Model support system interference on zero-lift drag at transonic speeds

In this paper the support system interference on the zero-lift drag of an axisymmetric and an aircraft type models is discussed. Two different techniques were adopted for the two models tested to evaluate the support sting interference. It is found from these tests that the presence of a rear sting support would result in a reduction in the zero-lift drag of as much as 20 to 50 percent of the true value. This apparent reduction in drag is found to be a strong function of the free stream Mach number close to unity. Detailed pressure measurements over the aft-body of the axisymmetric model suggests that due to the positive pressure field imposed by the sting over the boat-tail region of the model the free stream Mach number at which the shocks appear in the boat-tail region will be higher when the sting is present than that without it. This will result in an increased drag divergence Mach number for the model in the presence of the sting. It is argued that because of this reason the sting effect on zero-lift drag strongly depends on the Mach number close to unity