NIKE 1948 Field Test Program
During the summer and fall of 1948, 26 full-scale NIKE firings were conducted at WSPG. These were divided into three test series--48-0, 48-1, and 48-2-each based on a separate design of the NIKE for the phase development plan of the project. From these designs emerged NIKE Models 484 and 490, which were to constitute the final missile configuration.
Three NIKE missiles (Rounds 31, 32, and 33) not expended in the 1948 program were returned to DAC for modification of the ram pressure system and control system. These were reserved for use in the first part of the 1949 field tests.NIKE 48-0 Test Series
In a group designated as the NIKE 48-0 series, four Model NIKE-47 live (powered) missiles and one dummy, which had not been expended the previous year, were modified and fired in free-flight tests with the new Allegany single thrust-rocket booster. The primary objectives were to test the new launcher and booster, to obtain aerodynamic data on the booster-missile, and to continue to free-flight performance study.
The single booster, equipped with four suitably large trapezoidal fins, was first tested on dummy Round J, 17 June 1948. Although launching and early boost was satisfactory, this first flight was terminated by booster fin failure prior to separation.
After modifications had been made to strengthen the booster fins, three powered missiles (Rounds 14, 15, and 16) were fired in vertical flight tests, and a fourth (Round 17) at a slant elevation of 40 degrees north from vertical. In three of these rounds the motor burning time was shorter than expected. In the first test, a reduction in burning time of 2 or 3 seconds was apparently caused by incomplete filling of the acid tank, but high lateral accelerations could have uncovered the fuel tank outlet. In the third powered round, burnout occurred 5 1/2 seconds early. Uncovering of the tank outlets appeared to be the only possible explanation In this case. Burning time was two seconds short in the slant elevation firing, but due to the nature of the trajectory it was expected that some propellant would be trapped in the tanks as the openings became exposed. The firing at slant elevation presented no serious problems of launching, boosting, or missile performance.
Telemetered data obtained from missile-borne Bendix equipment, added for the 1948 tests, indicated lateral accelerations up to 4 1/2 to 6g during motor burning, apparently as the result of asymmetric thrust. The flight in which the motor had reached full burning time was detonated 1.9 seconds after burnout because the horizontal velocity was in excess of range safety limits. Because of the reduced thrust, the peak altitudes and times of flight were lower than predicted, but analysis of data further confirmed that the aerodynamic performance of the missile was satisfactory and the estimates of most aerodynamic characteristics were fairly accurate.
An improved explosive charge--17 ounces of cast TNT and 3 ounces of cast Tetryl--had been installed in the NIKE-47 powered missiles. As before, the charge could be detonated by beacon command or by a fail-safe system in the missile. In the four rounds fired, command detonation was accomplished when called for and the missile detonation was effective.NIKE 48-1 Series
Most of the 1948 field program was devoted to tests of the NIKE 48-1 series, consisting of four Model NIKE-47 dummies and 13 NIKE-48 live rounds of the cluster booster-missile configuration. Three of the dummies were fired in launching and free-flight tests; one was allocated for a functional check of the detonator system operation. The live missiles, of the same aerodynamic design as the NIKE-47, were equipped with roll stabilization and steering controls, operated in response to orders from a missile-borne programer. The programmed control tests of these missiles were divided into two phases: Phase I calling only for repeated roll stabilization from induced spins, and Phase I1 for pitch maneuvers in yaw and roll stabilized flights. Accordingly, the missiles were built to fulfill these test functions. For Phase I, the forward control fin mechanisms were locked, The power plant and general structural design of the NIKE-48 was very similar to the NIKE-47.
Of the 48-1 powered missile series, all but the first, which was destroyed by a booster explosion, were successful as far as launch, boost, and separation were concerned. In most of the 48-1 rounds, the motor operation was also successful; however, there was continued evidence of lateral accelerations produced during the burning phase, apparently as a result of eccentric motor thrust, In one firing (Round 27)) the motor produced thrust only for about 7 to 8 seconds. Test records indicated that the fuel system burst diaphragm only partially ruptured, causing an abnormally lean mixture and reduced cooling flow; the motor chamber wall was burned through near the nozzle entrance. Other than this instance, there were no significant occasions of premature burnout.
