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A motor glider is a
fixed-wing aircraft 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 dist ...
that can be flown with or without engine power. The
FAI Gliding Commission The International Gliding Commission (IGC) is the international governing body for the sport of gliding. It is governed by meetings of delegates from national gliding associations. It is one of several Air Sport Commissions (ASC) of the Fédérati ...
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.


History

In 1935, an occasional or auxiliary motor that could be retracted was suggested by Sir John Carden. This was incorporated into the
Carden-Baynes Auxiliary The Carden-Baynes Auxiliary was the first motor glider with a retractable engine and propeller; it is known as the Abbott-Baynes Scud 3 when engineless. Both aircraft, built in the mid-1930s, were still flying in 2010 as pure sailplanes. Deve ...
that first flew on 8 August of the same year. A later version of the
Budig glider The unusual German Budig glider participated in the second (1921) Rhön competition, though without distinction. It was later fitted with a low power engine, making it probably the first powered glider. Design and development The Budig glid ...
was powered.


Types

Most motor gliders are equipped with a
propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
, which may be fixed, feathered (e.g.
AMS-Flight Carat 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.Bayerl, Robby; Martin Berkemeier; et al: ''World D ...
), 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.


Fixed or feathering propeller


Touring motor gliders

Motor with fixed or full feathering propellers are generally classified as Touring Motor Gliders (TMGs). TMGs can take off and cruise like an
airplane An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad ...
or soar with power off, like a
glider Glider may refer to: Aircraft and transport Aircraft * Glider (aircraft), heavier-than-air aircraft primarily intended for unpowered flight ** Glider (sailplane), a rigid-winged glider aircraft with an undercarriage, used in the sport of gliding ...
. They are fitted with front-mounted engines, similar to a small airplane. The large
wingspan The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingspan o ...
s of TMGs provide a moderate
gliding 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 a ...
performance, not as good as that of unpowered gliders. However TMGs are more efficient than conventional
light aircraft A light aircraft is an aircraft that has a maximum gross takeoff weight of or less.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 308. Aviation Supplies & Academics, 1997. Light aircraft are used as utility aircraft co ...
. Most TMGs are designed with engines of 80 to and typically cruise (under power) at 85–. 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 The Phoenix Air Phoenix is a Czech shoulder-wing, two-seat motor glider, designed and produced by Phoenix Air and provided as a complete ready-to-fly aircraft.Bayerl, Robby; Martin Berkemeier; et al.: ''World Directory of Leisure Aviation 20 ...
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 Ceremonial ship launching involves the performance of ceremonies associated with the process of transferring a vessel to the water. It is a nautical tradition in many cultures, dating back thousands of years, to accompany the physical pro ...
like a conventional glider. Some TMGs, like the
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
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. The
landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Mart ...
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.


Retractable propeller

The retractable propeller is usually mounted on a mast that rotates up and forward out of the
fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...
, aft of the
cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the controls that e ...
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

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 An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.Gor ...
or
starter motor A starter (also self-starter, cranking motor, or starter motor) is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic ...
, 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. 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 A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...
two-cylinder
air-cooled engine Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat ge ...
s in the range of 18–30 hp (14–22 kW). They are lighter in weight, and simpler to operate than self-launching powerplants.


Self-launching

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 A reduction drive is a mechanical device to shift rotational speed. A planetary reduction drive is a small scale version using ball bearings in an epicyclic arrangement instead of toothed gears. Reduction drives are used in engines of all kinds ...
. 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 A single-blade propeller may be used on aircraft to generate thrust. Normally propellers are multiblades but the simplicity of a single-blade propeller fits well on motorized gliders, because it permits the design of a smaller aperture of the glid ...
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.


Other types


Cross-over

On the
Stemme S10 Stemme AG is a German glider manufacturer. Aircraft production is complemented by service, maintenance and repair of their sports and personal aircraft. Starting in 2014 many Stemme glider structural components were made under contract by Remos ...
, 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 In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
on the engine, which allows the aircraft to cruise at altitudes up to 30,000 feet (9,000 m). On the
AMS Carat 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.Bayerl, Robby; Martin Berkemeier; et al: ''World D ...
, the propeller folds forward, pointing straight ahead like a spear.


