he never even took off or landed vertically," Coleman says. "Yet he made $15,000. He said to me, 'You're dumb, Skeets, you're dumb.' I got $2,000, as I remember. But he was a character."

We may never see the Tail Sitters' likeness again--at least not with a human pilot in the cockpit. (And a good thing too, say some strategists and engineers.) It was a project that found eager support only during what one aviation writer has called an era of "technological euphoria." Anything seemed possible in light of the incredible power of the turbojet engine and the dawn of supersonic flight. During the late 1940s and early '50s, airplanes had been flown with tails and without, with triangular wings, wings that moved, wings that looked like backward ironing boards, doughnuts, and flying saucers, and barely any wings at all. Pilots had flown lying down and standing up. Engines had been buried in every cranny of an airframe's structure--there were ramjets, jet seaplanes, even jet airliners.

Click on Picture to enlarge

The Germans had already done a great deal of work on VTOL interceptors to attack bombers when the Reich no longer had many airfields from which to launch conventional fighters. The Focke-Wulf Triebfl[florin]gel was the most notorious: It had three huge wing-like rotors that free-wheeled around the fuselage under the drive of vectored-thrust ramjets at their tips, but it never actually flew. Only the Bachem Ba 349 Natter made it into the air. The Natter was a primitive rocket plane launched from a vertical rail. Unfortunately, it had no landing capability. "I'd hardly call the Natter a VTOL," says military aviation writer Bill Sweetman. "It was more of a VTOLIIBP--Vertical Takeoff and Land In Itty Bitty Pieces."

"With the advent of gas turbines, it became possible for the first time for a fighter-type aircraft to actually have an honest-to-God thrust-to-weight ratio greater than one," says George Spangenburg, a retired civilian Navy employee. "The recips couldn't do it." That ratio is the reason modern jets can not only climb straight up but also accelerate simultaneously--they have many more pounds of thrust than pounds of weight--and it's the reason a Tail Sitter could jump straight off the ground.

Spangenburg, today age 84, is a legend in naval aviation. "He essentially took contractor proposals and analyzed them for both cost and performance," says Robert Heisner, an ex-Navy fighter and test pilot and former commanding officer of the Patuxent River Naval Air Test Center in Maryland. "He was the guy who would tell the Navy what this or that widget would likely cost and do--or not do--without regard to the contractor's marketing hype. He was very good. His numbers were so close that some people accused him of having moles inside the contractors' shops, which of course wasn't true."

Click on Picture to enlarge

Spangenburg was never a fan of the vertical-takeoff concept. "Ever since I've been in this business," he says, "there has been a VTOL Mafia in the Navy that is trying to do VTOL and is extremely optimistic in their outlook. You can make VTOL look awfully damn good on paper, until you try to do it in real life."

Apparently, the Tail Sitters looked good on paper. According to Spangenburg, "The Navy did a great deal of study work leading up to the Tail Sitters, trying to justify some place to use them--how in hell to use VTOL now that you were able to do it." So VTOL was an answer looking for a question? "There has always been a faction that said 'Let's do VTOL just because we're able to do it,' without any real regard for service utility," Spangenburg says. "The study concluded that the best justification for the Tail Sitters would be as a 'convoy fighter,' where you could put one on a merchant ship and if the convoy was attacked the fighter could take off" and beat back the threat. Skeets Coleman would disagree. He traces the genesis of the Tail Sitters back to the stunning impact of the Japanese kamikaze threat. "The Navy took a real beating from the kamikazes," Coleman says. "The carrier was really threatened. The Air Force was calling them sitting ducks no matter how many airplanes you put on 'em.

"The philosophy was to put the airplane on the back of any ship, under a teepee, so you'd have a line to intercept any airplane coming toward the carrier fleet," Coleman says. "It was never intended to replace the carrier but to give it a picket-line type of fighter protection."

Click on Picture to enlarge

"The idea was to spread your air power around, among a number of smaller ships rather than on one or two huge, vulnerable aircraft carriers," said John Fozard in an interview before his death last July. From 1963 to 1978, Fozard was the chief designer of the Harrier, the British jet-powered VTOL effort that began as the Hawker P.1127 in 1957 and culminated with the McDonnell Douglas AV8B Harrier II, ultimately the only VTOL fighter to be produced. "Carriers are hard to sink, that's true, but if you can hit one hard enough that it develops a 10- or 12-degree list, your principal weapon--the aircraft--becomes useless."

Still others say that the Tail Sitters arose--excuse the pun--from the Navy's sense that tactical nuclear weaponry had made it impossible to ever again marshal World War II-size task forces--that now our forces would have to be dispersed so that no single bomb blast could take out an entire carrier battle group. "I don't recall ever hearing that justification," says Spangenburg. Whatever the justification for the Tail Sitters, one real-world problem made it impossible to use them as individual sentries standing guard out in the nautical boonies. Airplanes--particularly complex turbine-driven fighters--need an enormous amount of coddling. Every merchantman and frigate that carried a Tail Sitter would also need a crew of mechanics, armories, avionics technicians, and specialists trained to launch and retrieve it. "In the real world, it just doesn't make sense," Spangenburg says.

