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  • FLIGHT TEST FLY OFF: Evektor SportStar, Flight Design CT, Tecnam Sierra - Sporting heroes

FLIGHT TEST FLY OFF: Evektor SportStar, Flight Design CT, Tecnam Sierra - Sporting heroes

A new generation of light aircraft promises to bring affordable recreational flying to the masses. We flew three designs to see how good they really are

From humble beginnings as powered hang gliders, ultralight-microlight (UL-ML) aircraft have grown into capable aeroplanes. Advances in design, materials such as carbonfibre and modern engines have produced a class of aircraft with good performance at a price that eclipses old two-seater types like the Cessna 150.

Europe has led development of modern UL-ML aircraft, and with the approval in April of the US Federal Aviation Administration’s new light-sports aircraft (LSA) category, European manufacturers are among the first to enter the market.

The LSA classification is set to better define what modern UL-ML aircraft have become, but it also recognises their “fun and recreational” potential and does not subject them to the same level of regulation as heavier aircraft unless they are to be used commercially – for flight training, for example.

The LSA category sets a maximum all-up weight, including crew, baggage and fuel, of 600kg (1,320lb) in the USA. In Australia and Canada, where there are similar rules, the limit is 550kg. Europe’s Very Light Aircraft (VLA) rule sets a maximum weight of 750kg and different regulations for use. European definitions of a UL-ML vary, with the UK setting a weight limit of 450kg, while Germany allows 472.5kg, but insists the aircraft be fitted with a ballistic recovery parachute.

Typically, the modern UL-ML aircraft weighs between 250kg and 300kg empty. Add two crew, 130 litres (34USgal) of fuel and land-away baggage and you have an all-up weight of up to 580kg and an aircraft firmly in the LSA/ VLA category. But with just one pilot, 50 litres of fuel and no baggage the weight is only 420kg and the aircraft becomes a UL-ML again. This is a difficult area to regulate and makes the US decision to create the LSA classification look sensible, practical and timely.

Flight International decided to evaluate three modern European UL-ML designs that are among the first aircraft to receive US LSA approval. These are not toys – they are to some extent aerobatic, spinnable, capable of speeds up to 160kt (300km/h), with still-air ranges up to 1,750km (950nm). They are easy to fly, hangar and maintain and could be made instrument-flight-rules capable. They have the potential to revolutionise this aerospace sector in both performance and price.

The challenge was to test fly three competing LSAs over four days in early July, in three different European countries. The aircraft were the Czech Republic’s Evektor SportStar, Germany’s Flight Design CT-SW and Italy’s Tecnam Sierra.

As these are aircraft intended for recreational flying, the idea was to take a quick look at the competing designs to establish the subjective “pilot enjoyment factor” offered by each. This “enjoyment factor” is the driving force behind the LSA category – but all three designs also have strong commercial potential for such roles as training, towing or surveillance.

A points system was devised to assess the three designs in four different categories that make up the overall “pilot enjoyment factor”. These are:

  •  flyability – how well does it handle in the air, on ground and in its intended roles?
  •  usability – how practical is it, how comfortable and how well does it perform?
  •  affordability – how much does it cost to buy, run, service and maintain?
  •  survivability – how good are its passive and active safety features?

Factors such as company sales and technical support, additional options or planned upgrades are outside the remit of this report. The aim simply is to provide the reader and prospective buyer a good overall feel for the three competing aircraft in a comparative format.

Although the three aircraft were flown over a four-day period in three European countries – the Czech Republic, Germany and the UK (where Tecnam has a dealership), test conditions were similar – with temperatures of around 20-25°C (68-77°F), light winds of around 10kt, field elevations less than 1,000ft (300m), QNH altimeter settings of around 1015mb and light turbulence in the local test areas.

Evektor SportStar

Evektor is headquartered in Kunovice, in the eastern part of the Czech Republic. The company was established in the 1970s and in addition to manufacturing its own aircraft makes parts for larger aerospace companies and provides design capabilities to car manufacturers.

SportStar

The company produces the SportStar (maximum weight 550kg) for the LSA market and the EuroStar (maximum weight 450kg) for the European UL-ML market. Although they look alike, the SportStar is slightly wider, has a greater wingspan and an empty weight of 303kg versus 264kg for the EuroStar.

