Open Rocket

[Steven88]

Hello. I received the RockSim design file for my Big Nuke 3E from Loc. I have it downloaded in Open Rocket currently. At the bottom of the rocket design screen it says Warning: Discontinuity in rocket body diameter. I can’t tell that anything is out of whack. Is anyone able to help with the matter?

 

[dhbarr]

Set either the NC or the BT ( but not both! ) to "auto" if you just want it to go away.

Usually the cause is a stray fraction of an inch which is truncated or rounded on display.

 

[Voyager1]

Set either the NC or the BT ( but not both! ) to "auto" if you just want it to go away.

Usually the cause is a stray fraction of an inch which is truncated or rounded on display.

+1
That usually fixes this issue. If it doesn't, just post your sim file for folks to review, if you wish.

 

[Steven88]

When you install the motor into the bottom of the rocket on Open Rocket, and you choose a reloadable motor such as an Aerotech k560, does Open Rocket take into account the casing and closure weight to house the propellant, or must I add it in?

 

[neil_w]

When you install the motor into the bottom of the rocket on Open Rocket, and you choose a reloadable motor such as an Aerotech k560, does Open Rocket take into account the casing and closure weight to house the propellant, or must I add it in?

That's all include.

Also, for the future: https://www.rocketryforum.com/threa...ther-support-question-for-that-matter.157409/

 

[Joekeyo]

Ok. Before I commit to gluing tiny fins on this long rocket, is it really going to be stable?

 

[Nytrunner]

Ok. Before I commit to gluing tiny fins on this long rocket, is it really going to be stable?

You've created a Super-roc. Length/Diam is greater than 20. The normal "1 body diameter" rule is not good here, and with such a long skinny rocket, the CP will shift much more drastically as the rocket stabilizes in flight.

I design rockets so the CP-CG distance stays within 8-15% of rocket length during flight (and aim for 12% static margin).

You're right around 13% static margin which is good (despite having almost 6 "calibers"). Do a stability plot in the simulation (with windspeed ~5mph) and look at how the margin changes throughout the flight. This is a good learning example

 

[Joekeyo]

First of all I've never used OR in this capacity, it is quite interesting. My take is that the rocket is becomes unstable between 5 seconds and the apogee and then again around the 8 - 9 second mark. I will make the fins bigger and run some more simulations. I've had enough experience with rockets to think the design failed the smell test. Thank you for turning this into a good learning example.

 

[Nytrunner]

Yep, thats almost 1 ft of CP swing. That's a bit much even for a long model like this.

Use the preset plot config for Stability vs Time, and try to get it so Stability calibers doesn't drop below 3.5

 

[Joekeyo]

Ok. Changing the fin size didn't alter the CP plot. Thank you for the specific instructions. I can run with that. Learning experience indeed!