On the cover Flight test: DH60 Cir­rus Moth

By the end of the 1920s most of Bri­tain's light aero­planes were de Hav­il­land Moths of one kind or an­other. To­day BAE Sys­tems’ Her­itage Flight op­er­ates the old­est DH60 Cir­rus Moth still fly­ing

Pilot - - CONTENTS - Words: Dave Un­win Pho­tos: Dar­ren Har­bar

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The old­est fly­ing and most orig­i­nal Cir­rus Moth is lovely to look at and de­light­ful to fly but can be chal­leng­ing and twitchy

The wind in the wires sighs and soughs, and the ea­ger roar of the engine sub­sides to a muted mut­ter­ing as I ease the throt­tle back. It’s a pro­foundly vis­ceral ex­pe­ri­ence, en­hanced by the beautiful view. Off to star­board the two huge air­ship sheds at Card­ing­ton dom­i­nate the land­scape while, to port, the famed Old War­den air­field basks in Septem­ber sunshine. It’s a timeless scene, and one that could have oc­curred at any time over the last ninety years, as the air­craft I’m fly­ing is even older than the air­ship sheds. It’s an old cliché (which we all know should be avoided like the plague) but “ah – de Hav­il­land” was never more ap­po­site.

There is some­thing par­tic­u­larly spe­cial about fly­ing open-cock­pit bi­planes. Watch­ing the world go by through a pair of sturdy, wire-braced wings is a won­der­ful ex­pe­ri­ence, and on this oc­ca­sion it’s not any old bi­plane but one of the most in­flu­en­tial and iconic air­craft of all time: the im­mor­tal de Hav­il­land DH60 Moth. And not just any old Moth (if there even is such a thing) but the old­est and most-orig­i­nal in the world!

By the 1920s Bri­tain was be­com­ing an in­creas­ingly airminded na­tion and de Hav­il­land re­alised that the mar­ket needed a two-seat bi­plane that was not only rugged and pos­sessed pass­able per­for­mance, but also af­ford­able. Rather than start with a clean sheet, DH de­cided to build an air­craft loosely based on the 1924 three-seat DH51, but slightly smaller. In­ter­est­ingly, not only was the DH60 a scaled­down ver­sion of the DH51, but its mo­tor was de­rived from the DH51’S engine.

The DH51 was pow­ered by an Air­craft Dis­posal Com­pany (usu­ally re­ferred to as ei­ther ADC or Airdisco) air-cooled V-8 that pro­duced 120hp and was built us­ing many parts from war-sur­plus 70hp Re­nault V-8s. For the DH60 engine, Ma­jor F B Hal­ford (ADC’S chief de­signer) took one bank of cylin­ders and many other com­po­nents from an Airdisco V-8 and mounted them on a new crank­case. Named the Cir­rus I, it pro­duced 90hp and played a ma­jor role in mak­ing the Cir­rus Moth an im­me­di­ate suc­cess from a per­for­mance per­spec­tive, and the type soon ce­mented its rep­u­ta­tion as pos­si­bly the world’s first prac­ti­cal light air­craft. All de Hav­il­land had to do then was en­sure it was com­pet­i­tively priced, and at around £650 it was.

Or­ders flooded in, and by the end of the decade the fac­tory at Stag Lane in North Lon­don was mak­ing three air­craft a day. At that time 85% of the UK’S GA air­craft fleet were Moths of one kind or an­other, which prob­a­bly ex­plains why (in much the same way that the generic term for a light aero­plane in the US was ‘Cub’) most Bri­tons of the time re­ferred to all small air­craft as ‘Moths’. In­ci­den­tally, the rea­son the name ‘Moth’ was cho­sen was due to Cap­tain de Hav­il­land’s for­mi­da­ble rep­u­ta­tion as a lep­i­dopter­ist. Ul­ti­mately, more than 2,000 DH60S were pro­duced, in­clud­ing the sub­ject of this air test.

Based at Old War­den and owned by the BAE Sys­tems Her­itage Flight, G-EBLV was built in 1925 and is the old­est air­wor­thy Moth. In­trigu­ingly, even though it is al­most 95 years old it has only logged 317 hours!

One of the first things I no­tice is that, un­like the Tiger Moth I have flown, the engine is not in­verted. Although most DH60S were pow­ered by a DH Gipsy engine Lima Vic­tor is fit­ted with a Cir­rus III, which pro­duces 90hp at 2,100rpm. There’s an Au­to­mo­bile As­so­ci­a­tion badge on the star­board side of the cowl­ing. Why it’s there seems lost in the mists of time, but one con­nec­tion might be that the AA formed an Avi­a­tion Sec­tion in 1929, which helped Amy John­son plan her 1932 flight to Cape Town and (in as­so­ci­a­tion with the Royal Aero Club) pro­duced ‘Fly­ing Maps’. Al­ter­na­tively, it’s quite pos­si­ble that one of Lima Vic­tor’s pre­vi­ous own­ers was also an AA mem­ber.

