Tag: UTVA U-75

Flight Report – That 70s Plane: Flying The UTVA 75 Trainer

Posted in General AviationTagged , , , , , , 2 Comments

By me
All photos me too, copyrighted

Ever since the early days of Achtung, Skyhawk!, I’ve always been on the lookout for rare, interesting and historically significant aircraft puttering around the region – you know, the sort of machines that had it all really: rarity, backstory and a rich history to boot. As the winter’s soaked runways, persistent fog and oppressive low cloud finally gave way to dry grass, pleasant temperatures and clear sunny skies, I decided I might as well go one up this time and actually – fly one 🙂 .

Having spent my formative flying years listening to “oldtimers” and their stories of adventure on the many aircraft types indigenous to former Yugoslavia, the choice made itself really, especially since many of them are nowadays well up on the endangered list. The simplest solution was thus to go for the most modern and popular one, which eventually led me to Slovenia’s Maribor Airport (MBX/LJMB) and its resident UTVA U-75 two-seat trainer.

Responding to S5-DCI and owned by the Letalski center Maribor (LCM) flying club, this particular aircraft is itself already good for a classic AS review – but, being one of only a dozen or so still airworthy, I decided to bin tradition and focus this time on what this interesting machine is actually like to fly. So, instead of digging deep into its history (s/n 53171, mfd. 1980, ex. YU-DGF of AK Maribor, then SL-DCI and S5-DCI of the Slovenian Air Force until 2010, then to LCM 😀 ), I though I could put together a short flight report and attempt to describe what the U-75 feels like in its element…

The shape that launched a thousand student traumas… while it certainly won’t be winning any beauty contests, the U-75’s stocky build and generous size nevertheless make it stand out among its peers!

Author’s note: given that I have no experience flight testing aircraft (nor do I have the required skills or qualifications), this work is not a proper professional review – but rather the personal experience of a long-time light aircraft pilot and lifelong GA fan. As such, my observations will definitely not be something they will print in textbooks – but given the rarity of the U-75, they should nevertheless be an interesting read for the enthusiast!

Part 1: the basics

Even though the U-75 had already featured here in depth as part of a review of the type’s sole surviving four-seat example, for the sake of clarity and ease of reading I though it best to nevertheless run quickly through some of its more pertinent characteristics. Flying for the first time in 1976, the U-75 is a simple and robust all-metal semi aerobatic two seat trainer, designed to be suitable for everything from basic flying instruction (civilian and military) to initial aerobatics and even air-to-ground gunnery. Despite its not inconsiderable bulk, the U-75 weighs only 685 kg empty and 1,200 kg at maximum take-off (though it is usually flown at its maximum landing weight of 960 kg), which makes its 180 HP Lycoming IO-360 and its associated two-blade constant speed prop good for about 115 kts in the cruise. More importantly, its +5.5/-3 G stress limits with one person on board (and +4.4/-2.2 with two) give it a wide berth during maneuvers, while the tall wide-track landing gear, long-travel shock absorbers and large low pressure tires make (student) landings a doddle even on rough and unprepared strips.

With 138 examples made in total between 1978 and 1985, the U-75 would go on to become former Yugoslavia’s second most produced indigenous design – right behind the G-2 jet trainer – and was throughout the 80s and 90s used by civilian clubs and air forces across the land (in the latter often known as the V-53). And while it is today viewed with fond nostalgia, its life in service was much tarnished by a popular reputation for violent spinning (sometimes fatally), which bred considerable distrust in the design. In fact, the problems stemmed from the rearward position of its center-of-gravity, which made it a peppy and nimble performer – but at the expense of reduced longitudinal stability*. When pushed hard and then poked with a stick, it would indeed want to spin and keep on spinning; but when flown in moderation and per SOP, it had shown itself to be pretty docile in all flight regimes, a fact attested to by numerous operators who went aerobatic on a regular basis and without incident.

* in simple terms, the two extremes of aircraft behavior are stability and maneuverability. An aircraft that is stable is not maneuverable; likewise, an aircraft that is maneuverable is not stable. Given that this principle acts along all axes of the airplane separately, nailing down the exact amount of each is an art. In prototype form, the U-75 was found to be too stable longitudinally, which reduced its maneuverability in pitch and made it less suitable for the training role. The root cause was determined to be a CG position that was too far forward; to solve the problem, the heavy battery – originally fitted behind the cockpit – was relocated to the tail cone. This shifted the CG backwards sufficiently to solve the problem, but at the same time made the U-75 “nervous” in pitch when it reached its limits. In a hurried or badly executed maneuver, it was not hard to stall and send the aircraft over one wing, initiating a spin that – if not countered immediately – just kept getting worse. Approved procedures therefore called for entry into spin practice at a minimum of 5,000 ft AGL, and recovery to be initiated after just one turn; done properly, flight tests showed an 850 ft altitude loss could be expected. Done lower, slower and sloppier, you can well imagine the results…

Aside from its significance to the locals, the U-75 is then a classic ab-initio trainer, the sort of aircraft produced by aeronautical establishments all around the world. This itself invites a comparison to some of its peers, such as the Slingsby T.67 Firefly, Scottish Aviation Bulldog, the PAC CT-4 or the SAAB S.91 Safir; however, what I am actually going to do is compare it to the restrained and very unmilitary Cessna 172. The reasoning behind this approach is simple: many GA flyers have at one point or another flown a Skyhawk, with most (myself included) having logged treble figures in at least one of its variants. Despite their different roles, the two aircraft are alike in a number of respects, which makes establishing a baseline for the U-75’s comparison all the easier. And anyway, there’s no point in drawing parallels with an equivalent aircraft if there’s nobody reading (or writing) who flew them, is there? 🙂

Part 2: getting in

But, first things first. Entry into the cockpit is pretty straightforward and is standard stuff for low-wing aircraft: hand in recessed handle, foot on step and up onto the wing from behind. However, since the U-75 was designed from the outset to operate out of unprepared strips, the wing root is a good 80 cm above the ground, so the whole maneuver requires a bit of gymnastics – though not much more than trying not to trip over the 172’s main gear leg.

