Body Angle Of Attack Research Articles

Kinematic and Aerodynamic Response of Locusts in Sideslip

Effects of the sideslip angle on the wing kinematics and the aerodynamic forces and moments generated by the locusts were investigated in a low-speed wind tunnel. Three live locusts ( Schistocerca americana) were tested at tunnel speeds of 0, 2, and 4 m/s at three body angles of attack (0°, 3°, and 7°) and three sideslip angles (0°, −10°, and −20°). A sensitive custom-built microbalance was used to measure the forces and moments. The balance was synchronized with high-speed video system recording the wing kinematics. It was observed that the nose down pitching moment increases with the angle of attack increase. This is an indication of active and/or passive mechanisms restoring the body orientation in the vertical plane and providing pitch stability of locusts. The side airflow generates a large side force and positive rolling moment. In response to the oncoming side wind, the locust executes larger-amplitude flapping motion on the windward wings. Changes in kinematic parameters of locust wings are similar to those observed in dragonfly during the right-turn maneuver. However, the yawing moment increases with the sideslip angle increase indicating yaw stability. This could be due to the weathercock stability, since about two thirds of locust's body length and legs lie behind its center of mass.

High-speed video image analysis of ski jumping flight posture

Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers.

The Body Angle of Attack in Front Crawl Performance in Young Swimmers

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Comment on 'Effect of fuselage on delta wing vortex breakdown'

I T is shown in Ref. 1 that the presence of a fuselage significantly promotes the breakdown of delta wing leadingedge vortices. Applying the equivalent angle-of-attack concept only accounted for a fraction of the measured effect of the fuselage, predicting a 17% increase of the effective angle of attack compared to the measured 45% increase. The present comment describes a flow mechanism that can explain this discrepancy, i.e., the wing-camber effect generated by the fuselage-induced upwash along the leading edge of the delta wing. The effect of longitudinal camber on the breakdown of the leading-edge vortex on a slender delta wing is large (Fig. 1). For the same maximum local angle of attack on the delta wing max a positive camber of Aa/amax = 1 delays breakdown to occur downstream of the trailing edge, whereas a negative camber of the same magnitude, Aa/amax = — 1, causes burst to occur very close to the apex. Obviously, for a pitching delta wing the pitch-rate-induced camber will have similarly large effects on the breakdown of leading-edge vortices. It is described in Refs. 4 and 5 how the roll-rate-induced camber effect would be very similar to the pitch-rate-induced camber effect. In both cases, it is the motion-induced change of the local angle of attack at the leading edge that matters (Fig. 2). For the maximum reduced frequency and amplitude used in the roll oscillation test of a 65-deg, sharp-edged delta wing, the roll-rate-induced camber at the trailing edge was AaLE/a = 0.31. Following the suggestion in Ref. 7, static tests were performed with models deformed to produce the roll-rateinduced camber (Fig. 3). The results were as expected; i.e., the twisted-up side of the delta wing experienced later vortex breakdown than the opposite, twisted-down side, approximately at 70% chord compared to 45% chord (for zero roll angle <£ = 0). It should be noted that the variation of the induced angle of attack along the leading edge is linear, proportional to the local semispan, in the examples given in Figs. 1-3, whereas the variation is nonlinear, roughly inversely proportional to the local semispan, in the case of the body-induced wing camber. However, the results in Ref. 7 serve to illustrate how large the effect of camber is on vortex breakdown. Based upon these results one can expect that the bodyinduced negative wing camber along the delta wing leading edge is a very important parameter. Thus, a better approach than using any mean-alpha value for the delta wing, such as the equivalent angle of attack, is to use the body angle of attack a together with the body-induced wing camber at the trailing edge AaLE/a, to correlate measurements of the breakdown of delta wing leading-edge vortices in the presence of a fuselage.