Flight Test: Slingsby T61 Venture
Familiar to ATC members, the Venture certainly teaches basic training and airmanship skills but is stuck somewhere between glider and aeroplane
Familiar to many former ATC members, part glider, part aeroplane, the Venture is a challenge to fly well
This month’s flight test is a little different. For most Pilot features I usually only fly the aircraft for an hour or so but I already have a reasonable amount of time in SF 25 variants. Another interesting aspect is that this particular machine may well have been flown by many Pilot readers, as it flew with the ATC as XZ560 for some fifteen years. Even if you didn’t fly XZ560− or the Buckminster Gliding Club’s other Venture, Za665−there’s a good chance that if you were in the ATC between 1975 and 1990 you’ve flown a Venture. If you haven’t, well… In most of my flight tests for Pilot I’m being introduced to the aircraft; for this one let’s change the style slightly and I’ll introduce the Venture to you.
The Slingsby T61F Venture T2 (there’s a mouthful) is a version of the T61 that was ordered by the MOD for the Air Training Corps, and the T61 itself was derived from the Scheibe Falke SF 25 (see ‘Originally a German Falcon’, p62). They say that beauty is in the eye of the beholder, but of all the sobriquets that can be applied to the Venture ‘pretty’ isn’t one of them.
A cantilever low wing monoplane with slightly forward swept wings, the fuselage is a fabric-covered, welded steel tube structure with the forward section skinned with laminated glassfibre. Slingsby was just starting to learn about composites in the 1970s and, unlike the wood spar fitted to SF 25s and T61s, the Venture has a glassfibre main spar, encased in plywood. This modification produced a decrease in the empty weight and an increase in the MAUW, greatly increasing its utility. The wings, tailplane and rudder are skinned with plywood and fabric, and all control surfaces (except for the metal top-surface lift-spoilers) are also fabric-covered.
Of all the sobriquets than can be applied... pretty is not one of them
The engine is a Vw-derived Rollason RS2 air-cooled flat-four, which spins a twoblade, fixed-pitch Hoffmann prop. An interesting fact is that, as it was never certified as an aero-engine, the only production aircraft it can be used in is the T61. It is claimed to produce 45hp at 3,300rpm but with a five-minute limit. Maximum rpm is 3,500rpm but this has a thirty-second limit and, frankly, I don’t think you’re going to get much done in thirty seconds in a Venture. The max continuous is 2,950, but even then the oil temperature needs watching, especially in a climb, as the engine isn’t fitted with an oil cooler (which would have been a good idea). There is a sort of jacket around the inlet manifold that warms the manifold and possibly cools the oil slightly, but it’s no oil cooler. The fuel is contained in a single 32-litre fuselage tank just aft of the cockpit. Fuel quantity is displayed by a simple ball-and-tube arrangement, which is (not very usefully) behind you.
Although typically referred to as a monowheel, strictly speaking this could be construed as a misnomer as the undercarriage has four wheels−a large, single main wheel, a steerable pneumatic tailwheel and two small solid wheels on
nylon outriggers, which are located just outboard of the spoilers. The main wheel is non-retractable and is partially covered by an allegedly aerodynamic fairing. It carries a cable-actuated drum brake.
During the walkround a good tip is to try and get three fingers between the bottom of the sternpost and the top of the tailwheel. If you can’t, it’s had a heavy landing. I also like to give the tailplane a waggle and a good look at the attachment bolts as there is an AD regarding cracks around this area. There is also not a lot of up elevator travel−more on this later.
Before you get in it’s also worth considering using the small tap behind the seats to drain the fuel tank’s sump. This is wire-locked and often neglected, but should still be done occasionally. Note that it is independent from the gascolator and is fed from a separate standpipe.
