Blue Raven development thread: Flight simulation

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Adrian A

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Jan 21, 2009
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Lakewood, CO
The Blue Raven has an on-board flight simulation capability that will be accessible through the phone app. The flight simulation lets you try out different settings for your deployment channels and then test them by making the Blue Raven "think" that it's really flying. It will turn on its deployment outputs according to the deployment settings you gave it, and record all the usual flight data so that you can make sure that everything worked the way you expected. You can connect real ematches (without black powder, please) and the Blue Raven will fire them when the simulated flight conditions match your deployment settings. This is a good way to check a new battery or switch setup to make sure that everything is wired correctly.

Since the Blue Raven was designed with staging in mind, I included some extra flexibility in the simulation inputs so that you can realistically simulate what the Blue Raven would observe and do if it's installed on a booster, a second stage or even a third stage. Within the simulation setup, you can virtually connect each of the Blue Raven's four output channels to trigger any of the following simulated events:
  • Do nothing (no charge connected)
  • Virtual apogee charge: Puts the rocket into a medium drag configuration as if it has a small drogue
  • Virtual main charge: Puts the rocket into a high-drag configuration that results in a terminal descent rate of around 25 feet/second
  • Ignite a virtual 2nd stage motor.
  • Ignite a 3rd stage motor.
Because of the flexibility of this method, the default settings have the main channel and the 4th channel to the same virtual main chute ematch, and likewise for the apogee channel and 3rd channel. Or you can connect two different outputs to the same virtual airstart igniter, like I did in preparation for my 3-stage attempt at BALLS this year, so that whichever channel meets its conditions first will ignite the stage. The simulation will show different tilt-based ignition behavior depending on the initial launch angle you specify. You no longer have to guess about whether a configuration will do what you expect; just launch it virtually and take a look at the recorded data. Wonder if the backup main chute setting will really work to fire the main chute early if the apogee charge doesn't work? Just virtually disconnect the apogee channel and watch the effect of the main deploying when the rocket descent rate exceeds the threshold you selected for the backup main settings.

Here are some more details about the capabilities:
  • The first stage, optional 2nd stage and optional 3 stage motors each have their own user-specified burn duration (in 0.1 sec steps) and acceleration (in 0.1 G steps). This is an easy way to represent any motor from 1/2A to N or beyond, on any size rocket.
  • Rocket drag is simulated, including effect of altitude on air density all the way up to 150,000 feet.
  • Gravity is also a function of altitude.
  • Launch tower initial tilt is user-specified in 0.1 degree increments. The rocket attitude is simulated to follow the flight path, including the gravity turn showing up in one of the gyro axes
  • The sim works by adding simulated delta measurements to the real measurements your accel and gyro sensors are making during the flight. The effect of real sensor noise is captured, and If you move the Blue Raven during the simulated flight, you'll see the effect in the recorded data. The barometric sensor sim starts with your actual measured altitude as the pad altitude.
I'll follow up tomorrow with some plotted data from simulated flights.
Here are some of the promised plots:
This one was the 32,000 foot simulation that made me realize I wanted to add altitude compensation to the backup main deployment threshold.


Here's the inertial velocities. DR stands for down-range (in the azimuth direction of the tilt at launch) and CR stands for cross-range (direction of vertical cross DR)

Here are the voltages and currents recorded during the apogee and main firings:

The main and 4th channels (programmed as a main backup) are firing right on top of each other. I need to change the defaults to add a delay or better yet, a different altitude for the 4th channel.

Here are the recorded accelerations:


The unit was oriented with -Z up, and in the sim, the simulated rocket thrust direction is assumed to be the upward direction as measured at the start of the sim. The simulated upward direction is modified from that by a user-provided launch angle. Sorry it's a little confusing to explain. But if you'd like to run your sim with the simulated thrust in any particular direction relative to the board, you can do that. For example, is it o.k. to have the board mounted flat onto a bulkhead? The sim above represents that case. The Gs from the main chute opening and the landing impact are both simulated and showing in the recorded data, also.