THE RAF'S TAN­DEM TU­TOR

Air Cadets used to reach for the sky in the T31/TX Mk.3 - and thou­sands went on to fly­ing ca­reers

Pilot - - SLINGSBY TYPE 31/CADET TX MK.3 - Words: Dave Un­win Photos: Keith Wil­son

As we ap­proach 5,500ft I think of Al and Keith all snug and warm in the Euro­fox’s cock­pit and shiver en­vi­ously. “Those lucky bas­tards! I bet they’ve got that heater cranked up to gas mark 12,” I grum­ble to my­self. And then a thought oc­curs and I grin. They’re go­ing to get a shock when Keith opens his door! A sharp tug on the ca­ble re­lease knob, the towrope twangs away and WT900 de­cel­er­ates rapidly. It oc­curs to me that we’re al­most a mile high and I pat the cock­pit sill af­fec­tion­ately “Well old girl, one thing’s for sure, I bet you’ve never been up above the clouds be­fore!”

Which air­craft has in­tro­duced more Bri­tons to the joy of flight than any other? Some might say the Chip­munk or Tiger Moth, oth­ers the ubiq­ui­tous Cessna 150/152 se­ries or pos­si­bly its Piper PA-28 ri­val. I say it’s none of these. In fact, the air­craft in ques­tion doesn’t even have an en­gine! Take a snap poll, not nec­es­sar­ily at a fly­ing club−try a pub in­stead. There is a bet­terthan-even chance that if the per­son you talk to is over 45 and has ever ac­tu­ally han­dled the con­trols of a fly­ing ma­chine in flight, then it was quite pos­si­bly the sub­ject of this month’s test, the Slingsby Type 31.

From the early 1950s to the mid 1980s, count­less young would-be pi­lots took to the sky in a T31, as not only was it op­er­ated by sev­eral civil­ian clubs, but it was also for hun­dreds of thou­sands of Air, Sea and Army Cadets the first air­craft they’d ever flown. Con­se­quently, it is quite pos­si­ble that the T31 (known within the Ser­vices as the Cadet TX Mk.3 or Tan­dem Tu­tor) has in­tro­duced more Bri­tons to flight−and cer­tainly solo flight− than any other Bri­tish-built air­craft. Why? Well, the RAF took de­liv­ery of 131 Cadet TX Mk.3s be­tween 1951 and 1959, and only phased them out around 1986. But per­haps more per­ti­nently, most of those made more than 25,000 flights apiece, and one is on record as hav­ing logged a stag­ger­ing 120,000 launches! A sim­ple cal­cu­la­tion in­di­cates that the Air Cadets’ TX Mk.3s alone flew in ex­cess of three mil­lion launches, of which the vast ma­jor­ity were air ex­pe­ri­ence flights.

The sub­ject of this flight test was built at Slingsby’s Kir­by­moor­side fac­tory in 1953 as works num­ber 695. It be­came WT900 when it joined the RAF, and it spent a con­sid­er­able amount of time with 633VGS at RAF Kin­loss. Af­ter be­com­ing a civil­ian ma­chine in 1986, as BGA 3727 it was even­tu­ally pur­chased by Sea King pi­lot D J Gibbs who flew it at the Portsmouth Naval Glid­ing Club at Lee-on-solent, then moved it to RAF Cran­well be­fore both it and ‘D J’ joined the re­cently rein­vig­o­rated Buck­min­ster Vintage Glider fleet in 2018. By the time it ar­rived at Saltby it had logged al­most 25,000 launches, and it is a trib­ute to both the ini­tial de­sign and the con­struc­tion skills of the men and women who built the air­craft that it still flies to­day.