Electric

Although most motor gliders have
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
-fueled
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
s, 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 The Yuneec EViva is a Chinese low-wing, two-seat motor glider that was designed by Martin Wezel is now under development by Yuneec International of Kunshan, Jiangsu.Bayerl, Robby; Martin Berkemeier; et al: ''World Directory of Leisure Aviation ...
, Alpaero Exel, Aériane Swift, Electravia and Alatus AL12. 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 The Alisport Silent 2 Electro is an Italian mid-wing, single-seat motor glider, designed and produced by Alisport of Cremella and provided as a complete ready-to-fly aircraft. The aircraft was introduced at the Aero show held in Friedrichsh ...
, use the front electric sustainer (FES) system with a folding propeller in the nose. Advantages of electric power over gasoline include: * Faster and more reliable transition from gliding to powered flight, as the time and risk required to start and warm up an internal combustion engine is eliminated. For example, the Antares 20E transitions from gliding to powered flight in under 12 seconds. With a FES system maximum power can be available in 1–2 seconds. * For types that use a pylon, lower drag and sink rate are achieved with the pylon extended and the motor not running, as there is no radiator as required to cool a gasoline engine. For FES systems, the drag from the folded propeller in the nose is negligible if the engine does not start. For safe operation, the "Engine out and not running" performance is used to plan in-air restarts in the event of a problem (even for electrics). The reduced sink-rate of electric-powered motor-gliders "engine out and not running" allows a lower altitude for a safe in-air restart. * For types that use a pylon, belt reduction drive and associated reliability issues are eliminated. As an electric motor can turn at a lower RPM than typical gasoline engines, it can be mounted at the top of the mast without a reduction system, eliminating belt-drive issues. * Greatly reduced noise, allowing take-off from locations where other powered aircraft are not permitted. Disadvantages of current electric powered motor-gliders as compared to gasoline include: * Reduced range or climb altitude, as the energy stored per unit weight for available batteries is less than gasoline. * Gliders with pylon-mounted electric motors are slightly heavier than those with gasoline engines due to the batteries. An FES system weighs about the same as a two-stroke engine. * Increased cost. While electric motors are comparably inexpensive, low-weight batteries suitable for motor-gliders are a little more expensive than gasoline engines. Electric sustainer systems (with power to sustain flight but not self-launch) are optional for the
Schempp-Hirth Ventus-3 The Schempp-Hirth Ventus-3 is a sailplane produced by Schempp-Hirth. It replaces the highly successful Schempp-Hirth Ventus-2. Design and development It was announced at the AERO Friedrichshafen in April 2015 where a mock-up was suspended fr ...
, 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.


Jet

The first production self-launching motor glider fitted with a
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...
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 The Schempp-Hirth Ventus-2 is a sailplane produced by Schempp-Hirth since 1994. It replaced the highly successful Schempp-Hirth Ventus. Design and development The Ventus-2a and 2b are 15 metre sailplanes. The 'a' version has a narrow fusel ...
, Jonker JS-1 Revelation and the
HpH 304 HpH 304 is a family of sailplanes ranging from a single-seat composite Composite or compositing may refer to: Materials * Composite material, a material that is made from several different substances ** Metal matrix composite, composed of me ...
, all featuring sustainer jet engines. Other self-launching types include the experimental LET L-13TJ Blaník, a version of the Alisport Silent Club and a version of the
TeST TST-14 Bonus 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.Bayerl, Robby; Martin Berkemeier; et al: ''World Directory of Leisure Aviation 2011-12'', page 137. WDLA U ...
.


Use of engines in self-launching sailplanes

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. In
soaring competition Some of the pilots in the sport of gliding take part in gliding competitions. These are usually racing competitions, but there are also aerobatic contests and on-line league tables. History of competitions In the early days, the main goal wa ...
s, 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 The International Gliding Commission (IGC) is the international governing body for the sport of gliding. It is governed by meetings of delegates from national gliding associations. It is one of several Air Sport Commissions (ASC) of the Fédérat ...
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. 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. 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.


Licenses or certificates

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 The British Gliding Association (BGA) is the governing body for gliding in the United Kingdom. Gliding in the United Kingdom operates through 80 gliding clubs (both civilian and service) which have 2,310 gliders and 9,462 full flying members (i ...
, 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.. 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.


See also

*
Powered hang glider A foot-launched powered hang glider (FLPHG), also called powered harness, nanolight, or hangmotor, is a powered hang glider harness with a motor and propeller in pusher configuration. An ordinary hang glider is used for its wing and control f ...
*
Powered paraglider Powered paragliding, also known as paramotoring or PPG, is a form of ultralight aviation where the pilot wears a back-pack motor (a paramotor) which provides enough thrust to take off using a paraglider. It can be launched in still air, and ...


References

{{DEFAULTSORT:Motor Glider