http://uarc.ucsc.edu/flight-control/conduit/papers/AHS_2012_Juhasz.pdf

FLIGHT DYNAMIC SIMULATION MODELING OF LARGE FLEXIBLE TILTROTOR AIRCRAFT
Ondrej Juhasz
Roberto Celi
Doctoral Candidate
Professor
Department of Aerospace Engineering, University of Maryland, College Park, MD
Christina M. Ivler
Mark B. Tischler
Aerospace Engineer
Senior Scientist
Aeroflightdynamics Directorate (AMRDEC)
U.S. Army Research, Development, and Engineering Command, Moffett Field, CA
Tom Berger
Aerospace Engineer
University Affiliated Research Center (UCSC)
NASA Ames Research Center, Moffett Field, CA, USA
Abstract:
A high-order rotorcraft mathematical model is developed and validated against the XV-15 and a Large
Civil Tilt-Rotor (LCTR) concept. Rigid body and inflow states, as well as flexible wing and blade states
are used in the analysis.  The separate modeling of each rotorcraft component allows for structural
flexibility to be included in the presented formulation, which is important when modeling large air-
craft where structural modes effect the frequency range of interest for flight control,  generally 1 to
20 rad/sec.  Details of the formulation of the mathematical model are given, including derivation of
structural, aerodynamic, and inertial loads. The linking of the components of the aircraft is developed
using an approach similar to multibody analyses by exploiting a tree topology, but without equations
of constraints.  Assessments of the effects of wing flexibility are given.  Flexibility effects are evaluated
by looking at the nature of the couplings between rigid body modes and wing structural modes and
vice versa.  A model following control architecture is then implemented on full order LCTR models
with and without structural flexibility.  The rigid wing model is shown to give Level 1 handling quali-
ties, whereas the wing flexible model exhibits poor handling qualities.  Notch filters are introduced to
eliminate wing structural dynamics from the output equations. The aircraft response with notch filters
is shown to be much improved with respect to stability margins and handling qualities requirements
for the LCTR.