US 3156436 A
Description (OCR text may contain errors)
Nov. 10, 1964 R. P. WHITE HELIX ANGLE SENSOR AND ROLL CONTROL MEANS Filed June 20. 1960 SERVO PROGRAM ACTUATOR TRANSDUCER COMPARATOR l4 Flg. 2
V 32 TRANSDUCER TRANSDUCER PROGRAM COMPUTER COMPARATOR 22 6a 28 36 30 ERROR v 34 T o AMPLIFIER CALIBRATOR SERVO 4 ACTUATOR Flg. 3 INVENTOR. 8 RICHARD P. WHITE i T BY Mam United States Patent 3,156,436 HELEX ANGLE SENSOR AND ROLL CGNTRGL MEANS Richard P. White, San Diego, Calif, assignor to Ryan Aeronautical (10., San Diego, Calif. Filed June 29, 1am, Ser. No. 37,339 3 Claims. (ill. 244-44) The present invention relates generally to aerodynamic controls and more particularly to a helix angle sensor and roll control means.
The primary object of this invention is to provide a free floating, weathercocking vane for attachment to an aerodynamic vehicle, in particular a ballistic missile, to sense the helix angle or roll rate in relation to speed of the missile and, through a simple control system, to apply a correcting action by means of aerodynamic roll control surfaces to aid in maintaining the missile on course.
An ancillary object of this invention is to provide a helix angle sensor which is used in conjunction with velocity indicating means, in order to control the roll rate in proportion to the missile velocity for proper stabilization of the ballistic trajectory.
A further object of this invention is to provide a sensor for supplying a signal proportional to the rate of roll, the signal being compared to a program signal corresponding to the required roll rate and the resultant difference or error signal being utilized to operate the roll control surfaces'and correct any difference.
Finally, it is an object to provide a helix angle sensor and roll control means of the aforementioned character which is simple and convenient to assemble and install and which will give generally eflicient and accurate results over a wide range of operating conditions.
With these and other objects definitely in view, this invention consists in the novel construction, combination and arrangement of elements and portions, as will be hereinafter fully described in the specification, particularly pointed out in the claims, and illustrated in the drawing which forms a material part of this disclosure, and in which:
FIGURE 1 is a perspective view of a typical ballistic missile incorporating the helix angle sensor;
FIGURE 2 is a block diagram of the simplified control system; and
FIGURE 3 is a block diagram of a complete control system with a velocity sensing means.
Similar characters of reference indicate similar or identical elements and portions throughout the specification and throughout the views of the drawing.
The helix angle sensor includes a free floating, weathercocking vane 10, pivotally mounted on the body of a missile 12, so as to be fully exposed to the airstream flowing around the missile in flight. Any angular disparity between the longitudinal axis of the missile along its flight path and the direction of airflow causes deflection of the vane from its stable or neutral position in which the vane chordal axis is parallel to the missile longitudinal axis. Since in stable ballistic flight themissile is effectively at zero angle of attack, any deviation of the vane 10 must be caused by rolling or rotation of the missile about its longitudinal axis, the vane thus sensing the helical airflow due to the combination of roll and forward motion. Weathercocking vanes have heretofore been used to detect drift, yaw, or similar deviations of aircraft, but these are static conditions. In the present apparatus, the vane 10 senses a dynamic condition, the rate of roll.
In actuality, the vane 10 senses the helix angle, which is the hypothetical angle of pitch described by the wing tip of a rolling aerodynamic vehicle along a flight path,
the vane in this case representing a short span wing. The helix angle is computed as where 0' is the helix angle in radians, p is the rolling velocity in radians/ second, b is the wing span in feet and V is the free stream flight path velocity in feet/second. From this it will be apparent that the helix angle, represented by the vane 10 displacement 6 is constant for a given roll rate and velocity, at Zero angle of attack.
Thus it is clear that the analog voltage output of transducer 14 varies directly as p and b and inversely as V. The output of velocity sensor 24 is an analog voltage proportional to forward velocity V. In computer 28, the V component from transducer 14 and the V analog voltage from velocity sensor 24 are canceled. Mathematically, this cancellation is accomplished by multiplying by V, dividing both numerator and denominator by V to get Electronically, if the two analog voltages are combined degrees out of phase in computer 23, the output will be the difference in magnitudes and equal to pb T Since [2/2 is a constant, the output of computer 28 is proportional to the roll rate, p.
In the stabilization of a ballistic missile, the missile is required to roll at a particular rate at a particular speed to obtain proper stability. When the velocity of a missile is known accurately in advance, the required roll rate and thus the required vane displacement can be predetermined.
A simple arrangement for controlling a ballistic missile of known performance is illustrated in FIGURE 2, in which the vane 10 is connected to a pick-off or transducer 14 of suitable type, such as electro-rnechanical, electronic or any other well known device capable of producing an electrical output signal proportional to the angular displacement of said vane. The signal from the transducer 14 is fed to a comparator 16, to which is also supplied a signal from a program unit 18, the two signals being compared and the resultant error signal is applied to a servo actuator 20. Rolling of the missile 12 is accomplished by aerodynamic roll control surfaces 22 pivotally mounted in suitable positions on the missile frame and connected to move in opposition and cause the missile to roll about its longitudinal axis, the principle being well known. The servo actuator 20 may be of any suitable type, according to the particular requirements of individual missiles, many different units being readily available.
