As simulation has become an integral part of the overall life-cycle support of aircraft, the need for effective Virtual Engineering (VE) tools to support these activities has increased. FLIGHTLAB is a state-of-the-art, aircraft modelling and simulation software tool, that has been designed to address this need and is widely used in rotorcraft design, analysis, test and evaluation, and full-flight simulation applications. This VE tool supports the development and analysis of both fixed and rotary wing aircraft with an extensive library of modelling components which have been successfully used and validated in numerous, real-world applications. These components provide comprehensive modelling of aerodynamic, structural, control and propulsion disciplines. Analyses include performance, dynamic response, stability and control, airloads, and structural loads. Graphical User Interfaces and an interactive scripting language provide user-friendly operation. This paper describes the capabilities and validation activities that have been undertaken to support the development of the commercial VE toolset FLIGHTLAB over the last 20 years and discusses future rotorcraft challenges that could be addressed by enhancements to current generation VE tools.

A helicopter vibration controller is designed by optimizing a cost functional, which places a large penalty on fuselage accelerations at vibration frequencies. The solution to the optimal control problem leads to a feedback law where the fuselage accelerations are first filtered by undamped, second-order systems. This vibration control solution has been possible due to a recent extension of the well-known optimal control formulation. The extension allows frequency-dependent penalty functions on states and controls. The design approach is applied to a simulation-derived, nine-degree-of-freedom linear model of the Rotor Systems Research Aircraft in hover. Evaluation on nonlinear simulation with inflexible rotor baldes in hover and forward flight shows essentially complete elimination of vibration. Acceptable blade pitch amplitude is required for closed-loop control. The paper shows feasibility of the approach. Future work will address blade flexibilities and implementation considerations. Bis Subscripts Nomenclature= penalty on states w, p, and q -lateral swash-plate deflection = longitudinal swash-plate deflection = control penalty = state distribution matrix = linear-quadratic-Gaussian control design = frequency-shaped LQG = multiblade coordinates = number of blades = components of rotational rates = revolution of the rotor = Rotor Systems Research Aircraft = components of fuselage speed = control = system state = filter state = flapping angle = flapping angle of a particular blade = rotor flapping modal states = root location = frequency = rotor speed = blade azimuth angle = fuselage roll angle = real part of an eigenvalue = fuselage pitch angle = main rotor collective input -tail rotor collective input = cosine component = sine component

A new rtpprllach lo arli*e control of rolnrrrufl vibrations involver using feedback of fuselage acceleration\ thrnueh undamped oscillaturi, tuned to the frequency at whlrh vibrvlion is to be supprevred. Thii paper presents a simplified formulation of the aleorithm and investieates im~lementation considerations such as ssmoled-data ~~ ~ ~ ~-~~~~~ . F~~~~ effects and actuator dynamics. Digital compensation for these effects is designed, and the resulting controller is evaluated on a computer simulation of the Rotor Systems Research Aircraft for a wide range of flight eondilions.

A s t a t e -v a r i a b l e feedback approach i s u t i l i z e d f o r a c t i v e c o n t r o l of r o t o r c r a f t v i b r a t i o n . Fusel a g e a c c e l e r a t i o n s a r e passed through undamped second-order f i l t e r s w i t h resonant f r e q u e n c i e s a t N/rev. The r e s u l t i n g o u t p u t s c o n t a i n predominantly t h e N/rev v i b r a t i o n components, phase s h i f t e d by 180°, and a r e used t o d r i v e t h e b l a d e p i t c h t o canc e l t h i s component of f u s e l a g e v i b r a t i o n . The linear-quadratic-gaussian (LQG) method i s used t o design a feedback c o n t r o l system u t i l i z i n g t h e s e f i l t e r e d a c c e l e r a t i o n s . The design i s based on a nine-degree-of-freedom l i n e a r model of t h e Rotor System Research A i r c r a f t (RSRA) i n hover and i s evaluated on a n o n l i n e a r blade-element simulation of t h e RSRA f o r t h i s f l i g h t condition. The system i s shown t o e s s e n t i a l l y e l i m i n a t e v i b r a t i o n s a t N/rev i n a l l axes. The required blade-pitch amplitude i s w i t h i n t h e c a p a b i l i t y of conventional a c t u a t o r s a t t h e N/rev frequency. I n t r o d u c t i o n H e l i c o p t e r s encounter s i g n i f i c a n t v i b r a t i o n caused by t h e v a r i a t i o n s of r o t o r blade aerodynamic l o a d s w i t h azimuth angle. V i b r a t i o n reduces p i l o t e f f e c t i v e n e s s and passenger comfort and i n c r e a s e s o p e r a t i n g c o s t s and maintenance requirements. Use of h e l i c o p t e r s i n commercial a v i a t i o n has been hindered by high v i b r a t i o n l e v e l s . The r e d u c t i o n of v i b r a t i o n h a s , t h e r e f o r e , been of major i n t e r e s t i n t h e h e l i c o p t e r i n d u s t r y .Figure 1 shows v i b r a t i o n a c c e l e r a t i o n a t f o u r p o i n t s on a UH-1H fuselage.' The UH-1H h a s a twobladed t e e t e r i n g r o t o r which t u r n s a t 324 rpm, and a conventional t a i l r o t o r . The f i g u r e shows t h a t t h e v i b r a t i o n s i g n a t u r e v a r i e s s i g n i f i c a n t l y a t v a r i o u s p o i n t s on t h e h e l i c o p t e r . The f i r s t t h r e e N/rev harmonics dominate t h e v i b r a t i o n a t t h e p i l o t s t a t i o n and t h e instrument panel. P i l o t s t a t i o n v i b r a t i o n a t each of t h e s e f r e q u e n c i e s i s about 0.5 g. Other h e l i c o p t e r s e x h i b i t a s i m i l a r v i b r a t i o n s i g n a t u r e . With t h r e e o r more b l a d e s , t h e component a t N/rev has much g r e a t e r amplitude than t h e higher frequency v i b r a t i o n components. I n g e n e r a l , hingel e s s r o t o r s t r a n s m i t more v i b r a t i o n than a r t i c u l a t e d r o t o r s . P a s s i v e techniques, u t i l i z i n g mass-springdamper systems, a r e c u r r e n t l y used f o r r o t o r c r a f t v i b r a t i o n suppression. The weight of t h e s e systems and t h e i r l i m i t e d ra...

No abstract