Introduction

The Sluka is a fixed wing single-seat microlight manufactured by the Czech company Letov, an old established firm better known for producing larger aircraft and which among other things is currently engaged in making parts for the Airbus. It is a sign of the increasing acceptability of microlight aviation in general that such a firm has the confidence to produce a microlight aircraft.

The Sluka is imported into the UK by PFA stalwart and Popular Flying magazine editor Roger Jones, through his company Letov Air UK. The Sluka was quickly certified by the PFA - due no doubt to the Czech company's impeccable credentials - and is currently offered as a kit. Plans are afoot for a full Section S certification in the near future to enable the Sluka to be sold ready to fly. (Since this article was written, Roger has put the type-approval version on hold to free up more time for work on the forthcoming two-seater - Ed).

Construction

The Sluka bears more than a passing resemblance to an old American design, the Phantom. This is no bad thing because the Phantom, produced initially in the early '80s, was a classic of its type, well liked for its super-stable performance in turbulence, good handling and powerful controls. There are a dozen or so Phantoms still flying in the UK and any example in good condition is soon snapped up on the second hand market.

Like the Phantom, the Sluka is a high-wing design with a boom-type fuselage carrying the engine up in front of the wing with the pilot sitting directly under the centre of gravity. The undercarriage is of tricycle layout and the wings are braced with two lift struts per side. The ailerons are full span and the rudder and elevator are of generous proportions, promising good control.

Construction is all aluminium tube with the wings covered with removable dacron skins and using tabular batten inserts to provide the airfoil shape. This method of construction is nice and simple and very easy to repair should the worst happen.

One novel feature is a glass fibre moulding in the leading edge of the wing skin which runs full length to give a good entry shape to the airfoil. Indeed the whole wing skin sets very cleanly with no wrinkles and gives a very solid appearance. Tail surfaces use welded steel frames, similarly covered with presewn dacron skins. The cockpit area is enclosed with a well finished glassfibre pod, and lexan canopy and doors. Main undercarriage has composite legs which flex for suspension, and drum brakes are fitted to both main wheels. The nosewheel is connected to the rudder pedals for ground steering. Fuel capacity is a generous 45 litres and the tank is situated behind the pilot on the outside of the cockpit enclosure.

Power comes from a Rotax 447 turning a wooden two-bladed prop through a 2.58:1 B type gearbox. Most aircraft of this layout use fee-air cooling and dispense with the standard fan and ducting to save weight. The Sluka, however, keeps the fan, which should ensure more even and reliable cooling. Over all the standard of engineering is high and the aircraft appears well thought out without being needlessly complicated and hence expensive.

Rigging and de rigging is simple but relatively time consuming and definitely requires two persons. The wings remove by undoing the lift-strut ends and pulling out two securing pins on the leading and trailing edges at the root. The tailplane halves are hinged upwards after removing their lower bracing wires. Work is progressing on a design of trailer that supports the wings, so that one person can handle rigging and de rigging.

Taxying

Entry to the cockpit is via a door on the starboard side which hinges upwards and forwards. Best method of entry seems to be to reverse in and sit down on the seat first, then swing the legs in afterwards. Being 6'4" this was a little awkward for me, but then so are most aircraft - you should see me getting into the back seat of a Shadow!

Once inside the cockpit the initial impression is one of comfort. The seat is very well padded and seems to be a supportive shape which should make long cross country flights less of a chore. The control stick is situated centrally between the pilot's legs; this is normal for conventional aircraft but less usual for microlights, most of which are side stick. Each layout has its fans but personally I rather like the side stick arrangements as it leaves the lap clear to lay charts etc.

The throttle falls easily to hand and has a large adjustable friction nut. Fuel supply is gauged by a sight tube that runs down the edge of the seat. Due to the deep design of the tank this works well, providing a large clear easy to read scale.

