A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: a fixed-wing aerodyne equipped with a means of propulsion (MoP), capable of sustained soaring flight without thrust from the means of propulsion. [1]
In 1935, an occasional or auxiliary motor that could be retracted was suggested by Sir John Carden. [2] This was incorporated into the Carden-Baynes Auxiliary that first flew on 8 August of the same year. A later version of the Budig glider was powered.
Most motor gliders are equipped with a propeller, which may be fixed, feathered (e.g. AMS-Flight Carat), or retractable. However jet engine-powered motorgliders are now available from some manufacturers, some of which are intended for use only as "sustainer" engines, i.e. for sustaining gliding flight rather than as self-launching aircraft.
Motor with fixed or full feathering propellers are generally classified as Touring Motor Gliders (TMGs). TMGs can take off and cruise like an airplane or soar with power off, like a glider.
They are fitted with front-mounted engines, similar to a small airplane. The large wingspans of TMGs provide a moderate gliding performance, not as good as that of unpowered gliders. However TMGs are more efficient than conventional light aircraft.
Most TMGs are designed with engines of 80 to 100 hp (75 kW) and typically cruise (under power) at 85–100 knots (190 km/h). Most have fuel tanks capable of holding between 50 and 100 liters (13 to 26 US gallons) of fuel, giving a range under power of up to 450 nautical miles (approximately 830 kilometers). Modern TMGs like the Phoenix Air Phoenix are capable of higher speeds and longer range under power.
Some TMGs are equipped with folding wings to allow them to fit in standard small airplane T-hangars. Tow hooks are unnecessary, since aircraft with self-launch ability do not require access to winch or tow plane for launching like a conventional glider.
Some TMGs, like the Europa or the Phoenix, can also be supplied with interchangeable wings or wingtips so that they can be flown as a standard touring aircraft as well as a TMG. [3]
The landing gear configuration on TMGs usually incorporates two fixed main wheels, allowing it to be taxied on the ground without a wing walker. While some TMGs have only one main wheel, with auxiliary trolley wheels on the wings for taxiing, it is becoming more common to find them being manufactured with tricycle and conventional (two fixed main wheels – i.e. a "tail-dragger") landing gear configurations.
Since the additional drag of the stopped propeller and landing gear reduces their gliding performance, TMGs are seldom used in competition.
The retractable propeller is usually mounted on a mast that rotates up and forward out of the fuselage, aft of the cockpit and wing carry-through structure. The fuselage has engine bay doors that open and close automatically, similar to landing gear doors. The engine may be near the top or bottom of the mast, and newer designs have the engine fixed in the fuselage to reduce noise and drag.
Unlike TMGs, most gliders with retractable propellers are also fitted with a tow-hook for aero-towing or ground launch. They have a single-axle retractable main wheel on the fuselage like most unpowered gliders, so they do require assistance during ground operations. The two-stroke engines commonly used are not efficient at reduced power for level cruising flight, and instead must use a "saw-tooth" flight profile where the glider climbs at full power, then glides with the propeller retracted.
Sustainer motor gliders must be launched like an unpowered glider, but can climb slowly to extend a flight once the engine is deployed and started. They generally do not have an alternator or starter motor, so the engine is started by "wind-milling" the propeller in flight. The propeller may be a rigid 2-blade design, or may have more than two blades that fold at the hub when the engine is retracted. The propeller hub is usually attached directly to the crankshaft, but there is at least one example of a sustainer with a belt reduction drive, the DG-1000T. [4]
The smaller sustainer engines are usually not equipped with a throttle, but instead have a cable to open decompression valves in each cylinder to allow the engine to turn freely for starting. Sustainer engines are typically two-stroke two-cylinder air-cooled engines in the range of 18–30 hp (14–22 kW). They are lighter in weight, and simpler to operate than self-launching powerplants. [5]
Self-launching retractable propeller motor gliders have sufficient thrust and initial climb rate to take off without assistance, or they may be launched as with a conventional glider. The engines also have a starter motor and a large battery to allow the engine to be started on the ground, and an alternator to recharge the battery. A two-blade propeller is typically coupled to the engine via a belt reduction drive. In older designs, the propeller alignment must be checked by the pilot using a mirror, before it is retracted into the fuselage; however in current production gliders, propeller alignment is fully automatic.
Another solution is the single-blade propeller that offers the advantage of a smaller opening in the fuselage to retract the engine.
Internal combustion engines can benefit from mounting in the fuselage, rather than on the propeller mast. This allows them to be connected to a larger muffler for reduced noise when operating, something which is mostly relevant to European operation. It also allows the belt tension to be relieved when the engine is retracted to extend the life of the belt and bearings. The drawback of this arrangement is that engines fixed low in fuselages are more difficult to pre-flight and service, and highly stressed power transmission belts should not be bent or twisted.
