Germany's most efficient dive bomber, the Dornier 217E, has recently been equipped with an umbrella-type diving brake described as a "tail drogue." Superficially resembling a set of autogyro rotors, this device is the latest approach to problems of controlled. absolute deceleration of a diving airplane, which may ultimately supplant the split trailing-edge flap and the venetian blind flaps popularized on the Junkers Ju-87 and other current combat types. These conventional flap designs presented several distinct disadvantages in warfare. First of all, they imposed additional loading on plane wings already seriously taxed by the high-speed dive and subsequent pullout. They also increased the plane's vulnerability to antiaircraft fire because bullets and fire burst which formerly punctured the wing without serious consequences might easily ruin a diving flap. With one flap out of commission, the plane became aerodynamically unsound and resultant under-wing turbulences frequently caused crashes.
Thus, the tail-type diving brake, or drogue, gives certain tactical advantages to the Dornier 217E. Fixed to an activating post behind the tail assembly, the four-radially-arranged braking flaps are moved into the flight path whenever deceleration is required. Apparently, the flaps can be set in several positions, with their angle determining the amount of drag.
British analyses of the drogue indicate that the flaps are electrically operated by means of a simple screw and nut gear unit. The flap members (Fig A in accompanying sectional drawing) are attached by eccentric rods (Fig B) to the nut member (Fig C) which is, in turn, threaded into the screw tubular shaft (Fig D) bearing-mounted in the support frame (Fig E). A bracing member near the middle of the flap members is connected and pivotally anchored to the brace (Fig F). Provided with aerodynamic surfaces, these braces may act as supplementary brakes. An electric motor moves the screw member either clockwise or counter-clockwise, thus moving the brake.
Obviously, the drogue brake flaps, like more conventional types, are also vulnerable to flak fire. But the loss of any one or several members would not set up turbulences great enough to affect behavior of the airplane. All disturbance would be behind the plane. Actually, late versions of the drogue-equipped Dornier have a four-bolt jettison gear which releases the entire braking system if it is damaged and becomes at all troublesome. Provision is also made for quick removal of the mechanism and substitution of a streamlined tail cone whenever the plane is assigned to horizontal bombing missions. Subsequent appearance of Dorniers with and without the brake system has established its wide use on both horizontal and dive bombing.
This article was originally published in the November, 1942, issue of Air Tech magazine, vol 1, no 2, p 6.
The original article includes the referenced drawing and 5 photos of D0-217s with the dive brake in various stages of deployment.
Credits to European.