1 2 3 4 5 Cowl flap control level 1 Position bracket 2 Cowl flaps 4 Right cowl flap control 5 Left cowl flap control 3 Figure 6-54.  Small aircraft cowl flaps.  increases, absorbing more heat and the engine temperature  tends to decrease. Good inspection and maintenance in the  care of the engine cooling system aids in overall efficient  and economical engine operation. Maintenance of Engine Cowling Of the total ram airflow approaching the airborne engine  nacelle, only about 15 to 30 percent enters the cowling to  provide engine cooling. The remaining air flows over the  outside of the cowling. Therefore, the external shape of the  cowl must be faired in a manner that permits the air to flow  smoothly over the cowl with a minimum loss of energy. The engine cowling discussed in this section is typical of  that used on many radial or horizontally opposed engines.  All cooling systems function in the same manner, with minor  engineering changes designed for specific installations. The cowl is manufactured in removable sections, the number  varies with the aircraft make and model. The installation  shown in  Figure 6-55  contains two sections that are locked  together when installed. The cowl panels, made from sheet aluminum or composite  material, have a smooth external surface to permit  undisturbed airflow over the cowl. The internal construction  is designed to give strength to the panel and, in addition, to  provide receptacles for the toggle latches, cowl support, and  engine air seal. An air seal is constructed of rubber material, bolted to a  metal rib riveted to the cowl panel.  [Figure 6-55]  This seal,  as the name implies, seals the air in the engine section,  preventing the air from escaping along the inner surface  of the panel without circulating around the cylinders. The  engine air seal must be used on engines that have a complete  cylinder baffling system that covers the cylinder heads. Its  purpose is to force the air to circulate around and through the  baffle system. Inspect the cowl panels during each regular  engine and aircraft inspection. Removing the cowling for  maintenance provides an opportunity for more frequent  inspection of the cowling. Inspect the cowling panels for scratches, dents, and tears  in the panels. This type of damage causes weakness of the  panel structure, increases drag by disrupting airflow, and  contributes to the starting of corrosion. The cowling panel  latches should be inspected for pulled rivets and loose or  damaged handles. The internal construction of the panel  should be examined to see that the reinforcing ribs are not  cracked and that the air seal is not damaged. The cowl flap  hinges, if equipped, and cowl flap hinge bondings should be  checked for security of mounting and for breaks or cracks.  These inspections are visual checks and should be performed  frequently to ensure that the cowling is serviceable and is  contributing to efficient engine cooling. 6-36