As one would ex­pect of such a ven­er­a­ble fly­ing ma­chine, the prin­ci­pal ma­te­ri­als used in its con­struc­tion are the same as those used in the very ear­li­est aero­planes−wood and fab­ric. The fuse­lage is of fab­ric-cov­ered box girder con­struc­tion while the twin-spar wings are mounted on a py­lon just aft of the cock­pit. This py­lon is formed by the main fuse­lage cross frames and is skinned with ply­wood, while the wings are sup­ported by twin lift struts with di­ag­o­nal wire brac­ing and at­tached to the py­lon by a pair of long steel rods. The wings

The RAF took de­liv­ery of 131... and only phased them out in 1986

con­sist of lead­ing edge D-sec­tion tor­sion boxes, the lead­ing edge cov­ered in ply­wood and the rest be­ing fab­ric cov­ered. The spoil­ers− de­signed to in­crease drag and give the glider a steeper and more con­trol­lable ap­proach path−are lo­cated quite far for­ward in the up­per sur­face, at ap­prox­i­mately one third of the chord.

The large tri­an­gu­lar tailplane is also strut­ted with fab­ric-cov­ered con­trol sur­faces, while the fin is tiny and the rud­der huge! There is no trim­mer.

An in­ter­est­ing facet of the T31 is its ‘tail bal­last’ (a sub­stan­tial weight lo­cated on a bracket on top of the tailplane and held in place by a pip-pin). As the air­craft was specif­i­cally de­signed to be soloed from the front seat (to ease con­ver­sion onto the T.8) Slingsby in­cluded in the de­sign a quick, easy and safe method of securing ad­di­tional bal­last when flown solo.

The un­der­car­riage is as un­com­pli­cated as the rest of the air­craft, be­ing just a tail­skid and large un­sprung monowheel mounted be­hind a nose skid. WT900 has been mod­i­fied with a small tail­wheel to aid in ground handling. There are two Ot­t­fur launch hooks−an aero­tow hook set right in the tip of the nose and a C of G hook by the main­wheel.

But enough of dry his­to­ries and tech­ni­cal spec­i­fi­ca­tions, what is this in­ter­est­ing arte­fact of avi­a­tion his­tory like to fly? Well, the key to en­joy­ing a T31 is the same as for most other vintage fly­ing ma­chines−choose your day care­fully! Pick the right day and it’s great fun, pick the wrong

day and it can eas­ily end in tears. More than fif­teen knots straight down the run­way and even the ground handling can be fraught, while any ap­pre­cia­ble cross­wind is just too much like hard work. What you want is very lit­tle wind on the ground and fat, gen­tle ther­mals.

Let’s go fly­ing

So, with that in mind, let’s go fly­ing−but first, a word of cau­tion. Ingress− par­tic­u­larly re­gard­ing the rear cock­pit−is not easy. When I climbed into WT900 this sum­mer it was the first time I’d been in aT 31 for 45 years, and although time waits for no man, the weight put on over time is an­other mat­ter en­tirely. It’s snug, while the ‘Owner’s Notes’ (as supplied by DJ) state‘ the most likely way to dam­age this glider is get­ting in and out. Care­fully think where you are go­ing to put your hands and feet, and don’t step on or hold onto any­thing that doesn’t look solid (most of the glider!) It is pos­si­ble to wear a para­chute in the front cock­pit. V un­likely to be able to jump from the rear.’

Per­haps un­sur­pris­ingly, the field of view from the rear cock­pit is rather poor, but from the front it is ex­cel­lent. An­other good rea­son not to use the rear cock­pit is that when flown two-up the wing load­ing is quite high at 23.8 kg/ sqm( over 4 kg/ sqm greater than the T21). Fly­ing it solo greatly in­creases the chance of a soar­ing flight.

Once strapped down by the clas­sic RAF four-point har­ness, let’s ac­quaint our­selves with the con­trols and in­stru­ments. Trust me, this won’t take long, as the cock­pits are per­fectly in keep­ing with the rest of the air­craft− de­light­fully sim­ple.