Access to the cockpit isn’t the easiest. The canopy hinges forward and there are large metal stirrups on both sides, but being a monowheel it always rocks from side-toside as you saddle up. If there are two of you, don’t try and get in simultaneously− it won’t work. Two more helpful hints are: don’t leave the parking brake on for any length of time (it stretches the cable) and always leave the rotary selector for the four-point harness to locked−otherwise it knackers the springs. The canopy can be jettisoned, which is curious as when it was in service with the ATC cadets didn’t wear parachutes.
Another curiosity is that although the min/max cockpit loading is incredibly broad (from 22kg to over 200kg) neither the seats, sticks nor rudder pedals adjust. Having clearly considered that the cadets’ weights would vary considerably, it doesn’t seem to have occurred to the designers that their sizes would be equally variable. It’s not the most comfortable cockpit I’ve ever sat in. There’s only one brake lever (on the left stick), but two spoiler levers, one on the left and one in the centre. Like many Venture drivers, I tend to take off flying left-handed but land (and also glide) right-handed. Trim lever and fuel selector are between the seats. The panel is pretty basic, with variometer, ASI, turn-and-slip, and altimeter in front of the pilot, and the tachometer and oil pressure and temperature on the far right. A CHT gauge is an odd omission.
Automatic throttle setting
Starting up is slightly different to your typical air-cooled aero-engine. As you pull out the choke knob the throttle simultaneously and automatically moves in, because they are interconnected. Do not touch! The throttle is now perfectly set for a cold start, so stick back and pull the brake lever, select the single magneto on, turn the rotary master switch ninety degrees clockwise, check the small orange light has illuminated and pull the starter handle. If you’ve ever owned an old Fiat 500 and think that starter handle looks familiar, you’re right. If the engine has been set up correctly it will start readily and you’ll probably have to shut the choke and reduce power promptly. It’s also important to make sure that the starter handle is pushed completely home post-start, otherwise the Bendix won’t fully retract and you’ll hear the starter motor’s teeth chattering on the starter ring. Check that the oil pressure is rising and that the brake is working satisfactorily and we come to one of the most challenging aspects of flying a Venture−taxying it.
One of the reasons why the Venture is a good basic trainer is that it teaches real
airmanship. Quite obviously, this is not an aircraft that you should ever taxi faster than walking speed and, as it is not exactly over-endowed with power, should the ground be soft it is advisable to try to keep moving at all times−just not too fast! Furthermore, the big wingspan, monowheel (no differential braking) and barely steerable tailwheel combine to create a machine that is quite unwieldy, and great care must be taken whenever you’re moving near another aircraft, person or object. The turning circle is vast and turning out of wind can be a challenge, particularly on narrow runways.
This is an aircraft that has to be flown all the time and I use aileron to put the into-turn outrigger on the ground to add a little drag, particularly on grass. It’s debatable whether this actually does anything but at least it shows that you’re doing everything you can! However, sometimes you must either signal for a wingwalker or shut down, get out and turn it by hand. One thing you must never do is allow anyone to pick the tail up when the engine is running−there really isn’t a lot of propeller clearance and a prop strike is very likely. The bottom line with the T61 is that if you can manoeuvre it to the runway you can probably fly it (although not necessarily land it gracefully, of which more anon).
The pre-takeoff checks are very simple; you cannot even check the magneto! One thing you must do is double-check that the carb heat is working well. It is such an efficient ice maker that the engine really should be called a refrigerator, not a Rollason, so be particularly wary if you’ve had the engine ticking over for any time in either humid conditions or while standing on wet grass.
Before lining up take a long hard look at the windsock. That monowheel means there is not much control authority at the start of the takeoff roll, so if there’s a lot of crosswind (and particularly from the right) be ready for it to swing. Do not raise the tail at slow indicated airspeeds, as even a small crosswind will cause a Venture to weathercock most alarmingly. This is because that large fin has a pretty long arm to work through, while the low-power engine and small prop aren’t putting much airflow over the rudder. It’s at times like these that you curse the monowheel and ruefully wish you had two main wheels and differential braking.
