1. Aside from lateral directional research, investigations have also attempted to use active flow control applications for longitudinal control of fighter configurations. The flow field of leading edge vortices dominates the longitudinal stability of delta wings and other slender planforms. A phenomenon known as vortex breakdown (VBD) is common to this flow field, and its presence can dramatically alter the aerodynamic performance of a swept wing. The characteristics of this leading-edge vortex (LEV) flow field and the associated phenomena involve complex flow physics that have been studied and researched extensively since the 1950's*`. PVC devices have been extensively tested for the alleviation of vortex breakdown**, lift enhancement at high angles of attack*`, and as a means for controlling the strength and position of these vortices for aircraft pitch control0022. Of the various applications tested, a common restriction is the efficiency of the devices with respect to physical implementation in present and future fighter configurations. For example, it is more attractive for PVC devices to operate from existing aircraft components such as bleed air from propulsion units, rather than additional pumps and/or compressed air tanks. Therefore, for such pneumatic control research to be successful, attention must be paid to the energy requirements of the devices.
2. To examine the statement that a relationship exists between the migration of vortex breakdown and center of pressure, measurements of each are necessary. Several surveys of VBD on delta wing planforms have been recorded38as well as analytical methods for predicting the location of VBD39. However, little research hasreported the behavior and position of the CP for this class of wings. Some observations have shown the CP to exist in a region near the geometric center of the delta wing, 2/3 of the root chord (c,) from the apex, with forward migrations in the range of 0 - 5% cn for a less than 30 degrees"`. Again, this behavior is dependent on the model geometry and test conditions, which further necessitates measurement for a specific investigation.
3. From each actuator plenum, lines from the static pressure ports and run out of the HFC model and connected to a high range digital manometer. Here, plenum pressuresaremonitored by a Digitron Model 2083P digital manometer, with an accuracy of 0.1% of reading, and a maximum range of 100 [psi]. With each plenum having its own pressure line, the left and right actuator pressures from one set could be compared for symmetrical blowing. A t-valve was also connected to the digital manometer to allow measurement of the inlet pressure to the Venturi flow meter. A low range manometer was used to measure the pressure drop across the flow meter inlet and throat section. A Dwyers water-filled manometer provided this measurement with an accuracy of +/- 0.005 [inH;O] and a maximum range of 5 [inHzO]. These three pressure measurements contributed to the calculation of massflow rate andjet velocity for the system. Experimental Facilities