Self-sustainer engine

Self-sustainer redefined

Our two-stroke self-sustainer system is trend-setting. We have consequently advanced the well-known and almost 30 year old self-sustainer concept, and completely re-engineered the propulsion system.

The second propulsion system besides our very successful electric self-launcher Antares 20E had to meet the following requirements:

  • high climb rates, also at high altitudes
  • a reliable engine start in the air
  • noticeable improvements in terms of reliability
  • a very low vibration level
  • a high level of comfort

The self-sustainer system will be available for our models Antares 18T and Antares 23T. A high climb rate shall ensure safe and comfortable flying in alpine conditions. Sufficient power reserves to manage adverse terrain and weather conditions were taken into consideration. As a result, high temperatures of 30°C and more, high altitude airfields or mountain passes in the Alps, the Andes or the Rocky Mountains should no longer be a safety risk. Based on these guidelines, we decided to use a very powerful engine, and equipped our Antares 18T with the proven 30 hp Solo 2350C. This engine has a reduction belt drive and thus provides high propeller efficiencies at low propeller speeds. The propeller’s diameter measures 1.36 m / 4.46 ft. The resulting service ceiling is above 4,000 m / 13,000 ft.

Safe return

A safe and easy in-flight engine start was our highest priority during the development phase. This would for sure increase the pilot’s safety. In order to achieve this goal, we developed a propeller with wide outer blades. This added width increases the efficiency during wind milling starts as well as while climbing. The engine can thus be airstarted at relatively low speeds (approximately 110 kph / 60 kts) by windmilling the engine. As every pilot knows: a sailplane’s glide polar degrades extremely with the engine extended. At 110 kph / 59 kts, the sink rate of a glider with an extended engine reaches 1.8 m/s / 354 ft/min, which comes up to a glide ratio of 1:18. At 130 kph / 70 kts, as required to windmill-start many other sustainers, the sink rate already increases to 2.8 m/s / 550 ft/min, which equals a glide ratio of 1:12.9. This leaves only a very small margin when the motor does not fire up immediately. Unfortunately this problem has repeatedly led to accidents. The loss of altitude during in-flight starting is therefore crucial for the pilot’s safety.

While the altitude loss with a starter is only about 15 meters, the windmill starting procedure at 110 km/h takes already 55 meters.
When wind milling with 130 km/h, you will need 93 meters - almost twice the altitude as at 110 km/h. At 140 km/h the loss of height increases to a drastic 130 meters.
For security reasons the necessary windmill speed should not be higher than 120 km/h. Regarding these aspects our Antares 18T’s engine, which has an especially designed propeller, securely starts already at 110 km/h.

Another critical moment occurs because of a too small margin between the speed when the engine starts to windmill and the speed which triggers the engine speed limiter. The latter switches off the ignition. If this speed margin is too small, a pilot might - when the engine does not immediately fire up - more or less unintentionally fly too fast. At this point, the speed limiter will immediately shut the ignition back down while the engine tries to fire up. With our Antares 23T the margin between starting up the turbo and over-speeding is approximately 30 kph / 16 kts, a speed difference which even less experienced pilots should be able to safely manage.

The problem can be completely avoided when equipping the aircraft with a throttle lever. In this configuration an engine speed limiter is no longer required. We are offering this equipment optionally. 

Finally, in-flight starting gets even safer by installing an electric starter motor, which is also available as an option.

Simple and safe operation

It was our most important objective while designing the Antares 23T as well as our other models to achieve the highest possible safety level for the complete system. As with the self-launching Antares 20E, the pilot will best possibly be unburdened during engine operation. Following the example of our self-launching Antares model, the engine extension and retraction mechanism is mostly automated. A quick engine extension of roughly 10 seconds limits the altitude loss to a minimum during an in-flight start.

Comfort and performance in powered flight

A very low level of engine vibration directly translates into pilot comfort. The pilot’s stress-level during powered flight in an Antares 23T is substantially lower than in a “conventional” self-sustainer, plus the radio communication is not affected. The most important positive effect of a low vibration level, though, is in removing material fatigue issues. This results in superior reliability and low maintenance of the whole system.

We have achieved this by designing a novel and very rigid engine pylon and a specially cushioned suspension of the engine. The construction of the reduction gear also helps to dampen vibrations.

An optional display of cylinder head temperature combined with the setting of the (optional) throttle cable facilitates an operation of the powerful engine always at its optimum.

Fuselage fuel tank

A large fuel tank (16.2 l / 4.3 US gallons) located in the fuselage takes care of a good range during powered. Additional wing-tanks, which would have to be emptied before every road transport, are redundant.