Figure 2-17.  A Schleicher ASH 26e motor glider with the sustainer  engine mast extended. Figure 2-15.  A Grob G109B touring motor glider. Wheel Brakes Sustainer Engines Landing Gear normal landing checklist provides a landing gear check, but  during a low-altitude emergency, important items could be  skipped on any checklist. Therefore, it is good practice to  leave the main gear extended until reaching a safe altitude. Some gliders are equipped with sustainer engines to assist in  remaining aloft long enough to return to an airport. However,  sustainer engines do not provide sufficient power to launch  the glider from the ground without external assistance.  These sailplanes are launched by either aerotow or ground  launch.  [Figure 2-17]  A more detailed explanation of engine  operations can be found in Chapter 7, Launch and Recovery  Procedures and Flight Maneuvers. The wheel brake, mounted on the main landing gear wheel,  helps the glider slow down or stop after touchdown. The  type of wheel brake used often depends on the design of  the glider. Many early gliders relied on friction between the  nose skid and the ground to come to a stop. Current glider  models are fitted with drum brakes, disk brakes, and friction  brakes. The most common type of wheel brake found in  modern gliders is the disk brake, which is very similar to  the disk brake on the front wheels of most cars. Most glider  disk brakes are hydraulically operated to provide maximum  braking capability. Wheel brake controls vary from one glider  type to another. Glider landing gear usually includes a main wheel, a front  skid or wheel and a tail wheel or skid, and often wing tip  wheels or skid plates. Gliders designed for high speed and low  drag often feature a fully retractable main landing gear and a  small breakaway tailwheel or tail skid. Breakaway tail skids  are found on high-performance gliders, and are designed to  break off when placed under side loads.  [Figure 2-18] For safety reasons, the main landing gear remains extended  during the launch process. If there is a tow break or early  release, the pilot needs to focus on a safe return. The pilot’s  Figure 2-16.  A DG-808B 18-meter high-performance glider in self-launch. 2-8