Multichannel, Free-Flight Base Pressure Telemetry in Wind Tunnels

Abstract

Radio telemetry techniques permit the acquisition of aerodynamic data from free-flight models in wind tunnels, a method which ensures that the data are completely free from support interference effects. No serious difficulties were experienced in the development of a telemetry system to record simultaneously four channels of base pressure data from a free-flight model; however, precautions were necessary to prevent interactions between channels and to prevent interference between telemetered and extraneous signals. This telemetry system is based upon small, transistorized, transmitter units, placed aboard the model, which are directly modulated (FM) by capacitance-type pressure transducers. All units are powered from a single battery package. These units, one for each data channel, transmit to antennas located outside the tunnel. All units are interchangeable between models, and have built-in provisions for preselecting full-scale pressure range (0.0005-0.1 psid) to provide optimum data resolution under a variety of test conditions in three different wind tunnels (at nominal Mach numbers of 8, 10, and 20). Oscillograph traces resulting from tests of typical models, both in free flight and on a sting mount, are compared and discussed from an instrumentation point of view. Satisfactory system operation is demonstrated by comparing telemetered base pressure data to data obtained by conventional means during a test of a sting-mounted model.