The TeST TST-14 Bonus is a Czech high-wing, T-tailed, two-seats-in-tandem glider and motor glider, designed and produced by TeST Gliders.^[1][2][3]

The TST-14 motor glider was designed for private owner and flying school use and as such features wing tip wheels that allow independent taxiing and take-off.^[1][3]

The TST-14 is made out of composite materials, mainly epoxy resin and fiberglass with a sandwich structure and transverse ribs.

There are also a few parts in wood, carbon fiber , kevlar and aluminium.

Seen in plan view, it has a forward-swept wing, i.e. it has a negative nose angle.

This conformation is typical of most two-seater gliders, and justified by the fact that the possible passenger is positioned on the center of gravity .

The presence of the passenger does not , therefore , require any modification regarding the weight distribution (centre of gravity). Therefore, like all two-seaters, the pilot must sit in the front seat and weigh between 75 and 100 kg.

If he exceeds these weights, it will be necessary to add or remove ballast, which is placed inside the tip of the glider on two special plates.

Each wing weighs about 40 kg (88 lb) and has a single spar made with a carbon fibre composite flange plate and a polyurethane foam/fibreglass composite web plate ; at the ends of the wings there are 40 cm long winglets . Glidepath control is by upper surface air brakes made from aluminium.

The motor glider version is powered by a retractable 50 hp (37 kW) Rotax 503UL two-stroke engine and a 120cm wooden propeller.

The engine is equipped with cylinder head temperature (CHT) sensors, and despite being installed in an upside down position, the temperature never causes concern during take-offs with maximum and prolonged power.

The climb rate is much higher than most motor gliders (some have max =1.4 m/s)

Extension and retraction of the engine is fully automatic, controlled with two cockpit-mounted buttons and actuated by two electric servo motors.

The extraction of the engine from inside the fuselage occurs by pushing the yellow button, while the retraction occurs by pushing the green button.

Both buttons are enabled only if the magnetos are down (engine off).

While extraction is completed by pushing the yellow button only once, to carry out retraction you need to press the green button twice.

The first time causes the doors to open and a propeller stop blade to come out.

Sometimes, especially with the glider loaded, the propeller continues to turn even with the engine off : it is sufficient to slow down as much as possible and use the propeller brake.

After checking that the propeller's position is vertical, looking in the rearview mirror, you can push the button a second time, causing the engine to lower and the doors to close.

As soon as the button is pushed, it is not necessary to keep the button pressed, as the servo motor autonomously continues the opening or closing cycle, alerting the pilot of the end by turning off a flashing LED.

The engine can be used both for take-off and then retracted as soon as gliding is possible, or when weather conditions are no longer suitable for gliding.

In this case, you need to limit your speed to around 90 - 100 km/h and press the yellow button.

In about 20 seconds the extraction will be complete and the propeller will tend to rotate spontaneously due to the speed.

You need to lift the magnets and turn the key: starting will be immediate.

Flying is easy even with the engine extended (running or off), however the position of the engine produces a slight advancement and a certain raising of the center of gravity of the weights, .

The higher position of the center of gravity causes the tendency to accentuate the bank angle in turns, it is therefore necessary to limit the angle, not exceeding 30°- 40°.

The landing gear consists of dual fuselage-mounted tandem mainwheels and wing tip-mounted wheels.^[1][4][5]

The bigger wheel is cushioned and equipped with a drum brake.

It is located aft of the center of gravity.

Take-off occurs by rolling on the main and front wheels, and it is easier than in the majority of motor gliders, as it is not necessary to lift the tail of the glider during the take-off run.

99% of gliders with or without engines have single-track landing gear, even if there are multiple wheels, these are all aligned.

During takeoff they will certainly have one wing resting on the ground, unless there is an assistant holding it up.

The TST 14 has a propeller that turns counterclockwise, when viewed from behind, and produces some twist to the glider, which makes it easier to lift the left wing, compared to the right.

