Gust alleviation and modal suppression control technology
Optimal control of space shuttle vehicles by using gust alleviators to counteract atmospheric disturbances
Rheinfurth, M. H.↗
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The gust-alleviation characteristics and handling qualities of a free-wing aircraft
Free wing aircraft dynamic characteristics, discussing gust alleviation and handling qualities
Brown, J. H., Jr.↗
Single-degree-of-freedom roll response due to two-dimensional vertical gusts
Single degree of freedom roll response due to vertical random two dimensional vertical gusts
Houbolt, J. C.↗
The use of sensitivity analysis in designing optimal gust alleviation systems
Sensitivity analysis and optimal control theory used to design optimal gust alleviation systems, discussing gain and gear ratios
Hood, R. V.↗
Performance limitations of an inertial aircraft lateral guidance system subject to random gusts
Inertial aircraft lateral guidance system limitations in stochastic gust environment, comparing configurations using aileron or differential spoilers
Mackinnon, D.↗
Launch vehicle gust penetration loads
Saturn launch vehicle gust penetration loads, presenting separated flow and associated time lag effects
Ericsson, L. E.↗
The pulsed air gust generator
Pulsed air gust generator for sinusoidal streamwise perturbation of wind tunnel test stream, describing upstream blowing air jet array, flow calibration and mathematical model
Bicknell, J.↗
Elastic launch vehicle response to sinusoidal gusts
Separated flow and time lag effects on sinusoidal gust penetration loads and elastic launch vehicle response of Apollo-Saturn class
Ericsson, L. E.↗
The method of multiblade coordinates in the linear analysis of lifting rotor dynamic stability and gust response at high advance ratio
High rotor advance ratio from multiblade general coordinates method in linear analysis of lifting rotor dynamic stability and gust ratio
Hohenemser, K. H.↗
Concepts for a theoretical and experimental study of lifting rotor random loads and vibrations. Phase 5B: Analysis of gust alleviation methods and rotor dynamic stability
The effects of various gust alleviation methods on the random blade response in flapping were studied analytically, assuming a rigid rotor support. The analytical model assumes rigid flapping blades with elastic root restraints. Linearized equations which are approximately valid at low lift conditions were used. Because of the interblade coupling from the feedback devices, the method of multiblade generalized coordinates was most convenient and was extended to include coning, differential coning, and warping of the rotor. The numerical examples cover the dynamic stability characteristics as affected by feedback gains of three- to six-bladed rotors. The number of blades had large effects on stability limits and modal time functions at these limits. The random flapping response of the blades to atmospheric turbulence was determined at 1.6 rotor advance ratio using feedback gains below the stability limit. The most effective reduction of the flapping response per unit gain was achieved with a rotor coning angle feedback.
Hohenemser, K. H.↗
Analytical study of the performance of a gust alleviation system for a STOL airplane
An analytical study has shown that a gust alleviation system for a STOL airplane in a cruise condition could reduce the root mean square of the normal acceleration of the airplane flying in random turbulence by as much as 50 percent. This alleviation is obtained by driving the flaps in response to normal acceleration and by moving the elevator in proportion to the commanded flap deflection angle and to a pitch-rate signal.
Oehman, W. I.↗
Identification of M2/F3 stability and control derivatives from flight data containing gust effects
The application of the maximum likelihood identification technique to M2/F3 lifting body flight data containing wind gust effects is discussed. With the objective of this effort being the identification of the stability and control derivatives, it is shown first that the output error technique (or modified Newton-Raphson) fails to fit the recorded data accurately. The means of applying the maximum likelihood technique to this problem are then discussed and the results given which indicate an accurate fit to the data. The question of derivative signs opposite to the wind tunnel values is then addressed and the results of three techniques for dealing with this problem are presented. These techniques are a priori weighting, fixing parameter values, and rank deficient inverses.