Click on Picture to enlarge

"Maybe they just thought, 'Well, we'll see if this thing works, and if it does, we'll figure out [how to support it],' " Lockheed's Ernest Joiner says. "But I don't see how it ever could have worked. I hate to say that," he adds with a laugh, "because it was a lot of fun to do the program."

For military missions, VTOL aircraft suffer from another show-stopper as well: you cannot overload them. Once you have optimized a design so that it can take off straight up and no other way, adding extra fuel, bombs, missiles, guns, and ammo produces a very expensive, noisy, ground-hugging cockpit cooling fan.

That's the beauty of the Harrier, John Fozard explained. "The way aircraft are operated in real life is not VTOL but STOVL--Short Take-Off and Vertical Landing," he insisted. "You have to be able to overload them to a point where they can no longer make a purely vertical takeoff." Harriers, in fact, fit into a category called "flat risers": Once festooned with drop tanks, bombs, and missiles, a Harrier must trundle briefly down a runway or flight deck like a charging razorback before the combination of wing lift and downward-vectored jet exhaust thrust can urge it aloft. A true vertical takeoff is part of a Harrier's repertoire only at air shows, when the airplane is light and hardly combat-ready.

Click on Picture to enlarge

"The Tail Sitters were a passing phase because they were inevitably payload-limited," Fozard said. "Being able to use wing lift as well as jet lift is the key, and we didn't even appreciate how important that was at the time we were developing the P.1127." The now-familiar configuration and rotating-nozzle, vectored-thrust powerplant of the P.1127, which led to the Kestrel and then the Harrier, was laid down two years after Lockheed and Convair pulled the plug on the Tail Sitters program, citing engine and gearbox problems they had experienced.

In 1954, James F. Coleman was awarded the Harmon Trophy for serving as the first airplane pilot ever to accomplish a vertical takeoff, transition to forward flight, and change back to a vertical landing. What was never said is that Coleman was one of the last people ever to venture aloft in a machine that nobody knew how to fly, that no simulator had proved would fly, and that no computer could promise would be controllable.

Originally published in Air & Space/Smithsonian Magazine, Oct/Nov 96.

 

 

 

The XFY-1 Pogo

National Air and Space Museum

 

Click on Picture to enlarge

The XFY-1 On Its Erector

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.

Click on Picture to enlarge

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 power plants 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, caster 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 pogo stick, 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.

Click on Picture to enlarge

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.

Click on Picture to enlarge

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.

Click on Picture to enlarge

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 test pilot 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 prop wash, 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.

Click on Picture to enlarge

On 5th November, 1954, pilot "Skeets" Coleman flew a public demonstration of the XFY-1 Pogo at Brown Naval Auxiliary air Station. The aircraft showed an ability to convert from vertical to horizontal flight within 200 feet

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.

Click on Picture to enlarge

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.

Wingspan 7.8 m (25 ft 8 in)
Length 10.5 m (34 ft 11 in)
Height 7.2 m (23 ft 11 in)
Weight Empty 5,850 kg (13,000 lb)

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

 

 

The History Of The Convair Pogo

By Joe Braugher

 

Click on Picture to enlarge

The Convair XFY-1 Pogo was an experimental vertical takeoff aircraft of the 1950s. It was a result of a proposal issued by the Navy in 1948 for an aircraft capable of vertical takeoff and landing (VTOL) aboard platforms mounted on the afterdecks of conventional ships. In 1950, this requirement was revised to call for a research aircraft capable of evolving into a VTOL ship-based convoy escort fighter. In March of 1951, three prototypes were ordered from Convair under the designation XFY-1. Serials were BuNo 138648/138650. A similar aircraft was also ordered from Lockheed under the designation XFV-1.

Click on Picture to enlarge

The XFY-1 sat on its tail for landings and takeoffs. It had a large delta wing with two pods at the extreme and two large vertical fins above and below the fuselage. The aircraft rested on a set of small castor wheels at the tips of the wing and fin. At takeoff, the engines ran up to full power and the aircraft ascended vertically, then when it reached a safe altitude it gradually nosed over into conventional horizontal flight. At landing, the aircraft approached the landing pad while pitched up into a nose-high position and then descended to the ground under gradually reduced power. If an emergency were to occur, the ventral fin could be jettisoned so that the aircraft could make a crash-landing in conventional, wing-supported mode.

Click on Picture to enlarge

The XFY-1 was powered by an Allison YT40-A-6 turboprop (which consisted of two T38 turboprops coupled together) driving a pair of Curtiss-Wright 16-foot three-bladed contra-rotaing propellers in the nose. The engine offered a power of 5500 shp. The air intakes for the engines were located in the extended roots of the delta wing, and the exhaust was in the extreme tail.

