The auto-tow launch mode gives the Antares 18T and Antares 23T new independence. Extensive testing for launch type approval was conducted in October 2015.
With Antares 18T and Antares 23T, self-launches are almost possible. For reasons of safety, there is no approval. By contrast, by using an almost forgotten launch method, the autotow, these self sustainers can -thanks to their powerful engines – be launched into the air without risk and with very little effort. This allows them to reach altitudes from which they can continue to fly independently.
At our home airfield Zweibrücken, the Antares 18T has been operated in self-launch mode for testing purposes. The good performance of the engine, the possibility of power control and not least the starter, with which the engine can be started already on the ground, made this possible. With the 2675 m ( 8780 ft ) long runway at Zweibrücken, onto which a landing would be possible again at any time, this was also no problem. At the end of the runway, a safe height of 200 m was achieved. On short runways and with water ballast, however, self-launching is not an option – not to mention the fact that there is no certification for it. The Solo engine also lacks an important safety aspect: dual ignition. But what to do if no tow plane is available or the tow pilot is missing – not to mention a winch operation? Auto-tow requires just one helper to get behind the wheel. In Germany, the current SBO still requires an additional observer inside the vehicle. This makes this launch mode highly interesting for the Antares with a self sustainer engine.
To safely perform an auto-tow, the engine is already extended and started while on the ground. After releasing at 220 m, it is then possible to continue the climb using the engine.
If the engine fails during the towing operation, a release altitude of 200 m is still achieved. In this case, a shortened circuit can then be flown safely with the engine extended.
Extensive auto-towing tests were completed in Reinsdorf near Berlin for the approval of this type of launch. On the three-kilometer grass runway, all eventualities of this type of takeoff were played out and recorded on video for the approval process. In addition to ‘normal take-offs’, take-offs with the engine extended and at idle, take-offs with partial load, with simulated engine failure (ignition off) and also rope breaks at various altitudes were tested. The most important finding of these tests is that the pilot does not behave any differently than during winch launching, and the requirements placed on the driver are the same as for a winch operator. Nothing special, then. Another important fact that quickly became apparent was that the engine must be idling during the towing process. Then the Antares 18T can climb at its optimum speed of 120 to 130 km/h (109 to 118 kts). If the engine is operated at partial load during the starting process, there is a risk that the rope parachute will open during the first gearshift of the car.
After takeoff, an engine at partial load tends to overspeed. Somewhat unusually for the drivers of the four-wheel drive BMW 530 that was used: they had to accelerate very quickly right at the start of the launch and only reduce to the correct towing speed after the acceleration phase. It is also advisable to deactivate some of the driver assistance systems by selecting the Sport driving mode. If the many electronic assistants were not switched off, there would, despite the dual-clutch gearbox, be short delays during gear changes which in turn could cause the cable parachute to open. And this had to be prevented at all costs.
A Tost hook, which can be effortlessly be fitted to the trailer hitch, was used for the tests. In addition to the approval for the Antares 18T and Antares 23T, the airfields must of course also include the auto-tow take-off mode in their approval. The national regulations apply to the inclusion of the launch mode Auto Tow in the permit.
Auto-tow launching is a much desired option for Antares 18T and Antares 23T pilots, as it provides even more independence for these aircraft with self-sustainer engine. The first extensive test launches in auto-tow with the Antares 18T showed that this type of launch can be a useful addition to winch launching or aerotow.
Auto-towing trials for the Antares 23 were conducted at Reinsdorf near Berlin. The aim was to investigate whether the Antares 23 could still reach altitudes from which it could continue flying independently when towed by a car, even with a full water ballast. After all, the Antares 23 with full ballast tanks weighs almost a metric ton ( 2200 lb ). The data obtained during the test were also be used to verify our mathematical models of auto-tow launch for large flight masses. Since the maximum flight mass is identical for the Antares 23T and the Antares 23E, it was possible to use an Antares 23E that happened to be available for testing.
Unlike the flight test with the Antares 18T, the motor remained retracted in the fuselage during testing with the 23. For purposes of certification, the aircraft had to be flown up to the maximum permitted speed for winch launch – which was well beyond the operating speed range for the motor.
It was found that with increasing towing speed greater release heights were achieved. During the first flights with a take-off mass of 642 kilograms ( 1020 lb ), i.e. without water ballast, with flap position +1 and a towing speed of 140 to 150 kph (76 to 81 kts ), an altitude of around 280 meters (920 ft) was achieved. At speeds of 160 to 165 kph ( 86 to 89 kts ), this figure reached 300 meters ( 984 ft ). This occurred in a headwind of 20 to 30 kph, ( 11 to 16 kts ) which came from the side at around 30 degrees.
A 258 hp BMW 530d Touring with all-wheel drive was used as a towing vehicle during the test flights on the grass field, which was a good two kilometers long (6560 ft) (we did not use the full length of about 2,800 m / 9190 ft ). The dyneema rope used had a length of 370 meters (1214 ft).
The flights with full water ballast – the Antares 23E then weighs 901 kilograms ( 1986 lb ) – resulted in significantly lower release altitudes. Takeoffs at about 140 kph ( 76 kts ) towing speed ended at 200 meters ( 656 ft ) altitude, tows at 145 to 155 kph ( 78 to 84 kts ) at about 250 meters ( 820 ft ). This meager altitude gain speaks rather against the auto-tow launch with the 23 with water ballast.
Control during towing was similar to that during winch launch and brought no surprises. The required control forces were low.. No large control surface deflections were required to keep the wings horizontal from the start of the takeoff run. Moreover, with a slightly tail-heavy trim, it was not necessary to apply too much elevator pressure during the climb.
With the flights we found that the Antares 23E takes off at 70 to 80 kph (43 kts). The speed increases further when a clear climb attitude is assumed. In this phase it is important that the tow vehicle continues to accelerate above 90 kph (49 kts), other then that, the pilot must be careful not to adopt too large a climb angle, as is also the case for winch launching. The launch is safe and effective at flight speeds above 120 kph ( 65 kts ). For this, the car has to accelerate to around 110 kph ( 59 kts ). Of course, with a corresponding headwind, a lower speed is sufficient. The Tost coupling, which can be easily attached to trailer hitches, was again used for the tests.
The Antares will be certified for auto-towing without water ballast for types 18T, 21E and 23E/T. To be able to use it, pilots need a license entry for auto-towing and airfields must include auto-towing as a take-off mode in their permit.