Aeroprobe probes used in Boeing’s test of new concept

Preliminary tests were conducted to assess the flight characteristics of a circular wing that could actually deploy helicopter blades. The blades could emerge from the disc to provide lift for vertical takeoff, and then retracted inside the disc and allow the disc to serve as the lifting surface. The aim of this effort was to evaluate the lifting characteristics of a compound wing consisting of a fixed disc and two fixed blades protruding in the spanwise direction from the disc. A model was constructed and tested in a 6’X6’ wind tunnel to measure forces and moments as shown in the figure below. In this figure the model is carrying only a circular disc.

Measurements were made with an Aeroprobe seven-hole probe in the wake of the model. These measurements were obtained along a plane perpendicular to the free-stream direction. The Aeroprobe system consisted of a 2-D traversing system that was programmed to traverse the probe along a two-dimensional grid defined on the plane of measurements. In the figure below we present measured in-plane velocity vectors obtained with the Aeroprobe seven-hole probe. Also shown are projections of the periphery of the disc and the flat blade. The circular disc is projected in the shape of an ellipse because it is placed at an angle of attack. The plane of measurement is the starboard part of the flow field. Two wing-tip vortices are captured, one emanating from the outboard part of the circular wing and another along from the tip of the blade. These are co-rotating vortices, and their strength was calculated by the researchers. Of great interest is the fact that the disc vortex is generating a considerable upwash in the domain of the blade.

Measured velocity vectors in the wake of the disc/blade at an angle of attack. The coordinates are rendered dimensionless in terms of the disc diameter.