Even though the US limit is 600kg, Evektor has set the SportStar’s weight at 550kg to comply with the more stringent LSA limits in Australia and Canada. Given two normal adults and full internal fuel (120 litres), this 550kg limit can realistically be achieved. Maximum load-factor limits are +4/-2g.

Roles intended for the SportStar are recreational flying, touring, towing and basic flight training, where its low wing and “bubble” canopy make it an ideal candidate. The aircraft can also be fitted with basic or amphibian floats. To date more than 500 EuroStar/SportStars have been sold, with production running at around 100 a year and a delivery time of eight to 12 weeks. Evektor sees a potential LSA market for over 900 aircraft a year for the next 10-11 years.

The SportStar is principally of all-aluminium construction, although composites are used for some panels. The wing design is Evektor’s own. The 100hp (75kW) Rotax 912S engine, which powers all three of the aircraft evaluated, uses automotive premium unleaded petrol. The 912S can also run on avgas or mogas for limited periods if commercial lead-free petrol is not available. On the aircraft assessed, the engine drove a three-blade variable-pitch propeller, but other fixed/variable-pitch, two/three-blade options are available.

Engine control is via a push/pull throttle lever centrally mounted at the base of the instrument panel, with no mixture control. The throttle has a novel “twist function” to allow for finer rpm control without moving the lever. A propeller control lever is centrally located on the cockpit floor and operates around a “gated” quadrant with fully forward (lever vertical) equating to full fine pitch.

The airframe is both riveted and bonded, which adds to the strength and durability and prevents panels “unzipping” in the event of an incident. Aluminium was chosen by Evektor for ease of construction, simplicity of repair by owners and mechanics and increased resistance to normal “wear and tear” in the flight-training role.

Flight controls are conventional rod and cable to ailerons, elevator (on the fixed horizontal stabiliser) and rudder. Seating is side-by-side with dual floor-mounted control columns. Pitch trim uses an elevator trim tab and is adjusted via a small lever located between the seats. Ground manoeuvring is by a steerable nosewheel controlled by the rudder pedals. Brakes are hydraulically actuated discs on the main wheels operated by toe pedals on top of the left-hand pilot’s rudder pedals only. No parking brake is fitted.

The manually operated split flaps have four positions (0° for take-off, 15° for take-off and approach, 30° or 50° for normal or short landing). Electric flaps are an option. The mechanical flap lever is centrally mounted between the seats and its position, when pulled up in stages, equates to the flap position. The cockpit can be heated by ducted engine air and cooling/ventilation is by small opening panels in the side and front of the canopy.

Electrical power for flight instruments, lights, communications (single VHF and transponder), navigation (GPS, VOR and ILS) is provided by an engine generator charging a single 12V battery. The instrument console features five standard flight instruments, although the assessed aircraft had the E2B compass directly above the central artificial horizon (instrument layout is a customer option). Engine indications are on the right-hand side of the panel, using conventional analogue gauges, but are not tilted and rather deep set.

Fuel capacity for new SportStars has been increased from the former single 65 litre tank located centrally behind the seats, to 120 litres in two integral wing tanks. This has allowed baggage capacity to be increased in volume and in weight to 25kg. Navigation is provided by a GPS moving-map display and a radio-magnetic indicator showing VOR/ILS signals.

A rocket-boosted recovery parachute is fitted and fires out upwards and sideways through an aperture in the forward left-hand engine panel, and is linked to an emergency location transmitter (ELT). The operating handle is coloured bright red and located centrally at the base of the instrument panel next to the choke lever ( identical in size and shape, but black).

Flight Design CT

Flight Design is headquartered in Stuttgart, although production of the CT is carried out in Ukraine. The company started life in the early 1990s making hang gliders and powered microlights, but switched production in 1997 to the CT, an EASA-certificated UL-ML. The aircraft has evolved from the original CT to the CT-2K and now the CT-SW (Short Wing), which received US LSA approval in April.

CT_flaps

To date roughly 400 CT-series aircraft have been sold worldwide. Production is running at 10 a month and the order backlog extends into 2006, says Flight Design. As well as recreational flying, touring and towing, other roles envisaged for the CT were light reconnaissance and police surveillance, hence its high wing, large windows and detachable doors.

