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Flap‐Lag Damping in Hover and Forward Flight with a Three‐Dimensional Wake

Manjunath, AR and Nagabhushanam, J and Gaonkar, Gopal H and Peters, David A and Su, Ay (1993) Flap‐Lag Damping in Hover and Forward Flight with a Three‐Dimensional Wake. In: Journal of the American Helicopter Society, 38 (4). pp. 37-491.

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Official URL: http://ahsjournal.org/resource/1/jhesak/v38/i4/p37...


Prediction of lag damping is difficult owing to the delicate balance of drag, induced drag and Coriolis forces in the in‐plane direction. Moreover, induced drag” is sensitive to dynamic wake, bath shed and trailing components, and thus its prediction requires adequate unsteady‐wake representation. Accordingly, rigid‐blade flap‐lag equations are coupled with a three‐dimensional finite‐state wake model; three isolatcd rotor canfigurations with three, four and five blades are treated over a range of thrust levels, tack numbers, lag frequencies and advance ratios. The investigation includes convergence characteristics of damping with respect to the number of radial shape functions and harmonics of the wake model for multiblade modes of low frequency (< 1/ rev.) to high frequency (> 1/rev.). Predicted flap and lag damping levels are then compared with similar predictions with 1) rigid wake (no unsteady induced now), 2) Loewy lift deficiency and 3) dynamic inflow. The coverage also includes correlations with the measured lag regressive‐mode damping in hover and forward flight and comparisons with similar correlations with dynamic inflow. Lag‐damping predictions with the dynamic wake model are consistently higher than the predictions with the dynamic inflow model; even for the low frequency lag regressive mode, the number of wake harmonics should at least be equal to twice the number of blades.

Item Type: Journal Article
Publication: Journal of the American Helicopter Society
Publisher: Amer Helicopter Soc Inc
Additional Information: Copyright of this article belongs to Amer Helicopter Soc Inc.
Department/Centre: Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited: 10 Feb 2011 05:26
Last Modified: 09 Nov 2018 06:11
URI: http://eprints.iisc.ac.in/id/eprint/35477

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