Be­fore mov­ing in for the pre­flight I stand back and ad­mire the air­craft from a dis­tance. The de Hav­il­land Com­pany al­ways de­signed hand­some ma­chines, and even if I hadn’t known it was a DH prod­uct I would have guessed−the ex­traor­di­nar­ily cur­va­ceous rud­der would give it away!

Lima Vic­tor is finished in the clas­sic DH scheme of ‘Moth Sil­ver’ for the wings and tail, while the fuse­lage colour was the owner or club’s choice. As many Moths were bought by clubs, spe­cific fleets had spe­cific colours. The Lon­don Aero Club had its Moths painted yel­low, Mid­lands’ were green, and New­cas­tle’s red, while the Lan­cashire Aero Club had Lima Vic­tor finished with a blue fuse­lage. One of the most fa­mous

avi­a­tors of the era, Sir Alan Cob­ham, de­liv­ered it to Wood­ford.

As you’d ex­pect of a fly­ing ma­chine de­signed in the 1920s, much of the ma­te­rial used in its con­struc­tion is or­ganic; mostly spruce, ply­wood and cot­ton. The fuse­lage is es­sen­tially a box built around four square-sec­tion longerons made of spruce, braced by cross-mem­bers and skinned with stress-bear­ing ply­wood sheets. Al­ready I was be­gin­ning to un­der­stand why the air­craft had been such a suc­cess. Not only is this a very cheap and sim­ple yet ro­bust de­sign, but any com­pe­tent car­pen­ter equipped with only ba­sic wood­work­ing tools could make quite ma­jor re­pairs to the air­frame.

The wings are made mainly of spruce, cov­ered with fab­ric (the wingtips are alu­minium tube), sep­a­rated by wide-chord in­ter­plane struts and braced by stream­lined fly­ing wires. The up­per wings are mounted on a cen­tre sec­tion, which is ba­si­cally an aero­foil-shaped 68-litre fuel tank car­ried by six stream­lined hol­low steel struts (four ver­ti­cal and two slop­ing), which are braced fore and aft by more stream­lined fly­ing wires. A 45-litre aux­il­iary tank sit­u­ated for­ward of the front cock­pit was an op­tion.

As the up­right engine is bolted to the top longerons, the for­ward field of view is some­what im­peded by the tall cylin­ders. This would be es­pe­cially no­tice­able when taxy­ing, and I be­gin to ap­pre­ci­ate why de Hav­il­land in­verted the engine on the Tiger Moth. The de­sign of the ex­haust is also note­wor­thy, as it runs along the port side and ends well aft of the rear seat.

De Hav­il­land’s patented dif­fer­en­tial ailerons are fit­ted to the lower wings only. An ex­cel­lent at­tribute of the Moth is that it pos­sesses one of my favourite fea­tures: fold­ing wings. Once the spring-loaded quick re­lease bolts in the lead­ing edge of the wing root are re­moved, the wings pivot about the rear spar to fold aft. A tem­po­rary jury strut helps sup­port the wings which, once folded, re­duce the air­craft’s span by two-thirds from 9.14m to 2.98m. When not in use, it is se­cured to the fuse­lage by leather straps next to the ex­haust. Much was made of the fold­ing wings, and some pe­riod ad­ver­tise­ments show a Moth be­ing towed by an Austin 7.

The un­der­car­riage fea­tures large di­am­e­ter, nar­row wheels, fit­ted with rel­a­tively high­pres­sure tyres and mounted on a sin­gle axle. Although the pro­to­type had an un­bal­anced rud­der, all pro­duc­tion air­craft fea­tured a horn balance and, like many air­craft of this era, the trapez­ium fin is tiny and the shapely rud­der huge. The strut-braced tailplane and large two-piece el­e­va­tor are also cur­va­ceous, and I note with con­sid­er­able in­ter­est that the trail­ing edges of the el­e­va­tor are ex­tremely close to the ground and that the tail­skid is non­steer­able. As the wheels are not fit­ted with brakes, taxy­ing could soon get tricky in any­thing stronger than a gen­tle ze­phyr.

