KZ-II KUPE

In 1935 Viggo Kramme was building his first aeroplane, a Flying Flea, when a passing flying student by the name of Gustav Zeuthen offered to design something better. The single seat KZ-I that resulted was quickly followed by a two-seater, the KZ-II Kupe. Only thirteen were built before the German occupation brought production to a halt. I am being given the chance to sample one of the two airframes that survived, which is now based at the Danmarks Flymuseum at Stauning Airport.

This Danish two-seater is a lovely, graceful aeroplane with obvious Miles and de Havilland influences. It has a wide-track undercarriage, long, tapered wings with built-in slats in the leading edge and a slender in-line engine. The fuselage is made from welded tube with wooded formers and stringers covered with fabric, and the wings from wood, again covered in fabric. This one is finished in silver dope.

To gain entry, climb up the wing walk – there’s one on each wing – slide back the side window, reach in and unhook the catch, then swing up the clamshell door until it sits on the roof. Pause to admire the worn and faded but still beautiful leather upholstery on the seats and then step on them (unavoidable) and down into the cockpit.

The side-by-side seats are slightly reclined, more so in the tail-down parking position and more than usually set back from the instrument panel, which makes for a roomy cockpit. It is perhaps a little narrow at shoulder level, but there’s plenty of headroom and overall the feel is light and airy. The roof has clear panels but is mainly varnished plywood and wood formers... and very pretty it looks, too.

One handle each

The single control column divides into two at the top, giving each occupant a handle to work with. The throttle and mixture levers are on the left wall, and there’s a second throttle lever on the right wall. There are two fuel tanks in the wings, each holding 60 litres. Fuel taps are on the centre console, just in front of the seats.

There’s a sliding window on each side for letting in some breeze in the summer. There is only one set of instruments, on the left, but I can see them easily from the right seat. Two big chrome levers are hard to miss. The top one controls the airbrake, a big flap that drops down under the centre-section. My companion, the museum’s Kupe pilot Bent Pedersen, says, “We don’t use it,” and when I ask why not, he says, “It makes like being on top of a beach ball”. I take this to mean that it makes the aircraft unstable in yaw and pitch. I then realise that Bent means – “We don’t use it today,” because it’s too windy. Bent is a Dane and communication is a little strained. The lower lever doubles as both a handbrake and as an intensifier for the differential brake that comes in at full rudder.

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The tail surfaces are rather small, although the rudder looks adequate. Bent, though warns me that the aircraft is directionally unstable and the rudder must flown at all times. Bent starts the engine by priming it then swinging the propeller. He does this standing behind the prop between it and the wing. He has set the handbrake and can just about reach the throttle on the left wall of the cockpit through the open door if it had been set too far open... but I’m covering the throttle just in case.

The engine, a 75hp Gipsy Minor (the aircraft originally had a 90hp Cirrus) burbles into life and rumbles happily away creating a surprising amount of breeze at around 600rpm. Bent climbs in, locks his door, does up his straps, releases the handbrake and makes a ‘you have control’ gesture. The seats aren’t adjustable and perhaps I should have bought a cushion, because I have to use my toes to get full rudder. This isn’t a problem, though.

The Kupe is easy to taxi. The nose tapers so sharply, having a four-in-line rather than a flat-four engine, that you can see most of where you’re going without S-turning, but I weave from side to side anyway to make extra sure. This earns a quiver of alarm from Bent, who thinks I’ve lost control of the steering, but before he grabs the controls, I’ve turned back on line and he relaxes. He probably finds S-turning unnecessary, being more used to the aircraft (and rather taller than me).

Wallowy ride

Despite having a free-castoring tailwheel, a rather small rudder and a 15kt wind from behind and one side, the Kupe is easy to steer. This is because it has a wide track undercarriage and effective differential brakes. These are cable-and-drum, rather than hydraulic-and-disk. The ride is slightly wallowy on coil springs, but these obviously have some kind of shock absorber built into them, because it’s basically firm. Sitting reclined and some way back from the windscreen gives a slightly lordly feel, and the cockpit’s faded and well-used look adds considerably to the charm.

