Read how your company can use
VisualFoil Plus to improve the
design of aircraft propellers.
Problem
Propellers rapidly loose efficiency over a narrow range of helical
tip Mach number in the transonic regime. This limits the thrust produced
by a given power plant and sets an upper limit on the operational airspeed
of the aircraft.
Solution
Rapid loss of efficiency at high subsonic mach numbers is due in part
to compressibility effects. At a given station along the propeller diameter,
the drag coefficient generated by the blade cross section can rapidly increase
over a narrow speed range. In addition, the cross section may generate a
negative lift at higher mach numbers which can compound the problem.
The following solution procedure is recommended:
Use VisualFoil Plus to compute the lift and drag coefficients generated
by the blade cross sections at various stations along the propeller
diameter.
Use the results from VisualFoil Plus to generate a chart of drag
coefficient versus sectional helical Mach number to determine the drag divergence
Mach number for each station.
Determine if the drag divergence Mach number for each section falls
within the desired (design) operational envelope of your propeller.
Use the airfoil modification features of VisualFoil Plus to fix the
blade cross section and increase the drag divergence Mach number for the
problem sections.
About VisualFoil Plus
VisualFoil Plus is an easy-to-use software package for analyzing airfoils
in both incompressible & compressible flows. The incompressible flow
analysis is based on a fast linear-strength vortex-panel solver coupled with
an ODE boundary layer solver. The compressible analysis is based on a finite
volume (FV) Euler equations solver based on either flux vector splitting
for flux difference splitting. The o-grid is generated automatically and
the solution converges within seconds to a few minutes (depending on the
grid resolution) on an ordinary Pentium based PC. Prices for VisualFoil Plus
start at $695 for the 3 months lease. More information can be found at
Julian D. Maynard and Seymoour Steinberg, "The Effect of Blade-Section
Thickness Ratios on the Aerodynamics Characteristics of Related Full-Scale
Propellers at Mach Numbers up to 0.65", NACA Report 1126.
Julian D. Maynard and Leland B. Salters, Jr., "Aerodynamic
Characteristics at High Speeds of Related Full-Scale Propellers having Different
Blade-Section Cambers", NACA Report 1309.