Fas­ci­nat­ingly, and in com­mon with many other DH de­signs, as de­liv­ered from the fac­tory

there is no carb heat. In­stead, as the car­bu­ret­tor is mounted quite close to the cylin­ders, it was as­sumed that they kept the car­bu­ret­tor suf­fi­ciently warm to pre­vent the for­ma­tion of carb ice.

Pete gen­er­ously of­fers me my choice of seat and I’m sorely tempted by the rear cock­pit, but I know that he’ll want to do the for­ma­tion fly­ing so I take the front. Be­fore climb­ing in I study the rear cock­pit, which is a de­light of pe­riod in­stru­men­ta­tion, in­clud­ing a sin­gle pointer ‘height me­ter’ and a P11 com­pass. To my mind, the P11 al­ways looks more like a ship’s com­pass than an air­craft’s, though it com­ple­ments the Moth’s cock­pit per­fectly.

Ac­cess to the front cock­pit is rea­son­able for an air­craft of this type, as there is a small door on the star­board side. The front cock­pit is very sparsely fur­nished with only an ASI and height me­ter (it’s not an al­time­ter; it doesn’t have a ‘Kolls­man’ window), and has only a stick, throt­tle and rud­der ped­als−not even a trim lever!

The two pairs of brass mag­neto switches are mounted ex­ter­nally, on the star­board side and just in front of each cock­pit. They bear a strong re­sem­blance to large Ed­war­dian light switches, while the un­usual seat belt is the worst I’ve ever seen in an aero­plane. It’s al­most a chest strap!

Start­ing a ma­chine of this vin­tage is al­ways some­thing of a rit­ual, but the engine is soon run­ning smoothly and, after gen­tly warm­ing it up, Pete eases us out of our park­ing space and passes con­trol to me. If there were any real wind, wing-walk­ers would be a ne­ces­sity, but there isn’t and I man­age to get us to the run­way unaided. How­ever, al­most as soon as we be­gan to roll, it’s ob­vi­ous the Cir­rus Moth is quite a bit dif­fer­ent to a Tiger. There seems to be more engine vi­bra­tion, prob­a­bly be­cause the engine does not sit in rub­ber engine mounts but is bolted di­rectly to the longerons. The

DH60 is also not as be­nign to han­dle on the ground as a Tiger as the field of view is sig­nif­i­cantly worse, mak­ing S-turn­ing not only pru­dent but es­sen­tial. This is due mainly to the up­right engine, although the much larger di­am­e­ter wheels do make the air­craft sit some­what higher than its younger sib­ling. Fur­ther­more, while a DH82 pro­vides a rel­a­tively com­fort­able ride on its fat, low-pres­sure tyres and nice soft, coil spring un­der­car­riage, the DH60 feels much more skit­tish on its thin, high­pres­sure tyres and rather crude un­der­car­riage, which uses only rub­ber blocks in com­pres­sion for shock-ab­sorp­tion. While taxy­ing you need to be very cau­tious, yet con­versely oc­ca­sion­ally bold. Re­mem­ber the tail­skid doesn’t steer, so in the ab­sence of a wing­walker you must blip the throt­tle with the stick well for­ward (to un­load the skid) while ap­ply­ing full rud­der in the de­sired di­rec­tion.

With such sim­ple sys­tems the pre-take­off checks are min­i­mal, so I line up and very slowly open the throt­tle. My ini­tial im­pres­sions of the ma­chine be­ing some­what ‘fid­gety’ are re­in­forced as we ac­cel­er­ate. Lift-off oc­curs at around 45 knots (in com­mon with most air­craft of this era the ASI is cal­i­brated in mph, not knots, but I’ll use knots for the sake of con­sis­tency). How­ever, flick­er­ing once or twice the ASI’S nee­dle flops back life­lessly to zero. I re­port this to Pete, who calls out the speeds over the in­ter­com. I know 60-65 is a good climb­ing speed and, when Pete con­firms we’ve at­tained sixty, I note the at­ti­tude and try and hold it.

In fact as the name sug­gests the Moth does not so much fly though the air as flut­ter upon it. This is a func­tion of its very low wing load­ing, which is barely 5.5 lb/sq ft, even when flown at the MAUW of 1,350 lb. Our as­cent is leisurely at some­where around the 500fpm mark, as I try to main­tain a con­stant at­ti­tude and ac­cept the speed and climb rate that this pro­duces. This is the best way to fly most aero­planes, and is es­pe­cially true of air­craft that have a low wing load­ing. Such light ma­chines have very lit­tle in­er­tia, and there is noth­ing to be gained (but a great deal to be lost) by chas­ing the air­speed. All those wires and struts hang­ing out there in the breeze are gen­er­at­ing a lot of drag, and you’ve only got ninety horses do­ing the pulling. I also get the dis­tinct im­pres­sion that, although

While taxy­ing you need to be very cau­tious...

it will clearly climb or turn, it is not es­pe­cially en­thu­si­as­tic about do­ing both si­mul­ta­ne­ously. As men­tioned pre­vi­ously, there’s not a huge amount of sur­plus thrust but plenty of ex­cess drag. If you in­cline the lift vec­tor out to one side, the rate of climb suf­fers ac­cord­ingly.

