Author Topic: OpenRocket, unexpected results...  (Read 242 times)

Offline grub00

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OpenRocket, unexpected results...
« 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:
  • CTI Smoky Sam I motor at ~500 N-s impulse in a 38mm adapter
  • 44" SkyAngel parachute

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.

Offline grub00

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Re: OpenRocket, unexpected results...
« Reply #1 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.

Offline grub00

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Re: OpenRocket, unexpected results...
« Reply #2 on: May 27, 2017, 02:49:01 PM »
Yep, 1KG of ballast in the nose cone sent it up to 1800 feet, same motor.

Offline mdutch

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Re: OpenRocket, unexpected results...
« Reply #3 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.
Mike Dutch
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URRG & MRSI Founder
"I just Want to Fly ROCKETS"

Offline RKeller

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Re: OpenRocket, unexpected results...
« Reply #4 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.
« Last Edit: May 28, 2017, 09:12:03 PM by RKeller »
Riley Keller
URRG
TRA#15415
L1 25 Oct 2014 Estes MDRM CTI H133
L2 25 June 2015 Rocketry Warehouse DYOK, CTI L1030RL 14.7k ft mach 1.57

I'm addicted to building stuff, rockets are just a way to get high