Self-launching engines are equipped with a throttle that allows the engine power to be adjusted for ground operations. Self-launching engines are typically in the range of 50–60 hp (38–45 kW). The higher engine output power requires liquid cooling with a separate radiator mounted on the propeller mast. Engines commonly used are two-stroke piston engines, or Wankel rotary engines. [6]
On the Stemme S10, the propeller folds into the nose cone, and is connected to the rear-mounted engine with a drive shaft. It also has two retractable main wheels, allowing it to be taxied without assistance, and to soar with low drag. These features make it a cross-over between the touring and retractable propeller motor gliders. It does not have a tow-hook, so it must self-launch. The S10-VT variant has a two-position variable-pitch propeller and a turbocharger on the engine, which allows the aircraft to cruise at altitudes up to 30,000 feet (9,000 m). [7]
On the AMS Carat, the propeller folds forward, pointing straight ahead like a spear.
Although most motor gliders have gasoline-fueled internal combustion engines, a number of electric-powered self-launchers have been developed including the Lange Antares 20E and 23E, Schempp-Hirth Arcus E, Schleicher AS 34Me, Pipistrel Taurus Electro G2, Silent 2 Targa LE (Lithium Electric), and the closely related Air Energy AE1 Silent, Yuneec Apis 2, Yuneec EViva, Alpaero Exel, Aériane Swift, Electravia and Alatus AL12. [8] [9] [10] [11] Some types use a pylon behind the cockpit to extend a propeller. 11 different types, from 7 manufacturers, such as the Alisport Silent 2 Electro, use the front electric sustainer (FES) system with a folding propeller in the nose. [12]
Advantages of electric power over gasoline include:
Disadvantages of current electric powered motor-gliders as compared to gasoline include:
Electric sustainer systems (with power to sustain flight but not self-launch) are optional for the Schempp-Hirth Ventus-3, HPH Shark and ESAG LAK-17B. These three all use the FES as used for self-launching lighter gliders, such as the Alisport Silent 2. [12]
The first production self-launching motor glider fitted with a jet engine was the Caproni Vizzola Calif. The jet engine was mounted inside the fuselage behind the wing, with fixed intake and exhaust ducts coupled to the outside air stream for engine operation. Since then a new generation of jets have been offered for the Schempp-Hirth Ventus 2, Jonker JS-1 Revelation and the HpH 304, all featuring sustainer jet engines.
Other self-launching types include the experimental LET L-13TJ Blaník, [14] a version of the Alisport Silent Club and a version of the TeST TST-14 Bonus.
The engine cannot always be relied upon to start in flight, so the pilot must allow for this possibility. The generally accepted practice is to get in position for landing at a suitable airport, or off-airport out-landing field, before extending the propeller and attempting an engine start. This allows for a safe landing in the event that the engine cannot be started in time. [15]
In soaring competitions, starting the engine is usually scored the same as an out-landing in an unpowered glider. To detect the use of the engine, GNSS Flight Recorders used in motor gliders must have a noise sensor that allows recording the sound level along with position and altitude. In many competitions, the rules require that the pilot start the engine at the beginning of the flight, before starting the task, to ensure an engine start later in the flight will be detected.
Gliders without an engine are lighter and, as they do not need a safety margin for an engine-start, they can safely thermal at lower altitudes in weaker conditions. So, pilots in unpowered gliders may complete competition flights when some powered competitors cannot. [16] Conversely, motor glider pilots can start the engine to extend a flight if conditions will no longer support soaring, while unpowered gliders will have to land out, away from the home airfield, requiring retrieval by road using the glider's trailer.
The presence of an engine can increase the safety of gliding, as a powerplant increases the ability of the pilot to avoid storms and off-airport landings. An opposing view is that motor gliders are against the spirit of the sport, and, more importantly, that they sometimes give pilots a false sense of security.
Touring motor gliders are seldom used in competition, but they can be useful in training for cross-country flights. [17] After take-off, the engine is switched off, and the trainee flies the aircraft as a glider. Landings in unfamiliar fields can be practiced while the motor idles. If the trainee chooses an inappropriate field, or misjudges the approach, the instructor can apply power and climb away safely.
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In Europe, powered gliders are categorized into gliders with retractable propellers/engines, which can be flown with an ordinary glider pilot license (GPL), and touring motor gliders (TMG), which require a license extension to the standard GPL. In the United Kingdom, where gliding is regulated by the British Gliding Association, pilots of self-sustaining gliders, like those of pure gliders, do not have to be licensed with the United Kingdom Civil Aviation Authority.
In South Africa, Touring Motor Glider (TMG) is an independent National Pilots License category under Recreation Aviation, Part 62, subpart 17.
In the United States, a private glider pilot certificate allows the pilot to fly unpowered gliders, self-launching motor gliders (including touring motor gliders and gliders with retractable engines or propellers), and sustainer motor gliders. An instructor must provide instruction and sign the logbook of the pilot to authorize the launch method, which may be by airplane towing, ground launch (winches, bungee, auto tow), or, in the case of a suitable motor glider, by self-launching. In the US, motor gliders are classified as gliders, and may be operated by a glider pilot without the medical certificate required to operate an airplane.
