The best of both worlds: neatly designed, and constructed using a blend of traditional and modern techniques, Spacek’s top performing two-seater is most definitely not ‘just another’ Rotax-powered European ultralight | Words and photos: Marino Boric
Czech designer Igor Spacek has been active in the European ultralight field with his Spacek/SD Planes aircraft since launching the SD-1 Minisport in 2007. A decade later comes the SD-2 Sport Master, the numeric part of the designation standing for the number of seats.
While we have flight-tested the SD-1 (Pilot, December 2017) the two-seater is something of an unknown quantity, not yet available in the UK and rarely seen at airfields even on the Continent. For this reason we went to the German importer, Uwe Post in Hamm to see and fly the SD-2. This visit presented some real surprises.
If you had strolled through the exhibition halls at AERO in Friedrichshafen, you would have seen hundreds of similar ultralight two-seaters. Among this mass, Igor Spacek’s low wing SD-2 could easy be overlooked. Indeed, Uwe Post and SD Planes stood out primarily because of the sleek and distinctive single-seat SD-1.
When I visited Uwe at Lippewiesen airfield (EDLH), Hamm in north-west Germany, he wheeled out from the hangar first Spacek’s original creation, the SD-1, and then the new SD-2. From a distance, the two aeroplanes look very different.
To my eye, the single-seater has some similarities with Reno racers, with those sexy bumps on the cowling, while the SD-2 looks more like a down-to-earth UL two-seater. The two aircraft appear fundamentally different, but as you look closer you discover many similarities.
For example, both aeroplanes have almost identical tail units and flying surfaces. When I asked about this, Uwe smiled and said “actually, the wings are the same? they’ve just been extended for the SD-2”.
Post is known to many in Germany as the former Flight Design dealer. He started his relationship with Igor Spacek in 2011 with the SD-1, which received German certification in the 120kg class in 2013 (in the UK it is an SSDR?a single-seat deregulated microlight?Ed).
The single-seat SD-1 proved to be a fortunate choice for Uwe, as it almost immediately became a best-seller, as revealed by his demonstrator’s serial number, 194. SD-1 production has now topped 210, sold in kit form or as ready-to-fly (RTF) aircraft.
First conceived as a personal homebuild project, the SD-1 drew so much attention it was quickly put into production as a kit of parts. Only later, when it was certified under German LTF-UL regulation could it be manufactured in RTF form as well. Initially the aircraft was available with a taildragger undercarriage but the tricycle-gear version soon followed.
While a Hirth two-stroke unit could?and has?been used, the lack of reliable and affordable small four-stroke engines on the market led SD Planes to develop its own engine, based on the proven Briggs & Stratton V-twin industrial engine (power output 24-33hp).
In large part the success of the SD-1 was probably due to the low cost of the remarkably complete fast-build kit, which comes in at €12,000 before tax, the engine being included in the price!
This success encouraged Spacek to design the two-seater version, which made its maiden flight in 2016. The two aircraft share many parts. For the SD-2, Spacek took the SD-1 wing (Riblett GA 37U-A315 profile), extended the span from 5.98 to 8.60m and exchanged flaperons for classic ailerons and Fowler flaps.
The tail unit remained almost identical: T-shaped, with an all-moving horizontal surface that has an electrically-actuated anti-servo/trim tab and is statically balanced. The tail is of similar construction to the wings: expanded polystyrene ribs attached to a composite spar and covered by a plywood skin.
The fuselage was widened to give a 1.17m cabin width, so that two people can sit side-by-side, and the small ‘racer’ canopy from the SD-1 gave way to a huge perspex dome, which gives the SD-2 a very different look.
I can’t believe it’s not composite
From a distance, the SDs look like typical plastic aircraft. Their high-gloss finish was shining in the autumn sun during my visit, and my first thought was that these had to be all-composite aircraft.
In reality, the structure of Spacek’s creations is a mixture of tradition and modernity, which becomes apparent only when you get closer and look in the cabin. The whole fuselage is actually a wood truss structure, predominantly in 15×15mm section spruce, covered with plywood in different thicknesses and then coated with an outer surface of GRP (glass-reinforced polyester).
Only minor parts such as the wingtips (made of GRP with a foam core) the engine cowling, and the upper side of the fuselage are all-composite. The plywood on the hull has a thickness of 1.5-3mm, while the wings and tail are covered with 1.5mm and 0.8mm plywood respectively.