Final checks complete, roll slowly out onto the runway, line the aircraft up with the centreline and push the throttle open smoothly. Maximum static rpm is 2,800 and a quick glance at the tachometer is prudent. As mentioned earlier, the engine is claimed to produce up to 45hp but only at 3,500rpm (so you don’t have anywhere near 45hp on takeoff). In fact, when taking off close to the MAUW the power-toweight ratio is more likely a pretty bleak 20kg/kw, if not worse. If it’s down on revs take it straight back to the shed, for even if the engine is working well the acceleration will not produce exhilaration. In fact acceleration is probably too strong a word to describe the start of the takeoff run, a more apt description would be that it gathers speed. It certainly won’t leap into the air−ventures never do, and its best to expect a protracted ground roll. On the plus side, the ailerons come alive quite quickly, enabling you to keep the aircraft balanced on the main wheel with neither outrigger touching the ground. As the needle of the ASI starts to move, the elevator becomes effective, but don’t pick up the tailwheel too quickly.
Eventually it will lumber into the air but another potential ‘gotcha’ here is that, although it will fly in ground effect at very low speeds, it is imperative that you do not initiate a climb until you have achieved 55 knots. This is the magic number so fly level in ground effect until you’ve attained 55 (which can take a surprisingly long time), then allow a gentle climb to develop while maintaining 55. However, if you decide to take off with wet wings (and I’d advise against it) add another five knots. That thick wing may look unsophisticated, and the aerofoil is far from laminar, yet for some reason it is remarkably intolerant of being wet.
If you’re heavy on a hot, windless day the rate of climb can be quite depressing, and care must be taken to keep the oil temperature within limits because it will get hot. As mentioned earlier there isn’t a CHT gauge, which initially I found rather odd. However, its omission is probably deliberate, as I suspect the cylinder heads
probably get toasty too, and seeing the oil and CHTS creeping towards their respective red lines is just going to worry you. Curiously the cockpit placard promulgates a maximum oil temperature of 90˚C, while modern thinking is that over 100 is good as it gets the water out (oil being hygroscopic).
Anyway, at a safe height reduce power to below METO, re-trim for 55kt and explore the general handling. Of course, those big wings do mean that plenty of rudder is required when turning, due to the adverse yaw, and the roll rate is certainly far from sprightly. Typically, a stopwatch is used to measure the roll rate−but with the Venture a calendar will suffice. The ailerons are heavy, and response slow. In fact, this is not a machine for the ‘high gain’ pilot, as sometimes you need to make a control input, and then see what it does. In test pilot speak, it could be described as an ‘open-loop’ system. Try the spoilers. There’s quite a big nose-down pitch trim change with full spoiler extension, and although they don’t feel very effective a good exercise is to try landing without them. You’ll need a surprisingly long runway.
Examining the stick-free stability shows it’s positively stable in pitch and yaw, and neutral in roll, while an exploration of its slow flight and stall characteristics reveals they’re very benign. Even if you get the nose way up and really abuse the controls it’ll just fall off on one wing into a spiral dive. In fact, the centre of gravity is so far forward I think it may well be impossible to spin it (and I have tried!) The Venture is possibly unique in that even with the cockpit completely empty the centre of gravity is still within limits. The minimum cockpit load with up to 22 litres of fuel is 22kg, and remember that the tank is behind the seats. A sensible cruising speed is around 60-65kt IAS, and as the engine is barely sipping ten litres an hour this equates to an endurance of around three hours and a still-air range (no reserve) of about 180nm.
Shall we turn off the engine now? I always ask, as for pilots who’ve only ever flown power the sight of a stationary prop can be a little perturbing. The first step is to reduce power to 1,500rpm for one minute to allow temperatures and pressures to stabilise, then throttle to flight idle, ignition off. As soon as the engine stops pitch up slightly to stop the prop windmilling and then use the starter motor to drive it to the horizontal. This not only improves the view but also slightly reduces the drag−and let’s face it, we need all the help we can get. The book claims a best glide of 22:1 and a
minimum sink of 220fpm but I feel both claims are optimistic. Engine on or off, performance is barely adequate although, to be fair, it is quite an old design.