Once on top, the two-part sideways hinged canopy (jettisonable in flight) opens upwards, and is then fixed in place by a manually folding arm tucked to the inside of the canopy frame. This setup is not really ideal for tall people (like me), since it is quite easy to bang one’s head against the canopy while maneuvering to enter the seat. Thankfully, the frame is pretty large overall so – heads notwithstanding – getting in and out is not difficult or haphazard by any measure.

Thankfully for its crews, the U-75’s exterior size is matched by its interior, with more space on offer than in Cessna’s premium piston singles, let alone the Skyhawk. The elbow room for either seat is impressive, and even larger pilots would still have plenty of space to work without body contact. Note the chunky seat belts and the canvas cover behind the seats that doubles as a parcel tray

While it is immediately obvious that all structural components and cockpit controls are built to last – everything feels decidedly more robust and durable than on the 172 – the overriding impression is of rudimentary finishing work, with rough and unprotected edges in abundance all over the cockpit. Admittedly, given the U-75’s military nature, comparing these and other creature comforts with those of the Skyhawk is apples to oranges – but despite the lack of padding and soundproofing and any form of interior trim at all, the cockpit is physically very comfortable and quite airy. Headroom however is slightly less generous than on the 172 (even when you lower the seat fully), and anybody over 1.8 m and wearing a headset will fill slightly hemmed in from above – though it is still manageable and not much of an inconvenience on shorter flights (under two hours).

While there are no basic Ts and sixes here, the U-75’s cockpit is in some respects pretty well though out, with a couple of good ergonomic touches. One in particular is the central pedestal, which contains pretty much all system controls, including the throttle (yellow lever), propeller control (blue lever), mixture control (plunger), alternate air source (red-topped plunger), demist controls on the side, parking brake (orange switch) and, out of shot, the fuel selector (which, like on the 172, has a very welcome BOTH setting). One particular level that is missing – and would have been fitted in the hole below the alternate air – is the underwing stores emergency release handle. Like many trainers, the U-75 also includes another set of throttle and prop controls on the left of the pilot’s seat. Absent from the shot is the flap level, a large Piper-like affair between the seats; its settings are simple, UP, notch 1 (take-off and landing) and notch 2 (landing only). For my taste, the sticks are of perfect height – not to low, not to high – and though they’re designed to accept either hand, they fall slightly more easily into the right. The only really annoying feature is that on both throttle quadrants the prop control is on the left and the throttle on the right; whereas the manifold pressure gauge (controlled by the throttle) in on the left and the RPM gauge is on the right. As is the norm for all Yugoslav designs, the flight instruments are all metric, while the engine instruments – usually cherry-picked from various Western designs – are mostly imperial.

Once seated, both the sitting position and the view ahead are pretty good, though the frame of the canopy initially gave me the impression of peering through a postbox; once on the move though, I quickly got used to it. The rudder pedals can be adjusted fore and aft, but this is generally avoided since the mechanism is known to stick. The brakes themselves are actuated by separate toe-operated paddles inboard of the pedals – a solution similar to that used on the Super Cub, where they’re heel-operated. With larger shoes (or military boots) on larger feet, this does not seem to be a particularly used-friendly solution, and it took me some fumbling and toe jabbing before I’d gotten used to it. The rudder pedal edges are also contoured to accept the outline of a thick boot – a feature not really compatible with the sneakers I was wearing that day.

Helping matters however is that the brakes are quite powerful, so even a slight jab at them (regardless of its elegance) produces some results. Then there’s also the fully steerable nose wheel, which makes ground maneuvering pretty painless – indeed, I’d managed to get the hang of it after just a few dozen yards. In fact, on steering alone (without differential braking), the turn radius is just 7 meters – noticeably less than the 8.3 the Skyhawk can achieve using BOTH steering and brakes at the same time. The shock absorbers and tires make the ride quite smooth even over rough terrain, but at the same time do not let the aircraft roll to much in the turns if you keep the speed moderate (though the aircraft’s low CG position has a lot to do with this).

Part 3: airborne

System-wise, all pre-departure checks are no more complicated than on the 172, and follow pretty much the same pattern. Having been designed from the outset to meet the FAA’s FAR Part 23 criteria, the U-75 holds no surprises, and there’s none of the “Eastern Bloc system exotica” that its looks and origin would lead one to believe. With the engine being essentially the same as on today’s Cessna 172S (albeit with a constant speed prop), the run-up is also straightforward and over in a jiffy.

As I was briefed by the instructor occupying the right seat, the standard flap setting for departure from both paved and soft fields is notch 1, which gives 20° of flap. The aircraft manual quotes a 225 meter max performance run on grass and with zero wind; however, we had the advantage of concrete and a quartering eight knot wind, so despite the 880 ft field elevation and 25° Centigrade outside, we opted for a more leisurely departure. Adding power, there’s a very noticeable swing to the left – far more pronounced than on the Skyhawk – which can be neutralized only with a large amount of right foot. What’s more, significant pressure on the pedal is constantly needed at high power, and with no rudder trim available, this tends to become wearisome after awhile (though I suspect the rigging of the tab of the vertical stabilizer was to blame for this). Being both lighter and more powerful than the 172, the acceleration was noticeably better, and with slight backward pressure on the stick we were already airborne at 110 km/h (59 kts), having used up around 300 meters of runway.

Passing 50 ft, LCM club procedures call for acceleration to the U-75’s best climb speed (Vy) of 130 km/h (70 kts), retracting the flaps at 300 ft AGL and then setting maximum cruise power, an easily remembered 25″ MP and 2,500 RPM (equivalent to roughly 80% power). In this regime, the rate of climb with full fuel and two of us on board varied between 4 and 5 m/s (800-1,000 fpm), but the day’s thermal turbulence made getting a constant figure impossible.

Once in the cruise – in our case at 3,000 ft towards one of Maribor’s training areas – the power came back to the 65% setting of 22.5″ and 2,350 RPM, which gave a solid 160 km/h (86 kts) indicated and 169 km/h (91 kts) true. While this is not particularly impressive for the available power, the thick wing profile and large landing gear do create a quite lot of drag; increasing the power by two inches MP gave around 170 km/h (92 kts) indicated, but since we were in no hurry, I soon throttled back to best cruise and set about seeing what’s what.

