Is it ROCKSIM or a CG issue I'm having??

OK here's the issue. I just finished my MADCOW Scooter and I'm having issues with the CG and I'm wondering why? The file with no changes aside from the chute seems to be accurate. It shows the mass @ 6.5oz see below with a CG of 2.06. According to MADCOW it should weigh 6.0oz

View attachment mcr_scooter.rkt

When I add a G80T-7 it brings the CG to 0.97, which for me I would prefer something around 1.25 to 1.50

So I decide to add .5 oz of nose weight and with the motor it moves the CG to 1.28 so I'm happy with it. Of course this matter until I find out exactly what my rocket weighs.

So I weigh it and it comes in @ 6.3 without motor the retainer.

Here's where I get confused. Keep in mind my weight is slightly lighter than what's listed in the original file.

I change the mass over ride to 6.3oz. and remove the nose weight to get an accurate display of the properties. I also remove the motor. I put the substainer at 6.3 and check the box. It makes the changes to file. I load the same motor G80T-7 and it comes in at 4.45 OVER STABLE!! What;s odd is that my rocket is actually lighter than the original so why would the CG be off by so much?? I want to get this right. If I have to friction fit the motor I'm cool with that, but there's not much more I can do it right. And to think I was going to add nose weight? I'm thinking there might be something wrong with the file itself? I check all the properties of the parts and they are correct as far as material is concerned.

Can anyone shed some light on this?

Thanks in advance.

You didn't set the CG location when you set the mass over ride and the default value is very very wrong.

UhClem said:

You didn't set the CG location when you set the mass over ride and the default value is very very wrong.

Click to expand...

You're absolutely right! I'll go back and do it. Never changed it before so I'll look for the setting.

OK I figured it out. What I don't understand is according to the rocket specifications MADCOW puts the CG @ 20.75 from the tip, but the rocket is only 22" in length. There's something wrong with that?

try these numbers(as I got them from rocket reviews) CP 18.26"/ CG 16". those should keep things pointed in the proper direction .
rex

I went ahead and basically made a new rocket in ROCKSIM and now the numbers seem to work well.

See the file View attachment MADCOW Scooter.rkt

The numbers seem to work better. I even added .5000 the weight of the retainer for a total weight of 7.7 oz

To double check the CG I placed the rocket fully loaded minis motor on a body tube and came up with the following numbers without the motor.

It balanced perfectly at 14.5" from the tip of the nose cone. With a G80T-10 it's marginal at .83 I still think it could use some nose weight.

What's odd is when I add nose weight it doesn't change the CG?

AfterBurners said:

When I add a G80T-7 it brings the CG to 0.97, which for me I would prefer something around 1.25 to 1.50

So I decide to add .5 oz of nose weight and with the motor it moves the CG to 1.28 so I'm happy with it. Of course this matter until I find out exactly what my rocket weighs.

Click to expand...

OK, Hold up there buckaroo, you have me confused. You keep saying CG, but it looks like you are talking about stability margin. Which is it?

T-Rex said:

OK, Hold up there buckaroo, you have me confused. You keep saying CG, but it looks like you are talking about stability margin. Which is it?

Click to expand...

Stability sorry

No worries, just making sure....

Rex R seems to be leading you in the right direction, so I'll shut up...

Y'all have fun and play safe!

I'll point out that the G80 is not the heaviest non-hpr load, the G64 has that distinction (151g vs 128g for the G80), thus balancing for the G80 could get you into trouble if you wanted to use an RMS G.
rex