The instrument panel is positioned fairly high up, giving plenty of knee room for vertically unchallenged people like me, and contains the standard Sluka package of: ASI; Alti; VSI; Compass; Tacho; CHT and hours meter. The instrument panel is also rubber mounted to help reduce vibration damage.

Starting is achieved via an in-cockpit recoil start cord, which is pulled up from the front of the cockpit as on many trikes. This is a little awkward; the harness has to be undone to reach forwards, and then once the engine has started and is warming up you have to slip back into the harness while all the time holding the stick-mounted brake lever to stop the Sluka running forwards. An electric start would be nice, but having said that the recoil start does have the advantage of low cost and weight, and of course simplicity.

Taxying is very straightforward. The steering is very easy as the rudder pedals are connected to the nosewheel and speed is controlled with the throttle. The brakes on the test example where not particularly effective, but adequate as long as stopping is accompanied by some anticipation. Visibility when taxying is good, with only small blindspots caused by the high wings.

Flying

Once all the normal pre take-off checks were completed I lined up on the runway at Halton ready for the off. Acceleration is very rapid and we were quickly airborne. The wind was a healthy 15kt on the nose for the takeoff, so the distance was going to be short - but this was very very short, something like 20m.

Beforehand I was a little sceptical of the published takeoff distance of 30m in still air (100m to clear a 15m obstacle) and I still think it may be a trifle optimistic - but not by much. Control throughout the takeoff run is easy with no tendency to swing and only a little back pressure required to unstick.

Climbout is brisk with the Sluka ascending at quite a steep angle. While leaving the circuit at Halton to find a quiet bit of sky in which to play, I took the opportunity to stopwatch the climb. With an airspeed of 50mph, which feels comfortable for an everyday climbout, I measured a healthy 900ft/min. Initial impressions of the controls were of crisp good manners.

Noise level in cockpit at full power is pleasantly low, but for long periods you would still be better off with a headset or earplugs.

Once leveled off at 2000ft it was time to start exploring the handling and performance in detail. Pitch control has a stable feel about it with control pressures building up positively, but not excessively, either side of the trimmed speed. Trimming itself is via a length of bungee cord with knots in it, pulled through a keyhole shaped slot on the side of the stick. Pulling more knots through the slot pulls the stick forwards resulting in - yes you've guessed it - more knots! This may sound rather primitive, but in practice it works well.

A good test for pitch stability is to increase the airspeed by 5-10mph and then release the stick. A well behaved aeroplane should then return to the original trim speed and attitude after going through a minimum number of porpoise like search cycles called Phugoid oscillations.

The Sluka demonstrated textbook pitch stability - after the stick was released the nose rose, the airspeed then fell to slightly lower than trim speed and the Sluka then lowered her nose in response to this and the airspeed then settled back to trim speed and stayed there.

An aeroplane with reduced pitch stability may require several cycles to regain steady flight at trim, and an aeroplane with little or no pitch stability may either enter an ever steepening dive or climb, or may perform phugoid oscillations which start as gentle porpoises and grow to ever larger big-dipper proportions.

Performance-wise the Sluka needed 4500rpm for 50mph, while 5000rpm gave 60mph and full power resulted in it being possible to get to Vne (83mph), and possibly above, in level flight. This is excellent performance and should result in good range to boot.

However, it is not a good thing to be able to exceed Vne so easily, indeed the Section S airworthiness requirements specifically forbid it and require Vne to be nearly 20% higher than the maximum straight and level speed (Vc) I can only assume that production versions will have a higher Vne figure, a point that Roger was unable to clarify at the time. The Sluka certainly looks sturdy enough and the present Vne does feel very conservative.

Aileron response is excellent - I timed 3s from 45 degree bank one way to 45 degrees the other. The aileron forces are a little higher than I would have liked, but at t least this gives a pleasant feeling of solid stability when in the cruise. The aileron movement has a large amount of differential to try to counteract adverse yaw.