Engine-off handling is rather ‘loggy’, and plenty of rudder is required when entering or exiting a turn. Without power, the stall is even more of a non-event. There is ample pre-stall buffet, and if the speed is reduced sufficiently slowly it never really stalls but instead simply mushes with a high sink rate. I think the limited up elevator plays a part here. It’s a very safe aircraft and (to paraphrase Northrop test pilot Max Stanley) can just barely kill you.
It’s a very safe aircraft and can just barely kill you
It is a truism of aviation that having retracted the undercarriage there is always the possibility of it failing to extend or lock into position. Similarly, and irrespective of the type of engine, there is no cast-iron guarantee that it will start again having stopped it. I only ever shut it down within easy gliding range, and−unless the airfield is very quiet−usually restart the engine prior to joining the circuit. An air start (diving to use the airflow to turn the prop) can use quite a lot of height−the starter is much more efficient. The engine cools down very rapidly, but that’s what windchill will do. It usually likes a bit of choke.
Back in the circuit, wait until we’re close abeam the threshold at around 800 feet then select carb heat on, close the throttle completely and swap hands so that your right is now on the stick and your left on the spoiler lever. Control speed with pitch and the rate of descent with the spoilers. Trim for about 60kt, start with about ‘half’ spoilers and see what happens. Then on very short final carefully ease them right out while simultaneously adding back stick. The speed washes off quite quickly, so just fly level about a foot off the ground and keep… holding… off. You really need to get the stick right back on touchdown. There’s no damping on the big monowheel: get it wrong and you’ll be bouncing down the runway like a kangaroo on steroids. Get it right and, when landing on grass into a reasonable headwind, it’s not that challenging. However, swap the grass for tarmac and throw in a lively crosswind and you’d better be ready for some pretty deft footwork (or a diversion to a more amenable alternate!)
By now you’re probably thinking ‘Dave, you’re really not selling it to me. It sounds a slow, cumbersome and uncomfortable compromise, being neither an efficient sailplane nor an effective powered aircraft−what’s the attraction?’ Well firstly, cost. The Buckmister Gliding Club hires G-BUFR out at £60 per hour wet. Hangarage aside, Ventures are very affordable aircraft, both to buy and run−and if the rumours regarding them transitioning to Annex II are true they should become even more affordable. In fact, they never should have been EASA aircraft in the first place, as they are ex-military machines.
The Venture is an excellent basic trainer on which to teach real airmanship, such as ‘flying the wing’ and reading the sky, even how to taxi properly! Finally (and just like that other great British trainer the Tiger Moth) although a Venture is easy to fly, it’s not so easy to fly well.
No luxuries in a cockpit that was designed to be a place of work
The luggage shelf might have been designed for stuff to fall down your back
Well worn trim lever and fuel cock. How many hands have operated these levers over the years?
The fuel gauge is sited nicely out of view behind the pilot — but at least it is in the cockpit
Just like the Red Baron’s triplane, wooden skids protect the wingtips in the event of a wobble
Fixed outrigger wheels twang around on nylon lollypop sticks, keeping the wings more or less level
All the ‘suspension’ compliance is in the tyre sidewalls. At least the step is functional
Awkward cockpit access demands that you climb in one at a time or risk a painful clash of heads
The fuel filler cap is about the raciest feature of the otherwise very slow moving Venture
Just like its original manufacturer’s gliders, the T61 is designed to be readily dismantled for transport
Jet jockeys might call them airbrakes — glider pilots will recognise them as lift ‘spoilers’
The Venture in its element — not a great glider, but an aircraft designed to teach gliding technique independent of launch winches or tow planes
The view over the nose isn’t brilliant, nor is there much prop clearance, tail-up
Dave sweats holding the Venture in formation: manoeuvrable it ain’t
Easy to fly, yes — but like any good trainer not so easy to fly well