Open Rocket "Velocity at Deployment" Setting?

[billdz]

On my sim of a dual deploy rocket, I'm getting the same "Velocity at Deployment" reading regardless of motor delay time, regardless of motor. Something must be wrong because I'm checking the green "OK" check even if delay time is way off. My guess is that the sim is showing "Velocity at Main Deployment" rather than velocity at drogue deployment, although this would not account for the green check. Any ideas? Is there any way to change this to "Velocity at Drogue Deployment"? I believe this question has been answered before in this forum but I can't seem to locate it with searches.
Thanks,
Bill

 

[boatgeek]

If it's dual deploy, did you set the parachute to deploy at apogee? If so, it will have minimal speed at deployment. In real life, there will be a velocity component from weathercocking, which is somewhat motor-dependent, but I haven't toyed with those settings much to see how they are reflected in OR sims.

 

[billdz]

Yes, thanks much, that was the issue, I remember the prior thread now. The chute must be set to deploy at "First ejection charge of this stage," not at apogee. Although "Velocity at Deployment" is apparently still showing velocity at main deployment, not velocity at drogue deployment.

 

[Buckeye]

Plot velocity vs. time and see whatever you want to see.

Yes, OR will simulate weather cocking and show a horizontal velocity at apogee.

If you are simulating DD, why would you not choose deploy at apogee for the first event?

 

[billdz]

Plot velocity vs. time and see whatever you want to see.

Yes, OR will simulate weather cocking and show a horizontal velocity at apogee.

If you are simulating DD, why would you not choose deploy at apogee for the first event?

Good point, guess it just bothered me that I was getting a green check even though the delay was way off. I use motor ejection as a backup to the altimeter.

 

[cerving]

Be careful using motor eject as a backup with DD... they're often short and end up being the primary deployment, sometimes at a significant velocity. I'd set the motor delay to be your expected time to apogee plus one or two seconds. If the maximum delay time on your motor is too short for that to work, then don't use motor eject backup... dump the powder from the motor.

 

[ksaves2]

Also, Do multiple simulations at a variety of windspeeds. Vary the launch rod a few degrees downwind of the "prevailing" wind (ie. with the wind). What you will see is if your rocket weathercocks with a particular motor or windspeed, it will take a curving path to apogee and there is a much greater chance there will be a lower velocity deployment than if one points a rocket that is known to weathercock "into the wind". In that case, the rocket weathercocks into even more of an angle into the wind that results in a much higher velocity at deployment. Sim it. Rocksim has that video feature which makes it easy to see. This will save on stress on the apogee recovery harness if a larger drogue is used and definitely saves on deployment stress of an apogee only/main deployment is used on a smaller rocket. An hour playing with a simulator under a variety of conditions can be enlightening. Kurt

 

[billdz]

Be careful using motor eject as a backup with DD... they're often short and end up being the primary deployment, sometimes at a significant velocity. I'd set the motor delay to be your expected time to apogee plus one or two seconds.

Also, Do multiple simulations at a variety of windspeeds. Vary the launch rod a few degrees downwind of the "prevailing" wind (ie. with the wind).

Thanks, good advice, flew last Saturday and all was well.