Factors Influencing the Accuracy of Rockets

Citation

Blitzer, Leon (1943) Factors Influencing the Accuracy of Rockets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nwt2-9712. https://resolver.caltech.edu/CaltechTHESIS:03142025-230200985

Abstract

The inaccuracy of rockets arises primarily from the failure of the axis of the jet to pass through the center of mass of the projectile. This causes the rocket to rotate, during burning, about a transverse axis through the center of mass, with the result that the direction of thrust of the motor is altered from its initial direction as determined by the projector.

A theoretical analysis of the forces acting on a rocket during its accelerating period leads to the following conclusions concerning the effects of malalignment, burning time, fin size and projector length on the accuracy of rockets with velocities less than 800 ft/sec:

(i) The deflection of the rocket is directly proportional to the malalignment of the jet.

(ii) For projector lengths less than one-fifth the burning distance the deflection of a rocket increases rapidly with the burning time until the burning time equals the period of oscillation of the projectile in free flight, or until the burning distance equals half the yaw oscillation distance in free flight. Further increases in burning time produce no significant change in the deflection.

(iii) In the same range of projector lengths, increasing the fin size from that required to make the projectile barely stable in free flight to that which reduces the period of oscillation to the burning time diminishes the deflection by a factor of about 0.7. Still further reduction in the period by increasing the fin size decreases the deflection roughly proportionally to the period attained.

(iv) When the ratio of projector length to burning distance is in the range between 0.01 and 0.50, the deflection decreases roughly linearly with the logarithm of this ratio.

On the basis of certain simplifying assumptions, formulas are derived for the effect of wind on the motion of rockets with velocities less then 800 ft/sec. The effect of the wind is to deflect the UP into the wind during burning and down wind after burning, the relative effects of each depending mainly upon the burning time. The formulas developed apply to the mean deflection for a given set of firings of a sufficient number of rounds so that malalignment and other such random effects average out.

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