Deflector Air baffle Figure 6-50.  Cylinder baffle and deflector system.  Figure 6-51.  Regulating the cooling airflow.  Figure 6-52.  Augmentor.  Augmentor Exhaust gases  Cooling air  Heated air  Exhaust gas and cooling air mixture the engine. Unless some controls are provided, the engine  could overheat on takeoff and get too cold in high altitude,  high-speed and low-power letdowns. The most common means of controlling cooling is the use of  cowl flaps.  [Figure 6-51]  These flaps are opened and closed  by electric motor-driven jackscrews, by hydraulic actuators,  or manually in some light aircraft. When extended for  increased cooling, the cowl flaps produce drag and sacrifice  streamlining for the added cooling. On takeoff, the cowl flaps  are opened only enough to keep the engine below the red-line  temperature. Heating above the normal range is allowed so  that drag is as low as possible. During ground operations, the  cowl flaps should be opened wide since drag does not matter  and cooling needs to be set at maximum. Cowl flaps are used  mostly with older aircraft and radial engine installations. Some aircraft use augmentors to provide additional cooling  airflow.  [Figure 6-52]  Each nacelle has two pairs of tubes  running from the engine compartment to the rear of the  nacelle. The exhaust collectors feed exhaust gas into the inner  augmentor tubes. The exhaust gas mixes with air that has  passed over the engine and heats it to form a high-temperature,  low-pressure, jet-like exhaust. This low-pressure area in the  augmentors draws additional cooling air over the engine. Air  entering the outer shells of the augmentors is heated through  contact with the augmentor tubes but is not contaminated with  exhaust gases. The heated air from the shell goes to the cabin  heating, defrosting, and anti-icing system. Augmentors use exhaust gas velocity to cause airflow over  the engine so that cooling is not entirely dependent on the  prop wash. Vanes installed in the augmentors control the  volume of air. These vanes are usually left in the trail position  to permit maximum flow. They can be closed to increase the  heat for cabin or anti-icing use or to prevent the engine from  cooling too much during descent from altitude. In addition to  augmentors, some aircraft have residual heat doors or nacelle  flaps that are used mainly to let the retained heat escape after  6-34