Mark:
I’ll give this a try on my clean computer but it will probably be next week
before I can run all the cases.
Bill
On Sun, Jan 3, 2021 at 7:42 PM <mark.spiegl@xxxxxxxxx> wrote:
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