Air Force Bases

Propulsion and Aerodynamic Test Program Jan 1947 - Dec 1947

In November 1946, while the field test program was still in progress and before the seriousness of the booster difficulties was fully realized, a planning conference was held at WSPG to map out a tentative but optimistic missile test program for the next two years. This program was designed to lead in a systematic sequence of stages to the development of a practical missile which could be flown under command of radar and computer as soon as the latter equipment became available. Thus the system guidance loop would be demonstrated in action. The development test program envisioned the successive construction of a family of missiles controllable to a gradually increasing degree. In case of troubles or malfunctions, it was decided that the firing program would be interrupted or expanded and recognized errors rectified before proceeding.

Radar Development

In 1947 radar development effort was directed toward the determination of the best antenna configuration and antenna axes orientation. After investigating various alternatives, the requirement of tracking the target through the zenith was eliminated. This region was not considered sufficiently important to justify the additional complexity in a guided missile system in which the intercepts usually occur on the incoming course. Considerable development and experimental work was also devoted to radar gain control. Since the speed of response of the gain control circuits in a monopulse was no longer limited by the lobing rate, the initial work was directed toward proving an instantaneous gain control circuit in which the gain would be properly set for the level of such return pulse. Such a circuit was tried successfully but was later replaced by a simpler wide-band integrating type of automatic gain control.

During the fall of 1947, the improvised experimental monopulse radar set was equipped with a 6-foot X-band lens and put through extensive three-coordinate operation, tracking various aerial targets at Whippany, New Jersey. Accuracies considerably better than one angular mil were consistently attained for short periods and one decimil deemed within reach. While much work was destined to be done before achieving consistent high accuracy, the superiority of this type radar over any previously available system was already convincingly demonstrated.

While the above tracking tests were in progress, basic advances were made in the improvement of rapid-fading plumbing for the monopulse radar then under development for the field test program at WSPG. Comparison studies were conducted on hybrid rings and tees to determine the advantages of each, particularly in regard to wide-band operation. Hybrid rings in tandem proved to be the better and were adopted for the final R&D monopulse plumbing. At the same time, studies were made to find the best method of fabricating the plumbing to meet the close mechanical tolerances required.

The NIKE-47 test missiles were beacon-tracked at WSPG with an SCR-584 radar modified for operation in the X-band. Radar tracking in these tests was generally good. Acquisition of missile in the launcher and automatic tracking of missile during boost and separation were accomplished and verified as a solution to the missile acquisition problem. However, the microphonic response of the beacon to boost shock was troublesome. A greater signal output was considered necessary to improve the signal-to-noise ratio, and better antenna pattern in the missile tail aspect appeared desirable.

The 1947 missiles were also equipped with improvised "fail-safe" circuits to enable detonation of the missile in the event of loss of contact between the ground radar and the missile-borne beacon.

Computer

Studies of the various computer sections and their detail design were continued. The problem of radar-to-computer data transmission received particular attention due to the great accuracy required of the voltages representing the missile and target positions in space. Two possible methods were under consideration: (1) the construction of exceptionally accurate potentiometers to be directly driven by the radar shafts, as in gun fire director systems; or (2) a two-speed synchro data transmission system driving two-speed potentimeters in the computer.

The original AAGM assumptions on the aerodynamic capabilities of the missile proved to be unnecessarily conservative. Investigation revealed that the time of flight could be shortened and computer computations simplified by adopting a flight path which-though departing from the optimum in range-would follow a single dive order sustained until the missile had turned from vertical flight onto a ballistic trajectory through the predicted point of intercept. This control scheme was eventually adopted for the NIKE R&D Test System.

The original scheme of stabilizing the missile in roll was replaced by a more flexible scheme which was actually easier to mechanize but conceptionally more involved. In place of keeping the "belly" fins precisely vertical, it holds the plane of the "transverse" fins normal to the vertical orientation plane in which the free gyro is released at take-off.

NIKE-47 Missile

Because the NIKE-47 was designed to serve generally the same functions in tests of launching and unmaneuvering vertical flight as the NIKE-46, the basic configuration of the 1946 missile was retained. However, in light of the previous year's test results, several modifications were made to incorporate newly-designed equipment.

