ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR PROGRESS REPORT for 1 September 1952 to 1 December 1952 UPPER ATMOSPHERE TEMPERATURE AND PRESSURE MEASUREMENT REPORT IO. A-14 By H. F. Schulte PROJECT DIRECTOR: W. G. DOW Submitted to the Geophysics Research Division, Air Force Cambridge Research Center, Cambridge, Massachusetts. The work reported herein is of a preliminary nature and the results are not necessarily in final form. Approved by: N. W. Spencer Project Engineer Project No. M824 U. S. AIR FORCE, AIR FORCE CAMBRIDGE RESEARCH CENTER CONTRACT NO. AF 19(122)-55 December, 1952

PERSONNEL EMPLOYED DURING PERIOD OF REPORT W. G. Dow Project Director H. C. Early Research Engineer Part time F. Etiz Technician Part time (student) W. G. Kartlick Research Technician D. L. McCormick Machinist Part time H. F. Schulte Research Engineer Part time H. S. Sicinski Research Physicist H. L. Smith Research Engineer Part time N. W. Spencer Project Engineer J. Ching Tu Research Technician Part time (student) H. C. Weston Technician Part time (student) ii

ABSTRACT Results of some secondary experiments conducted in the University of Michigan Aerobee of September 1951 are presented. Further gyroscope tests have been performed and the results indicate satisfactory operation. Preparation of the October 1952 Aerobee is described and the allocation of funds from the new contract for future work is explained. iii

TABLE OF CONTENTS Page PERSONNEL EMPLOYED DURING PERIOD OF REPORT ii ABSTRACT iii HOT-WIRE ANEMOMETER 1 INERTIA SWITCH AND TAKE-OFF MOTION INDICATOR 3 GYROSCOPE TESTS 5 MISSILE PREPARATIONS 6 MEETINGS 7 OUTLINE OF FUTURE WORK 8 PERSONNEL AND FISCAL INFORMATION 9 iv

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN PROGRESS REPORT for 1 September 1952 to 1 December 1952 UPPER ATMOSPHERE TEMPERATURE AND PRESSURE MEASUREMENT REPORT NO. A-14 HOT-WIRE ANEMOMETER A fundamental question still to be answered concerning the validity of the method developed by this project for determining ambient pressure and temperature from supersonic missile measurements is the perturbation of cone surface pressures by the boundary layer. Answering the question requires a rather thorough investigation of the boundary layer during the measurement period. It would be exceedingly difficult to simulate flight conditions in a test chamber and conduct such an experiment. By far the most direct approach is through missile experiments. Of the methods of boundary-layer analysis, the use of a hot-wire anemometer or probe appeared to be the most practical and was accordingly chosen. This preliminary experiment was conducted to measure the range of variables encountered and to determine whether the fragile wire used could withstand the rigors of flight. Two probes were constructed and mounted on the conical nose section of the September 1951 Aerobee (USAF 18).* Each probe consisted of a fine * Progress Report No. A-8. Contract No. AF 19(122)-55, October, 1951.

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN tungsten wire 0.0005 inch in diameter and approximately 5/16 inch long, with each end soldered to a small support. The wire axis was placed perpendicular to the nose cone axis and parallel to the surface of the nose cone. One probe was exposed 3 mm above the cone surface to approximate a surface flow environment, while the other was situated 15 mm above the surface to experience the very-high-velocity air stream outside the boundary layer. Since the second probe was believed most susceptible to failure, a simple continuity experiment was utilized to indicate wire breakage, Less than 1 milliampere of current was used in this circuit. The surface wire would quickly become immersed in the boundary layer and be capable of sensing changes in the boundary-layer domain. A constant current of about 50 milliamperes was passed through the wire and a small dc amplifier connected across the wire amplified the voltage variations caused by the change in resistance of the tungsten as its temperature fluctuated. Both wires failed to sustain the flight. Contrary to expectations, the surface wire failed first at 24.0 seconds, followed by the outer wire at 31.4 seconds. Failure was probably caused by melting of the solder holding the wires in place or loss of strength in the wire itself due to elevated temperature, or a combination of both factors. It is felt that these difficulties can be overcome in future models. Since the experiment indicated that it is possible to construct hotwire probes for Aerobee rocket use, this technique is also being considered for the measurement of local stream velocities (speedometer applications) in the vicinity of the cone,