Given my previously noted lack of flight test qualifications, I decided to try and get an impression of the U-75 by flying a program based on the average PPL skill test (bits of which I dimly remember from ages past 😀 ). This I thought would give me the best impression possible in the allotted time frame (one hour 30 minutes), since I would get to see both how it behaves in regimes I’m familiar with from the 172 – as well as how a student might experience it during basic training. To this end, my “program” consisted of:

  • standard, 60° and 90° banked turns + snap roll
  • slow flight
  • stalling, both power on and power off
  • sideslip descent + gliding
  • flaps notch 1 and notch 2 approaches w/ crosswind
  • and route flying and navigation

Sadly, the pattern at Maribor was quite crowded that day, so there was no opportunity to perform a simulated engine-out approach without inconveniencing half the sky. To compensate, the ambidextrous nature of the U-75’s flight controls had allowed me to fly most of my program with each hand in turn and judge the ease and practicality of both. In the end – though I favor using my right hand as I do at work – flying with the left is often far simpler, since all relevant controls – flaps, lights, radio – are on the right side, allowing me to push and pull everything without having to constantly switch hands.

To cut to the chase without going through each maneuver separately, the handling came as quite a positive surprise – especially after everything I’ve heard said about it. The numbers themselves offer some clue to the above, as the U-75’s 65.3 kg/m² wing loading – only slightly up from the 172’s 64.4 kg/m² – promised similarly forgiving all-round behavior, while its 9.73 m wingspan – noticeably shorter than the Skyhawk’s 10.97 – bode well for rolling rates and a general willingness to maneuver.

Immediately after leaving straight & level fight, I found the stick to be very precise and informative, its travel pleasingly light in both axes – enough to get a good feel for the aircraft, but not twitchy enough to become tiring. Interestingly, the stick moves noticeably lighter in roll than in pitch, a setup exactly opposite to that of a glider. Thanks to the type’s large ailerons and powerful elevator (both blessed with considerable travel), the feel was matched by the aircraft’s physical response, with rolling and pitching done quickly and eagerly – but without the aggression of a thoroughbred aerobatic machine. Unsurprisingly, rates across all three axes were significantly higher than on the Skyhawk.

This harmony between stick and machine meant that I could achieve a remarkable degree of precision in most maneuvers already on the first time out, and all without any unnecessary flailing at the controls. Following my observations on take-off and in the climb, I was also quite surprised how little rudder was needed in turns – and that even left-hand maneuvers occasionally needed a poke of right rudder (though I again suspect tab rigging to be the cause). An additional characteristic that caught my eye/hand was that even in high bank turns, comparatively little backpressure was needed on the stick – and when I did find myself losing altitude, little additional force was necessary to return everything back to textbook state. As the numbers in the previous paragraph suggested, the U-75 was indeed very willing to sustain most maneuvers without much fuss and manhandling from my side, which immediately inspired a dose of confidence in its handling as a whole.

But what impressed me most of all was its stall response. Given the legends, tales and accident reports relating to U-75s going vertically, I was ever so slightly apprehensive about this part – not due to fears of ending up in a spin**, but a perception that an aircraft with such a reputation will likely not be well behaved once the going gets tough. I am pleased to say that I was quite off the mark, for the U-75 had exhibited flight simulator-like behavior, even with power on: just a very slight shudder and forward tug on the stick saying that it would like its nose to point down if I don’t mind. Honestly, it made the 172 look dramatic! Another thing of note is that despite the day’s turbulent thermal weather, it resisted wiggling its wings near the stall – and as soon as it even slightly went to the side, quick pedal action would sort everything out in an instant.

** although owners who had spun the U-75 say it is not as big a deal as folklore suggests (again, if done properly), I had shied away from attempting one, due to both my lack of experience on the type – and the fact that S5-DCI itself was barred from spinning by LCM club rules.

Some mention should also be made of the engine. Despite its nominal take-off rating of 180 HP, throughout the program we kept it at its 25″/2,500 RPM maximum cruise setting, which – according to the manuals – left us 150 HP to play with. Despite the abuse and the 20 °C at altitude, the engine oil temperature remained hovering around 95 °C (right in the middle of its 80-110 °C normal operating range), while the designated cylinder registered around 190 °C (deep enough for comfort within its 80-220 °C green arc) – which says a lot about the airflow through the engine compartment. Helping matters were the U-75’s distinctive cowl flaps, located on top of the cowl just ahead of the windshield, which lead to the odd situation of the front cylinders running hotter than the rear pair. Another thing of note is that despite its semi-aerobatic credentials, the U-75 sports the standard version of the IO-360, which is not equipped with fuel and oil systems for inverted flight (these would have been identified by the additional prefix AE).

Criticisms? Well, the only major thorn in my eye at this time was the trim wheel, which was far too coarse and lacking in feel; it resisted operation too much and even a slight turn resulted in an out-of-proportion change in stick force. However, as with the rudder, this may very well have been down to the rigging of this specific aircraft.

With the program completed, we settled back into the cruise, where the plan was for me to do some navigation of the greater Maribor area and see how the U-75 behaves en-route. In a number of critical areas, it didn’t fare all that well: its military genes mean that comfort was never allowed to compromise the training experience, the result of which is a cockpit with no soundproofing at all (as noted previously). The upshot is that ambient noise is off the scale, and even with headphones on it all becomes pretty annoying pretty quickly (especially since S5-DCI has no squelch control, which leaves the headphone mikes free to pick up the drone and amplify it back to you). The position and height of the stick also mean that you have very little space in your lap – so with a kneeboard on and the right seat occupied, you’re going to struggle to read an unfolded map, despite the nominally generous size of the cockpit.

However, as uncomfortable as it may be, the U-75 nevertheless does have something going for it as a navigation platform. In common with most other low-wing aircraft, the view outside is excellent, and the relatively small span of the wing means you can often have a good look down. Once trimmed (after much frustration), it will fly hands off for a surprising amount of time – without rudder input even – though having someone in the right seat to balance things out certainly helps. More importantly, the extensive glazing means you can easily keep tabs on surrounding traffic, and it never took us long to spot neighboring aircraft without having to bank or pitch or stand on our heads. So while the average GA tourer is in a completely different league in terms of comfort – so much so you’d be excused for sending hate mail to the UTVA works following a long cross-country – the U-75 is nevertheless a practical and safe platform for finding your way around.

