The pressure distributions over a 6:1 fineness ratio ogive cylinder model have been obtained over a wide pitch range in the rectilinear flow provided by the CoA 8 ft x 6 ft low speed wind tunnel and the curvilinear motion provided by the CoA Whirling Arm facility. The pressure distributions were integrated first to obtain the local normal-force loading distribution along the body and then the overall normal-force and pitching moment and hence the centre of normal-force. A comparison of the results showed that the main difference between the aerodynamic characteristics was a considerable positive increase in normal-force loading over the whole of the afterbody in curvilinear motion which varied little with the magnitude or sign of the pitch angle. Some smaller changes were also apparent in the forebody loading characteristics. These changes resulted in the body developing considerably more normal-force and nose-down pitching moment in curvilinear motion than in rectilinear flow with the resultant large rearward movement of the centre of normalforce. It was found possible to estimate the main features of the loadings, but the theoretical methods available did not predict very well the variations in loading obtained experimentally at the extreme beginning and end of the parallel afterbody.

The effect of flow curvature on the aerodynamic characteristics of an ogive-cylinder body

This report presents the results obtained from two series of wind tunnel tests made on an ogive cylinder body of 6:1 fineness ratio in the CoA 8ft x 6ft Low Speed Wind Tunnel.
The distribution of pressure on the body was measured over an incidence range of -1 to 10 degrees. The local loading distributions were then obtained by integration of the pressure coefficients; further integration yielded the overall normal force and pitching moment coefficients and hence the centre of pressure position.
The results showed that the aerodynamic characteristics were very sensitive to conditions in the base region and that unexpectedly large loadings were present over the last 10% of the body length. There are indications that the bluff asymmetric model support system may be the source of some additional interference effects at the higher incidences, even though it is some 3.7 body diameters downstream of the base.
The experimental results have been compared with theoretical estimates obtained by an inviscid ring source method of estimation for axisymmetrical bodies. The theory overestimated the loadings of the ogival nose and under estimated the loadings over the parallel afterbody; in particular the large loadings over the rear of the afterbody were not predicted. The agreement between theory and experiment does not worsen appreciably at the higher incidences as would be expected because of the presence of flow separations.
The theoretical results are very sensitive to the base closure assumed, thus it may be possible to achieve closer agreement by suitably altering the closure.

Starting in 1946 as the College of Aeronautics, the Cranfield Institute of Technology was granted university status in 1969. In 1993 it changed its name to Cranfield University.

The Experimental Determination of the Subsonic Aerodynamic Characteristics of an Ogive-Cylinder Body Including a Comparison with Theoretical Estimates: Volume 1

D.I.T.P. Llewelyn-Davies

Papers

The Experimental Determination of the Subsonic Aerodynamic Characteristics of an Ogive-Cylinder Body Including a Comparison with Theoretical Estimates: Volume 1