Open Rocket - "Velocity at deployment" not changing, why?

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billdz

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Hi,
I've been using OR for four years and thought I had it figured out, but tonight I have an issue. The "Velocity at deployment" number reads the same (24.6, too high) regardless of how drogue deployment is set up. I've tried "Deploys at Apogee" plus 0 seconds, also tried adding a few seconds. Also tried "Deploys at first ejection charge of this stage" and setting the delay at the "Optimum delay" number, also tried plus and minus several secoonds from optimum. Nothing seems to have any effect on deployment velocity.

What am I doing wrong? I'm guessing there is an override somewhere that I've missed.
Thanks,
Bill
 

dmo

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I do not think you are doing anything wrong. Plot the Lateral velocity for your sim. The "high" value is almost certainly there, not the vertical velocity which is what is effected by the timing of the deployment charge.

The simulation is done in multiple dimensions but the result table only shows one value for each column. For values like deployment velocity, the code shows the highest of the available values, but it doesn't bother to tell you which value you are seeing.
 

billdz

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I do not think you are doing anything wrong. Plot the Lateral velocity for your sim. The "high" value is almost certainly there, not the vertical velocity which is what is effected by the timing of the deployment charge.

The simulation is done in multiple dimensions but the result table only shows one value for each column. For values like deployment velocity, the code shows the highest of the available values, but it doesn't bother to tell you which value you are seeing.
The "Velocity at deployment" number is vertical velocity or lateral velocity? Not sure I'm following you about the "multiple dimensions". I'm attaching the plot.
If you post the design file, someone may be able to provide you with specific insight.
Attached.

This started when I had the idea of launching this Big Nuke 3E on an M1350. The sim indicates that over a kilogram of nose weight is required for stability. Now, after adding the weight in the sim, I can't get a green "no warnings" circle.

Any help appreciated.
Big Nuke sim plot.jpg
 

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dmo

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OK, should have, but did not think about this being a dual deploy rocket. The warning is not coming from the apogee deployment event, but from the "main" deployment event. So, to get rid of the warning just use a slightly larger drogue.

I doubt that you could see it on the plot for a motor this big, but the 24.6 m/s being reported is the negative velocity of your rocket under the drogue. OpenRocket is looking for < 20 m/s, hence the warning. Again it comes down to showing only 1 value from several different possibilities without any indication of which one. I do not think openRocket has anything similar to RockSim's simulation detail panel, which helps with these situations.
 

H. Craig Miller

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The issue that you are having is not understanding the data output that you are viewing. The "Velocity at deployment" data field reflects the velocity at the time the "main" (the last parachute to deploy) deploys. Applying this to several design variations, the velocity at deployment is:
  • Simple model rocket (one stage with one parachute): Velocity at deployment is the velocity at the time the "main" parachute deploys - displayed deployment velocity changes as the ejection delay time changes.
  • Complex model rocket (two stage with one upper stage parachute): Velocity at deployment is the velocity at the time the "main" parachute deploys - displayed deployment velocity changes as the ejection delay time changes.
  • Complex mid or high power model rocket (two stage with one lower stage parachute and one upper stage parachute): Velocity at deployment is the velocity at the time the "main" parachute deploys - displayed deployment velocity changes as the upper motor ejection delay time changes; the lower stage deployment velocity can only be determined by analyzing the flight plot.
  • Complex mid or high power model rocket (one stage with dual deployment--one drogue parachute and one main parachute): Velocity at deployment is the velocity at the time the "main" parachute deploys - because the displayed deployment velocity is that during descent under the drogue, changes in the ejection delay time do not affect the displayed velocity at deployment; the velocity at the time the drogue deploys can only be determined by analyzing the flight plot.
  • Complex mid or high power model rocket (two stage with with one lower stage parachute and upper stage dual deployment--one drogue parachute and one main parachute): Velocity at deployment is the velocity at the time the "main" parachute deploys - because the displayed deployment velocity is that during the descent under the upper stage drogue, changes in the upper motor ejection delay time do not affect the displayed velocity at deployment; the lower stage deployment velocity and the upper stage drogue deployment velocity can only be determined by analyzing the flight plot.
With this in mind, your simulation is functioning correctly.

I hope this is helpful to those utilizing more than one recovery device in an OpenRocket simulation file.
 
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dmo

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The "Velocity at deployment" number is vertical velocity or lateral velocity? Not sure I'm following you about the "multiple dimensions". I'm attaching the plot.
OpenRocket does simulation in 3 dimensional space, so velocity has components in the x, y, and z planes. When you select "deploy at apogee" the sim is run until the rocket reaches max altitude, then it computes the velocity. In a single deploy rocket, that is the "velocity at deployment". The "vertical velocity" will be zero for that deployment event, but that does not describe the total velocity of the rocket. If the rocket is going straight up, then "deployment velocity" and "vertical velocity" are the same, in all other cases the "deployment velocity" will also have a horizontal component. Take an extreme example where a rocket comes off the rail and make a hard turn flying nearly horizontal. In that case, "apogee" will occur shortly after motor burnout, if not before, so you could have a horizontal velocity of several hundred m/s. That horizontal velocity would show up in the "velocity at deployment" value. Not sure if openRocket is capable of detecting when a launch like that would occur or not, but if you tilt the launch rod or have wind in you simulation, you will get a horizontal velocity in your sim.

Of course, as described by Craig Miller above, in dual deploy sims, the "velocity at deployment" is just the velocity under the drogue, no matter what happens at the apogee deployment.
 

billdz

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OK, should have, but did not think about this being a dual deploy rocket. The warning is not coming from the apogee deployment event, but from the "main" deployment event. So, to get rid of the warning just use a slightly larger drogue.
The issue that you are having is not understanding the data output that you are viewing. The "Velocity at deployment" data field reflects the velocity at the time the "main" (the last parachute to deploy) deploys.
Thanks, guys. Darn, I knew "Velocity at deployment" was at main deployment, guess I just forgot, it's been awhile since I did dual deployment, at least with a drogue that produced a speed over 20 m/s. I have mostly been using Chute Release with a single chute.
 

billdz

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One other related question. I increased the size of the drogue and eliminated the "high velocity" warning. But I'm still getting a "Body calculations may not be entirely accurate at supersonic speeds" warning. What causes that? I'm not getting any such warning on my other supersonic rockets.
 
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