TECHNICALITIES

BA­SI­CALLY, IT WAS ALL ABOUT TELLING THE TRUTH

Flying - - CONTENTS - By Peter Gar­ri­son

Spit­fire: find­ing fault by telling the truth

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 out­turn 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 Grif­fon­pow­ered 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.”

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 liq­uid­cooled fighters or pug-nosed air-cooled ones were bet­ter per­form­ers, but it is strik­ing that test pilots had al­most noth­ing to say on the

THERE HAS BEEN MUCH DIS­CUS­SION OVER WHETHER POINTYNOSED LIQ­UID-COOLED FIGHTERS OR PUGNOSED AIR-COOLED ONES WERE BET­TER PER­FORM­ERS.

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 17,000pound 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.

THE BF 109’S COCK­PIT WAS SO CRAMPED AS TO IN­DUCE CLAUS­TRO­PHO­BIA AS THE HOOD WAS CLOSED.

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

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

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