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN INERTIA SWITCH AND TAKE-OFF MOTION INDICATOR Although the internal camera carried in the September 1951 Aerobee photographed a clock and a motor-driven mechanical counter, it was necessary to provide an indication of the exact take-off time. This was done by attaching a weight to the lever arm of a microswitch which in turn operated a panel light photographed by the camera. The acceleration imposed upon the weight at take-off caused the switch to close the light circuit and thus provide an indication of take-off. Since the magnitude of the mass required about 7G to activate the switch, the question arose as to when the switch closed during the booster burning period. It was desirable, of course, to have the indication of takeoff coincide with the very first motion of the missile. To check the acceleration switch, a take-off motion indicator was constructed which utilized a second photographed panel light and a switch. The switch was so arranged that when the missile moved approximately 1/4 inch, the circuit was completed and the light operated. The experiment corroborated the accelerometer indication of takeoff to -0.11 seconds. This tolerance results because these data were recorded with a camera taking approximately seven frames per second and there is always an uncertainty during the last portion of the previous frame and during the time the shutter is closed. An interesting consequence of mounting this switch on the outside surface of the missile is that the switch was exposed to the airstream and experienced a stagnation temperature of at least the melting point of solder. The switch construction required the moving parts and associated electrical _____________________________________ 5 ________3

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN connections to be soldered in place. The circuit closed at take-off and did not open until 39.5 seconds later, at which time the solder softened sufficiently to allow the moving parts to open-circuit. ________________________________ 4 _________________________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN GYROSCOPE TESTS To assist in the evaluation of any possible errors in the missile aspect as measured by the attitude gyro, an additional series of tests was recently completed. The experiments were to determine the precession of the gyroscope as a function of the rotation of the rotor gimbals about some axis inclined to the total angular momentum vector, and also as a function of the inclination angle. It appears from these preliminary tests that the precession resulting from rotation depends on the total number of rotations and not on revolutions per unit time or inclination angle, except when this angle equals zero, in which case the effect vanishes. During the period of time approximating missile use (180 seconds), the magnitude of the precession is of the same order as the precession introduced by the earth's rotation. Since the sign of the gyrostat precession originating from missile rotation depends on the direction of missile rotation, it would seem possible to arrange the system so that these two precessions would act to cancel each other, and thus reduce the total precession from all sources. Another series of experiments is planned to substantiate these preliminary findings, _______________________ 5 ______i________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN MISSILE PREPARATIONS The month of September was devoted to the final missile preparations for the October 1952 Aerobee Rocket firing (USAF 51). During this time the gyro panel assembly, cameras, Alphatron amplifiers, Alphatron gages, and their motor-driven valves were installed in the instrumentation rack. All electrical interconnections were made, and each portion of the equipment was operated by means of the remote-control box. Following the completion of this activity, the vacuum calibration of the Alphatron gages was begun. This work and the final checking and preparation of the instrumentation for shipment to Holloman Air Force Base, New Mexico, continued during the early part of October. All work after 1 October 1952 concerned with the October 1952 Aerobee and subsequent firings will be supported by funds from a new contract, A new series of Progress Reports will be prepared for the contract, the first of which will be issued in January, 1953. For further details, see the Fiscal section of this report. 6

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN MEETINGS The 7 October 1952 meeting of the Upper Atmosphere Rocket Research Panel held in Washington, D, C., was attended by Professor W. G. Dow, Project Director. 7 _______________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN OUTLINE OF FUTURE WORK As indicated in the Fiscal section, the remainder of the time allocated to this contract will be used to continue the past missile data analysis and complete the preparation of papers for journal publication. _______________________ 8 ______1________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN PERSONNEL AND FISCAL INFORMATION Mr. Alan Fisher, employed as a technician, has terminated his association with this project. As mentioned earlier, a new contract, effective 1 October 1952, has been approved to extend the present investigations to 30 September 19553, The contract number is AF 19(604)-545 (University of Michigan, Engineering Research Project No. 2096), and is titled: Research in Temperature, Wind and Related Properties of the Atmosphere and Ionization in the High Atmosphere. Funds provided by this contract enabled the project to complete preparations for and participate in the October 1952 Aerobee firing. Reduction and analysis of data obtained from this and subsequent missiles will also be part of the research program. A new series of Quarterly Progress Reports covering this activity will be submitted, the first of which (Report No. C-1) will be issued in January 1953. All data analysis and related work in connection with missiles fired prior to 1 October 1952 will be completed with funds already allocated for that purpose from the present contract, No. AF 19(122)-55. This contract had a termination date of 31 December 1952, but an extension of six months without additional funds has been granted to complete the work and prepare a final report. No capital property was acquired during the period which contributed directly to the research endeavor. ________________________________________ 9