Ash.
This wood is one of the most valuable of those employed, being extremely tough and resilient. There are two varieties in use, English and American, the former being considered the better material. It is used mainly for longerons, undercarriage struts, and for all kinds of bent work. It possesses the quality of being readily steamed to comparatively sharp curves, and will retain the bend for a considerable period. The strength and characteristics of ash vary greatly with the climate under which it is grown, and it is also much heavier than spruce, the weight per cubic foot ranging between 40 and 50 lbs. Difficulty is also experienced in obtaining lengths greater than 20 ft., and even in lengths up to that figure, continuity of grain is somewhat rare. It is notable that on various German machines, ash in conjunction with a species of mahogany is used for the laminæ of the air-screw.