The cameraplane is ready, so after a quick magneto and slow running check, a slightly nervous, “Are you happy to fly?” from Bent and a nod and full-and-free check from me, he tells the cameraplane to go. Bent has the only headset, so he makes the radio calls. Communication in the cabin is going to be by shouting and hand signals from now on.

I open the throttle and we accelerate, slowly at first, then gathering pace. I’ve got the stick fully forwards, but it takes about four seconds before the tail comes up. The elevator feels a touch on the light side. As we have a side wind I’m careful not to lift off prematurely and I leave the aircraft to gather speed on its main wheels for around 250 metres. It shows no sign of lifting off by itself, but a moderate tug on the stick gets us clear of the runway... and drifting sideways, because I have neglected to apply into-wind aileron, being more focused on the cameraship than being lined up on the runway.

Bent grabs the stick just long enough to bank and yaw us on line, then returns it to me. Even though the Cessna 172 cameraplane isn’t far ahead and is throttled well back, it takes the Kupe a while to catch up. Only when we draw alongside can I throttle back. During this climb and catch up, I find I’m pulling quite hard on the stick, so reach all the way across Bent to the left wall, where there’s a trim lever. Nudging that back unloads the stick and I don’t need to use the lever again for the rest of the flight.

During the formation work with the cameraplane, I get to know the Kupe. It’s less noisy than most aeroplanes, and flying without any ear defenders isn’t a problem. The view out is better than in many later touring aircraft, although there are some significant blind spots in the canopy structure. It’s a very comfortable aircraft, with large, soft seats and loads of room. Elastic pockets are provided for map stowage.

The controls are well-harmonised, with light ailerons and elevator, and a slightly heavier rudder. They are crisp and effective, but the aeroplane is stable in pitch and roll, although you do need to keep your feet on the rudder pedals. The roll-yaw coupling for steering just with feet is adequate, but this isn’t an aircraft prone to dropping a wing if left unattended for a minute or two in still air, so you don’t even need to use your feet.

Opening the throttle brings the Kupe forwards fairly promptly. Retarding the throttle is slower in drawing the aircraft back from the cameraplane – an indication of good streamlining. But when the cameraman indicates (with hand signals) that he wants me to drop down or move in or out, the Kupe is so responsive that I can move it to the required position almost immediately.

Well-mannered

You do need to use rudder in turns, but not as much as in, say a Tiger Moth or Piper Cub, so the Frise ailerons are effective in countering adverse yaw. In short, it’s a well-mannered, wellbehaved little aeroplane that gets a lot of performance from its 75hp. The cruise speed is 90mph, top speed nudging 100mph. When the cameraman requests a breakaway so that he can photograph the Kupe banking away from the camera, the aircraft responds well and I am able to use top rudder to avoid tracking away (thus saving time in regaining formation). The roll rate is just right – brisk, but not twitchy. Bent points at the cockpit placard forbidding banking by more than 60 degrees, just in time to stop me banking a little further.

The cameraplane drops down to land and drop the cameraman on the runway for some circuit photographs. While this is going on I usually climb into the upper air for some stalls. However, Bent is reluctant to let me stall the Kupe properly in case it drops into a spin; I suspect intentional stalls are frowned on, if not actively forbidden in all the museum aircraft.

I set up a cruise climb anyway, intending to get near to the stall and see what I can learn. The Kupe isn’t a great climber, probably managing about 500fpm initial climb rate fully loaded, which we are – they filled it with fuel before the shoot. In a cruise climb we’re making around 300fpm. As we reach 1,500ft, I throttle back and maintain straight and level to assess the level stall. I see Bent reach for the throttle, obviously worried about stopping the prop (no electrical system, remember) and get there just ahead of him, adding a couple of hundred rpm.

I get something like a stall, and manage to hold back stick long enough to see that the nose drops and the aircraft mushes, but it doesn’t drop a wing. Bent seems reassured by this gentle approach to stalling, so I try a turning stall, but with a mere 40-degree bank and one-third throttle. Again I manage a stall that is understated, and with the stick all the way back, the Kupe rolls level without doing anything dramatic. Impressively docile.