In that other important route performance metric – fuel – the U-75 is pretty much on par with the 172, with our 65% power setting (mixture full rich) registering 30 liters/hour (7.5 GPH) on the flow meter. With the manufacturer’s 15% reserve fuel policy giving us 128 liters (34 USG) usable out of the 150 liters (40 USG) carried in total, this works out to an endurance of around 4.5 hours. At the same altitude, power/mix setting and ambient conditions, the POH for a late 70s 172N puts out a fuel flow of 25 liters/hour (6.7 GPH) which, with 136 liters (36 USG) available before hitting the 45 minute reserve, gives an endurance of 5.3 hours. However, I normally fly a 1979 Skyhawk with a very accurate digital flow meter, and the real-world figures in nearly identical conditions are all in the lower 7s, which gives an actual endurance of between 4.75 and 5 hours.

A charismatic 70s Yugoslav trainer, more noise than is believable, a green ergonomic mess of a panel and a guns/rockets/bombs toggle switch on the stick – fine ingredients for a fulfilling afternoon! Despite the large canopy frame, the view out is excellent in all directions (even back), though on clear days the sun coming in through the top of the canopy does lead to sauna-like conditions.

Part 4: stopping being airborne

With both zone and en-route work completed, I opted for a handful of touch-and-goes, to see how the U-75 manages that most difficult of maneuvers – landing. On the first three approaches, I went with a flaps notch 1 configuration – and quickly discovered that the little Utva could out-accelerate a brick going down. All that drag means that its glide is quite steep, with the manual quoting a L/D ratio (flaps up) of just 1/6.72 at 150 km/h, 1/7.1 at the 140 km/h (76 kts) recommended engine-out speed, and just 1/8.42 at its 116 km/h (63 kts) best glide – a condition where even the unaerodynamic 172 manages 1/9.2. In our case, these figures were decidedly lower, partly due to my ham-fisted flying – but mostly due to keeping our speed high to avoid disrupting the traffic flow and potentially shock cooling the engine. The ideal speed was therefore pegged at the same 130 km/h as in the climb, which gave more than adequate circuit performance while still keeping us below the maximum flap extension speed of 140 km/h.

Flying, both on and off work, a high-wing aircraft blessed with ample wingtip clearance, I was naturally apprehensive about touching down wing low in the day’s 6 knot crosswind. While this is just a light breeze everywhere else, the U-75 is deemed to be particularly sensitive to it, and is in fact limited to a 90° crosswind component of just 8 knots – HALF of the 15 knots limiting the Skyhawk. To avoid making a complete mess of it so early on, I elected instead for a jet-style crabbed approach with an appropriate bootfull just before the wheels hit the ground. The type’s powerful rudder made this a non-issue, though with experience I’m sure a proper sideslip approach could be flown easily and without danger to both the airplane and ego (especially since the 6° dihedral places the wingtip approximately 1.1 meters above the ground).

Glossing over my first landing – an inglorious thump from too high a flare – I’d soon gotten my hand in and discovered that the U-75 is quite easy to land softly, mostly due to the very tolerant trailing link main gear. As can be expected, the cushioning of the low wing and a more pronounced ground effect mean you can float a long way if you’re not careful, but it doesn’t take too long to get used to it. Indeed, pilots who flew the U-75 in precision landing competitions told me that it is far easier to place on a specific spot than the 172, and it was always the preferred mount with many podium finishes. Interestingly, despite the high degree of flap, the touchdown attitude is noticeably nose up, far more than on the Skyhawk; however, the slope of the nose does not impair forward visibility at any point. The touchdown speed in our case was around 100 km/h (54 kts), though this can be brought down a bit if a greaser is not your intention.

To step up the fun – and illustrate just how draggy the U-75 can be – for the next approach I was instructed to come in high, fast and close, rolling onto the runway heading just 1,200 meters away at 1,100 ft above ground, doing 150 km/h (81 kts). To reach the threshold, I’d have to fly a virtual glide slope of 16° – 10 more than the steepest ILS recognized by law. Pulling the throttle back to idle, setting the prop full fine and dropping flaps fully to notch 2 (30°), I found myself in a visually disconcerting steep descent at 110 km/h (59 kts) and slowing – eventually even having to add power just to make it to the runway. The maximum rate of descent I remember seeing was on the order of 8 m/s (1,500 fpm) with no forward acceleration.

As an encore, I had planned for the final landing to be a “minimum stopping distance” affair – but the traffic crowding in behind us and the necessity of taxiing a full kilometer to our turn off point meant I had to scrub the idea and get my behind off the runway ASAP. But, since I’m already throwing numbers around, the manual suggests a landing distance over a 50 ft obstacle of around 450 meters, with the run itself just 240 meters.

Post script / conclusion time

While the comparatively short time aloft (and my aforementioned lack of test pilot credentials) prevent me from making any worthwhile objective conclusion, from a purely subjective standpoint I was nevertheless pretty smitten with the U-75 – perhaps most of all because it was nothing like popular lore said it would be. While a pure aerobatic aircraft might have been more exciting (at least during maneuvering), the Utva is definitely not boring or dull; indeed, on fun factor alone it might even top the Super Cub and Citabria (both of which I’d had the privilege to fly). While it is not perfect – and living with its faults day to day would likely start to wear quite thin very soon – its charisma, origins and historical relevance had definitely been worth the trip!*** Simply put, to actually go somewhere, I’d undoubtedly choose the better equipped, more comfortable and far quieter Skyhawk; but to have a bit of good old fashion stick-and-rudder fun without much fuss and effort, it would definitely be U-75 all the way 🙂 .

*** despite their widespread use across the width and breadth of ex-Yugoslavia, airworthy examples are nowadays increasingly difficult to find, with – by my count – less than 10 still operational and in civilian hands. Their somewhat expensive maintenance, pretty specific role and an increasing lack of spares make them a financial handful for smaller flying clubs, while their specific character is unlikely to tempt the wallets of many private pilots and owners. Despite this, the few examples that are flying will likely continue to do so for some time to come, with one – 9A-DIH at Čakovec Airfield (LDVC) in Croatia – soon set to return to flight after nearly a decade on the ground!

