Sounding Rocket Flight Vibration gRMS/Re Ratio

In the sounding rocket community, there is no empirical method for estimating the flow-induced airframe vibration environment for new flights based on the predicted trajectory of those new flights and past measured vibration environments of similar vehicles. This paper defines such a method. It discusses the processing of flight vibration data to determine root mean squared vibration magnitude, the computation of Reynold’s number based on day-of-flight trajectory and atmospheric condition as a function of flight time and altitude, the proportionality ratio between these two quantities, the estimation of future flight vibration magnitudes using this proportionality ratio, and the relationship between empirically estimated flight vibration magnitudes and the overarching spectral content. This method is demonstrated using data from a single sounding rocket flight for which actual trajectory and atmospheric data were available. The analysis shows that day-of-flight air density and temperature profiles, winds at altitude, separated airflow velocities along and across the airframe as a function of flight-path angles of attack, and changes in characteristic length related to motor staging impact Reynold’s number and estimated vibration levels. The resulting ratio of vibration magnitude to enhanced time-varying Reynold’s number is shown to predict finer vibration magnitude features than emerge from using only total vehicle velocities and nominal atmospheric properties. The trend across several classes of sounding rockets is also shown.