In the United States, a powered glider may be certificated for up to two occupants, up to 850 kg maximum weight, and with a maximum ratio of weight to wing span squared of 3 kg/m2. [18] Similar requirements exist in European JAA/EASA regulations, at a maximum weight of 750 kg.
In Canada, a glider pilot license allows the pilot to fly unpowered gliders. For self-launching motor gliders (including motor gliders and gliders with retractable engines or propellers), and sustainer motor gliders an aeroplane permit or licence is required. An instructor must provide instruction and sign the logbook of the pilot to authorize the pilot to carry passengers.
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinct from rotary-wing aircraft, and ornithopters. The wings of a fixed-wing aircraft are not necessarily rigid; kites, hang gliders, variable-sweep wing aircraft and airplanes that use wing morphing are all examples of fixed-wing aircraft.
The Schempp-Hirth Discus is a Standard Class glider designed by Schempp-Hirth. It was produced in Germany between 1984 and 1995 but has continued in production in the Czech Republic. It replaced the Standard Cirrus. It was designed by Klaus Holighaus.
The Schempp-Hirth Ventus is a sailplane produced during 1980–1994 by Schempp-Hirth, a German sailplane manufacturer. It was designed by Klaus Holighaus and replaced the Schempp-Hirth Mini-Nimbus. Schempp-Hirth manufactured 613 Ventus sailplanes.
The Schempp-Hirth Duo Discus is a high-performance two-seat glider primarily designed for fast cross-country flying, including gliding competitions. Often, it is used for advanced training.
The Schempp-Hirth Nimbus-4 is a family of high-performance FAI Open Class gliders designed by Klaus Holighaus and manufactured by Schempp-Hirth Flugzeugbau GmbH in Kirchheim, Germany. The Nimbus-4 first flew in 1990.
The Politechnika Warszawska PW-6U is a Polish two-seat training sailplane designed at the Warsaw University of Technology for basic flight instruction and transition training to the PW-5 single-seater. It was manufactured at PZL Świdnik from 2000 and at ZS Jezow from 2007.
The Silent Club is a single seater sailplane of Italian manufacture. It is of the FAI type DU Class glider. It is sold by Alisport ready-to-fly or kit-built as pure glider or self-launching glider. The self-launching version is fitted with a single-blade propeller belt-driven by a two-stroke engine or optionally by an electric motor.
The AMS-Flight Carat A is a single-seat, high performance motorglider. The sailplane was originally designed and built by Technoflug in Germany and is now manufactured by AMS-Flight in Slovenia.
A glider is a fixed-wing aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. Most gliders do not have an engine, although motor-gliders have small engines for extending their flight when necessary by sustaining the altitude with some being powerful enough to take off by self-launch.
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.
The Antares is a glider built by Lange Aviation produced with three different wingspans, 18, 20 and 23 meters. The 20 and 23 meter variants can be equipped with a 42-kW electric motor and SAFT VL 41M lithium-ion batteries.
Lange Aviation GmbH is a German company that manufactures gliders and develops electric power-plants for other aircraft. It was founded by its present managing director, Axel Lange, in 1996 as Lange Flugzeugbau GmbH in Zweibrücken. The company currently has 42 employees. At the end of September 2007, the business was re-capitalised. Lange Faserverbundtechnik GmbH acquired all material and intellectual properties of the Lange Flugzeugbau GmbH and it continued the production of the Antares gliders at the airport at Zweibrücken. The company has operated since 2008 under the name Lange Aviation Gmbh.
A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding. This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplanes are aerodynamically streamlined and so can fly a significant distance forward for a small decrease in altitude.
The Aviastroitel AC-7M is a Russian mid-wing, T-tailed, two-seats in side-by-side configuration motor glider that was designed by Vladimir Egorovich Fedorov and produced by Aviastroitel, now Glider Air Craft.
The Hirth Hi 20 MoSe was a German motor glider designed in the late 1930s. Based on the Göppingen Gö 4 side-by-side seat training glider, it had a foldaway propeller, column-mounted above the fuselage and shaft-driven by a small internal piston engine.
The Silent Family Silent Glider M is a German ultralight trike motor glider, designed by Helmut Grossklaus and produced by Silent Family of Westerrade. The aircraft is supplied as a complete ready-to-fly-aircraft.
The ASG 32 is a Two Seater Class glider manufactured by Alexander Schleicher. The prototype had its maiden flight in Poppenhausen on 31 May 2014. Deliveries began in 2015.
Albastar AS are gliders produced by the Slovenian company Albastar Ltd. They are currently in the development stage.
The Schempp-Hirth Ventus-3 is a sailplane produced by Schempp-Hirth. It replaces the highly successful Schempp-Hirth Ventus-2.
Front electric sustainer (FES) is a propulsion system for gliders that uses an electric motor powered by batteries and a foldable propeller. It is produced by LZ Design d.o.o. in Logatec, Slovenia.
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