SPINS have been responsible for 40 per cent of fatal airplane accidents in the Army in 1927 and 45 per cent of those in the Navy during the last five years. These accidents happen to the most experienced pilots, as no airplane is fool-proof and every representative airplane manufacturer in this Country has had a recent model that has exhibited vicious peculiar spinning qualities. A majority of fatal accidents in the military service abroad result from spins, and it has been unofficially estimated that it costs $200,000 to kill a naval pilot.
The spin is defined and the forces and couples involved are described. The physiological effects on the pilot, and the causes thereof, are explained.
With the object of preventing accidents due to spin, the United States Navy effected negotiations for use of Handley Page wing slots on service airplanes of the Army and Navy and has conducted numerous tests of airplanes fitted with them.
The author describes the principle upon which they operate to nearly double the stalling angle of the airplane and greatly increase the lift per square foot of the wings. Automatic slots, used for maintaining lateral stability, assist in control and are of advantage in landing in and taking off from restricted areas. Manually operated locks are being installed on automatic slots in use by the Navy to enable the pilots to make voluntary spins and, by unlocking the slots, to recover from them at will. On the heavier planes, slots are extended the full length of the leading edge of the upper wing and connected with a trailing-edge flap, so that full advantage can be taken of the high lift from the slot at a normal landing-angle.
For greater lateral control, spoilers are fitted in the top surface of the wings just behind the slot to destroy the lift of either wing and increase the drag in the direction of turn.
The importance of accurate fit of the auxiliary airfoil to the contour of the leading edge of the wing is discussed, and the author narrates several experiences in flight tests, one of which seemed likely to terminate fatally because, as determined afterward, friction prevented the slot on one wing from opening as readily as that on the other. In another test, ice that accumulated on the plane did not prevent the slot opening.
When slots on the Vought Corsair were unlocked in a spin, that on the low wing opened with a bang and brought the plane out of a spin in half a turn. In a dive, the slots can be opened full-out at 140 m.p.h. air-speed by jerking the control stick back with both hands.
A list of Navy planes being fitted with slots, and a list of permissible airplane maneuvers in the Navy, are given.