DCI back in the hangar, dwarfing pretty much everything in there…

Sources:

  • ab-ix.co.uk – UTVA 75 production list
  • UTVA 75 and Cessna 172N POH and checklists
  • and various human sources and U-75 crews

Rare Aircraft – 2+2: The Four Seat UTVA 75

Posted in Rare Aircraft, Yugoslav And Croatian Aviation HistoryTagged , , , , , , , , , , , , , , , , , , , , 2 Comments

By me
Photos as credited

While the very mention of its name often invokes fond nostalgia and strong apprehension in equal measure, there’s no denying that the pudgy little UTVA 75 remains one of the most famous, significant – and perhaps maligned – aircraft ever produced by the Yugoslav aviation industry. One of a number of piston props conceived, designed and built solely in-country, it had left a lasting mark on the local aeronautical landscape, having over the years seen off generation after generation of young pilots, service in a bewildering number of roles in every nook and cranny of the land – and the occasional appearance in the odd accident column…

But for all its past ubiquity, the type has become somewhat of a rare sight today, with most of the airworthy civilian examples nowadays confined to flying clubs in Serbia, Bosnia and Herzegovina and Macedonia. Outside military dumps, finding one elsewhere requires a bit of luck – so much so that even the locals (many of which had flown them extensively in the 80s and 90s) raise an eyebrow when one happens to rumble by.

So imagine my surprise when – having so far only five examples under my camera’s belt – I became aware of a beautifully curious four-seat example parked just 70 km away at Novo Mesto Airfield (LJNM) in southeastern Slovenia. Having only seen such a “quad” in one 80s photo, I was through the roof even before I found out it was the only such example in existence – a fact that (as if any further persuasion was necessary!) had seen me grab my car keys and set off across the border to see what’s what… 🙂

It may be fully white and featureless – making it particularly unsuitable for photography in direct sunlight – but being the only survivor of its kind had meant that I just had to have a crack at it whatever the conditions…

Wings of the nation

But, before we cover this prime example of Achtung, Skyhawk! material, a bit of history to introduce this compact little type to readers who may have never seen one in the metal 🙂 . Flying for the first time on 19 May 1976, the UTVA 75 – known under the factory designation U-75 – was designed to be a simple, straightforward basic trainer* that could be efficiently used both in civilian and military roles. Even though the Yugoslav aviation industry had always put much stock in this segment, its offering of such aircraft was next to abysmal at the time, with the late 40s Ikarus Aero 2 and mid-50s Aero 3 being the only machines widely available for the role. Despite having given wings to post-WW2 Yugoslavia, they were both very much outdated designs, sporting wood & fabric structures, tandem cockpits, narrow-track tailwheel landing gear, basic instrument fits – and flight characteristics that often did not inspire much confidence in the student.

* interestingly, the project had originally envisaged a whole family of aircraft stemming from one basic design, including a four-cylinder two-seat utility machine dubbed the M-10, and – most interesting for us 🙂 – a six-cylinder touring four-seater called the M-11. Eventually though, financial difficulties (which had also seen the temporary inclusion of Polish aircraft manufacturers in the design between 1973 and 1975) had left the M-10 as the sole survivor, paving the way for its development into the U-75.

Designed around more modern principles, the U-75 had a lot going for it in the trainer role: it was robust, simple, easy to maintain and had just enough power to pull a few basic aerobatic maneuvers – but not enough to allow the student to correct every mistake with liberal application of the throttle. Additionally, it had a side-by-side seat configuration, a large instrument panel suitable for more advanced avionics (including blind-flying gear) – and, most importantly, was built entirely of metal (prolonging its service life in the aerobatic role) and used a wide-track tricycle gear with low pressure tires that made it safe and relaxing to operate even on poor airstrips. Other features had included a tailhook for towing gliders or banners, while the military could be content with a removable pylon under each wing, which could accommodate jettisonable fuel tanks, cargo drop containers (carrying 100 kg (220 lbs) each), light bombs of 50 kg (110 lbs) – and even unguided 12-tube 57 mm rocket packs and twin 7.62 mm machine gun pods.

One of the Croatian AF’s post-1991 examples (now decommissioned) doing what it was designed for during low-level training near Zadar (LDZD). Of interest, the fleet would in the early 2000s be repainted into a mint CroAF scheme and be transferred to a bespoke military register (photo from: www.aeroflight.co.uk).

Designed from Day 1 to meet the requirements of the FAA’s FAR Part 23 regulations concerning UTILITY category aircraft, the U-75 can also boast a +6/-3 load limit – and was found in actual operations to be rather crash-worthy, since its wing and wing box were strengthened to cope with the rigors of “external cargo” 🙂 . Despite hailing from “the East”, under the hood the U-75 sports quite a bit of Western hardware, including a four-cylinder, fuel-injected 180 HP Lycoming IO-360-B1F whirling a Hartzell HC-C2YK-1 BF/F 7666A two-blade constant speed propeller.

With a MTOM of 960 kg, this package is responsible for a maximum level-flight speed of 215 km/h (116 kts), a maximum ceiling of 4,000 m (13,100 ft) and – combined with a wing profile suitable for low speed maneuvering – take-off and landing runs of only 125 m (410 ft) and 100 m (328 ft) respectively. The efficiency of the constant speed prop also means that the U-75 can be relatively frugal in a stable cruise, registering a range of 800 km (432 NM) on 150 liters (40 USG) of internal fuel. When fitted with two 100 liter (26 USG) drop tanks however, the U-75 was supposed to be able to reach an impressive 2,000 km (1,080 NM) – though this was a theoretical calculation only, since the aircraft had never been test flown to this extreme (the tanks themselves were never used in actual training operations).

Equipment-wise, the standard 75 was provided with the usual VFR instrument setup, including everything from the Basic 6 with the addition of an ADF receiver (all of which were powered from a simple and unremarkable 14 V electrical system). The armed versions used by the Air Force would also be provided with a simple optical aiming sight on the left side, while all models could be additionally equipped for night VFR operations. Interestingly, the instruments used were an unusual East-West mix, with the artificial horizon, turn and bank indicator, ADF, manifold pressure/fuel flow gauge and the tachometer all sourced from the US, with the rest of the instrumentation either indigenous or acquired from other European states that had used the metric system.