The CT-SW is of all-carbonfibre construction with Kevlar strengthening. The wing uses a symmetrical aerofoil section of the company’s own design. Basic empty weight is around 295kg when fitted with recovery parachute. The aircraft is certificated as an LSA with an all-up weight of 600kg, but still fits the German UL-ML category with two occupants, a reduced fuel load and mandatory parachute.

The Rotax 912S drives a three-blade, fixed-pitch “Neuform” propeller. Engine control is via a central console-mounted, slide-type throttle lever with no mixture or propeller controls (US LSAs must have fixed-pitch propellers).

Carbonfibre designs can have the disadvantage of being more expensive to manufacture and repair than all-metal, and must normally only be in reflective white finish to prevent differential heating and twisting of the structure. But carbonfibre structures are normally stronger and more crash-resistant, and can offer more aerodynamically efficient shapes with less drag. Fuel capacity is 130 litres carried in two integral wing tanks. Load-factor limits are +4/-2g.

Flight controls are rods to the ailerons and all-moving horizontal stabiliser and cable to the rudder. The aircraft has side-by-side seating and dual floor-mounted central control columns with top-mounted push-to-talk button and wing-leveller engage/disengage button. All three control surfaces can be trimmed using small, console-located manual trim wheels, but in practice only the pitch trim was required. This adjusts a geared trim tab at the rear edge of the horizontal stabiliser.

Wheel and parking brakes are hydraulically actuated discs controlled by a central-console lever. Ground manouevring is by a steerable nosewheel controlled by the rudder pedals. The electrically operated flaps have five positions (-12° for cruise, 0° for take-off, 15° for take-off and approach, and 30° or 40° for normal or short landing). The cockpit can be heated by ducted engine air and cooling/ventilation is by cockpit louvres.

Electrical power for flight instruments, lights, communications (single VHF and transponder), navigation (GPS) and flaps is provided by an engine generator charging a single 12V battery. The panel features four standard flight instruments, but instead of an artificial horizon the assessed aircraft had a central turn and slip indicator with surrounding airspeed and vertical-speed indicators and altimeter. An E2B-type compass was fitted at the top of the forward windscreen. Navigation was provided by a Honeywell GPS moving-map display.

The CT-SW has a novel, simple “wing-levelling” autopilot to allow the pilot to conduct limited hands-free/head-in cockpit tasks. The recovery-parachute operating handle is on the rear cabin wall and linked to a fuselage co-mounted ELT.

Tecnam Sierra

Tecnam is headquartered in Naples, Italy. Established in the 1980s, the company dedicates roughly 70% of total production to the Sierra, which is certificated to European VLA and US LSA regulations (its 580kg maximum weight putting it beyond the Australian/Canadian LSA limits of 550kg). About 180 Sierras have been delivered to date.

Empty weight is 320kg and no recovery parachute needs to be fitted under EASA VLA or US LSA rules. Again flight training is an intended role, hence the low wing and bubble canopy design like the SportStar, and the aircraft comes in an almost “ready to go” training configuration in Europe thanks to its VLA certification. Present production rate is six a week and order backlog is around six months.

The Sierra, like the SportStar, is principally of all-aluminium construction, with maximum load limits of +4/-2g. Fuel capacity is 100 litres carried in two integral wing tanks. Baggage capacity is 25kg. The wing design is Tecnam’s own and on the aircraft the 100hp Rotax 912S drove a three-blade fixed-pitch propeller, although a variety of fixed/variable-pitch, two/three-blade options are available.

Engine control is via one of two push/pull throttle levers, one centrally mounted at the base of the instrument panel and one, slightly raised, on the left-hand side of the instrument console, again with no mixture control. This allows flying from the left-hand seat with the pilot’s left or right hand on the control column.

Flight controls are conventional rod and cable to the ailerons, all-moving horizontal stabiliser and rudder. Seating is side-by-side with dual floor-mounted control columns. Electric pitch trim is operated by two separate buttons on top of each control column (one for increasing up, one for increasing down) that control a trim tab at the rear of the horizontal stabiliser. Trim tab position is shown by a small, graduated gauge with a red pointer.

