Flight test: Slingsby Type 31/Cadet TX Mk.3
PUBLISHED: 14:08 06 March 2019 | UPDATED: 14:09 06 March 2019
Air Cadets used to reach for the sky in the T31/TX Mk.3 - and thousands went on to flying careers | 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 better-than-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 bit of history
It may seem incredible, but it took until 1950 before the British gliding movement finally realised that the solo method of flight training left something to be desired, and that ‘something’ was considerably fewer accidents! Although intended to produce lots of pilots, the ‘solo system’ primarily produced a lot of busted gliders.
Interestingly, Slingsby Sailplanes of Yorkshire already manufactured a fine two¬seat trainer, the wonderful T¬21B, or Sedbergh.
However, while the old ‘Barge’ was many things, one thing it wasn’t was cheap. The Air Cadets, in particular, needed a ‘cheap ‘n’ cheerful’ two¬seater, and Slingsby had just the thing: a tandem two¬seat development of the T¬8 Tutor (known by the RAF as the Cadet TX.2), which had in turn been derived from the Kirby Kadet. (The Air Ministry changed the spelling from ‘Kadet’ to ‘Cadet’ in 1943, you can probably guess why.)
Its fuselage was loosely based on that of the T¬29 Motor Tutor (an adapted T¬8 powered by either a 25hp Scott Squirrel or a 40hp JAP) but was both slightly longer and wider. Interesting factoid alert: when the TX Mk.3s were finally pensioned off in the mid¬eighties several were converted into ‘Motor Tutors’! The prototype first flew in 1949, with the first production T¬31B flying the following year.
This machine differed from the prototype by having spoilers and a small additional wing bracing strut, and while nowhere near as good as a T¬21, it was some 40% cheaper as it was of simpler construction and used a lot of Tutor bits.
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 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 a T31 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 D J) 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 23.8kg/sq m (over 4kg/sq m 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.
A typical cadet
To prove my thesis regarding just how many pilots started their careers in a TX Mk.3 I spoke to several eminent aviators of my acquaintance. It soon became apparent that if they were ‘airmen of a certain age’ then the first aircraft they ever soloed was almost always a T¬31.
They ranged from a couple of Air Marshals, several high¬time jetliner captains, to club CFIs and myriad sport pilots. In fact there were so many that we could fill this issue with their reminiscences!
Occasional cameraship pilot Al Munro’s flying life started with a week’s flying in Cadet TX Mk.3s, and he shares his memories of flying with the air cadets, and his subsequent career here.
“It was a Monday morning in late July 1958 when a bunch of raw cadets assembled in the 614 Gliding School hangar at the famous Battle of Britain station RAF Hornchurch, long since a housing estate. The course was a week long, with twenty¬something dual flights in the T¬21 and T¬31, to be followed, if successful, with three solo flights in the T¬31 and then a BGA ‘B’ certificate. The instructors were a mixed bunch, with beribboned ex¬wartime pilots including the station commander, national service pilots and a couple of civilians. Their patience was almost inexhaustible.
“The gliders were comparatively new, but the winch had seen better days as a twin drum barrage balloon launcher. It had a manual gear shift and 1,100ft was about the maximum height for a T¬21 winch launch, with the T¬31 making about 900ft. You can imagine that lessons were quite rushed and spins were never more than a 270° turn. However, with spare bodies on the ground to retrieve gliders, turnaround was fast and we probably made eighty or more launches every day.
“The T¬21 was the ‘hot ship’, while the T¬31 was regarded as a retrograde step. Downwind the wisdom was ‘Now stick your hand out at 45 degrees lad, and make sure that it’s pointing inside the airfield. And if it isn’t then fly straight to the airfield and land.’
“We all completed our three solos with flying to spare, so it was dealer’s choice. One cadet opted for an endurance flight and his instructor kept the T¬21 airborne over the Hornchurch sewage works by sniffing out a thermal. My answer was ‘aerobatics please Sir’, so that meant the CO, one Flt Lt Bill Verling. We did two loops in a T¬21 starting at 1,000 feet and ending pretty low.
“That was the day my blue touch¬paper was lit, and it’s never really gone out. After the gliding came a flying scholarship at Fairoaks on the Tiger Moth (thirty hours and a PPL), then off to Imperial College for an aero engineering degree. That meant about 150 hours Chipmunk flying at White Waltham.
“I joined the RAF in 1964 and, after basic training in the Jet Provost Mk4 at Acklington and advanced training in the Gnat T1 at Valley, I got my first taste of a fighter (the Gloster Javelin) in 1966. My first operational posting was on Javelins with 60 Sqd at RAF Tengah in Singapore. After that, and a period instructing naval pilots at Linton¬on¬Ouse on the Jet Provost, I flew Phantoms with several squadrons before becoming an instructor with 228 (the Phantom OCU) at Coningsby.
“I finished my military career as a Tornado instructor, and after leaving the RAF flew A320s with Excalibur and TransAer, instructed at Leicester Aero Club, and flew air experience flights for the ATC on the Chipmunk at Newton. I currently fly sailplanes and the EuroFox tug with the BGC at Saltby and – to bring this T¬31 tale to a suitably circular conclusion ¬ on 1 August 2018 I flew with Dave in WT900, sixty years to the day since my solo in an identical TX Mk.3.”
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 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 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 ground-roll 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!