In service, the U-75 was always much blighted by a popular reputation for violent spinning (sometimes fatally), which bred some distrust in the design. However, while it could indeed be thrown into a serious spin if the pilot was determined enough, most of the type’s spinning accidents were due to it being flown contrary to manufacturer recommendation. Even before it had entered series production in 1978, official flight tests had concluded that the U-75 had no abnormal tendencies to spin if flown by the book – a fact also testified to by numerous operators who had never had any such problems, despite regularly putting their machines through various aerobatic and near-aerobatic routines**.

** one of the main causes of the 75’s willingness to spin if pushed was the location of the (rather heavy) battery. Initially, it was to be located immediately behind the cabin; however, it was calculated that this would shift the CG too far forward, making the aircraft too stable and docile for its intended training role. To combat this issue, the battery was relocated to the extreme of the aircraft – the tail cone – thus moving the CG backwards and making the aircraft less stable and more maneuverable (but still well within accepted limits).

Interestingly, the U-75’s public perception parallels another love-hate civil aircraft, the sporty Mitsubishi MU-2 twin turboprop. From a purely statistical viewpoint one of the unsafest designs around, the MU-2 had gained its unenviable reputation mostly due its users’ inexperience with turboprop hot ships, coupled with poor and insufficient training (especially in the US). Once these issues are surmounted, owners swear on them to no end, with numerous examples having clocked up accident-free flight time that runs well beyond 15,000 hours.

By the time production had ended in 1985, the U-75 had become one of the most produced indigenous Yugoslav designs, with 138 examples made (including the prototypes) – though not coming close to the country’s other notable aviation product, the Soko G-2 Galeb jet trainer, of which 248 were made 🙂 . Being a wee little piston prop had also meant that the U-75 was very usable outside military and training circles, with a good number eventually making it into various civilian flying clubs and to various private owners following Yugoslavia’s collapse. Despite 20 years of attrition still a common sight in Serbia, Bosnia, Macedonia and (very occasionally) Slovenia, the type is – as noted previously – sadly absent from Croatian skies, with the only examples operated after 1991 having flown with the Croatian Air Force. Used initially for limited combat operations during the war, the type would continue to soldier on in the basic training role until 2007, when it was withdrawn and replaced by the Zlin Z-242L…

The only CroAF U-75 to return to civilian life, 9A-DIH - formerly known as 008 - is unfortunately not airworthy... though major steps are being taken in that direction.

The only CroAF U-75 to return to civilian life, 9A-DIH – formerly known as 008 – is unfortunately not airworthy… though major steps are being taken in that direction.

2+2=78

The story of the four-seat U-75 would, however, begin not long after the first of the standard machines had started rolling off the production line. For all the variety produced by the Yugoslav aviation industry, no manufacturer of the time had a modern touring machine on offer, with most of their light aircraft output catering to utility and training needs – leaving various imported Cessnas and Pipers to fill the gap. Having been the newest indigenous design available when the industry had finally turned more of its attention to this segment – not to mention its connection to the stillborn M-11 – the U-75 had seemed to be a good place to start, its basic design offering a low-risk opportunity to quickly (and cheaply) produce a suitable aircraft for the role. From the very outset, the design goal had been to create something of a home-grown PA-28 that could be used both for personal flying and IFR training – as well as potentially exported abroad***.

*** even though the international public’s unfavorable perception of Yugoslavia’s engineering capability (in part well earned) might have put off people from buying its hardware, several of its aircraft were in fact highly regarded in Western aeronautical circles. Most notably, in a USAF fly-off competition in the 80s, the Soko G-4 Super Galeb jet trainer was judged superior in a number of respects to the visually similar BAe Hawk – however, the implications of a major Western power buying military hardware from a Socialist state (never mind its alliance) had sealed the aircraft’s international sales prospects well before it had even been flown.

However, since the whole project had had “cheap and cheerful” as its premise, the changes necessary to turn the standard 75 into a four-seater had to be kept minimal (in part to also reduce disruption on the production line). To this end, the design team had taken the type’s fourth prototype – registered YU-DRJ and sporting serial 53004 – and reconfigured its capacious cargo bay to give a bit more room, slotted in two additional seats – and then fitted a longer, extensively-glazed two-piece canopy to make entry into the back easier.

For visual reference, a bog-standard two-seater… (from Cavok Aviation Photos)

... and then DRJ, post modification. Pretty much the only dead giveaway at a glance is the new canopy (equipped with shades) (author: unknown, photo kindly provided by Mr. Dragan Kolundžić).

… and then DRJ, post modification. Pretty much the only dead giveaway at a glance is the new canopy (equipped with shades) (author: unknown, photo kindly provided by Mr. Dragan Kolundžić).

Dubbed the U-78, the new aircraft had in other respects remained identical to the stock 75**** (retaining even the towing hook under the tail). Even though it had also retained the original’s spartan mil-spec cockpit, production models were envisaged to sport a comprehensive IFR suite, sourced in full from Bendix-King and including the:

  • KI 525A HSI (slaved to a remote gyrocompass and with full ILS capability) + ADI
  • KI 229 RMI
  • KNS 81 RNAV system (a fascinating piece of kit used for early area navigation, covered in more detail here)
  • KN 62A DME
  • KT 79 transponder
  • and the system’s associated navigation and communication radios

**** there were indications in some sources that flush-headed rivets were used in lieu of the dome rivets of the standard model; available photo evidence however shows dome rivets on the fuselage, though it is not possible to discern their type on the wing. Informed opinion from a UTVA engineer is that it is highly unlikely (on a cost/benefit basis alone) that flush rivets were used anywhere on the aircraft.

However, back in the actual world, many of the finer details of both the design and DRJ’s service life remain a mystery; according to people in the know, the production documentation for the U-78 had always been scant at best, and what little was widely known was further lost during Yugoslavia’s violent dissolution in the early 90s. Furthermore, the aircraft had never been formally tested by the Vazduhoplovni opitni centar, or VOC – the state flight test center which was required to sign off each indigenous design – so no accurate or official performance numbers exists. Pretty much not even the people who had worked on the basic U-75 at the time have a complete and definitive picture of its capabilities…

What is known for certain is that DRJ – as the U-78 – had flown for the first time on 23 March 1979. Following standard factory testing, it would be transferred to the VOC at Batajnica Airbase (LYBT) just outside Belgrade, where it would continue to fly informally until 14 August 1981, when it had suffered an unspecified accident and was written off.