Ground manoeuvring is via a steerable nosewheel controlled by the rudder pedals. Brakes are hydraulically actuated discs on the main wheels operated by a prominent, central floor-mounted vertical lever. The parking brake uses the same lever and a small locking switch. The electrically operated flaps are fully variable between 0° and 40°. The flap lever is located at the base of the left-hand instrument console and the flap position gauge mounted at the top of the right-hand engine instrument cluster. The cockpit can be heated by ducted engine air and cooling/ventilation is by side louvres.

Electrical power for flight instruments, lights, communications (single VHF and transponder) and navigation (GPS) is provided by an engine generator charging a single 12V battery. The instrument console features four standard flight instruments, although the assessed aircraft had no artificial horizon or VOR/DME. An E2B compass was mounted on the far left-hand side of the instrument console. Navigation was provided by a Honeywell GPS moving-map display. Engine indications are on the right-hand side, with conventional analogue gauges, but are not angled towards the left-hand side of the cockpit.

Flyability assessment

The Sierra and SportStar have bubble canopies with excellent fields of view (FoV) in all sectors bar down through the wing. The CT-SW’s FoV is most impressive, especially with its large overhead skylight to reduce the high-wing “blindspot” and its detachable doors that would provide unrestricted views for downward-pointing cameras.

All aircraft handled well on the ground, were easy to manoeuvre on grass or tarmac, turned tightly – virtually around their inner wheel – could be steered accurately, started easily and braked firmly and progressively. Overall, the Sierra felt the most stable by a whisker on grass (however, the handbrakes on the CT-SW and Sierra are not my favourites because you run out of hands to hold the control column if you want to then juggle engine power against brake).

Control characteristics (free-play, friction, breakout, centring and lack of oscillation) were good in all three designs, but the CT-SW had the best combination of mechanical characteristics, control response and harmonisation.

Longitudinal stability tests demonstrated that all three aircraft had small, but positive conventional stick force and stick displacement for increasing/decreasing speed. Pitch trim change with power or flap change was minimal. Short-period manoeuvring showed all aircraft reacted to pitch input within half a second, but the CT-SW was especially powerful in its pitch response and had the most neutral stability with regard to speed change (which I like). All three aircraft showed a long-period phugoid response of around 30s, which would not be a hindrance to the pilot holding an accurate altitude during the cruise.

All three aircraft (none were fitted with a g meter) were flown up to an approximate maximum load factor of +3.5g in wind-up turn, at a constant speed of around 100kt and 2,000ft. All showed that the stick force per g needed was light and the gradient linear as g increased. There as no hint of wing buffet or accelerated wing stall.

Lateral and directional stability tests showed that all three aircraft could generate positive sideslip with increasing rudder, but that the generated sideslip needed to be countered by increasing opposite bank angle (conventional). The CT-SW, however, could generate so much sideslip that the test had to be aborted before getting to full rudder-pedal deflection because of concern for sideforces on the propeller. I have never been so sideways in an aircraft in flight before.

All aircraft could be rolled with rudder, with the roll direction the same as the applied rudder. Again, because of its powerful rudder, the CT-SW rolled as fast with rudder as many conventional aircraft do with aileron. A small amount of adverse yaw when ailerons were used to roll without rudder co-ordination was apparent in all three aircraft, but was quickly neutralised by the weathercock effect of the fin. All aircraft showed neutral or slightly positive spiral stability, so they would not continue to roll if the pilot centralised the aileron control, but was then distracted.

Tests showed Dutch roll was positively damped out, without pilot input, within 4-5s on all three aircraft. A roll from 45° left to 45° right took about 3s for the SportStar and Sierra, with a sustained roll rate of around 40°/s. The CT-SW took a similar time to roll through 90°, but the rate kept increasing to at least 60-70°/s. The CT-SW’s roll rate at cruise speed would put some military fighters to shame.

Stalling characteristics for the three aircraft were benign. The Sierra and SportStar gave more indication of pre-stall buffet than the CT-SW, as felt through the rudder pedals and control column, but in the stall itself the CT-SW had a pronounced pitch “nod” to aid recognition. Flapless stall speeds were 43-48kt, dropping to around 32-38kt with flaps down. The CT-SW’s stall speeds were 5-10kmh (3-6kts) greater than the other two at a similar flap setting.

