URRG

General Rocketry => Beginner's Corner => Topic started by: grub00 on May 27, 2017, 02:40:13 PM

Title: OpenRocket, unexpected results...
Post by: grub00 on May 27, 2017, 02:40:13 PM
I've jsut about finished my build I was workign on through the winter (Madcow V2 4"). I'm experimenting with openrocket to see how this thing will fly.  To start with, I copied the motor and chute specs from a forum post where a guy said he had used:

I built a rocket that closely approximates what was in the kit, and put an engine in it with the same impulse... The sim said it flew to an apogee of 165 meters.  The forum post said it went to about 650 meters.  I checked the rocket weight in the sim and its right on what MadCows assembly sheet says it should be (4lbs or 1.8 KG). Not sure what I'm doing wrong. I've attached the ork file if anyone wants to take a look.
Title: Re: OpenRocket, unexpected results...
Post by: grub00 on May 27, 2017, 02:44:02 PM
Welp...I think I might have the answer to my own question. I looked at the plot and the vertical acceleration looks like a wave function :) I think its because my CoG is too low and the rocket is all wibbley wobbely.
Title: Re: OpenRocket, unexpected results...
Post by: grub00 on May 27, 2017, 02:49:01 PM
Yep, 1KG of ballast in the nose cone sent it up to 1800 feet, same motor.
Title: Re: OpenRocket, unexpected results...
Post by: mdutch on May 28, 2017, 07:19:26 AM
Don't you just love it when someone takes the time to figure it out, and then answers their own question? Good for you sir.
Title: Re: OpenRocket, unexpected results...
Post by: RKeller on May 28, 2017, 09:09:34 PM
Open rocket kinda has a hard time with the boat tail on a V2. Where did it place the CP? I've found the V2 CP to be right at the front most point where the fins meet the body tube.