The loss of the only prototype – and the continued desire to press ahead with the project – had meant that the UTVA works would eventually need to produce a replacement. Interestingly, this would occur only in 1986, a year after production of the standard 75 had come to an end. This had meant that the new aircraft would not be manufactured outright in the classical sense, but rather assembled from the ground up using replacement parts (manufactured in advance to support the fleet in the future) and DRJ’s vertical stabilizer (which had survived the accident). Given serial 53263 – denoting it as the first of the post-production modifications – this new aircraft would officially be designated the U-75A-41 (though always shortened to just U-75A), and would initially carry the reg YU-XAC. Despite the different name though, XAC would not differ from DRJ (apart from dome rivets definitely being used throughout 🙂 ).

Flying for the first time on 14 May 1986, XAC would also initially pass to the VOC – again informally – before ending up with UTVA’s own flying club (AK UTVA Pančevo) as YU-BRJ. Sadly though, it would be completely destroyed on 24 March 1999 when the factory and its facilities were severely damaged in a NATO air strike.

I’m leaving on a container ship…

Even though XAC would – as proof of the design – go on to fly for a good number of years, forewarning of Yugoslavia’s 1991 implosion had quickly dashed many hopes of continuing development beyond the prototype stage. However, just before the country’s whole aviation industry would grind to a halt, the UTVA works had managed to cobble together one final aircraft, the lucky No. 3 that would lure me to Slovenia 🙂 .

Like XAC, this new machine could only come about in an unusual manner. Despite not having produced any new aircraft since 1985, the factory was still busy repairing, overhauling and scrapping in-service 75s – activities that would continue right up until the start of hostilities. At one point in the very late 80s, the company had come into possession of YU-DJO – a stock 75 manufactured in 1983 with the serial 53230 – which had been written off following an accident. Seeing their last chance at keeping at least something of the four-seater dream alive, the factory had decided to take what remained of the aircraft and rebuild it into an XAC-like model using any available spares and parts of other demobbed 75s.

What happens next, however, requires a short digression. The consensus among online sources and forums dedicated to Yugoslav aviation is that the aircraft had never actually been completed prior to the war, and that only an empty shell had been produced. Much doubt is also cast on the extent to which it would have conformed to the U-78/75A standard, especially since it was a rebuild of an existing 75 (using its basic fuselage), rather than a bespoke four-seat model.

These sources also state that the aircraft had remained at the factory until 2003, when it was sold – along with a regular 75 – to a buyer in the US. However, the buyer was said to have been unable to register the four-seater due to issues with its paperwork, with specific reasons given including missing/discarded documents, the aircraft being a composite of several different serial numbers and “unassigned parts” – as well as available documentation pertaining only to the bits belonging to DJO. Having thus sat around for a while, it was said to have returned to Serbia in 2008, to be restored, re-certified and sold on to a buyer in Slovenia shortly afterwards.

But, having had the great opportunity to personally interview the buyer in question, the story I was made aware of was quite different. It transpires that the aircraft had actually been fully completed and outfitted by spring of 1991 – and that its paperwork was, in fact, clean and in good order. Possibly intended for export right from the outset*****, the machine would soon be dismantled, crated up and – in the company of the aforementioned two-seater – shipped by sea to Mr. John Wallace of Oshkosh, Wisconsin, who had recently become the official distributor for UTVA aircraft in the US.

***** whether this export was just a fluke or planned from day one is not known with certainty. Given the ad-hoc nature of the build – with Yugoslavia already disintegrating – the project documentation was not diligently kept, so even UTVA employees are in the dark on this issue.

53230 nearing completion in early 1991, with a stock two-seater visible behind (author: unknown, photo kindly provided by Mr. Dragan Kolundžić).

Two of Yugoslavia’s best-known people movers, the U-75 (aptly in its four-seat guise) and the Zastava 101 family sedan (author: unknown, photo kindly provided by Mr. Dragan Kolundžić).

Interestingly, Mr. Wallace had specifically requested both versions of the aircraft, since he was interested in marketing both its military and civilian potential (that is, having a single design fulfill the training, light attack and touring roles). However, to be able to actively offer them on the market, Mr. Wallace had first needed to make some changes to comply with FAA regulations, most notably swapping the existing Yugoslav instruments and avionics for a US-spec cockpit suite sporting imperial measurements (in another point of contention, there is some doubt that US instruments had already been fitted in Yugoslavia – though this is believed to be incorrect).

But, by the time the changes had been made and the aircraft were ready for re-assembly, open hostilities in now ex-Yugoslavia had already started, leading to the introduction of a wide-ranging UN embargo against all of its former states. For Mr. Wallace this had meant that he could no longer import any new aircraft from Serbia, making both of his current examples – worthless.

Faced now with a whole new set of financial problems, he had immediately decided to sell the engines of both aircraft in order to try and recoup at least some of the funds invested in setting up the dealership and shipping the machines across the Pond. This had made the already unwanted machines even more useless, with both examples eventually consigned to languish around in Mr. Wallace’s garage, still packed up in their original shipping crates. Having absolutely no use for two engine-less jigsaw puzzles whose market value had been steadily decreasing, he had in 2007 decided to put the aircraft up for sale, going so far as listing them on – eBay 🙂 .

As it is often stated online, “if it looks stupid and it works, it’s not stupid” – which fully applied here, since the aircraft were quickly spotted on that very site by Mr. Leon Pogelšek of Ljubljana, Slovenia. Having recently completed his PPL, he had expressed a desire for his first aircraft to be indigenous, with the four-seater seeming like the perfect ticket for the job. However, since both aircraft were being sold as a single item, there was no other option but to buy the lot and possibly use the two-seater for spares.

With the sale finalized, the aircraft – complete with all papers and US instruments, as provided by Mr. Wallace – were once again loaded up into a container and shipped to Slovenia’s main port in the city of Koper. However, once they had arrived, they would immediately be launched into a world of legal issues, which even today – nine years on – conspire to keep the four-seater grounded. Despite the U-75 having been as common as trees in ex-Yugoslavia, no certified mechanics or service centers had remained in Slovenia by 2007, making the aircraft impossible to assemble and fly within the country’s existing regulatory framework (being a one-of uncertified example didn’t help the four-seater either).