All three could be controlled post-stall in roll using ailerons, and the sustained rate of descent in the stall was around 600ft/min (3m/s). Recovery was instantaneous with application of power or release of control-column back-pressure, with no additional height loss. Stall in approach configuration was close to impossible since at 25° nose-up you lose sight of the world let alone the simulated landing strip. Overall, in terms of stall recognition, I felt the Sierra SportStar and Sierra would be slightly better suited to the training role than the CT-SW.

All aircraft were accelerated in a slight dive to close to their individual never-exceed speeds (VNE). The CT-SW reached a maximum of 160kt, the SportStar 145kt and the Sierra 140kt. Possibly due to its lower drag, the CT-SW felt the quickest to accelerate and both it and the Sierra felt stable at VNE. The SportStar felt sensitive in pitch and roll and less comfortable than the other two when close to VNE.

The CT-SW would make an ideal surveillance platform for police forces and the Sierra and SportStar would make ideal basic training aircraft. All would be served adequately by a three-blade fixed-pitch propeller, avoiding the complexity of a pitch lever, although if long-range touring is important to the owner then a variable-pitch propeller makes sense.

Four circuit types were flown to assess how aircraft each flew as a “package”: normal landing flap, short-landing maximum flap, glide and flapless. All three aircraft had an approach speed around 55-60kt with first-stage flap of 15°, reducing to about 48-55kt with 30° for normal landing or 40-50° for short landing. Flare to land was simple to achieve and all aircraft had such a good field of view forward and down that height and attitude estimation was always exact. All landed well with no hint of ground cushion or gear “bounce” and all seemed equally happy on grass as on tarmac. Brakes were well suited for stopping. Kicking off drift in a crosswind was straightforward and easy to co-ordinate.

The Sierra had too much friction in its throttle lever at low power settings, making it difficult to control small changes of RPM on final approach. The SportStar with its RPM fine-adjust “twist” function was the opposite in this respect, but it would only work well on a relatively calm day when speed was stabilised on final approach so that the pilot was not twisting and pulling/pushing the throttle lever at the same time.

Flap selection on all types was straightforward, but I found the fully variable setting of the electric flaps on the Sierra to be somewhat “nebulous”, given the physical distance between the paddle-type switch and flap-position gauge. The best design was the CT-SW, which has a large five-position flap switch and large, digital, flap-angle display directly above it. Easy to use and intuitive, it seemed like “dial a flap” because of the speed at which the flaps moved when selected.

None of the aircraft exhibited any significant ground effects on take-off or landing. There was a noticeable swing to starboard when the Sierra accelerated with full power on take-off or during a roller landing, but the swing was easily controlled with about one-third opposite rudder-pedal deflection until after rotation.

All pitch out-of-trim forces could be easily and accurately trimmed out, although the electric “button” system on the Sierra was somewhat nebulous in operation because of the lack of feedback to the pilot. I am not sure this type of aircraft needs electric trim given the low stick forces associated with speed and flap changes.

Usability assessment

Entry and exit for the Sierra and SportStar was overwing: from the rear for the SportStar with its forward-hinged, upward-opening canopy; and from the front, with the aid of a small fixed step just below the wing root, for the Sierra with its backward-sliding canopy. It was then a simple matter of stepping into the cockpit and sitting down. The CT-SW has large, top-hinged side doors with low sills, so the technique was to sit in sideways first and then lift the inner leg over the control column and was easy. A single locking lever secures the door internally by pins at three positions on the airframe. The SportStar has a single-point canopy locking handle above and just behind the pilots’ heads. The Sierra has a canopy top lock and two side safety locks.

The floor-mounted control columns on all three aircraft fell naturally to hand and no instruments were obscured when the column was held during flight. All switches are well sized for purpose, logically grouped, logical in sense of operation and clearly labelled. My only slight dissatisfaction with the Sierra and SportStar was with the analogue engine instruments, which are offset on the right side of the instrument console but not angled towards the left-hand pilot, so scanning them was more of an effort. The CT-SW has a digital display of engine parameters with an angled face and warning lights to inform the pilot an engine limitation had been exceeded.

Given all three aircraft use the same Rotax 912S, with idle rpm around 1,600 and full power rpm around 5,800, internal noise was not obtrusive and normal (non-noise cancelling) headsets were acceptable.

