The OpenRocket additions of Nozzle Diameter and import of RASAero CD data are
nearing completion. I haven't looked at dispersion. I have one problem
remaining which has me stumped. (separate post)
I made a beta version of OR if anyone is interested. Copy the jar, the sample
data files, and run OR as usual. (java -jar)
If these additions are useful (assuming I can resolve the launch site bug) I
will write a wiki page demonstrating the export of RASAero CDs. In the
meantime I attached Chuck's explanation.
https://drive.google.com/drive/folders/1m_1Jprz2gERbV6psgEgPW-Q58zNcJGZd?usp=sharing
How-To.jpg
OpenRocket-beta-20210103.jar
Qu8K_OR.ork
Qu8K_RAS.CDX1,
RAS_CDfile_boost.csv,
RAS_CDfile_coast.csv.
--MCS
****************
Mark:
Step 1) Look over Pages 84-86 in the RASAero II Users Guide so you can see
what the Mach-Alt inputs will look like.
Step 2) Run the rocket on the RASAero II trajectory simulation. Pick logical
Mach points, Mach 0.01, 0.10, 0.5, 0.90, 1.05, 1.5, 2.0, 3.0 etc to the burnout
Mach number. For these Mach numbers, note the altitude during Boost, and the
altitude during Coast.
Step 3) Note that the Altitude from the trajectory simulation is Above Ground
Level. You'll have to add the Launch Site Elevation from the Launch Site
Inputs to the Altitude from the trajectory output for the Alt (Altitude) points
you'll be inputting. (The Alt-Altitude points you enter are Above Sea Level.
Apologies on that, and I need to add this to the Users Manual if the User is
attempting to do what you're doing here.)
Step 4) Use Mach-Alt during Boost.
Mach Alt
0.0 launch site elevation
0.5 launch site elevation plus 1,500 ft
etc.
Burnout 3.5 launch site elevation plus 19,500 ft
Run Aero Plots. Export to the Excel file. This is your aero database for
Boost.
Note that the fact that this is Power-On CD is built in, you're looking at data
during Boost.
Step 5) Use Mach-Alt during Coast. Note that the altitudes entered can
decrease (and for Coast should decrease) with increasing Mach numbers.
Mach Alt
0.0 launch site elevation plus 120,000 ft
0.5 launch site elevation plus xx,xxx ft
1.05 launch site elevation plus xx,xxx ft
etc. etc.
Burnout 3.5 launch site elevation plus 19,500 ft
Run Aero Plots. Export to the Excel file. This is you aero database for Coast.
Note that the fact that this is Power-Off CD is built in, you're looking at
data during Coast.
Apologies on having to add the launch site elevation to the altitudes from the
trajectory output. Mach-Alt was originally added to RASAero II to match wind
tunnel data, and for Users to run over simple altitude ranges. (What's my CD
at 50K ft, 100K ft, etc. [Above Sea Level]) If you are trying to specifically
match what RASAero II is doing automatically internally in the flight
simulation, a very close approximation is adding the launch site elevation to
the altitude displayed in the flight simulation output.
Remember of course that when the RASAero II aero data is used in Open Rocket,
there will be changes in the Altitude for a given Mach number during Boost and
Coast. You could take the Open Rocket Mach-Altitude points and rerun the two
RASAero II Aero Plots runs, but if the Mach-Altitude changes aren't too large,
there's no need to repeat the process.
Charles E. (Chuck) Rogers
Rogers Aeroscience