How long is the engine operating time with fully charged batteries?
13 minutes at maximum power and maximum climb speed. A longer powered engine operating time is achieved at horizontal flight, the flight endurance depends on the aircraft speed. The largest distance is covered by alternatingly climbing at optimum climb settings, retracting the motor, and then gliding at optimum glide angle.
The batteries are warmed up to reach the highest efficiency. How long does it take?
This is dependent on the battery temperature before you start heating. The batteries heat at a rate of approximately 1°C/min (1,8°F/min). For optimum performance the batteries are heated to between 20 and 30°C. However, power is available also at lower temperatures. The charger can provide energy for battery heating while the aircraft is on the ground. During the flight the batteries are kept at a constant temperature. This needs only a small amount of energy, as they are very well isolated.
Once I have used the whole climbing energy of the batteries, is it possible to extend
the motor and taxi back to the hangar?
Taxiing requires very little energy. There will, even after a “full discharge”, normally be enough energy left in the batteries to allow extending the motor and taxiing back to the hangar. The pilot should naturally make sure that the cell voltages remains within operating specs.
Is it possible to use the propeller to recharge the batteries while descending?
In theory, the combination propeller, engine and power-electronics can run as a wind turbine. However, the propeller is highly inefficient in this mode, so it would not really pay off.
Is it possible to "refuel" the batteries with solar cells in-flight?
There are several arguments against this technology:
- The surface of the fuselage and the elevator is not sufficient to charge the batteries. In order to achieve the necessary energy production the wing surface would have to be covered, too.
- The surface quality of the solar cells is not as good as a polished glider surface. The actual gliding performance of the Antares cannot be achieved with a wing fully covered with solar cells.
- The cost of this technology is very high, as the manufacturing and finish cost of such wings have to be added to price of the solar cells.
- White gelcoat is utilized to reflect the maximum amount of solar energy while solar cells are designed to capture as much of it as possible. The low efficiency of solar cells (max 25-30%) means that a lot of energy is turned into heat. Making the composite structure of the wing capable of dealing with this heat is very expensive.
Can the Arcus E run on Fuel cells instead of on Batteries?
The Fuel cell is an interesting technology. Sadly, current fuel cell technology is not capable of delivering the high power required for takeoff and climb. One could imagine a system where batteries provide most of the power for take-off and climb while a fuel cell system slowly recharges the batteries during unpowered flight. However, assuming we maintain system weight, this would mean a reduction in number of batteries and thus a substantial reduction in instantly available altitude. It would also mean a dramatic increase in system price and complexity. As a result, we do not see the application of fuel cells in series aircraft in the near future.
However, we continue to monitor this technology closely.