The single pilot sat underneath a cockpit canopy which slid toward the rear. The ejector seat was mounted on gimbals and tilted 45 degrees when the aircraft was in the vertical position. Entry to or exit from the cockpit required a special ladder, and was by all accounts rather awkward. During takeoffs and landings, the canopy was slid to the rear to give the pilot a better view.

The proposed armament (never actually fitted) was four 20-mm cannon fitted in the two wingtip pods. Alternatively, 48 2 3/4-inch folding-fin rockets could be fitted.

Before attempting the first flights, the prototype XFY-1 was attached to a complex tether system inside a huge hangar at NAS Moffett Field, California that allowed the aircraft to move up or down freely, but severely limited the lateral displacement. During the summer of 1954, test pilot James F. "Skeets" Coleman made several tethered flights in this system. The first un-tethered vertical flight was made on August 1, 1954. During the next two days, several vertical hovering flights were made during which the aircraft reached altitudes as high as 150 feet. The aircraft was then returned to San Diego for further tests at NAAS Brown Field. The first successful transition to horizontal flight took place on November 2, 1954, during which the XFY-1 flew horizontally for 20 minutes before coming back and landing inside a 50-foot square. This was the first successful VTOL flight in history in an aircraft that was not a helicopter or an autogiro.  For this feat, Coleman was awarded the Harmon Trophy.

Unfortunately, the XFY-1 was difficult to land because of a poor view from the cockpit of the landing area and the unusual pilot posture. The landing operation would probably have been difficult if not impossible for a pilot of ordinary ability to perform on a small deck aboard ship, especially in rough seas where the deck was pitching back and forth. In addition, the T40 turboprop was mechanically complex and was thoroughly unreliable and subject to frequent breakdowns.  The T40 was, in fact, the cause of the failure of several combat aircraft projects of the era.   In addition, by this time the performance of the XFY-1 was quite a bit less than that of conventional jet aircraft, and would probably not have been able to hold its own in air-to-air combat. For this reason, the XFY-1 program was cancelled after only 40 hours of flight testing.

Only one of the three XFY-1s actually flew. 138648 was used strictly as an engine testbed and 138650 was used only for static tests. The sole flight article (13864) was displayed for a while at NAS Norfolk, Virginia, but is now in storage at the Paul Garber restoration facility at Suitland, MD.

 

Specifications of Convair XFY-1 Pogo:

Engines: One Allison XT40-A-6 turboprop, rated at 5500 shp. Projected performance with the 6955 ehp XT40-A-16: Maximum speed: 610 mph at 15,000 feet, 592 mph at 35,000 feet. Initial climb rate 10,500 feet/minute. An altitude of 20,000 feet could be attained in 2.7 minutes, 30,000 feet in 4.6 minutes. Service ceiling 43,700 feet. Endurance was one hour at 35,000 feet. Weights: 11,760 pounds empty, 16,250 pounds gross. Dimensions: wingspan 27 feet 7 3/4 inches, length 34 feet 11 3/4 inches, vertical span 22 feet 11 inches, wing area 355 square feet. Armament was to have consisted of four 20-mm cannon or 48 2 3/4 FFARs

Sources:

  1. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.
     

  2. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.
     

  3. General Dynamics Aircraft And Their Predecessors, John Wegg, Naval Institute Press, 1990

 

 

The Convair XFY

 

Click on Picture to enlarge

Convair XFY-1 Pogo

The Convair XFY Pogo tail sitter was an experiment in vertical takeoff and landing. The Pogo had three-bladed contra-rotating propellers powered by a 5,500 hp Allison YT40-A-6 turboprop engine. It was designed in hope for a high-performance fighter aircraft capable of operating from small warships.

A weapon load of four 20-mm cannon or 46 x 70-mm Mighty Mouse unguided high-explosive rockets was proposed, but never fitted. Landing the XFY-1 was very tough, as the pilot had to look over his shoulder while carefully working the throttle to land. The Pogo's first transition from vertical to horizontal flight took place in November 1954.

Specifications (XFY)

General characteristics

  • Crew: One

  • Length: 22 ft 11 in (10.66 m)

  • Wingspan: 27 ft 7¾ in (8.43 m)

  • Height: ()

  • Wing area: ()

  • Empty weight: ()

  • Maximum Take-Off Weight: 16,250 lb (7,370 kg)

  • Powerplant: 1× Allison YT40-A-6 turboprop engine, 5,500 hp (4,100 kW)

Performance

  • Maximum speed: 610 mph at 15,000 feet (980 km/h at 4,570 m)

Armament

never fitted; planned were

  • 4× 20 mm cannon, or:

  • 46× 70 mm ‘Mighty Mouse’ rockets

 

Click on Picture to enlarge

 

 

 

USE YOUR BROWSER "BACK" BUTTON TO RETURN TO PERVIOUS PAGE

Last Updated

02/10/2014

 

POWERED BY

456FIS.ORG