The roll stabilization, however, gave considerable trouble. Its nature was tedious to explore and could not have been readily understood had it not been for a detailed and extensive analysis of the 28 channel records of the telemetry. As noted above, the first NIKE 48-1 test (Round 18) yielded no information because of a booster explosion. The next three Phase I tests (Rounds 19 through 21) showed that the aerodynamic roll damping was smaller than had been predicted and that the addition of artificial damping was required, this was accomplished by the installation of a roll-rate gyro by means of which a damping signal was fed into the aileron control circuit, beginning with Round 22. At high angular rates its signal is sufficiently large to dominate the situation and cause the ailerons to deflect in the direction to stop the missile independent of the momentary roll position. When the roll rate is reduced to a low value, the roll position gyro regains control and brings the missile to the desired orientation.
The fifth missile roll stabilized when commanded, so the sixth was fired as a Phase 2 steering control round. This missile (Round 23) showed a violent steering instability with resulting oscillations. The absence of any high frequencies formed a basis upon which to change the circuits for another steering control round, However, before the next steering round was fired, it was discovered that the only explanation for several discrepancies in data from Round 22 was that the roll gyro brush had been grounded. The stabilizations of Round 22 could be explained as entirely fortuitous, as all of them had occurred under conditions where some of the previous missiles had roll stabilized.
Therefore, another Phase 1 (Round 24) was fired to gain further information on the performance of the roll control system with the rate-gyro installed. The gyro operated satisfactorily in this test, but the need for more roll damping was indicated. This was obtained by doubling the rate-gyro voltage in Round 25, which was also a Phase 1 missile. Greatly improved roll stabilization resulted, so the second Phase 2 missile was fired as Round 26.
Although considerably improved over the first Phase 2 missile, instability was still present and an intensive investigation of the steering circuitry was undertaken. To verify the aerodynamic and missile dynamic data to be applied in this study, Round 27 was fired with a missile wired for step fin-position commands, in contrast to standard step accelerations, and the resulting transients were to give the necessary information. Round 27 was not adequate for this purpose, however, because of motor and timer malfunctions. Round 28 was then succesefully fired for the same objectives.
On the basis of these data and other information obtained in the study, the steering circuits were redesigned and Rounds 29 and 30 were fired after the changes. These rounds confirmed the general analysis and final remedy was tested in Rounds 31, 32, and 33 during May 1949. The remedy consisted of a refinement of the ram pressure responsive attenuator in the servo circuit, not only in the roll control system but henceforth also in the suitably changed shaping network of the steering order circuit.NIKE 48-2 Test Series
Another part of the 1948 NIKE missile program comprised the development and test of the NIKE 48-2 missile, a revised aerodynamic design. During the NIKE design studies early in 1948, trajectory computations indicated that, to obtain optimum range, the effective main fin area of the missile should be reduced by one-third. This conclusion was applied in the new fin design for the NIKE 48-2, and in addition, the fin thickness was reduced from 6% to 2 1/1% to decrease wave drag. Revisions to provide space for larger warheads were also made in the fuselage design, including an increase in length from 235 to 255 inches, changing the shape of the after-body from a boat-tail to a cylindrical shape, and attachment of an external tunnel fairing along the body to house electrical wiring and plumbing lines. Four dummy missiles of this configuration were fired in August and September 1948.
During June and July, however, tests of a 7.5% scale model in the AFG supersonic wind tunnel indicated that the NIKE 48-2 poeeessed unsatisfactory stability and roll characteristics. These tests resulted in several major configuration changes, such as returning to the original fin area, decreasing the distance between the control fine and main fins, and installing four small. tunnels instead of the single large tunnel. This modified version, now known as the NIKE 484, was aesigned for steering and roll tests to be conducted in 1949.System Tester
At Whippany the design and construction of the Analog System Tester had proceeded to the point where many of the computer components had been thoroughly bench tested. The target simulator part of the machine was essentially completed. When supplemented by parts simulating missile aerodynamics, it was pressed into service as a missile trajectory computer which took over in a more versatile and rapid manner the sort of tasks which had been preliminarily fulfilled by the improvised trajectory plotter made in Santa Monica in 1947.Planning Conferences
The sixth planning conference was held at WSPG in September 1948 during the Phase 1 and 2 overlap. The seventh conference followed in March 1949 at Santa Monica during the recess in the firing program while changes were made in the missile which led to the successful conclusion of Phase 2 in May 1949. In these conferences the status of progress was reviewed and plans were mapped out for the field program of Phases 3 and 4 scheduled for the winter of 1949-50, and for a comprehensive 490 series of firings to be scheduled for the second half of 1950, realizing that various improvements developed in the meantime would require proof testing. This would move the complete NIKE System Trials into 1951, which turned out to be the earliest year in which radar, computer, targets, and accessories could be ready for them.