Stepner, D. E.↗
Flutter suppression and gust alleviation using active controls
The effects of active controls on the suppression of flutter and gust alleviation of two different types of subsonic aircraft (the Arava, twin turboprop STOL transport, and the Westwind twin-jet business transport) are investigated. The active controls are introduced in pairs which include, in any chosen wing strip, a leading-edge (LE) control and a trailing-edge (TE) control. Each control surface is allowed to be driven by a combined linear-rotational sensor system, located on the activated strip. The control law, which translates the sensor signals into control surface rotations, is based on the concept of aerodynamic energy. The results indicate the extreme effectiveness of the active systems in controlling flutter. A single system spanning 10% of the wing semispan made the Arava flutter-free, and a similar active system, for the Westwind aircraft, yielded a reduction of 75% in the maximum bending moment of the wing and a reduction of 90% in the acceleration of the cg of the aircraft. Results for simultaneous activation of several LE - TE systems are presented. Further work needed to bring the investigation to completion is also discussed.
Nissim, E.↗
The passage of an infinite swept airfoil through an oblique gust
An approximate solution is reported for the unsteady aerodynamic response of an infinite swept wing encountering a vertical oblique gust in a compressible stream. The approximate expressions are of closed form and do not require excessive computer storage or computation time, and further, they are in good agreement with the results of exact theory. This analysis is used to predict the unsteady aerodynamic response of a helicopter rotor blade encountering the trailing vortex from a previous blade. Significant effects of three dimensionality and compressibility are evident in the results obtained. In addition, an approximate solution for the unsteady aerodynamic forces associated with the pitching or plunging motion of a two dimensional airfoil in a subsonic stream is presented. The mathematical form of this solution approaches the incompressible solution as the Mach number vanishes, the linear transonic solution as the Mach number approaches one, and the solution predicted by piston theory as the reduced frequency becomes large.
Adamczyk, J. L.↗
Unsteady lift forces on highly cambered airfoils moving through a gust
An unsteady airfoil theory in which the flow is linearized about the steady potential flow of the airfoil is presented. The theory is applied to an airfoil entering a gust. After transformation to the W-plane, the problem is formulated in terms of a Poisson's equation. The solutions are expanded in a Fourier-Bessel series. The theory is applied to a circular arc with arbitrary camber. Closed form expressions for the velocity and pressure on the surface of the airfoil are obtained. The unsteady aerodynamic forces are then calculated and shown to contain two terms. One in an explicit closed analytical form represents the contribution of the oncoming vortical disturbance, the other depends on a single quadrature and accounts for the effect of the wake.
Atassi, H.↗
Gust alleviation system to improve ride comfort of light airplanes
System consists of movable auxiliary aerodynamic sensors mounted on fuselage and connected to trailing-edge flaps by rigid mechanical linkages. System achieves alleviation by reducing lift-curve slope of airplane to such a small value that gust-induced angles of attack will result in small changes in lift.
Stewart, E. C.↗
Optimal control theory investigation of proprotor/wing response to vertical gust
Optimal control theory is used to design linear state variable feedback to improve the dynamic characteristics of a rotor and cantilever wing representing the tilting proprotor aircraft in cruise flight. The response to a vertical gust and system damping are used as criteria for the open and closed loop performance. The improvement in the dynamic characteristics achievable is examined for a gimballed rotor and for a hingeless rotor design. Several features of the design process are examined, including: (1) using only the wing or only the rotor dynamics in the control system design; (2) the use of a wing flap as well as the rotor controls for inputs; (3) and the performance of the system designed for one velocity at other forward speeds.
Frick, J. K. D.↗
A study of gust response for a rotor-propeller in cruising flight
Equations of motion for a rotor-propeller aircraft in cruising flight have been developed and implemented in a computer program. The formulation is based on Galerkin's method using coupled mode shapes for the blade and wing. This procedure is applied to the analysis of two types of rotors, gimballed rotor and hingeless. The results are evaluated by means of eigenvalue analysis of the stability of the system and frequency response analysis of the gust and control response.
Yasue, M.↗