NACA-ACR-L6C13

Abstract

<strong>INTRODUCTION</strong> <br>A jet, as it spreads by turbulent mixing, is known to entrain outside air in the mixing zone. Air is thus drawn into the jet and the external flow is caused to incline toward the jet axis. If the jet passes near the tail surfaces of jet-propelled airplanes, the jet-induced flow deviation will affect the stability and trim. This flow deviation and its effects or static longitudinal stability are herein investigated theoretically for both cold and hot jets. <br>The present Investigation was wall advanced when a British report by Squire and Trouncer on the cold jet (reference 1) became available in this country. The considerable rigor of the British analysis was found to be impaired by the use of an idealized cosine velocity distribution in the het, which produces errors as great as 11 percent. Also, the original version of the present analysis was found to be oversimplified in one respect, which resulted in comparable errors in the opposite direction. In the present revised treatment, most of the advantages of simplification are retained, but the basic analysis of reference 1 is used to establish the value of a constant. The approximate treatment given herein permits the representation of the jet-induced stream deviation by a single curve. A comparison of the present analysis for the cold jet with that of Squire and Trouncer is given in appendix A. Reference 1 does not treat the hot jet. <br>he first part of the present paper is concerned with the analysis of the flow inclination induced outside cold and hot jets and the jet deflection due to angle of attack. The last part is concerned with applications to the computation of the effects of the jet on longitudinal stability and trim. The computational procedure is out-lined in detail in the numerical example (table I to III) so that little reference to the text is necessary.