The program unit 18 is basically a timed mechanism which provides a substantially continuous signal rate so that, by comparison with the signal representing the actual roll rate sensed by vane 10, the necessary corrections can be made to adjust the rollrate to that required. Since the velocity of a missile varies throughout a ballistic trajectory, the rate of roll needed for stable flight changes also. Thus the program unit 18 provides a signal with the necessary variations timed to conform to the changes in velocity, which can be accomplished by a magnetic tape, variable impedance device or mechanical means.
Such programming means are known in the missile art signals and providing an output signal a error, which is applied to the servo actuator 20. The error signal operates the servo actuator 20 to turn the roll control surfaces 22 through equal and opposite angles 6,, to change the roll rate of the missile. As the roll rate is corrected, the excess displacement of vane is reduced and the offset of roll'control surfaces 22 is correspondingly decreased until the roll rate conforms to the program.
For more accurate control, or for missiles whose performance may be subject to variation due to unpredictable environment, the more complete system illustrated in FIGURE 3 may be used. In this arrangement, the vane 10 is connected, as before, to a transducer 14 which provides a displacement signal a In addition a velocity sensor 24 is utilized to measure velocity and is connected to a transducer 26, which provides a velocity signal V. The velocity sensor 24 may be a total head tube or similar device mounted on a nose probe or otherwise suitably mounted on the missile to detect airstream velocity. Both the displacement and Velocity signals are fed to a computer 28, the output of which is a signal representing the measured roll rate, this signal being applied to a comparator 30. Also connected to comparator 30 is a program unit 32 which provides a signal proportional to the required value of throughout the flight. The two signals are compared and the output of comparator 30 is an error signal which is applied to a calibrator 34, in which the error signal is adjusted to an amplitude suitable for driving the servo actuator 20, through. an amplifier 36, to operate the roll control surfaces 22.
The operation of the system is similar to that previously described, except that the instantaneous velocity of the missile is taken into account. Since the helix angle is dependent on both velocity and roll rate, the program unit 32 governs the adjustment of roll rate regardless of velocity. This is particularly useful for missiles which follow a generally ballistic trajectory but which require correction at some point in the trajectory, either by command signal or an internal program. When the missile is rolling at the proper rate relative to velocity, longitudinal stability is optimum and considerable control force is necessary to cause any deviation such as course adjustment. By decreasing the roll rate, however, the missile loses a certain amount of longitudinal stability and may be deviated more easily by simpler and lighter control means. Thus the program unit 32 may be utilized to decrease roll rate andlower stability while a change in trajectory is accomplished, and afterwards restoring stability by increasing the roll rate to the predetermined level.
The system is applicable as a substitute for rate gyros or angular accelerometers, which are more costly and complex. The vane 10 is not necessarily limited to the position ,on the missile as illustrated in FIGURE 1, but can be mounted at any suitable location, dependent on the structure of the missile and internal arrangement of equipment. Alternatively, the vane 10 may be incorporated into the tip of a stabilizing fin, or the like. Further, while the roll control means is illustrated in the form of aerodynamic surfaces, it will be evident that reaction means such as steering or vernier rockets could be utilized, with suitable connection to the servo actuator.
The operation of this invention will be clearly comprehended from a consideration of the foregoing description of the mechanical details thereof, taken in connection with the drawing and the above recited objects. be obvious that all said objects are amply achieved by this invention.
It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.
1. A helix angle sensor and roll control means for use in an aerodynamic body, comprising: a freely floating, weathercocking vane mounted on the body to pivot on an axis substantially radial to the longitudinal axis of the body to sense substantially helical airflow due to rotation and forward motion of the body; pick-01f means connected to said vane and providing a signal proportional to the angular deflection of the vane relative to the longitudinal axis of the body; velocity sensing means mounted on the body and providing a signal proportional to the longitudinal velocity of the body; computer means combining said signals and providing an output signal proportional to the roll rate of'said body; a program unit adapted to provide a signal proportional to the required roll rate of said body, corresponding to velocity, according to a predetermined program; a comparator connected to said computer and to said program unit to compare the signals therefrom and provide an error signal proportional to the difference between the signals; actuating means connected to receive and be operated by theerror signal from said comparator; and roll control means operatively coupled to said actuating means, whereby said roll control means is moved in accordance with the error signal to nullify deviation of said vane from that determined by said program unit.
2. A helix angle sensor according to claim 1, wherein the roll control means comprises'aerody'namic roll control surfaces pivotallymounted on the body.
rate and forward velocity and providing an output reference signal;
means combining said comparison and reference signals and providing an output error signal proportional to the difference between said comparison and reference signals; and
means controlling the roll rate of said bodyactuated by said error signal, whereby said error signal corrects the roll rate of said body to coincide with the predicted roll rate.
References Cited by the Examiner UNITED STATES PATENTS 2,967,679 1/61 Owen 244- 77 2,989,270 6/61 Waldow 244 14 SAMUEL 'FEINBERG, Primary Examiner. CHESTER L. JUSTUS, Examiner.