How accurate is openrocket?

[veebirdman]

So I finished my first scratch-built rocket. I designed it in openrocket, and it said it's stable, the center of gravity, and center of pressure seem to be good. So do I still need to do the swing test?

 

[Steve Shannon]

So I finished my first scratch-built rocket. I designed it in openrocket, and it said it's stable, the center of gravity, and center of pressure seem to be good. So do I still need to do the swing test?

No

 

[neil_w]

You *should* measure the mass and CG of the constructed rocket and enter them in as overrides in OR, *then* check stability with your desired motors.

 

[dhbarr]

Did you check that the real-life weight and CG roughly matched the sim?

Sometimes one or more components will be dramatically different than the sim which, coupled with a wind gust and/or some rod whip can make for an exciting couple of seconds.

You're probably fine, especially if it's a kit assembled according to the manufacturer's instructions and with the recommended motor.

 

[veebirdman]

I'll measure the CG, and put it in the sim. Don't know why I didn't think of that.

 

[veebirdman]

So I entered the new empty CG (which is different), through sustainer tab. I redid the the simulations, and it checks out. So would you guys not bother doing the swing test?

 

[dhbarr]

I would say you've done all your homework.

Another fun game is to add up the intended boost and coast times, then count them up during the flight to see how close your sim was on apogee.

 

[Buckeye]

So would you guys not bother doing the swing test?

No. Swing test gives too many false negatives. OR should be fine, assuming you did not add anything it doesn't know how to simulate.

 

[Steve Shannon]

So I entered the new empty CG (which is different), through sustainer tab. I redid the the simulations, and it checks out. So would you guys not bother doing the swing test?

Just make sure the actual CG with the motor installed is ahead of the estimated CP by at least one diameter and you should be fine. I would not do the swing test. It’s notoriously inaccurate.

 

[gna]

A couple of points about OR:
The first few builds I used OR on were way off, until discovered the databases. I was using the default OR settings, but I started substituting BMS or Estes tubes from the databases and they were more accurate.
Nosecones weights are all over the place.
I checked rockets all set for flight (parachute, motor, wadding) to get CG, but it's very close to with just motor installed.

 

[K'Tesh]

How accurate is OpenRocket? Depends on you. Do not blindly trust RocketReviews' sims. There's nobody doing quality check there. You should go and check out some of my tutorials on importing fins, and how to simulate nosecones, etc. to improve your sims' accuracy.

https://www.rocketryforum.com/showthread.php?62884-Open-Rocket-Tutorial-creating-nose-cone-shapes
https://www.rocketryforum.com/threads/kteshs-openrocket-tutorials.62884/


Then again, some things are just too hard to sim...

Pointy Side Up!!!