Aerodynamic-structural analysis of dual bladed helicopter systems

The aerodynamic and structural feasibility of the birotor blade concept is assessed. The inviscid flow field about the dual bladed rotor was investigated to determine the aerodynamic characteristics for various dual rotor blade placement combinations with respect to blade stagger, gap, and angle of attack between the two blades. The boundary layer separation on the rotors was studied and three dimensional induced drag calculations for the dual rotor system are presented. The thrust and power requirements of the rotor system were predicted. NASTRAN, employed as the primary modeling tool, was used to obtain a model for predicting in plane bending, out of plane bending, and the torsional behavior of the birotors. Local hub loads, blade loads, and the natural frequencies for the birotor configuration are discussed

Dual-Wing Systems with Decalage Angle Optimization

Dual-Wing general aviation designs are studied and compared with single-wing designs. It is demonstrated that with proper selection of gap, stagger, decalage, and mission requirements, total drag can be significantly reduced. Proper spanwise distribution of decalage is shown to enhance efficiency while raising the critical Mach number. Also, flight conditions have been chosen to result in operation at the proper Reynolds number, reducing the viscous drag even further

Comparison of the Flight Loads Spectra of Two Business Jets

Operational flight loads have been analyzed from two business jets, a Global 5000 and a Global Express XRS. It is shown that both airframes were subjected to nearly the same number of ground-air-ground cycles, even though the flight times were much different. Flights have been divided into various phases, and loads and turbulence data have been categorized by altitude bands within each phase. Cumulative occurrences of incremental vertical gust load factors have been compared and shown to be comparable for the two airframes. Maneuver load factors have been shown to spread over a wider range of values for the 5000 in every phase. This has been confirmed through comparison of combined loads with those from a CRJ100 and an ERJ-145XR. Derived gust velocities, obtained from the load factors are presented in the form of exceedance spectra. These results from both aircraft are shown to agree well

Comparison of Vortex Lattice and Prandtl-Munk Results for Optimized Three-Surface Aircraft

The results of Prandtl-Munk theory for prediction of the induced drag of three-surface general aviation aircraft have been examined and compared with vortex lattice results. Substantial differences between the two predictions have been shown in the presence of practical non-elliptic spanwise load distributions. At the same time, a parametric study has been carried out to determine the sensitivity of lift to induced drag ratio to different design variables. Using the resulting trends, a three-surface general aviation aircraft has been modeled and compared with its equivalent canard and conventional configurations. It has been demonstrated that while the three-surface geometry is more efficient than a canard configuration, it remains inferior to a conventional design

Three-Surface Aircraft -- Optimum vs. Typical

Comparisons of the induced drag for a three-surface general aviation aircraft were made using a vortex lattice method and Prandtl-Munk theory. Substantial differences between the two prediction methods have been shown in the presence of practical nonelliptic spanwise load distributions. At the same time, a parametric study using the vortex lattice method has been carried out to determine the sensitivity of lift to induced-drag ratio to different design variables. Using the resulting trends, a three-surface general aviation aircraft has been modeled and compared with its equivalent canard and conventional configurations. It has been shown that although the three-surface geometry is more efficient than a canard configuration, it remains inferior to a conventional design

Static Stability and Control Characteristics of Scissor Wing Configurations

A scissor wing geometry is introduced as an alternative to variable sweep and oblique wing designs. It is shown that this configuration offers certain enhancements to the stability and control of the aircraft in addition to aerodynamic advantages associated with sweep. It is shown that a scissor wing configuration can maintain a constant static margin throughout its flight Mach numbers. The dependence of the motion of the aircraft neutral point on the sweep angle is shown to be a function of the chord and span ratios. The control authority is studied and shown not to suffer with changes in the sweep angle. It is also suggested that with the use of wing mounted elevons, additional pitch and attitude control can be obtained over a range of sweep angles