[AR] Re: New Free RASAero II Software Released

From: "" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "CRogers168" for DMARC)
To: arocket@xxxxxxxxxxxxx
Date: Wed, 16 Sep 2015 00:15:06 -0400

Some RASAero II Useful Tips:

1) For two stage N motor to M motor rockets, where the upper stage
approaches and/or exceeds Mach 3, or for high thrust N motor minimum diameter
rockets which also approach and/or exceed Mach 3, select All Turbulent Flow and

a Surface Finish of Rough Camouflage Paint, see pages 34-35 and pages 37-39
in the RASAero II users manual. Rockets of this type have come back with
aerodynamic heating damage resulting in "scuffing" of the paint, increasing
surface roughness and tripping the flow to turbulent. For these types of
rockets RASAero II will have more accurate altitude predictions using the
All Turbulent Flow and Surface Finish - Rough Camouflage Paint settings.

2) When importing a RockSim file, be sure to check the Fin Airfoil inputs
and the Rail Guide/Launch Shoe inputs once the file has been imported into
RASAero II. See pages 39-42 in the RASAero II users manual. RockSim only
has Square, Rounded, and Airfoiled Fin Airfoils. RASAero II has 6 Fin
Airfoils available which are detailed on pages 13-15 of the RASAero II users
manual. If an airfoil, say an Hexagonal airfoil, was approximated in RockSim
as Airfoiled (a NACA airfoil in RASAero II), then RASAero II will load
this as a NACA airfoil. The RASAero II software has no way of knowing whether
the airfoil entered into RockSim was the actual airfoil, or an
approximation for the airfoil. The same goes for rail guides or launch shoes,
in
RockSim they are either modeled as launch lugs, or left off altogether. Most
Users appear to just leave the rail guides or launch shoes off the rocket in
RockSim. So again the User will have to add the rail guides or launch
shoes the rocket actually has into the RASAero II inputs.

3) RASAero II has new and improved supersonic Center of Pressure (CP)
models, which are more conservative and have a more forward Mach 2-3 CP than
the
previous RASAero models. Run the RASAero II Flight Simulation and take a
look at the rocket's maximum Mach number, which for some rockets is
approaching or exceeding Mach 3. Use the RASAero II Aero Plots feature to
make
the CP versus Mach number plot which is attached, and look up the Angle of
Attack 0-4 degrees CP. (Average CP for Angle of Attack 0 deg to 4 deg, CP is
moved forward.)

Have at least 2.0 calibers of stability margin on the Mach 3 (or maximum
Mach number) CP value. If the stability margin falls below 1.0 caliber, at
Mach 2-3 there may be coning, and/or pitch-roll coupling, and other
undesirable effects. The additional 1.0 caliber is additional stability
margin, to
make sure the stability margin never falls below 1.0 caliber. As an
example, a rocket might have a stability margin at Mach 3 of 1.25 calibers, but

there might be an error in the CP prediction of 0.25 caliber, lowering the
stability margin below 1.0 caliber into the coning/pitch-roll coupling
potential danger area.

Chuck Rogers
Rogers Aeroscience

[AR] Re: New Free RASAero II Software Released

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