If there are no other particular factors, such as crosswinds, during the take-off run, it is preferable to place the left wing on the ground.

In the absence of wind, taking off on asphalt, the lifting of the wing occurs after approximately 15 m.

In the back seat there are almost all the glider's management controls, namely:

- engine management: extraction and retraction buttons, accelerator, ignition, shutdown (magnetos), petrol tap

- flight management: elevator control bar, aileron rudder, variometer, altimeter, anemometer, any repeaters of the instruments located at the front, such as 8.33 KHz radio, cartographic instruments, final glide calculators, oxygen system

-landing management: airbrakes and main wheel brake

Some controls, however, are only present in the front seat: speed trim, compartment ventilation (a ventilation window is also present at the back), fuel primer pump.

The front pedal set (rudder) is adjustable in length, while the rear one is fixed; the rear seat, however, is wider.

The fuel tank is made of welded aluminum sheet, while the level sensor is capacitance type.

The take-off run is approximately 200 m with the pilot alone, and 250 m with the passenger too.

Landing, if necessary, can take place in approximately 150 m , the position of the airbrakes is variable, but they are normally used between 30 and 60%.

The aircraft was type certified to the Joint Aviation Authorities JAR 22 standard for gliders on 10 Dec 2001. The TST-14 was not certified in the United States as the company explains, "due to the expense involved". The aircraft can be registered with the US Federal Aviation Administration as a Special Light Sport Aircraft glider or in the Experimental - racing/exhibition category.^[2][5][6]

TST-14 Bonus

Pure glider version, with a gross weight of 472.5 kg (1,042 lb)^[3]

TST-14M

Main production motor glider version, powered by a 50 hp (37 kW) Rotax 503UL two-stroke double ignition powerlant^[1]

Data from Sailplane Directory and company website^[1][4][5]

General characteristics

• Crew: one
• Capacity: one passenger
• Length: 8.24 m (27 ft 0 in)
• Wingspan: 17 m (55 ft 9 in)
• Height: 1.10 m (3 ft 7 in)
• Wing area: 12.01 m² (129.3 sq ft)
• Aspect ratio: 23.92:1
• Airfoil: Wortmann modified
• Empty weight: 280 kg (617 lb) 300 kg if present ballistic parachute
• Gross weight: 450 kg (992 lb) 472 kg if present ballistic parachute
• Max takeoff weight: 450 kg (992 lb) 472.5 if present a ballistic parachute
• Fuel capacity: 22.6 litres (5.0 imp gal; 6.0 US gal) approximately 2.5 hours of flight, if the engine is always on
• Powerplant: 1 × Rotax 503UL double ignition two-stroke, twin cylinder inline aero engine, 37 kW (50 hp)
• Propellers: 2-bladed wooden, 1.20 m (3 ft 11 in) diameter

Performance

• Maximum speed: 150 km/h (93 mph, 81 kn) gust or aerotow speed
• Cruise speed: 115 km/h (71 mph, 62 kn) max speed by motor = 140 km/h
• Stall speed: 65 km/h (40 mph, 35 kn)
• Never exceed speed: 205 km/h (127 mph, 111 kn)
• Range: 275 km (171 mi, 148 nmi) only if the engine is always on
• Service ceiling: 4,000 m (13,000 ft) ceiling by motor, more by sail
• g limits: +5.2/-2.6
• Maximum glide ratio: 40:1 at 115 km/h (71 mph; 62 kn)
• Rate of climb: 3.5 m/s (690 ft/min) 2.5 m/s if passenger is on
• Rate of sink: 0.65 m/s (128 ft/min) at 85 km/h (53 mph; 46 kn)
• Wing loading: 39.06 kg/m² (8.00 lb/sq ft)
• Fuel consumption: 0.074 kg/km (0.26 lb/mi)

• List of gliders

• Official website
• Photo of TST-14 in flight
• Photo of TST-14M showing engine installation