{"id":3346,"date":"2011-05-18T11:20:29","date_gmt":"2011-05-18T18:20:29","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=3346"},"modified":"2011-05-18T11:20:29","modified_gmt":"2011-05-18T18:20:29","slug":"sustainable-soaring","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/sustainable-soaring\/","title":{"rendered":"Sustainable Soaring"},"content":{"rendered":"

Glaser-Dirks Flugzeugbau, the German sailplane manufacturer, has introduced the DG-1001te<\/a>, a two-seat, electric turbo craft that can sustain flight and even show a modest rate of climb, but is not capable of self-launching.<\/p>\n

The \u201cturbo\u201d designation is common on European craft that rely on a pop-up motor to maintain flight in unfavorable soaring conditions.\u00a0 Following an aero-tow or winch launch, the sustainer engine is used to allow \u201cget-home mode\u201d operation, or to maintain altitude while the pilot searches for areas of better lift.<\/p>\n

Until recently, single- and two-cylinder Solo two-stroke engines served on many applications.\u00a0 Electric motors are beginning to find favor, though, because of their ease of starting and the fact that their light weight and high power output counterbalance the added weight of batteries.\u00a0 The battery pack can be kept small because of the small power output required to keep sailplanes airborne \u2013 under five horsepower at best gliding speed for even large birds.<\/p>\n

Luka and Matija Znidarsic, father and son team from Slovenia, led the charge for electric sustainers with a nose-mounted propeller drive and controller of their own design which they installed and flew on an LAK-17a.\u00a0 Later, they enlarged the motor and installed it in the smaller Silent 2 to achieve self-launching capabilities.\u00a0 Such a system requires a small enough propeller to allow folding it along the nose of the aircraft and a high enough landing gear clearance to avoid striking the unfolded propeller on the ground.<\/p>\n

For Motorseglers<\/em> that cannot accommodate a propeller in their nose (it helps if the plane has a nicely symmetrical shape to allow incorporating a prop spinner seamlessly), the \u201ctraditional\u201d folding mast and propeller are most common.\u00a0 Glaser Dirks has opted for this on the DG-1001te, the electric sustainer version of their flagship soarer.<\/p>\n

The firm makes a Solo-powered self-launching 1001M, a small Solo-engined 1001T, and an electric-powered 1001te.\u00a0 The latter required \u201ca comprehensive market analysis\u201d in an attempt to find a practical motor.\u00a0 After several vendors were unable to meet the production or time-line requirements for DG, the designers turned to Enstroj, the Slovenian company usually associated with Pipistrel.<\/p>\n

\"\"<\/a>

DG-1001te in flight. Note small diameter of Emrax motor, simple mount<\/p><\/div>\n

The standard Emrax 222 can deliver a peak 30 kilowatts at 1,700 rpm, but DG elected to modify the windings to increase the output speed to 2,650 rpm.\u00a0 72 Kokam SLPB7821621H cells are used for energy storage.\u00a0 To mitigate fire risks, designers took several measures.\u00a0 First, they developed a battery management system to protect individual cells from harmful over- and under-voltages.\u00a0 They inserted the cells on mounting plates of high-strength aramid flame-retardant resin.\u00a0 They used aluminum covers for the battery packs to dissipate heat.\u00a0 They also built two battery compartments, the largest with 48 cells mounted in the motor bay and the smaller with 24 cells in the former fuel tank area.\u00a0 Batteries in both areas are arranged in 12-cell modules, each with monitoring electronics.<\/p>\n

Pitronik supplied the motor controller, adapted from their unit normally used with the Emrax 222.\u00a0 An Eltek Valere battery charger replenishes energy between flights, and everything is connected through a CANBus interface.<\/p>\n

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DG-1001te motor compartment, showing smaller of two battery packs and simple retraction system <\/p><\/div>\n

In its current configuration, the motor produces 22 kW at 2,650 rpm for a weight of 11 kilograms (24.2 pounds) and a controller weight of 5.6 kg (12.32 pounds). \u00a0<\/strong><\/p>\n

According to DG, test runs show the electric sustainer to produce about 15 percent higher output than the internal-combustion version, with a higher rate of climb for pulling out of down air.\u00a0 With two motor runs of about 10 minutes possible (20 minutes being the demonstrated run time) on the moderate battery packs, the plane should be able to climb far enough to gain 100 kilometers (62 miles) in gliding distance.<\/p>\n

Videos of the power system being tested show a 10-second extension to start time, with no extra seconds required for pressing a primer bulb, attempting a restart, or other potentially disastrous time wasters associated with two-stroke mid-air restarts.<\/p>\n