Flightpath angle and effective flightpath angle which

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flightpath angle and effective flightpath angle, which is elaborated below. The TPP angle-of-attack plots were obtained by first transforming the flapping measurements of the laser transducers in a rotating coordinate system to a non-rotating coordinate using the multiblade coordinate transformation (refs. 14 and 16). The results yielded, among other parameters, the sine and cosine components, β 1s , β 1c , of the blade flapping in the nonrotating system. The TPP angle-of-attack, α TPP , was then calculated using the following equations: α = θ γ s.s. (3) α TPP = α β 1c – i s (4) where γ s.s. quasi-steady flightpath angle (deg) θ aircraft pitch attitude (deg) i s inherent shaft tilt angle (–3 deg) α aircraft angle-of-attack (deg) The calculation neglected the effects due to small sideslip and winds during the controlled acoustic tests. The effective glidepath angle, α eff , which accounts for the decelerating effect (ref. 17) was calculated using: γ γ eff s s V g = + sin sin ˙ . . 1 (5) The acceleration along the flightpath, ˙ V, was calculated approximately by a numerical differentiation of the air- speed with respect to time, assuming calm air conditions. The airspeed was first appropriately conditioned with a 0.2 Hz low pass filter. The quality of the approximation has not been assessed with the calculations using the INU or LDGPS derived data. The results are plotted in the lower part of figure 13 showing the effect of deceleration. As the aircraft deceler- ated (see also fig. 14, with its abscissa now being shown in airspeed for the 6 deg decelerating approach of
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8 fig.13(b)), the TPP angle-of-attack increased signifi- cantly. The value of the TPP angle-of-attack was gener- ally between the effective flightpath angle and the quasi- steady flightpath angle. Most of the increase in the TPP angle-of-attack during deceleration was due to an increase in aircraft pitch attitude (see fig. 15), with an accompany smaller increase in TPP tilt back with respect to the rotor shaft, to generate the desired level of approximately 0.05g of deceleration. The result was a significant increase in the effective rate of descent, as seen from the rotor, as indicated in figure 16. For the three multi-segment noise-abatement profiles, the TPP angle-of-attack values were again seen to lie between the quasi-steady flightpath angle and the effective flight- path angle, which included the effect of deceleration. This is shown in figure 17. Within the critical range of 1000ft of horizontal distance from the center mics, the TPP angle-of-attack increased and exceeded 10 deg for the HAI-Light run #22. The resultant effective rate of descent of approximately 1500 fpm was reached for the run in the airspeed range of 50–60 knots when flying over the microphones, as can be seen in figure 18. For the Quiet approach run #14, figure 18(a), the effective rate of descent, when flying over the center mics, was increased from the scheduled 500 fpm, which was based on quasi- steady considerations, to some 800 fpm due to the effect of deceleration. Similarly, significant increases in the rate
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