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

Pilot - - CONTENTS - Words Dave Un­wim

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.

Pho­tos Keith Wil­son

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’

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

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

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

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