The wings are detachable, their spars comprising full carbon composite main booms with end caps made from extruded sections. The two integral fuel tanks (each containing fifty litres) are made of composite sandwich, and are bonded to the main spar along with the expanded polystyrene foam ribs.
The slotted flaps are made of carbon/PVC foam sandwich and the statically balanced ailerons are of plywood/polystyrene foam construction. Connection of wings to fuselage is performed by two main and two auxiliary pins. Removal/fitting of wings (fuel tanks must be emptied) takes some twenty to thirty minutes.
Currently the SD-2 serial number six is being delivered. Until now all SD-2s have come factory-built, but Spacek lists several different kits on his website. The published completion time for the ‘Advanced’ kit is 300-600 hours.
The combination of old and modern construction has tangible advantages. The structure all had to be very light because the SD-2 was originally designed for 472.5kg MTOM (maximum take-off mass).
According to SD Planes, the SD-2 in a basic form, equipped with an 80hp Rotax 912 with a fixed pitch propeller and Galaxy parachute recovery system, weighs a mere 275 kilos. With a 100hp Rotax under the cowling and a variable pitch prop, the weight rises to around 300kg.
Installing glass screen instruments, leather upholstery and glider tow hook adds another twenty to thirty kilos. These are, however still very low numbers?and would be respectable even for an all-composite aircraft.
The SD-2’s structure is very strong but also easy to repair. Work is in progress and the aircraft will soon be certified in Germany to 600kg MTOM, which will allow a huge payload of over 300kg. The SD-2 will be able to lift its own weight?although not, of course, in countries where the MTOM limit is lower.
The tricycle undercarriage has a steerable nosewheel 30cm in diameter, while the mainwheels have a diameter of 35cm. The undercarriage legs are made from composite and the hydraulic brakes are operated by a hand lever mounted on the centre console.
The seats, side panels and the luggage compartment are trimmed in deluxe white leather and, while this model is called ‘SportMaster’, the first impression is that it is no more sporty than the typical ultralight, even if it is very well built.
As much as anything, this is because the fuselage profile looks so traditional?especially the underside, with its ninety-degree angles. (Only later I would understand how wrong first impressions can be!)
Plenty of performance…
Under the hood of the test aircraft is the classic 100hp Rotax 912 ULS, driving a three-blade Neuform propeller with Flybox electrically-adjustable pitch control. Spacek has designed the aeroplane to take engines with power output between 65 and 120hp, and up to 110kg in weight.
The SD-2 can also be delivered with an 80hp Rotax 912, and soon with the turbocharged Rotax 914. The 912iS will come a bit later, but Uwe reckons that, in terms of performance, the 100hp 912 ULS offers the best value for money.
Boarding the aircraft requires a certain flexibility but is relatively easy even without a step, since the wing is relatively low. Once I’m up on it, I lean on the upper edge of the fuselage, place my foot in front of the seat and slide into it. It would be easier to step onto the seat, but given the beautiful white leather I refrain.
The cabin is flooded with light, thanks not only to the huge canopy but two additional windows behind the seats, over the luggage compartment. The seats are fixed, but the rudder pedals are easily (and quickly) adjustable.
This cabin is something special, there is striking contrast between the wood structure visible in the footwells, those white leather seats and side panelling, and the black instrument panel made of carbon fibre.
Today glass screens have become standard in the ultralight world. In this case, Uwe has fitted Dynon products?as you might only expect, as he is also a Dynon dealer. Other agents install Garmin and Trig avionics but here we have two huge Dynon SkyView HDX screens, and between them are the radio, transponder and autopilot controls and?mounted slightly lower down?the Flybox propeller and flap control units, plus the ignition key.
The centre console carries the choke, heater and throttle T levers, rotary fuel selector, canopy release and hand-operated brake lever.
Taxying is intuitive and precise thanks to the steerable nosewheel. The suspension dampens out bumps in the uneven grass fairly well and we soon at arrive at the runway.
One last engine check and we are ready for the off. The outside air temperature is 12°C, air pressure is 1028hPa and the SD-2 is close to the 600kg MTOM.
Uwe sets the control of the variable pitch propeller to fine, allowing 5,700rpm, and pushes the throttle fully forward. What follows is not the typical everyday ultralight experience. The SD-2 accelerates as if shot from a catapult and hits fifty mph in five seconds.
