OpenRocket and BaddAzz Defender MK II

[Alaskamike]

I am new to the MPR world and am having trouble with modeling flight performance with OpenRocket. I just ordered a BaddAzz Defender MK II and wanted to explore engine performance with OpenRocket (I don't want to lose this rocket on its first launch, so I wanted to see how small I could safely go). Well, I downloaded the rkt file from the BaddAzzRocketry website and loaded it into OpenRocket. First I ran a sim with an E18 and it said the rocket would only go up about 25m. So, I upped the engine to an F24 and now it goes to about 30m. My expectation is that the E should have gone to 1500 - 2000', and the F should have been 3000+. As a check I loaded a rkt file for an Estes Hi Flier and it reached 150m on an A8-3, which is about what I would expect.
Any idea what I'm doing wrong?
Thanks.

Mike

 

[rocketgeek101]

I just took a look at the file, and for some reason the rocket is unstable (CP in front of CG). Must be a flaw with the file? Anyhow that's whats causing your problem. Try adding mass to the nose until you have a proper margin of stability.

 

[kruland]

The .rkt file for this rocket has overridden the CG at the stage. When OR loads this file, the cg ends up behind the CP which causes the rocket to be unstable. When I remove the CG override at the stage, it simulates to ~2200ft on an E15.

I think there is a bug in OpenRocket's rocksim importer.

Kevin

 

[Alaskamike]

Thanks for both replies. I saw the CG/CP issue, but didn't know what to make of it. I'll remove the CG override and give it a go!
Thanks again.

Mike

 

[RDE]

we want pics

 

[Alaskamike]

Will do!

 

[CZ Brat]

Negative stability causes ultra low altitude. That's because the rocket would be doing loop-de-loops right above your launch pad. Sounds like kruland and rocketgeek figured out why OR thought you were unstable. Good luck, and would love to see pics. I just went to Baddazz website for first time today. I like the look. Especially yours. Those open fins are cool looking.

 

[kruland]

If somebody could open that .rkt file in real RockSim and let me know where the CG shows up, I would appreciate it.

Kevin

 

[grouch]

Can't speak to the OpenRocket thing but I can tell you that a CTI E75 will push the thing around 1500' or so. The flight is very fast, high and perfectly straight. I have flown it on the E22 Smokey and it was a little wobbly off the pad but once it got going it was straight and true. It's a great flying little rocket. I am not sure if I will ever fly mine on anything larger than the E75 as the flight is just on the edge of my visibility. Super cool.

 

[Eric1]

Try an F85! 4600'!!!

 

[blackbrandt]

C'mon!!!
F240 anybody?