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Here is a first for me. The simulations were well under the altimeter measurement. 3FNC Loc Vulcanite on an Aerotech H128 with Perfectflight MAWD:
Altimeter = 1939'
Rocksim (best scenario) = Rasaero (best scenario) ~ 1775'
Best scenario settings include "polished" finish (hardly), no turbulent flow in Rasaero, and some tweaking of rod angle (eyeballed at first) to get max altitude for the given wind speed (measured at ground with my anomometer). Mass, components, and other launch site conditions were faithfully recorded and simulated. Well below Mach. The latest eng and rse files from the Aerotech website were used.
Even under best scenario simulations, I can't achieve what the altimeter reports. Using a fixed Cd in Rocksim requires Cd ~0.4 to achieve 1939'. Not likely for a slender rocket with my finishing skills.
I then dug into the motor files. I went to Thrustcurve.org and noticed that the H128 has two versions of simulator files, one with more impluse than the other. I plugged in the hotter eng file into Rasaero, and voila, the simulation now says ~2050', which seems like a more realistic correlation.
My conclusion: Rocketeers fret way too much over their simulation settings while taking the accuracy of thrust curves for granted. Motor files and variation are all over the place. Some published thrust curves have T=0 at t=0, while some start impulsively at t=0. This inconsistency also makes a difference in the simulation. Put standard deviation bounds on the motors and hope for the best in your sims.
Altimeter = 1939'
Rocksim (best scenario) = Rasaero (best scenario) ~ 1775'
Best scenario settings include "polished" finish (hardly), no turbulent flow in Rasaero, and some tweaking of rod angle (eyeballed at first) to get max altitude for the given wind speed (measured at ground with my anomometer). Mass, components, and other launch site conditions were faithfully recorded and simulated. Well below Mach. The latest eng and rse files from the Aerotech website were used.
Even under best scenario simulations, I can't achieve what the altimeter reports. Using a fixed Cd in Rocksim requires Cd ~0.4 to achieve 1939'. Not likely for a slender rocket with my finishing skills.
I then dug into the motor files. I went to Thrustcurve.org and noticed that the H128 has two versions of simulator files, one with more impluse than the other. I plugged in the hotter eng file into Rasaero, and voila, the simulation now says ~2050', which seems like a more realistic correlation.
My conclusion: Rocketeers fret way too much over their simulation settings while taking the accuracy of thrust curves for granted. Motor files and variation are all over the place. Some published thrust curves have T=0 at t=0, while some start impulsively at t=0. This inconsistency also makes a difference in the simulation. Put standard deviation bounds on the motors and hope for the best in your sims.