Back on ARocket again after a hiatus due to IT/e-mail issues.
Just a reminder that a while ago a new version of the RASAero II software was
released which, of interest to this group, included a modification to the
power-on base drag models for very large nozzle exit diameters at supersonic
and hypersonic Mach numbers, for more accurate power-on drag coefficient (CD)
predictions for the first and second stages of launch vehicles. If you're
using RASAero II for launch vehicle aero data, be sure to download and use
RASAero II Version 1.0.1.0.
A couple of tips for using RASAero II for launch vehicle aero data:
1) Be sure to enter the nose tip radius on the nose cone input screen. For
many launch vehicles there is typically a large nose tip radius. Enter in the
nose cone basic shape (tangent ogive, power law, elliptical), and then add the
large nose tip radius.
2) For trajectory runs RASAero II continuously varies the aero data with
altitude. When generating aero data for input into other programs using the
Aero Plots (Pages 46-59 in the Users Manual), or the Run Test aero tabular
output (Pages 68-74 in the Users Manual), the default is the aero data will be
generated with the altitude held constant at sea level.
For entering a schedule for the altitude with Mach number along the ascent
trajectory, the Mach-Alt input feature (Pages 66-68 in the Users Manual) can be
used.
Typical Mach-Alt values to be used for a launch vehicle are:
Mach Alt (ft)
0.0 0.0
5.0 100,000
25.0 100,000
I recommend just holding the altitude at 100,000 ft, once 100,000 ft is reached
in the Mach-Alt inputs.
Again, there's no need to enter anything in the Mach-Alt inputs when running a
trajectory in RASAero II, the altitude with Mach number for generating the aero
data is done automatically along the trajectory. The Mach-Alt input is only
used for the Aero Plots and the Run Test aero tabular output. If you make no
input, then the default of sea level will be used.
But if you're typing aero data from the Aero Plots or the Run Test tabular
output for a launch vehicle into another program, then the Mach-Alt input
feature should be used.
Chuck Rogers
