Rocksim CP Locations

The Rocketry Forum

Help Support The Rocketry Forum:

daveyfire

Piled Higher and Deeper
TRF Lifetime Supporter
Joined
Jan 26, 2009
Messages
3,218
Reaction score
55
Location
thank u, next
I've noticed lately when I'm designing rockets in RockSim, they sim as "marginally stable" using the Barrowman method. However, from my experience, the designs just *look* like they would be stable. Using the RockSim CP calculation method, they are stable. So how much do you guys trust the Rocksim CP numbers? Are they any more trust-able on unconventional designs than conventional ones? Thanks!
 

illini

Well-Known Member
Joined
Oct 9, 2003
Messages
1,280
Reaction score
0
Short answer: Swing test and add nose weight if necessary.

Slightly longer answer: Don't trust either completely, and the more unconventional the design the less I trust either method since they are approximate formulas. See "short answer" for my solution.
 

rstaff3

Oddroc-eteer
Joined
Jan 18, 2009
Messages
11,759
Reaction score
14
On fairly conventional designs, I trust the Rsim numbers 100%. On the more unique designs, I often go for an extra 1/2 caliber of stability from the Barrowman. I swing test when unsure.

Nothing is 100%, I've had swing tests fail also.

PS Check the thrust-to-weight ratio, speed off the rod, etc!
 

daveyfire

Piled Higher and Deeper
TRF Lifetime Supporter
Joined
Jan 26, 2009
Messages
3,218
Reaction score
55
Location
thank u, next
POST 700!

w00t :D

The bird in question is a 6" x 9 foot rocket that's fairly conventional (eNvy, it's a L3 cert bird that'll fly lower than the planned 15K of Fundamental), so swing testing it would be like trying to fling my cousin around my head on a piece of tubular nylon :p The only "non-conventional" thing about it is it's boat tail, which is 6" diameter to 4" diameter... awww what the heck here's the sim file for you guys to check out!

EDIT: OBTW, I plan to fly on either an M1297W, an M1315W, or an M2500T... T/W even on the baby M is 10:1!
 
Top