Fault Finders

The Spitfire prototype first flew in March 1936, with a 1,000 hp engine. Flying

"There are those who have flown them and those who have not, and it is idle for the former to try to explain matters to the latter.”

A Vickers Supermarine test pilot, Jeffrey Quill, was talking about the Walrus, an amphibious biplane flying boat designed in 1929 by RJ Mitchell, who a few years later would create the fabled Spitfire. Quill, perhaps wishing to produce some music for the ears of his employers, described the ungainly airplane as “perhaps one of the best and most useful ... ever produced.”

Such fulsome praise seldom flows from the pens of experimental test pilots, whose job is to detect the flaws of new designs and then to “explain matters” to the designers.

The Spitfire prototype, wearing an all-over aqua blue paint job, Royal Air Force roundels on the fuselage sides and wings, and the identifying number K 5054 on its tail, first flew in March 1936. It had a 1,000 hp engine and a two-blade, fixed-pitch wooden propeller. The pilot, “Mutt” Summers, was delighted with the airplane; when he taxied in after landing, he said, “I don’t want anything touched.” The name Spitfire was assigned by the Vickers board, initially to the displeasure of Mitchell, who grumbled, “Sort of bloody silly name they would choose.”

Over the course of the war, the Spitfire would change. Its power would double, and its top speed would go from 350 to 460 mph. As its performance increased, its few vices were magnified. Considerable effort was needed to hold it in a dive, and as its speed increased, its controls grew heavier, the ailerons of early models eventually becoming almost immovable as their fabric surfaces bellied inward; metal skins later somewhat alleviated that problem. Spins were sometimes disorienting; the pilot, according to Peter Caygill's fascinating history Flying to the Limit, might be "thrown about the cockpit" by violent pitching oscillations. The Spitfire had a tendency, on recovering from one spin, to flick into another. While its lateral and directional stability was good, its longitudinal stability was marginal, and in some circumstances would disappear altogether — not, by the way, an uncommon characteristic among World War II fighters.

During Hitler’s unsuccessful attempt, from July to October 1940, to gain control of English skies, the Spitfire’s principal antagonist was the Messerschmitt Bf 109. The two types were fairly matched; the Spitfire could out-turn the Messerschmitt, but the Messerschmitt could out-dive the Spitfire. In 1941, the Mark V Spitfire, with a more powerful Merlin engine, appeared, and overmatched the 109 until the appearance in 1942 of the Focke-Wulf 190, which led, in turn, to the Mark IX Spitfire and still later to the 2,050 hp Griffon-powered Mark XIV.

One of the striking peculiarities of aircraft of this period, which makes nonsense of disputes about which was the fastest, is that most were fitted with two-speed gear-driven superchargers. Because different airplanes had different supercharger gearings, when two types were flown side by side, one might outrun the other up to, say, 12,000 feet, where the slower became the faster, but only until 23,000 feet, where the first again drew ahead. Reports of top speed make sense only in the context of specific altitudes, and they, in turn, only in the context of the tactical role the airplane was expected to play.

The flying qualities of Spitfires, so appreciated on the prototype’s first flight, gradually deteriorated until, when the Mark 21 version (Roman numerals were abandoned at XX) arrived near the end of the war, test pilots reported that its “handling qualities compare unfavorably with all earlier marks of Spitfire and with other modern fighters.” It was considered hazardous for instrument flying. The Air Fighting Development Unit’s report ended with the remarkable statement that “No further attempts should be made to perpetuate the Spitfire family.”

If there was a single airplane to which test pilots conceded praise, it was the Merlin-powered P-51 Mustang. Flying

The decline of the Spitfire was due to its having been conceived as a light, fast racehorse of a fighter, and then saddled with bigger and bigger engines and propellers that eventually overwhelmed its airframe. Increased power was inevitable; it meant higher speed, better acceleration and climb, and the ability to carry more formidable armament, but there also had to be a proper proportion between power and size. The dates of inception of various fighter designs correlate with the availability of increasingly powerful engines. The Mustang, faster than the Spitfire but inferior in climb and maneuverability, was similar to it in size and, like it, conceived for an engine of about 1,000 hp. Then, with the arrival of 2,000 hp engines, such as the Rolls-Royce Griffon and the Pratt & Whitney R-2800, came increasingly massive fighters like the Typhoon, Tempest and Corsair, and the gigantic Thunderbolt. Pilots, conversely, as may be seen in photographs from the period, became proportionately smaller.

There has been much discussion over whether pointy-nosed liquid-cooled fighters or pug-nosed air-cooled ones were better performers, but it is striking that test pilots had almost nothing to say on the subject, as long as the engine kept running. The liquid-cooled inline cowlings certainly looked sleeker, but, as Lockheed’s Kelly Johnson, who designed the P-38 Lightning, pointed out, cooling drag was inescapable: There had to be a big air intake and radiator somewhere.

Remarkably, the massive 17,000-pound Thunderbolt, which its own designer, Alexander Kartveli, called “a dinosaur,” gave a good account of itself in mock dogfights with a captured 10,000-pound Focke-Wulf 190, even though the 190 was both faster and a better climber.

I have always liked to imagine that those swift, powerful and tough fighters of World War II were delightful to fly, but it seems not always to have been so. The Bf 109’s cockpit was so cramped as to induce claustrophobia as the hood was closed. There was no headroom in the Airacobra, and the spinning drive shaft between their legs gave some pilots the fantods. Mustang pilots basted in the heat from the radiator behind them. The P-40 was prone to “self-stalling” — pitching up at low speed. The Corsair’s “very nasty” low-speed handling — the famous bent wing was prone to stall asymmetrically — was so bad that the Navy at first refused to clear it for carrier landings.

If there was a single airplane to which test pilots conceded praise, it was the Merlin-powered P-51 Mustang. Mating Merlin and Mustang had been a British idea. The first Mustangs, built in 1940 to a British order, used the same 1,000 hp Allison V-12 as the P-38, P-39 and P-40, and consequently displayed lackluster climb, speed and high-altitude performance. Fitting the very clean airframe with the 1,450 hp Merlin “turned an aircraft of limited value into a world beater,” Caygill noted.

Comparisons of the Mustang and the Spitfire were inevitable. One interesting superiority of the Mustang was its roll control, which British pilots judged to be the best of any fighter’s they had tested. The Spitfire’s wing was not so stiff as the Mustang’s, and at high speed would twist opposite to the aileron deflection. At 400 mph, the Spitfire required a stick force of 71 pounds, and twice the aileron deflection, to generate the same roll rate as was produced with 23 pounds on the Mustang.

It is with airplanes as with friends. Our relationship with them is most likely to endure when we are as honest about their vices as about their virtues. The indispensable qualifications of a test pilot are steady nerves, an inability to panic and, above all, a willingness to tell even unwelcome truths.

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, "Technicalities" and "Aftermath," with FLYING readers.

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