Each pi­lot has only a stick, rud­der ped­als, spoiler lever and ca­ble re­lease knob. In­ter­est­ingly (and per­haps some­what sur­pris­ingly, as it was in­tended for cadets) noth­ing ad­justs. A small cen­tre con­sole car­ries the in­stru­ment panel, which is as un­clut­tered as you would ex­pect. WT900 is as de­liv­ered from the fac­tory, and only fit­ted with an al­time­ter, ASI and Cobb-slater ‘Cosim’ var­i­ome­ter. Both the al­time­ter and ASI are of the types generic to other air­craft of this era, with the ASI in par­tic­u­lar be­ing some­what op­ti­mistic. It goes up to 130kt with the nee­dle trav­el­ling through 630° in the process. How­ever, on the T31 Vne oc­curs be­fore 360° of travel, and in prac­tice you very rarely use more than the first 180° of the dial.

The Cosim is an amus­ingly ar­chaic de­vice, con­sist­ing of a red and a green pith pel­let in a pair of ta­pered ver­ti­cal glass tubes con­nected to a flask. A per­pen­dic­u­lar scale along­side the tubes in­di­cates feet per sec­ond, coloured ar­rows at the base of each tube match the pel­lets and sig­nify whether you’re climb­ing or de­scend­ing. It is sur­pris­ingly sen­si­tive for such a prim­i­tive in­stru­ment and watch­ing the dif­fer­ent coloured pel­lets bob­bing up and down cer­tainly adds to the charm of fly­ing a T31, par­tic­u­larly when it is the green one! Although lit­tle heard in this coun­try, I be­lieve that the Cosim is the source of the Amer­i­can ex­pres­sion for lift; ‘green air’. Any­way, it’s head­ing for lunchtime, so it must be launch time.

Now, when Fred Slingsby watched the pro­to­type’s maiden flight 69 years ago I doubt he ever imag­ined that his creation would still be fly­ing in 2018, let

The cock­pits are... de­light­fully sim­ple

alone be­ing aero­towed be­hind an over-pow­ered ul­tra­light. He de­signed it to be winch-launched, and to be hon­est it re­ally isn’t pleas­ant to aero­tow (from ei­ther end) although it’s not so bad with a slower tug, such as the Euro­fox. The Vt (max aero­tow speed) is only 52kt, but the T31 does at least have a nose hook, and we’ve found that with half flap and about 50kt in the Euro­fox, it tows rea­son­ably com­fort­ably, the T31’s ASI show­ing 45kt. The tug pi­lot needs to be made aware to use only shal­low an­gles of bank and to re­main in the over­head un­til at least 1,500ft agl has been at­tained, and not to go too far away and never down­wind. To shoot the air-to-air photos that ac­com­pany this fea­ture re­quired a long, high tow that is prob­a­bly best de­scribed as ‘in­ter­est­ing’− and also un­for­get­table!

A winch launch re­quires a white weak link and a sym­pa­thetic, com­pe­tent winch driver. Vw (max winch launch speed) is only 46kt, and forty is prefer­able. As the T31 goes up the wire it will ap­pear to be go­ing very slowly, but the winch driver must re­sist the temp­ta­tion to add power.

Once the towrope or winch ca­ble has been cast off, the speed should be above forty if ridge soar­ing, and around 35 knots if ther­malling. The wing re­ally wasn’t built to go fast, but fi­nally and re­luc­tantly stalls at around 28kt solo, and 33 dual. At ther­malling speeds the pri­mary con­trols are all quite light and pleas­ant, although when be­ing aero­towed they firm up con­sid­er­ably −and there’s no trim avail­able to ease the load. One ad­van­tage of the very slow speed is that it’s quite easy to cen­tre in a ther­mal, the green pel­let shoots up the tube and ev­ery­thing is great−and gets even bet­ter if an in­quis­i­tive buz­zard or cu­ri­ous red kite joins you.