Pretty soon though, a workable solution was found, whereby the assembly and overhaul of the quad would be contracted out to a company based at Lisičji jarak Airfield (LYBJ) in Serbia – and headed by a former UTVA executive and engineer – with the two-seater used as payment for the work done (being a low-timer with prime potential for resale)******.

****** unfortunately, the identity of this aircraft is virtually impossible to determine today, since its documentation had been handed over during overhaul. However, it is known that it was one of reportedly six examples sent to Sudan around 2008/2009, where they had resurfaced under the designation SAFAT 03. Interestingly, that designation had initially been used for an upgraded, Sudan-built version of the U-75, which had failed to gain any meaningful orders and progress beyond the prototype stage…

In the event however, the work would drag on for four years – having even been handed over to a third party at one point – during which only the wings would be attached and a new engine and propeller from another U-75 fitted (both of which with only eight hours on the clock). Dissatisfied with the pace of the work so far, Mr. Pogelšek would in early 2013 ship the aircraft over to an official UTVA service center in Sremska Mitrovica – a road trip of 80 km that had, once again, seen the aircraft disassembled into its original state.

Here, the aircraft would be fully completed, outfitted with the type’s original instrumentation and test flown, making it finally suitable for delivery and operation. Wary of the legal requirements that had prevented it from being assembled in Slovenia, Mr. Pogelšek had originally wanted to register it in Serbia – but was informed by the Slovenian CAA that it was also possible to have it on the Slovenian register. Being a unique, uncertified example, it was initially allocated to the country’s experimental register, becoming S5-MZT the same year (M – experimental/homebuilt). However, it was soon decided that – given its commonality to the stock U-75 – the aircraft could even be added to the standard register (prefixed with D like in all former Yugoslav states), becoming S5-DZT in the process. Under this registration, it would be flown to Slovenia sometime in June 2013 (the exact date eluding Mr. Pogelšek’s recollection), making this the longest time it had been airborne in its entire life – for a grand total of just 7 hours and 13 minutes accumulated by the airframe.

The future is now

Unfortunately, soon after its arrival at Novo Mesto, the Slovenian CAA had withdrawn its approval for registration, effectively grounding the aircraft then and there (the exact reasons for this change of heart appear to fall into a domain I wish to steer clear of 🙂 ). Given that the issue was still not resolved at the time of writing, the aircraft had remained immobile for the next three years, though Mr. Pogelšek has made overtones to eventually register it in Hungary and potentially return it to airworthy state. Being employed in the art world, Mr. Podelšek plans on eventually turning the aircraft into a “mobile canvas” (more precisely, an “aero art” flying installation), and repainting it with stylized images of themes from Yugoslavia’s industry – thus paying homage to both the cultural and technical aspects for former Yugoslavia.

In the mean time, it remains the perfect “poster aircraft” for Achtung, Skyhawk! – and provides an almost unparalleled glimpse into a bit of left-field aeronautical thinking that I hope my readers will enjoy! 🙂

Something’s rotten in the Kingdom of Denmark… and the UTVA factory at Pančevo. A decidedly odd sight for the locals… four people in an UTVA 75…

Unlike similar aircraft, the 75A sports two individual seats in place of a one-piece bench. But, while this may sound like a nice touch, the space and structural constraints in the cabin mean that none of the four seats can recline even one inch.

DZT’s only external difference from both the U-78 and XAC is the shape of the canopy, which has a slanted as opposed to a straight rear edge. The reasons for this change are unknown; however, it is possible that this was a concession to ease of production, since this shape avoided the need to modify the fuselage and rear cabin frame (interestingly, straight-edge version had afforded less visibility to the rear passengers).

Having descended from what was primarily a military trainer, the A is naturally quite airy and full of light, with good view afforded in pretty much every direction except below and aft.

The same logic applies to the cockpit as well, which means that the pilot is spoiled for choice in terms of throttle and prop controls, with one set (the yellow level) on the left sidewall, and one in the traditional place in the throttle quadrant. Combined with an ambidexterous stick, this means the aircraft can be easily flown with both left and right hands, appealing to civilian and military pilots alike. However, like DRJ and XAC, DZT and had retained the basic setup of the standard trainer.

While the instrument panel itself is pretty conventional – reminiscent in layout to a 60s Cessna – the UTVA-75’s traditionally quirky central pedestal gives the cockpit an unusual feel. From top to bottom, the quadrant features the prop control (blue lever) and throttle (leverless… lever), with dual heating/ventilation on each side of the engine controls; the mixture is the first blue-red plunger below the throttle, with the brake block and elevator trimmer below (whose indicator – barely visible – is horizontal as opposed to vertical). To the right is the parking brake plunger and the injector air intake lever, which is a fancy name for an alternate air source. Finally, the small metal lever at the bottom of the pedestal is the fuel selector.

Always a relevant test of any light aircraft: how will I – with my 1.91 m / 6ft 3in frame – fit inside! Sadly though, the crossbeam near my knees (another remnant of an aircraft always designed to have two seats) makes sitting in the back somewhat uncomfortable. Likewise, the rear fuselage being relatively low, closing the canopy and sitting upright was a challenge…

Customarily, I would once again like to extend my sincerest thanks for their time and assistance to:

  • Mr. Leon Pogelšek, the current owner of S5-DZT
  • Messrs Matej Jevšček and Štefan Može of AK Novo Mesto
  • Mr. Mario Hrelja, who was one of the people responsible for DZT’s thorough refit
  • and Mr. Dragan Kolundžić, engineer at UTVA and author of several publications on its aircraft, without whose patience and education on the U-75 this article would not have been nearly as informative!

Sources:

  • Istorija vazduhoplovstva Pančeva: UTVA 75 (The History of Aviation in Pančevo: UTVA 75) by Dragoslav Dimić & Dragan Kolundžić
  • UTVA-75 factory catalogue from the mid-80s
  • Safat Aviation Complex – SAFAT 03 product page
  • My City Military Forum – U-75 discussion (in Serbian)
  • Paluba.info – U-75 discussion (in Serbian)