My respect for this aeroplane just grows and grows. Amazing to think it entered production as early as 1937. So far, it seems to have all the virtues and none of the vices. It even has wings that fold back from the centre section – the intention back in the thirties was for pilots to be able to tow their Kupe home and store it in the family garage. Few did then and few do with today’s folding wing designs, but designers go on building them.

The Kupe has handling and performance that isn’t far behind today’s Rotax-powered LSAs and microlights made from carbon fibre (although it is a little on the slow side as a cruiser). Of course, there is a downside, which is how long it must have taken to build the aircraft. The tapered wing with built-in slots, all the many carefully-made fairings (especially those on the undercarriage) and that lovingly sculpted round wooden fuselage must have taken a lot of skill as well as time to produce. Such an aircraft manufactured today would price itself out of the market.

Landings

We’ve worked our way back at the airfield and I’m about to find out how the Kupe behaves when it comes to landings. Conditions are far from ideal – there’s a 20kt wind offset from the left, giving us at least a 10kt crosswind component, and that’s coming at us from a line of fir trees, which is likely to produce turbulence.

Bent recommends an approach speed of 75mph, although in calm conditions, with one on board and low fuel it is possible to approach at 50mph, 10mph above stall (40mph). With the airbrake extended this can produce a very short landing – Bent estimates 150 metres. However, even in calm conditions the aircraft with full fuel and two on board normally lands in double that distance.

The indicated speed I’m looking for during the approach is 120kph, and this isn’t especially difficult to hold. Nor is it especially hard to remain lined up, although I am crabbing by a large angle to stay tracking down the runway. Bent is sitting next to me with folded arms – great for my confidence, but I suggest he puts a hand on the stick and follows through.

Actually he does rather more than follow through and the first attempt is as much under his direction as mine. Unfortunately our having to shout to communicate and my difficulty in grasping Bent’s English means the usual calm voice directing the landing from the left seat isn’t available. I’m going to have to learn to land the Kupe by demonstration.

I round out a little late, judging by Bent’s direction, and then try to touch down too early. Bent clearly wants to make this a three-point landing and keep flying to the last moment. Whether it’s the turbulence, having two hands on the stick or something about the Kupe’s reaction to crosswinds and turbulence, we have a bit of a battle and make a rather untidy arrival in a squeal of tortured rubber.

We do touch down more or less on three points and there’s no doubt about our ability to keep lined up with rudder. As planned, we make this first landing a touch and go. With a somewhat untidy arrival, we don’t do much more than touch the wheels before I open the throttle. As usual in these situations, power straightens everything out and we make a clean lift off in air that seems to have become smooth again. This time I bank and yaw to stay lined up. During the tight, low circuit that follows (again by pre-arrangement) Bent taps the ASI a couple of times. The aircraft feels OK to me, but he clearly doesn’t like me banking more than thirty degrees unless we’re over 100kph indicated (about 60mph). He’s also hot on my having the slip ball exactly centred.

My second attempt goes rather better and this time I allow the wheels to run much further down the runway – almost to a full stop – before opening up to go around. We have a good 400 metres in front of us and we use most of it before I sense that we’ve really and truly reached flying speed and lift off. There isn’t a lot of excess power in this aircraft with two on board. It’s only on my third and final attempt that Bent really leaves the landing to me.

The penny’s dropped by now and I realise that the three-point attitude is actually quite nose high. We float a long way, but now that I’m getting used to the handling, quite a lot of the crosswind and nearly all the turbulence seems to have vanished. I succeed, finally, unaided, in holding the aeroplane off to the right degree and we touch down (still with a squeal of tyres) more or less on three points.

At this point I’m a little slow to realise that I still have some throttle, closing it just ahead of Bent, whom I can sense reaching for the throttle lever on his side. With the throttle closed, the Kupe slows down fairly rapidly, meanwhile needing more than a little footwork from me to stay lined up. Several times I go to full rudder and feel the resistance of differential brake.

At last we slow down to walking speed and everything gets much calmer. Bent leaves me in charge to taxi through the gate at the airfield boundary and up to the hangars. I reach the appointed spot on the grass, Bent reaches to turn off the mag switches and the engine runs down. When one thinks of what contemporary two seaters were like, the Kupe must have seemed remarkably modern in 1937. It was quite an achievement for the two Danes who had just one design behind them.