Like all air­craft that fly upon the air rather than through it, the sen­sa­tion of flight is pure and sim­ple, and this is fur­ther en­hanced by the open cock­pit. The air­craft’s slow speed and im­pact-ab­sorb­ing con­struc­tion cre­ate a feel­ing of safety and se­cu­rity. Even the very nec­es­sary ri­tual of don­ning fly­ing suit, gloves, scarf, hel­met and gog­gles adds to the en­joy­ment of the flight. I’ve al­ways said you should dress for the oc­ca­sion, and on these oc­ca­sions it’s go­ing to be cold. But the view more than makes up for it! Be­ing towed up so high for the pho­to­shoot gave me an in­cred­i­ble per­spec­tive on a lovely morn­ing. The fan­tas­tic view from the front seat was en­hanced by the open cock­pit, for which I must ad­mit a strong pref­er­ence. You wouldn’t think that the few mil­lime­tres of Per­spex im­posed by

The best glide ra­tio of a T31 is barely 18:1

an en­closed cock­pit would make that much dif­fer­ence, but they do−they make all the dif­fer­ence in the world. The sen­sa­tion of flight is so much stronger when you can feel, even smell, the air you’re fly­ing in. I oc­ca­sion­ally fly my open-cock­pit D.9 above the clouds, but as much as I en­joy do­ing so, the rau­cous racket of the en­gine al­ways in­trudes. Float­ing high above the beau­ti­ful Vale of Belvoir with just the gen­tle sigh and sough of the wind in the wires was a truly vis­ceral and mem­o­rable ex­pe­ri­ence.

Of course, as with most things, all this plea­sure does come at a price, and in this case that price is per­for­mance−or, to be more pre­cise, a dis­tinct lack of it. The best glide ra­tio of a T31 is barely 18:1, and this is achieved at only 37 knots. Con­se­quently, even a small head­wind has a pro­foundly detri­men­tal (and to the oc­cu­pants, pro­foundly de­press­ing) ef­fect on the air­craft’s progress over the ground.

Sooner or later (gen­er­ally sooner) it’s time to re­turn to base. Af­ter a pru­dently tight cir­cuit (it is so im­por­tant not to go too far down­wind) turn fi­nal, ex­tend the spoil­ers and pitch down for about 45kt. The spoil­ers are not the most ef­fec­tive air­brakes ever de­vised but−if needed−the T31 sideslips with ease, charm and grace, while si­mul­ta­ne­ously sink­ing like a rock. Rud­der it straight, a gen­tle flare, pause, then sink softly onto the grass. If the land­ing has been made into a wind of any strength, the ground-speed at touch­down is re­mark­ably slow and the groundroll cor­re­spond­ingly short. Upon land­ing, the pi­lots’ ex­pres­sions, be they ab ini­tio or a 1,000-hour vet­eran are al­ways the same – grin­ning from ear to ear.

In con­clu­sion, all I can say is that if you want the sen­sa­tion of flight dis­tilled to just about its purest form (but don’t want to use your legs as the un­der­car­riage), then you re­ally need to fly an open cock­pit glider!

sim­ple and safe, thanks to its mount be­ing onview, the tail bal­last weight is fit­ted for solo flight LEFT:

con­tin­u­ing the theme, the T31 is both read­ilyde­rigged and easy to in­spect BELOW:

has been fit­ted with a small rollerto suit Saltby tar­mac op­er­a­tions, the tail­skid ABOVE:

Who needs brakes? To slow the Tan­dem Tu­tor, all you do is al­low it to nod for­ward onto the skid

Fur­ther min­i­mal­ism: why would you need more than one wheel or sus­pen­sion for such a light ma­chine?

The sim­ple spoil­ers – which hinge open to ex­pose the wing struc­ture – ‘spoil’ lift and pro­vide the drag-in­duc­ing func­tion of an aero­plane’s flaps, al­low­ing the ap­proach an­gle to be con­trolled

As there’s no prop wash, the slip in­di­ca­tor is noth­ing more com­pli­cated than a length of yarn on the pi­tot/static

Aero­tow for the T31 from its Saltby base

Tug­gie’s view of the T31 on tow (and nicely in po­si­tion)

You need launches to be slow – 45kt IAS on aero­tow, forty when winched – and steady

The sim­ple, hon­est and in­ex­pen­sive ve­hi­cle that launched thou­sands of fly­ing ca­reers

I see you! The front seat of­fers a com­mand­ing view

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