The self-sustainer redefined
Our implementation of a two-stroke self-sustainer system is a trend setter. In developing this system, we have advanced the well-known and almost 30 year old self-sustainer concept, and completely re-engineered the propulsion system.
Lange Aviation is well known for developing a very successful electrical propulsion system with the Antares 20E self-launcher.
We applied our skills to improve the design of the self-sustainer system to ensure we fulfilled the following requirements:
- high climb rates, also at altitude
- a reliable engine start in the air
- marked improvements in reliability
- very low levels of vibration
- a high level of comfort
The self-sustainer system is available for the models Antares 18T and the Antares 23T. Having a self-sustainer system with a high rate of climb also makes safe and comfortable flying in alpine conditions possible. Hereby, sufficient power reserves for overcoming adverse environmental conditions were taken into consideration. As a result, high summer temperatures of 30°C or more, high elevation airfields or mountain passes in the Alps, the Andes or the Rocky Mountains should no longer be a safety risk. Based on this, the decision was made to use a very powerful engine, and thus the Antares 18T was equipped with the proven 30 hp Solo 2350C. This engine, being equipped with a reduction belt drive, allowed for the realization of a highly efficient propeller running at low propeller rpm. The propeller diameter is 1.36 m / 4.46 ft. The resulting service ceiling lies above 4,000 m / 13,000 ft.
During the developmental phase it was of fundamental importance to make possible a safe and simple air- start of the engine. Doing so yields a marked increase in pilot safety. In order to achieve this, a propeller with wide outer blades was developed, giving it good performance both during windmilling air-starts and during climb under power. This makes it possible to windmill air-start the engine at a relatively low speed (approximately 110 kph / 60 kts). As every pilot is undoubtedly aware; the glide polar of a sailplane deteriorates substantially when the engine is extended. At 110 kph / 59 kts, the sink rate with extended engine already reaches 1.8 m/s / 354 ft/min, which yields a glide ratio of 1:18. At 130 kph / 70 kts, as required to air-start many self-sustainers, the sink rate has already increased to 2.8 m/s / 550 ft/min, which yields a glide ratio of 1:12.9. This leaves very little leeway if the motor does not immediately run. Regrettably this has repeatedly led to accidents. It can be concluded that the loss of altitude during air- starting is decisive for pilot safety.
Another critical moment occurs through the too low difference in airspeeds between the speed where the engine starts to windmill and the speed where the rpm limiter is triggered, switching off the ignition. If this difference is too small, then the danger exists, that when the engine does not immediately start, speeds are reached where the engine starts, only to immedi- ately be switched off by the rpm limiter. With the Antares 23T, the difference between starting speed and over-speed is approximately 30 kph / 16 kts. This is a speed difference which also less experienced pilots should be able to safely handle.
Furthermore, the problem can be avoided complete- ly if the aircraft is equipped with a throttle lever, so that the rpm limiter can be omitted. A throttle lever is available as an option with the Antares 23T.
Air-starting can be made even safer by installing an electric starter motor. An electric starter motor is also available as an option with the Antares 23T.
Simple and safe operation
One of our most important objectives, also during the design of the Antares 23T, was to achieve a highest possible level of total system safety. With the Antares 20E, this was, amongst others, achieved by relieving the pilot as much as possible during engine operation. Following the example of the Antares 20E, the various engine extension and retraction mechanisms of the Antares 23T are extensively automated. Furthermore, fast engine extension (approx. 14 sec) also helps limiting altitude loss during air-start.
Comfort and performance in powerde flight
Very low levels of engine vibration translate directly into pilot comfort. The stress-levels that the pilot has to endure during powered flight are substantially lower than the levels endured during flight with a “normal” self-sustainer, and radio transmissions are not affected. The low vibration levels also have a highly positive effect on wear and tear on the rest of the aircraft, which again leads to a substantial increase in engine reliability.
As a result, the required maintenance effort for the whole aircraft decreases. In order to achieve this, a novel and very rigid engine pylon was combined with special “two-stroke” engine suspension elements. The design of the reduction gear also helps to dampen out vibrations. The optional combination of cylinder head temperature indications and throttle lever makes it possible to always get optimal performance from the powerful engine.
Fuselage fuel tank
A large fuel tank (16.2 l / 4.3 US gallons) located in the fuselage gives the aircraft a good range, and it also makes additional wing-tanks, which need to be emptied before every road transport, superfluous.