The missile boat-tail section was redesigned and strengthened, with corresponding booster structural changes, for improved application of boost thrust and smoother separation of the booster from the missile. Improved rigidity of the booster assembly was effected by an overall strengthening of components, together with structural additions to give improved guidance of booster along launcher rails, to place the boost thrust against the missile base, and to prevent side movement of the booster relative to the missile during separation. Pointed caps which had previously served to streamline the booster motors and apply the thrust to the trailing edge of the missile rear fins, were deleted. The after-body of the NIKE-47 was designed to rest snugly in a cylindrical sleeve mounted within the booster structure. This arrangement afforded positive contact between the booster and missile during separation, thus preventing the booster from developing an angle of attack or sideward velocity before the boat-tail was sufficiently clear of the booster structure, as had been experienced in some of the 1946 tests.

A number of changes were also made in the internal design and performance characteristics of the multiple rocket booster to correct the separation problems arising from uneven or unequal thrust forces during the boost phase, The single Aeroplex K-6 propellant grain used in the NIKE-46 booster was replaced with two grains of Aeroplex K-14, which burns at a slower rate and with consequent lower chamber pressures. The thrust was reduced from a nominal 22,000 pounds to 18,000 pounds per motor, but the duration of burning was extended from about 2 to 2.5 seconds. Changes were made to give more positive support to the propellant grain, and measures were taken in the field to keep the propellant grains at fairly even temperatures during a conditioning period prior to the firing. A new igniter was also developed.

The power plant system for the NIKE-47 was rebuilt around an improved design of the Aerojet Mode1 21-AL-2600 acid-aniline motor. This motor was ten pounds lighter than that of the NIKE-46, but it possessed essentially the same capabilities, delivering 2600 pounds (sea level) thrust for about 21 seconds. In the new power plant system, a single-unit inertia-actuated starter valve-propellants feed regulator replaced the two previous separate components. Burst diaphragms in the propellant tank air inlet lines not only prevented premature mixing of the fuel and oxidizer, but also the premature entry of propellants into the motor.

NIKE-47 Test Program

Five dummies (without motors) and four powered missiles were fired in the NIKE-47 series. These tests were conducted as a continuation of the tests begun in 1946 to study launching techniques, and to obtain additional aerodynamic and performance data on the missile in free flight. The NIKE-47 firings were conducted in the following order:

DateRound No.Missile No.
9-22-47D47-E
9-26-47E47-F
10-7-47F47-G
10-16-47G47-H
10-23-47H47-I
10-28-471047-12
10-30-471147-13
12-9-471247-15
12-9-471347-16

The five dummy missiles (Rounds D through H) were made of hollow steel bodies with standard missile aft sections and fixed fins. Satisfactory flights were obtained in all dummy rounds, their peak altitudes ranging from 29,300 to 34,000 feet. The boosters for these rounds were equipped with nozzles outwardly canted (four at 15 degrees and one at 17 1/2 degrees) to minimize any turning moment about the center of gravity due to uneven thrust cessation among the four independently burning rockets. Clean separation was indeed achieved. Telemetering transmitters carried on the boosters gave good, informative records of booster burning pressures. With the various improvements in powder grain support and in nozzle manufacturing, it seemed that the quadruple boosters now gave an acceptable performance and separation. However, the deviation from the predicted climb path was excessive. Precise inspection and measurements of the canted nozzles disclosed dimensional variations which gave rise to unpredictable burning behavior and fusion, and hence thrust eccentricities, the elimination of which would have required the development of new manufacturing processes. To obviate this difficulty, it was decided to return to straight nozzles for the four powered missile launchings.

Following the dummy tests, four powered but uncontrolled missiles were fired, all of them with the new Aerojet power plant already described. With one exception, they gave evidence of satisfactory boost and separation. In one round the separation method performed admirably under extremely adverse conditions. Two of the four rounds attained peak altitudes of about 120,000 and 115,000 feet in smooth trajectories; the other two rounds were frustrated by premature detonation. Analysis of the aerodynamic data obtained in the tests showed that the drag was very close to the originally estimated values or much higher than the 1946 values. This effect was to be further investigated in the 1948 flights.

Launcher and Accessory Devices

Several improvements were made on the launcher. Its four 20-foot rectangular cantilever rails were replaced by heavy walled steel tubing which was easier to repair or replace in case of accidental damage. Guiding action during launch was now applied entirely to the booster structure rather than partly to the missile body. A second launcher was built portable so that it could be disassembled for transportation and set up on any flat surface in the field for firing. Erection was accomplished by means of a hydraulic strut instead of the electric winch of the earlier models. Eventually the launcher rails were shortened by three feet so that the effective guide length was reduced from fifteen and one-half feet to twelve and one-half feet, which was considered to be the best compromise between guidance and accessibility.

A number of accessory devices were developed which greatly facilitated the assembly, checkout, and handling and servicing of the missiles at the Proving Ground and enabled the crews to carry on a continuous work schedule.