Open Cock­pit

Fly­ing fast and close to other air­craft is some­times scary but al­ways fun — and ‘or­di­nary’ pi­lots can try it too

Pilot - - CONTENTS - STEPHEN SLATER Stephen is CEO of the Light Air­craft As­so­ci­a­tion, Vice-chair of the Gen­eral Avi­a­tion Aware­ness Coun­cil, flies a Piper Cub and spent seven years help­ing re­store the ‘Big­gles Bi­plane’ 1914 BE2C replica

There’s fly­ing fast and then there’s just pure speed

Anew world record was set a short time ago, which I don’t think has gained the pub­lic­ity it de­serves. On 28 Au­gust 2017, at Clarks Field, Idaho, USA, the Ab­so­lute Pro­pel­ler-driven Pis­ton-pow­ered speed record was bro­ken by Steve Hinton Jr. His mod­i­fied P-51D Mus­tang, Voodoo achieved an av­er­age speed of 531.53mph, with the fastest of four laps of the Fai-de­fined 3km cir­cuit reach­ing 554.69mph. Oh, and adding to the thrills, the record was set at 70ft agl!

When I de­scribe Hinton’s Mus­tang as ‘mod­i­fied’, I think that’s a bit of an un­der­state­ment. Like many of its kind in un­lim­ited air rac­ing (where Voodoo won the leg­endary Reno ‘Gold’ award in 2012, 2013, 2014 and 2016), the former USAF and Royal Cana­dian Air Force Mus­tang fea­tures rad­i­cal changes to boost its per­for­mance. For a start the wing­span is around six feet shorter than stan­dard and the lam­i­nar flow wing sec­tion is also al­tered as well as its plan­form, giv­ing a wider wing-root and more ta­pered wingtip.

On Voodoo this isn’t just about dra­gre­duc­tion, but also about shock­wave and pres­sure man­age­ment as the air­craft gets close to su­per­sonic speed. In fact, on some of its test flights the air­craft was sur­rounded by the air vapour ‘halo’ that nor­mally ac­com­pa­nies tran­sonic flight!

Then there’s the en­gine. Typ­i­cally, in mil­i­tary ser­vice, a late model Rolls-royce Mer­lin could just about de­velop 2,000 horse­power. A typ­i­cal un­lim­ited rac­ing en­gine de­vel­ops 3,500 or more, us­ing pres­surised me­chan­i­cal fuel in­jec­tion and a su­per­charger run­ning at around 150 inches of mer­cury, or five bar of boost pres­sure. Tur­bocharg­ers aren’t used be­cause the en­gine com­part­ment and struc­ture can’t dis­pose of the ex­tra heat. Tur­bocharg­ing would also mean ex­tra cool­ing for the lu­bri­ca­tion oil, adding to both weight and drag.

In ad­di­tion to run­ning a spe­cial brew of 140-plus oc­tane fuel, anti-det­o­na­tion in­jec­tion (ADI) pre­vents charge det­o­na­tion due to the high man­i­fold pres­sures. On the record flight Voodoo prob­a­bly con­sumed around sixty gal­lons of an ADI mix­ture — 50% wa­ter and 50% methanol — in­jected di­rect into the cylin­ders. In ad­di­tion, to help keep the over­worked en­gine cool, a spray-bar throws up to 45 gal­lons of wa­ter onto the front of the ra­di­a­tor. This not only cools the en­gine by the latent heat ef­fect of con­vert­ing wa­ter into steam, it also con­trib­utes a lit­tle ex­tra per­for­mance. The air­craft’s for­ward speed forces the ex­pand­ing steam through a noz­zle in the fuse­lage, gen­er­at­ing thrust in what is called the Mered­ith ef­fect.

Ul­ti­mately the lim­it­ing fac­tor for the speed of these air­craft is the loss of efficiency as the pro­pel­ler tips break the sound bar­rier. Re­vised re­duc­tion gears in the Mer­lin en­gine are used to re­duce pro­pel­ler speed and the Voodoo team uses a rel­a­tively small di­am­e­ter four-bladed pro­pel­ler with wide ‘pad­dle’ blades to max­imise thrust at max­i­mum rpm. How­ever, if you’ve ever heard the chain­saw tran­sonic rasp of a Har­vard pro­pel­ler on a cold morn­ing, just imag­ine the noise Voodoo made, with prop tips su­per­sonic at low level at 550mph!

Of course, the pi­lot­ing of such an air­craft re­quires spe­cial skills. One la­conic un­lim­ited racer com­mented, “well, it’s still just an aero­plane, but when you take six feet off the wing­span and dou­ble the power, things get a lit­tle more squir­rely”. And that’s be­fore you fac­tor in clas­sic tail­drag­ger han­dling, com­bined with lim­ited vis­i­bil­ity through a mi­nus­cule drag-re­duc­tion canopy and an ap­proach speed of not much un­der 200mph! All I can say of Steve Hinton Ju­nior and his con­tem­po­raries is; re­spect!

Now I know that there’s as much chance of you or I get­ting our hands on an un­lim­ited air racer like Voodoo as we have of strap­ping our­selves into Lewis Hamil­ton’s Mercedes For­mula One rac­ing car, but if you were to fancy air rac­ing, there are some op­tions open to us. First, the Royal Aero Club’s ‘3Rs’ (Records, Rac­ing & Rally As­so­ci­a­tion) runs a train­ing event and or­gan­ises an­nual air races around the UK and in Europe. So long as you have 100 hours P1 and your air­craft can reach a con­tin­u­ous 100mph in level flight, you could par­tic­i­pate in hand­i­cap races in­clud­ing such pres­ti­gious events as the King’s Cup or the Sch­nei­der Tro­phy. Check out http://www. roy­alae­ro­clu­br­rra.co.uk/

If you fancy even more thrilling, wingtip to wingtip rac­ing around a tighter course in pur­pose-built rac­ing air­craft, then the re­cent resur­gence of For­mula One air rac­ing in the UK, France and Spain might just be for you. The sport has been around since the late 1940s, when the ‘for­mula’ was cre­ated in Amer­ica to of­fer a lower-cost alternative to the ‘un­lim­ited’ war­birds. The con­cept has proved a suc­cess ever since, with the diminu­tive rac­ers, pow­ered by tuned Con­ti­nen­tal 0-200 en­gines pro­vid­ing close rac­ing at speeds up to 250mph at events across the USA.

For a num­ber of years, in the late 1960s and early 1970s, there was a thriv­ing rac­ing scene in Europe, but it then went into abeyance. The air­craft re­mained though, rang­ing from the func­tional and fast Cas­sutt, to the breath­tak­ingly beau­ti­ful Cos­mic Wind and Midget Mus­tang, and Bri­tish de­signs in­clud­ing the Tay­lor Titch and Rollason Beta. Now, as part of the Air Race 1 World Se­ries, some of these air­craft are back in ac­tive com­pe­ti­tion once again.

In mid-novem­ber, three Bri­tish pi­lots are trav­el­ling to Thai­land to up­hold national hon­ours in the next round of the se­ries. Trevor Jarvis (see Oc­to­ber’s Pi­lot), Des Hart and Yves Clarke will be wav­ing the flag for the UK, against pi­lots from the USA and Europe. The races are set to be broad­cast live on the in­ter­net and I, for one, will be watch­ing and cheer­ing ‘our lads’ on!

De­scrib­ing Hinton’s Mus­tang as ‘mod­i­fied’ is an un­der­state­ment

The re­cent resur­gence of F1 air rac­ing might just be for you

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