CG / CP Question

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

JRThro

Well-Known Member
TRF Supporter
Joined
Jan 17, 2009
Messages
4,054
Reaction score
4
Location
Houston, TX
Is it true in general that if you lengthen the body tube of a simple 3FNC or 4FNC rocket, the CG will move forward more than the CP will? I would think that forward displacement of the CP, if any, would be very small.

I can't see any reason why that wouldn't be true, but it's worth asking you guys with more experience.

I have two Quest Commander kits, and I'm thinking of bashing them together by using both BT's in one build, with no other changes. Just want to be sure that I'm not reducing the stability of the model.

Or will it now be too overstable, and if so, any recommendations?

Thanks!
 
Your initial thoughts on the subject are right on.

In fact, you should be able to go from an 18mm mount to a 24mm mount with no trouble or nose weight if you do that.

Overstable? Possible. But that's only a bad thing if launching in high winds.
 
Originally posted by Fore Check
Your initial thoughts on the subject are right on.

In fact, you should be able to go from an 18mm mount to a 24mm mount with no trouble or nose weight if you do that.

Overstable? Possible. But that's only a bad thing if launching in high winds.

Thanks, Fore Check!

As I said, that's what I thought, but it couldn't hurt to ask.

The Commander uses the same size body tube as the Antari, it's just about 1.5" longer. So there's no way a 24mm motor mount would fit in there; it's barely big enough for the 18mm mount, with no spacer rings. And I'm not going to do a transition to a bigger BT so I can use a 24mm motor mount, not as this point.

I'm using, or planning to use, the motor mount tube from the second Commander kit in a scratch build of the Shrox Orion as published in Apogee's newsletter #78. Here's the link: https://www.apogeerockets.com/education/downloads/newsletter78.pdf

Also, here's the link to Apogee's newsletter archive, which is just full of useful information: https://www.apogeerockets.com/education/newsletter_archive.asp
 
Originally posted by JRThro
I'm using, or planning to use, the motor mount tube from the second Commander kit in a scratch build of the Shrox Orion as published in Apogee's newsletter #78. Here's the link: https://www.apogeerockets.com/education/downloads/newsletter78.pdf

Also, here's the link to Apogee's newsletter archive, which is just full of useful information: https://www.apogeerockets.com/education/newsletter_archive.asp

BTW, the Orion that Apogee sells is an upscale of that Shrox original one.
 
Back
Top