Application of circulation control for three-axis control of a tailless flight vehicle

Abstract

The application of circulation control (CC) manoeuvre effectors to a tailless flight vehicle enables the possibility of providing control moments about three axes without the use of conventional control surfaces. Strong similarities exist between the use of split flap elevons and CC units used as trailing edge devices for the provision of three-axis control. Both control types can produce independent roll and pitching moments by lateral symmetric operation. Yawing moments can also be produced by simultaneous blowing from upper and lower CC slots increasing the local section axial force. An existing datasheet method for predicting the lift and pitching moment increments for plain flaps is modified to support some aspects of sizing CC devices; however, there are some significant gaps such as high fidelity models for the prediction of Coanda jet separation from the curved trailing edge, which require further research. A case study is presented in which the provision of three-axis control moments using CC is evaluated for a tailless 20 kg class gas-turbine-powered model aircraft. Wind tunnel experiments are used to demonstrate the validity of the aerodynamic design of the vehicle and the ability to produce control moments from CC sufficient to meet basic trim and manoeuvre requirements. The peak values of CC control gains achieved for δ CL/ δ Cμ is 20 and the control gain for δ CD/ δ Cμ for use as part of a ‘thrust’-based yaw control scheme from blowing from both upper and lower slots is low (∼0.5); however this is sufficient to trim the case study aircraft at 8° of sideslip at cruise conditions with 10 per cent mass flow bleed from the engine. For lateral symmetric operation of CC controls, the change in pitching moment with control lift increment has been shown to be similar for both CC and flaperon devices