It’s doing nearly seventy three seconds later, and is airborne and climbing well before we are halfway along the 900m runway What comes next surprises me even more, because at an indicated air speed of 125kph (68kt – the instruments are metric) the aircraft is storming into the sky at around 1,600 feet per minute.
The nose is approximately 45 degrees above the horizon, but the visibility to the side and over the wings is very good. In the stabilised climb with 28.7in manifold air pressure (MAP) and engine speed reduced to the maximum continuous 4,700rpm, I note 1,500 feet per minute.
With these climb rates you can get away fast when you want to, but you do have to take care to reduce the power in time not to bust circuit height.
More numbers to conjure with: in level flight with 23.4in MAP/4,780rpm, I calculate the true air speed (TAS) to be 127 knots at around seventeen lit/hr fuel consumption. Coming back to 25.9in/4,500rpm in the relatively cold prevailing conditions (OAT 6°C) delivers 108kt TAS and fuel consumption drops to twelve litres per hour.
This consumption can be further reduced to just eight lph by throttling back to 14.1in/4,400rpm/78kt TAS, trading speed for low fuel burn.
We then open up the throttle and the aeroplane willingly picks up speed. At 4,400 feet the outside temperature has dropped to 1°C, and the SD-2 settles at 25.9in MAP/4,530rpm/136kt TAS for a consumption of around sixteen to seventeen litres per hour. Experimenting a bit with different pitch/power settings, chasing Vmax, the top level speed I record is 141kt TAS at 25.7in/4,570rpm, still at 17 lph. Exactly the same speed was reached with 25.6in/5,020rpm but with a higher consumption of 19 lph.
The notable thing throughout these speed trials is the way the aircraft’s wooden fuselage structure effectively dampens the engine noise and vibration, making the SD-2 quieter than many carbon-fibre composite ultralights – you really could fly it without a headset.
The aircraft sits well in the hand and willingly follows pilot input. If you trim it properly and leave it to fly hands-off, the well-behaved SD-2 flies straight ahead. This machine is stable, but it still needs to be flown: you have to keep the ball centred to avoid slipping inadvertently.
It can be controlled with only the tips of two fingers?the applied forces on the stick are low and the SD-2 is more sensitive in pitch than in roll (which, it must be said, is not generally regarded as ideal – Ed) a characteristic that is probably attributable to the all-moving tailplane. The aircraft is quite manoeuvrable, rolling from 45° of bank one way to 45° the other way in around 2.5 to 3.0 seconds.
In slow flight its behavior is, as far as I can tell, benign. As the final 600kg MTOM certification is still pending (the SD-2 is currently operating on a Permit to Fly) we do not attempt to stall the aeroplane. Uwe assures me that hitting the legally required Vmin is a no-brainer, and that the aircraft just pitches down on stalling and does not drop a wing. However, as I say, I was not able to verify this.
Returning to the airport, we have to reduce speed to fit in with circuit traffic. This aeroplane zips along happily at over 230kph and we need to decelerate to 180. The Flybox electric flap controller has four positions: 0°, 15°, 30° and 40°. The first notch of the flap is set at 120kph.
With the second notch set (30°), we fly at 100kph and turn on to final. Full flap is, according to Uwe, rarely required and used only if you need to make a very steep approach. We flare briefly and the wheels touch the runway at about 75-78kph (40-42kt).
A surprising aircraft
In conclusion, I must say the SD-2 really surprised me. Before I flew it, I thought it would be just an ‘honest’, medium-performance aeroplane with a 75% cruise speed of somewhere around 110kt. I was so wrong! The SD-2 truly belongs in the ultralight major league and matches the maker’s claimed 230kph (124kt) at 65% power.
The combination of new and traditional construction techniques allows the sleek SD-2 to achieve surprisingly high cruising speeds at moderate fuel consumption, even when powered by a carburettor engine.
Its mixture of performance and fuel economy makes the aircraft cost efficient, and it comes at a relatively low entry price, allowing it to excel in what is a highly competitive market.
This is true especially if the aircraft is kept close to standard specification: the ready to fly 80hp basic model costs €115,000 including tax in Germany; the fully specified 100hp version as tested is priced at €150,000 inc. tax (UL-GmbH Uwe Post, www.sdplanes.de).
UK SD Planes agent JK Aviation gives details of the SD-2 on its website but notes that the two-seater is ‘currently not available in the UK’ ?Ed.
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