With auto-towing the Antares 18T and Antares 23T you may now experience a new kind of independence. We have executed first extensive flight-tests to obtain the official approval for the unique launch procedure.
Auto-towing an Antares 18T
Our Antares 18T and Antares 23T are equipped with powerful engines and therefore close to being self-launchable. However, for safety reasons self-launching will not be officially approved. But it is well possible to launch our sustainers with the help of their powerful engines, without any risk. You may take advantage of an almost forgotten technique: auto-tow. The powered ships will so be catapulted up to an altitude where you may easily continue your flight, with or without engine power.
During flight testing on our home airfield Zweibrücken the Antares 18T has self-launched already multiple times. Thanks to the engine’s good performance, the possibility to control its output and last but not least thanks to its starter, which allows firing up the engine already on the ground, self-launches were a good option. On Zweibrücken’s 2,675 meter (8780 ft) runway, where you can land at any time, this has never been a problem. At the end of the runway the glider had always reached a safe altitude of 200 m (660 ft). On short runways and ballasted with water a self-launch would not be a good idea, though - not withstanding the fact that this launch-method is not officially approved. The Solo-engine is missing an important safety feature: double ignition. But what if there is no tow plane available or if there is no tow pilot around - not to be talking about winch launching? For an auto-tow you need just one helper to get airborne, somebody who drives the tow-car. In Germany, according to the current national rules (SBO), a second person has to be in the car to observe the launch procedure. Auto-towing a sustainer equipped Antares is a great option!
Sailplane and tow-car
For a safe auto-tow the sustainer engine has to be taken out and started while on the ground. After getting off tow in about 220 m (720 ft) the glider can continue to climb under engine power.
If for any reason the sustainer should fail during the launch procedure, the aircraft will still reach a release altitude of 200 m (660 ft) and is then able to fly a short and safe pattern with the engine unit extended.
In order to certify the launch procedure, we have performed extensive auto-tow tests in Rheinsdorf, close to Berlin. On the 3 km (9840 ft) grass runway (formerly serving MIG 21s), all eventualities of this launch mode could be tested and were recorded on video for the certification process. In addition to normal launches with engine extended and idling, we also performed starts with the engine running on partial power as well as simulated engine failures (ignition off). We have also tested rope breaks in various heights. A most essential finding: The pilot must act like during a normal winch-launch procedure, and the requirements the car-driver has to meet are very similar to winch operating. In other words; nothing special. Early in the testing it also became clear that it was important to have the engine idling during the tow. This allows the Antares 18T to climb at an optimal speed of 120 to 130 kph (65-70 kts). If partial power is applied during the launch, the risk remains that the cable parachute opens when the tow-car first shifts gears. This situation is clearly visible in the picture below.
..the cable-parachute opens
After taking-off, the sustainer tends to over-rev when running under partial load. The driver of our 4WD BMW 530 found it a bit unusual to have to accelerate as fast as possible, and to to continue this acceleration throughout the acceleration phase. After this, the power could be reduced and the speed of the car was continuously adjusted so that the aircraft flew with the appropriate towing speed. In addition it is recommended to select the car's sports-mode (if available) in order to switch off some of the driver assistance systems. With those systems running we have experienced short retardation moments when shifting gears - even though the car is equipped with a dual-clutch gearbox. These short moments could result in an opening of the cable-parachute, which by all means needs to be avoided.
In order to obtain an official approval for auto-towing we will now have to evaluate comprehensive data. An assignment of almost the size of a student research project. Cable-parachute and coupling could still be optimized. For testing we used a TOST-coupling, which is without any effort quickly hooked on a custom trailer hitch. An additional retrieve-winch on our auto-tow device would have made sense. After launching you would no longer have to wind the cable up by hand. In addition to approving our Antares 18T and Antares 23T, airfields, too, would have to be authorized to execute auto-tows on their facilities. National regulations for this launch-method may be different according to your preferred soaring-country.
Trailer hitch coupling by TOST
The release cable for emergency operation is guided to the front. The cable may also be installed through the back door's rubber seal.
To release the cable from the car in an emergency situation, the driver only needs one hand.