While we wait for the Miles Mag­is­ter flown by Bob Mor­com and car­ry­ing pho­tog­ra­pher Dar­ren to join us, I be­gin a pre­lim­i­nary as­sess­ment of the con­trols and stability. The han­dling seems some­what bet­ter than a Tiger, although any­one who has ever flown a DH82 will read­ily ad­mit that this isn’t say­ing much! In­deed, although us­ing the ailerons with­out a co­or­di­nated rud­der in­put does gen­er­ate a sig­nif­i­cant amount of ad­verse yaw, it doesn’t seem as bad as a Tiger. This is be­cause the DH60 has rel­a­tively straight wings and lim­ited di­he­dral, while the DH82 has swept­back wings and more di­he­dral. This ar­range­ment tends to pro­duce yaw-to-roll cou­pling, and is quite pro­nounced in a Tiger Moth.

An­other as­pect of the gen­eral han­dling sig­nif­i­cantly dif­fer­ent to the Tiger’s is that the DH60 seems less speed-sta­ble. As for its lat­eral and di­rec­tional stability, both are pos­i­tive, although just barely so. The di­rec­tional stability is quite ‘soft’; if you skid the air­craft, put the rud­der to neu­tral and then hold it in place with your feet it’s not so bad, but if you let the rud­der ‘float’ the yaw os­cil­la­tion is al­most di­ver­gent, but to be hon­est this isn’t sur­pris­ing−look at the size of the fin! As for the field of view, be­cause the front cock­pit is sit­u­ated be­tween the two wings it’s some­what con­strained down ei­ther side, and im­me­di­ately above.

On the plus side, you get less of a draught in the front cock­pit than the rear, as long as your turns are nicely co­or­di­nated. If they are not, and you are ei­ther slip­ping or skid­ding, it soon be­comes ob­vi­ous when the air­flow strikes your head! You can also def­i­nitely feel it ‘in the seat of your pants’ if the air­craft is be­ing mis­han­dled. But when it all comes to­gether it is most grat­i­fy­ing, and there is cer­tainly a sense of pro­found sat­is­fac­tion to be had from ex­e­cut­ing a well-co­or­di­nated 360° turn in a vin­tage bi­plane.

Un­sur­pris­ingly, although you can main­tain ei­ther the same speed or same al­ti­tude, you will not be able to do both.

Some­thing’s got to give, and you must ei­ther add power or de­scend (to main­tain speed) or slow down (to main­tain height).

The ‘Mag­gie’ ap­pears. Pete takes con­trol and slides us smoothly into for­ma­tion. It’s a bit bumpy and he does an ex­cel­lent job, leav­ing me to keep an eye out for traf­fic. While we wheel and swing high above Old War­den, with the bright yel­low Mag­is­ter framed be­tween the sil­ver wings and with the gi­gan­tic air­ship sheds in the back­ground, the whole ex­pe­ri­ence has a cer­tain air of time­less­ness.

Once all the pic­tures are in the can we break away. Pete re­turns con­trol to me and I con­tinue my eval­u­a­tion. Slow flight is very be­nign, with the stall some­where around 34kt. As the stall is ap­proached the Moth starts to mush, there’s a lit­tle buf­fet and then it breaks with a slight wing drop. It’s noth­ing dra­matic but not quite as gen­tle as a Tiger, which has slats, and an up­per wing set at an an­gle of in­ci­dence a few de­grees greater than the lower wing (so that it stalls first and ‘nods’ the nose down). On the Cir­rus Moth, both sets of wings are set at three de­grees. Just as with the Tiger− and in­deed most aero­planes−do not try to pick the wing up with the ailerons post-stall. This will only ex­ac­er­bate the sit­u­a­tion and may even in­cite a spin.

For the brief tran­sit back to Old War­den Pete rec­om­mends set­ting 1,500rpm, which gives an IAS of around 60kt, for a fuel flow of about 22 lph. Con­se­quently, the still air range (no re­serves) is around 180 nau­ti­cal miles.