The latter is still present though: with a full deflection of aileron abruptly applied from straight flight, I measured a temporary yaw angle against the roll of 20 degrees. This is not too bad because although rudder is required to maintain balanced flight when rolling, the rudder itself is very powerful and only a moderate deflection is required to co-ordinate. This also encourages the pilot not to slip into the bad habit of not using his feet and thus helps coordination when it is needed for crosswind landings etc.

The rudder control itself is powerful and had a nice solid neutral position. Just a little left pedal pressure is required to counteract engine slipstream effect.

Steep turns are fun and presented no problems. The earth could be made to spin round very satisfactorily in a 60 degree bank and I amused myself in this way for a little while.

After looking at the control response I went onto try the stall. To slow down requires positive rearwards pressure on the stick and this, coupled with all the normal slow speed symptoms, means that there is plenty of warning of the approaching stall. The stall from engine idle is very docile: the Sluka enters mild pre stall buffet about 38mph and then refuses to go any slower than 35 mph. She just sits there in gentle buffet, fully controllable, refusing to stall proper even with full up elevator. Power on, the stall is more pronounced, again preceded by mild buffet with the nose finally dropping into a gentle stall at 31mph indicated. There was no tendency to drop a wing during the stall, and even when abused with large amounts of rudder she resisted any attempt to spin. All in all, very safe low speed manners.

Now it was time to try a few landings. I joined circuit for a small grass strip at Merrymead Farm a few miles north of Halton, where I would not be interrupted by other circuit traffic.

The wind by now had increased a little and was gusting close to 20kt, and because it was my first landing in the Sluka I chose a powered approach so I could react to any sudden loss of speed through the now considerable wind gradient. I opted for a 60mph approach speed, but this proved very conservative as the Sluka was easily controllable without undue effort and cut through the turbulence well.

The hold off is easily judged and a surprisingly feather light touchdown was achieved. Inspired by this success I then flew another circuit. Climbout was once again very rapid and we were almost instantly leveled off at 500ft on downwind, nice and tight for a short circuit. This time I tried a glide approach and also brought the approach speed down to 50mph. Again no problems were found, despite the blustery wind, and an accurate touchdown was easy.

After another couple of circuits I found that I could fly quite happily within an imaginary runway only 30m long, ending just in from the approach threshold. With the strong wind and good control of the Sluka, I could touch down within 5m of the threshold fully held off at a groundspeed of no more than 10-15mph. Applying full power then resulted in an almost immediate takeoff within the confines of my imaginary runway.

Now that's what I call STOL performance!

Boy this was fun! But, time was pressing and I had to get back to Halton. The wind was about 45 degrees off the runway heading so it provided a good opportunity to test crosswind landing capability. I set up the approach with the forward slip method - into wind wing low and opposite rudder to maintain the runway centre line. The Sluka was once again easily controllable all the way down to another flattering touch down.

Summary

The biggest thing hampering the Sluka's market potential is of course the single seat. But that brings several advantages too. First is of course the attractive price - well below that of the lowliest new two-seat. It also gives a performance advantage: the Sluka has an excellent turn of speed, is very economical and, unhampered by weight considerations, has a generous fuel capacity giving 3.5h and 200+ miles range. The STOL performance is well ahead of any comparable two seat and the handling is excellent.

Above all the Sluka is wonderful fun to fly with a nice blend of punchy climb, good solid stability and superb nimble manoeuvrability. If carrying passengers does not unduly turn you on, then single seat is definitely the way to go.

The kit appears to be very complete and well thought out and should be very straightforward and quick to build. With such a simple structure any repairs should be cheap and quick.

It is a shame that nearly all the new kit aircraft coming on the market these days appear to be imports. I am sure that we could be making such machines ourselves and I would much prefer to buy British and fly the flag so to speak. However, the Sluka comes from a relatively poor, former Eastern Bloc country struggling to develop trade. So with this in mind and the quality of the product, I wish them well - they deserve it.