Showing papers in "College of Aeronautics Report in 1985"

Ground Effect on a Rotor Wake

Abstract: The effect of the ground on a rotor wake in forward flight has been investigated experimentally in the working section of an 8ft x 4ft straight-through wind tunnel. A three bladed fully articulated rotor with a solidity ratio of 0.07 and diameter of 1.06m, powered by a hydraulic motor, has been tested at a height of 0.47 rotor diameter above a solid ground board which has an elliptical leading edge. Tests have been run at various low advance ratios (<0.1) with two collective pitch settings. A three-element hot wire anemometer probe has been used to measure the average value of the three components of velocity simultaneously in the forward half (advancing side) of the rotor wake and in the main stream surrounding it. The rotor wake and the ground vortices have been visualized by smoke. Surface flow patterns on the ground board have located the interaction region between the rotor wake and the oncoming flow on the ground board. Theoretical estimates of the flowfield based on Heyson's vortex cylinder model (Ref.2) are compared with the experimental results. Both experimental results and theoretical estimates show that the ground-induced interference is an upwash and a decrease in forward velocity. The upwash interference opposes the vertical flow through the rotor, and have large effects on the rotor performance in producing thrust. The streamwise interference decelerates the mainstream and becomes more noticeable as the wake boundary is approached. 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.

Stability Theorems Concerning High Order Explicit Algorithms for the Linear Advection Equation

Abstract: Analysis of the stability of an N-point explicit algorithm for the linear advection equation involves the calculation of the roots of a polynomial of degree N-1. A theorem is proved to show that if the algorithm is of the nth order (n

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

Abstract: 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.

An Assessment of the Suitability of the BHGA Structural Test Rig for Aerodynamic Testing of Hang Gliders

Abstract: In response to a proposal by the BHGA to use their structural test rig to carry out aerodynamic testing of hang gliders, the existing structural test facility and the modifications already made for aerodynamic testing are described. Improvements to the instrumentation are discussed together with an assessment of the flow quality and recommendations made, based on experience gained from existing aerodynamic test facilities. 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.