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A-9 / A-4b Boost-Glide Vehicle

The A-4 with wings was initially designated the "Glider A-4" and then "Wing Projectile" [Flossengeshoss] in 1939, before being designated the A-9 in 1940. During World War II, the Germans developed the V-2 rocket and worked on winged missiles such as A-9, A-10, and A-4B. To the modern eye the V-2 resembled a classic spaceship, complete with fins. It is more appropriate to say that spaceship designs resemble the V-2, for that missile was very much in the forefront during the postwar years, when science fiction was in its heyday. The V-2 needed fins to compensate for the limited effectiveness of its guidance, and their design was trickier than it looked.

The V-2’s fins were designed with only minimal support from Peenemunde’s big supersonic wind tunnels. But these tunnels came into their own later in the war, when investigators began to consider how to stretch this missile’s range by adding wings and thereby turning it into a supersonic glider.

In haste and desperation, winged rockets entered the realm of hardware late in the war, as an offshoot of the V-2 program. The standard V-2 had a range of 270 kilometers. Following the Normandy invasion in 1944, as the Allies surged into France and the Nazi position collapsed as the Russians closed in from the east, a group of rocket engineers led by Ludwig Roth sought to stretch this range to 500 kilometer by adding swept wings to allow the missile to execute a supersonic glide.

Dornberger and Von Braun faced insistent demands that they pull a rabbit from a hat and increase the V-2’s range. The rabbit was the A-9, with its wings promising a range of 465 miles, some three times that of the standard V-2.

Perhaps the most important result of the German effort in this field was to show that winged missiles were superior in performance to finned missiles. Thus, the next stage in the development of the V-2 rocket was to have been the addition of wing. The necessary wind-tumiel tests had been made in connection with the development of the winged ground-to-air rocket Wasserfall and ballistic computations had shown that this change alone would increase the range of the V-2 rocket from about 250 to about 400 miles.

Once the Germans came up with a good configuration for the V-2, they stuck with it. They proposed to use it anew in a two-stage missile that again sported fins that look excessively large to the modern eye, and that was to cross the Atlantic to strike New York. But there was no avoiding the need for a new round of windtunnel tests in studying the second stage of this intercontinental missile, the A-9, which was to fly with swept wings.

As early as 1935 Adolf Busemann, another colleague of Prandtl, had proposed the use of such wings in supersonic flight. Walter Dornberger, director of V-2 development, describes witnessing a wind-tunnel test of a model’s stability.

The model had “two knifelike, very thin, swept-back wings.” Mounted at its center of gravity, it “rotated at the slightest touch.” When the test began, a technician opened a valve to start the airflow. In Dornberger’s words, “The model moved abruptly, turning its nose into the oncoming airstream.

After a few quickly damping oscillations of slight amplitude, it lay quiet and stable in the air that hissed past it at 4.4 times the speed of sound. At the nose, and at the edges of the wing supports and guide mechanism, the shock waves could be clearly seen as they traveled diagonally backward at a sharp angle.

As the speed of the airflow fell off and the test ended, the model was no longer lying in a stable position. It made a few turns around its center of gravity, and then it came to a standstill with the nose pointing downward. The experiment Dr. Hermann had wished to show me had succeeded perfectly. This projectile, shaped like an airplane, had remained absolutely stable at a supersonic speed range of almost 3,500 mph.”

Work on the A-9 languished for much of the war, for the V-2 offered problems aplenty and had far higher priority. But in 1944, as the Allies pushed the Germans out of France and the Russians closed in from the east, Dornberger and Von Braun faced insistent demands that they pull a rabbit from a hat and increase the V-2’s range. The rabbit was the A-9, with its wings promising a range of 465 miles, some three times that of the standard V-2.

Much was uncertain about the A-9’s aerodynamics and guidance, yet the leading Peenemünde engineers seemed to prefer the A-9 because it was an interesting problem.

Peenemunde’s Ludwig Roth proceeded to build two prototypes. The V-2 was known to its builders as the A-4, and Roth’s A-9 now became the A-4b, a designation that allowed it to share in the high priority of that mainstream program. The A-4b took shape as a V-2 with swept wings and with a standard set of fins that included slightly enlarged air vanes for better control. Certainly the A-4b needed all the help it could get, for the addition of wings had made it highly sensitive to winds.

The venture was ill-starred from the outset. When winds blew on the wings during liftoff, the marginal guidance system could not prevent the vehicle from rolling and going out of control. In this fashion, the first winged V-2 crashed within seconds of its December 1944 launch. A month later, a second attempt was launched successfully and had transitioned to gliding flight at Mach 4 when a wing broke off causing the missile to break up high in the air.

General Dornberger describes how this second flight went much better: “The rocket, climbing vertically, reached a peak altitude of nearly 50 miles at a maximum speed of 2,700 mph. [It] broke the sound barrier without trouble. It flew with stability and steered automatically at both subsonic and supersonic speeds. On the descending part of the trajectory, soon after the rocket leveled out at the upper limit of the atmosphere and began to glide, a wing broke. This structural failure resulted from excessive aerodynamic loads.”

This shot had achieved its research goals, for it was to demonstrate successful launch and acceleration through the sound barrier, overcoming drag from the wings, and it did these things. Gliding flight was not on the agenda, for while windtunnel tests could demonstrate stability in a supersonic glide, they could not guard against atmosphere entry in an improper attitude, with the A-4b tumbling out of control.