Comprehensive Hierarchical Aeromechanics Rotorcraft Model

CHARM is a computer software product that models the complete aerodynamics and dynamics of rotorcraft in general flight conditions. CHARM represents the culmination of over twenty-five years of continuous development of rotorcraft modeling technologies at CDI, and incorporates landmark technical achievements from a variety of NASA, DoD, and company-sponsored initiatives. CHARM is ideally suited for performing advanced rotorcraft aerodynamic design and research on emerging rotorcraft technologies, and offers a high level of accuracy and computational performance combined within one easy-to-use product. CHARM is available for licensing as a stand alone analysis or as a module that couples directly into existing flight simulation or analysis software.

AH64D Apache modeled with CHARM
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Key attributes of the CHARM analysis include:
  • CHARM's Constant Vorticity Contour (CVC) full-span free-vortex wake model is the most sophisticated wake model available of this type.
  • CHARM's coupled free-vortex/fast panel solution provides a unique capability for modeling full aircraft interactional aerodynamics - rotors, wake and fuselage.
  • CDI pioneered the use of Hierarchical Fast Vortex/Panel methods in rotorcraft analyses. The HFV/HFP algorithms in CHARM are the most advanced, efficient and accurate found in the industry and have been extensively tested and validated. These algorithms provide enormous CPU savings in high resolution calculations and allow real-time solutions in flight simulation applications.
  • CHARM has been coupled to acoustic prediction software to provide fast prediction of rotor loading and thickness noise.
  • CHARM has a two decade history of published validations and successful use in industry and government research. CHARM is currently in use at all major U.S. rotorcraft manufacturers as well as NASA, the U.S. Army and the U.S. Navy.
  • CHARM is easy to use and reliable.
  • CHARM is available as a module that plugs directly into alternate rotorcraft analysis or flight simulation software.

BERP-tip blades modeled with CHARM's
lifting surface blade model and full-span wake model

The following is a partial list of applications for which CHARM has been specifically designed and demonstrated:

  • Detailed prediction of rotor power and propulsive force as a function of thrust and flight condition.
  • Detailed prediction of rotor aerodynamic loads, blade motion and vibration.
  • Highly sophisticated vortex wake modeling largely from first principles.
  • Time-accurate modeling of rotor/wake/airframe interactional aerodynamics.
  • Coupled multiple rotor/multiple lifting surface solutions for realistic airframes.
  • Coaxial and ducted rotor UAV design.
  • Superior performance predictions at extremely low advance ratio and in hover.
  • Accurate evolution of the aerodynamic and structural dynamic solutions simultaneously to model rotorcraft response to pilot inputs.
  • A capability for real time free wake modeling for simulation applications.
  • Modeling of rotorcraft systems within wind tunnels and in ground effect.
  • Prediction of thickness and loading noise, including BVI noise, using an automated interface with NASA/Langley's WOPWOP
  • Prediction of rotorwash in operations near the ground and ships to model multiple aircraft interactions and brownout

Modeling of the wake/body interaction for the V-22 in flight using CHARM


CHARM's high level of modeling accuracy and computational performance has been made possible through the incorporation of key innovative technologies including those listed below.

  • CHARM incorporates the most advanced free vortex wake model currently available, combining a full-span model using curved elements with an analytical tip vortex roll-up analysis to provide a highly accurate wake simulation that directly computes wake roll-up and vortex core properties from first principles. No empirical constants are required - a distinct advantage for design work and modeling transient maneuvering flight for which wake characteristics are continually changing.
  • CHARM's lifting surface blade aerodynamics model is better suited for analysis of complex tip shapes and other 3-D effects than the more commonly used lifting line models.
  • CHARM's coupled wake/panel calculation is unique, incorporating state-of-the-art fast vortex and fast panel methods to allow fully coupled rotor/wake/airframe solutions. CHARM provides two orders of magnitude reduction in computation time and memory requirements over direct panel methods for high resolution solutions. Bringing this capability and level of computational performance to the designer affords the opportunity to explore high risk technologies, expand design parameter ranges, and evaluate components at a level of detail and computational speed never before possible.
  • CHARM includes extensive 3-D graphics capabilities that allow highly detailed visualization of the rotor/wake motion and wake/surface interaction.

UH-60 helicopter in forward flight, modeled in a wind tunnel.

A key feature of CHARM is its widely documented success in modeling a broad spectrum of rotorcraft metrics - including performance, blade loading, BVI noise, flow fields, and hub loads - and its many man-years of successful use in support of research and design activities throughout the rotorcraft community.

For further information, contact Dan Wachspress at CDI (609) 538-0444 x114.