The CT-SW and Sierra have fixed rudder pedals and moveable seats, the SportStar the opposite. There seemed an adequate range of adjustment in all three to cope with most sizes of pilot. All three aircraft have comfortable seats and easy to adjust shoulder/lap four-buckle straps (none had an anti-g bottom fifth strap or an inertia reel facility). In each, the low instrument coaming meant that field of view, even in a flapless approach, was good and there will be no need for cushions for the more vertically challenged pilots. Systems in the aircraft are basic, but adequate.

Limitations to be manually respected by the pilot were minimal and were principally flap speeds, maximum speed and load factor. The speed limits are clearly shown on all airspeed indicators. Since all the assessed aircraft have a +4/-2g limit it seems to make sense to equip them with a g meter to help avoid inadvertently overstressing the aircraft.

Typical fuel consumption for the all-metal aircraft at range speed (approximately 110kt) was 14-15 litres/h. Given a 15 litre fuel reserve on landing, this equated to a still air range of approximately 1,100km for the Sierra and around 1,300km for the SportStar. Even these impressive figures were bettered by the CT-SW which, with its cruise flap setting of -12° and lower drag, had a consumption of around 10 litres/h for a range of around 2,000km.

Landing and take-off distances varied slightly, but were in the order of 150m for both. It would be best to use a grass strip no shorter than 250m to give some margin for error. Standard-atmosphere climb rates for all of the designs were around 1,000ft/min and service ceilings around 14,000ft.

Affordability assessment

The three designs all have an extensive list of available options. Purchase price as tested, which should be used only a guide, was €90,000 ($107,400) for the CT-SW (including German VAT), €60,000 for the SportStar and €95,000 for the Sierra (including Italian VAT). Operating costs including depreciation, engine and maintenance reserves work out at around €45 per flight hour for a typical 200h per year. Hull insurance is around €3,000 a year.

The aircraft require alternating 50h minor and 100h moderate inspections, both of which can be pilot performed, and need to be inspected annually by a licensed engineer. Consumables like brake pads, spark plugs, filters, oil and petrol make the additional running costs similar to those of a car. With costs similar to a luxury car, these designs offer the aircraft owner good value and a high performance/price ratio.

Survivability assessment

Given that these aircraft may be flown by inexperienced pilots, they should have the best possible levels of active and passive safety. None of the designs could be flown while wearing a personal parachute and any overwater transit would have to be planned carefully unless a lightweight dinghy could be carried. The CT-SW and SportStar both have recovery parachute and ELT fitted, although I was not happy with the position of the parachute operating handle in the SportStar next to the identically shaped (but differently coloured) engine choke handle. All the designs seemed robust and rugged and in no way inferior to the present generation of basic trainers.

Pilot enjoyment factor

These three LSA designs are all outstanding, but the challenge was to quantify a pilot enjoyment factor for each. My choice for second place was tied. The Evektor SportStar is a great overall package and rightly deserves its number-one seller spot given its range of options, solid performance and value for money. The Tecnam Sierra is a ready-to-go certificated EASA VLA design that looks like a solid and reliable next-generation workhorse for flight training. But the Flight Design CT-SW’s combination of handling qualities, performance and usability made it my favourite. It has a “strap on and go” quality that encapsulates the LSA ideal.

The challenge set by Flight International leads to three conclusions. First is that a new era has dawned as outstandingly capable aircraft have evolved from their UL-ML heritage. These LSA-type aircraft will make sporty and safe two-seat flying affordable for large numbers of private owners without them having to share aircraft through a syndicate or hold a full pilot’s licence.

Second is that these designs are “real” aircraft in every sense and outperform the old Cessna 150 in virtually every flight regime. The three LSA designs tested were a delight to fly whereas the older types now in use are often expensive, sluggish, boring and lacking in usability.

The third conclusion is double-edged. These are real aircraft and their only link to the early days of ultralights and microlights is the weight categorisation. Pilots who fly these LSAs will need to be better trained and the recreational flying community needs to face this fact. The FAA’s decision to create the LSA class looks sensible, practical and timely.

European regulators need to recognise this is a difficult sector to regulate and that there are still many inconsistencies, anomalies and grey areas in the regulations. One hope is that Europe will follow the FAA’s lead to create a LSA class below the present VLA category.

PETER COLLINS/KEMBLE, KUNOVICE & STUTTGART

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