Back in the cir­cuit, the clas­sic curved glide ap­proach all the way round from the end of the down­wind leg to short fi­nal

The clas­sic curved glide ap­proach, all the way round from the end of the down­wind leg, seems ap­pro­pri­ate

seems ap­pro­pri­ate, with Pete call­ing out the speed. I can see that the wind has fresh­ened slightly, and that we have what is best de­scribed as a ‘cheeky cross­wind’ at about 45° from star­board. As I arc around base onto fi­nal Pete calls that I’m about eight knots faster than the briefed speed, but doesn’t sug­gest I slow down. I can see from the wind­sock that it’s a lit­tle gusty and de­cide that a bit more speed would be no bad thing! I also know that the Moth is light and draggy with lit­tle in­er­tia. When I close the throt­tle and flare the

speed will soon wash off and it won’t go far.

The land­ing isn’t at all bad and I con­vert it into a touch and go, con­fi­dent that the next land­ing will be even bet­ter. Well it isn’t, and we hop, skip and bounce in a some­what undig­ni­fied fash­ion to a stop. Pete is very nice about it and says that “it was one of those land­ings that felt worse than it looked”. How­ever, it still felt pretty bad! As we slow I can feel through my seat that the Moth will cheer­fully ground loop if I let it. Re­mem­ber, this is an air­craft that was built when run­ways sim­ply didn’t ex­ist. In­stead, an air­field was ex­actly that−a field for aero­planes usu­ally con­sist­ing of a large, of­ten vaguely cir­cu­lar, area of grass. There­fore, you al­ways landed into wind, (which is just as well, as the demon­strated cross­wind com­po­nent is only six knots) and the re­as­sur­ing drag of the tail­skid kept you straight dur­ing the roll­out.

Con­clu­sions? Well, I hugely en­joyed fly­ing this iconic air­craft which, de­spite be­ing al­most a cen­tury old, is a real fun fly­ing ma­chine. It was both an hon­our and a priv­i­lege, and I’d like to thank Peter Koso­gorin, John Hur­rell and the BAE Sys­tems Her­itage Flight for this won­der­ful op­por­tu­nity.

While writ­ing this re­port I thought a lot about pi­o­neer­ing pi­lots such as Jean Bat­ten, Fran­cis Chich­ester and Amy John­son, who all flew DH60S vast dis­tances. Like most other wood-and-fab­ric fly­ing ma­chines, the Cir­rus Moth is an air­craft that flies upon the air, not through it. Con­se­quently, you choose the days you fly it care­fully, for though it is a de­light­ful ma­chine in calm air, the whole ex­pe­ri­ence would be much less en­joy­able on a bumpy, blus­tery day and would quickly be­come quite tir­ing. Ac­cord­ingly, my pro­found respect for th­ese brave ad­ven­tur­ers has in­creased still fur­ther. John­son flew her Gipsy Moth Ja­son from Croy­don to Dar­win be­tween 5 and 24 May 1930. Even to­day, in our world of ELTS, GPS and Sat­phones this would be an epic flight, but ninety years ago...? In­cred­i­ble!

ABOVE RIGHT: si­lencer and long ex­haust make for neigh­bourly noise level

BE­LOW: neat lock plate for the pro­pel­ler hub bolt, in­di­vid­u­ally pinned drive bolts

ABOVE LEFT: Cir­rus ‘four’ is der­vived from half an ADC (neé Re­nault) V8

‘Light switch’ op­er­ates the mag­ne­tos – and is lo­cated where the prop-swinger can see it and con­firm the pi­lot is do­ing what he says!

BE­LOW LEFT: dis­tinc­tive de Hav­il­land tail pro­file – and a tail skid that pro­vides suf­fi­cient brak­ing for grass-field op­er­a­tion

BE­LOW RIGHT: the for­ward star­board in­ter­plane strut serves as an ideal mount for the pitot/static ar­ray

ABOVE: there are no brakes, so the use of chocks – al­ways ad­vis­able – is vi­tal when hand-start­ing the Cir­rus engine

ABOVE: grav­ity feed main tank and a fuel sight gauge mounted up where it is... well, very much in sight

BE­LOW: read­ily in­spected wing fold­ing pins, se­cured sim­ply by leather straps with vin­tage car hood press-studs

There’s min­i­mal in­stru­men­ta­tion for the oc­cu­pant of the front cock­pit – just suf­fi­cient for the needs of an in­struc­tor mon­i­tor­ing a stu­dent in the back

ABOVE: the air­craft is flown solo from the rear cock­pit, where the panel fea­tures no fewer than three flight in­stru­ments, a rev counter and an oil pres­sure gauge

ABOVE: at a gen­tle sixty-knot cruise the Cir­rus Moth’s fuel con­sump­tion is a mod­est 22 litres per hour

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