Does it matter where the CoP is on the rocket as long as it's below the CoG?

[ignisDei]

So I know that the CoP has to be below or behind the CoG for the rocket to be aerodynamically stable but I am wondering if it matters that the CoP is significantly further up the rocket that the wings as seen in the image the CoP is close to the center, does this affect the performance or not?

 

[tg08]

Ideally, the COP should be roughly 1 body tube diameter behind the COG. This allows for minimum weathercocking, but sufficient stability. Your design looks good stability-wise.

 

[JoePfeiffer]

No. All that matters is that it be behind, you'll see different opinions about how much is enough and how much is too much.

 

[neil_w]

If your CP is abnormally far forward, it seems likely that your fins are very small. So while your rocket might be stable, it may still not be a great performer if the conditions are less than ideal.

 

[Orestes Mayo]

So I know that the CoP has to be below or behind the CoG for the rocket to be aerodynamically stable but I am wondering if it matters that the CoP is significantly further up the rocket that the wings as seen in the image the CoP is close to the center, does this affect the performance or not?

Is this Cp from the sim? It does look a bit to far forward.

Have you tried calculating it yourself?

 

[NTP2]

Is this Cp from the sim? It does look a bit to far forward.

Have you tried calculating it yourself?

How I don’t think I’ve ever seen the math for that?

 

[rcktnut]

How I don’t think I’ve ever seen the math for that?

There is a way, but I trust the sim to get it right!
https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-center-of-pressure/

 

[3stoogesrocketry]

So I know that the CoP has to be below or behind the CoG for the rocket to be aerodynamically stable but I am wondering if it matters that the CoP is significantly further up the rocket that the wings as seen in the image the CoP is close to the center, does this affect the performance or not?

Re run your stability with your beeper and parachute and shock cord and wading slid down the body until it bottoms out in front of the motor mount. G forces will compress them downwards on ignition. I'm guessing you will be unstable at that point.

 

[Orestes Mayo]

How I don’t think I’ve ever seen the math for that?

Its the barrowman Equation. Looks complicated but its really a series of measurements that you pop into an equation.

https://www.rocketmime.com/rockets/Barrowman.html

 

[NTP2]

Its the barrowman Equation. Looks complicated but its really a series of measurements that you pop into an equation.

https://www.rocketmime.com/rockets/Barrowman.html

Basically you’re recommending being a human open rocket, if it works for you I guess.

 

[neil_w]

Basically you’re recommending being a human open rocket, if it works for you I guess.

Some people really do Barrowman by hand, for assorted reasons. Not something I'm interested in.

 

[NTP2]

Some people really do Barrowman by hand, for assorted reasons. Not something I'm interested in.

Me to! Let computers do what they do best.

 

[Orestes Mayo]

Basically you’re recommending being a human open rocket, if it works for you I guess.

Nah dude lol . You stated you had the OR and didn't trust it so how else do you find Cp. I was just answering your question.

 

[NTP2]

Nah dude lol . You stated you had the OR and didn't trust it so how else do you find Cp. I was just answering your question.

I am not the OP?!

 

[3stoogesrocketry]

Basically you’re recommending being a human open rocket, if it works for you I guess.

He's recommending you continue your education and stop relying on others to do your work. So far on this fourm you seem to just want answers or to be part of something without truly doing much effort.

I am not the OP?!

Your right your not but you still asked the question.

 

[NTP2]

He's recommending you continue your education and stop relying on others to do your work. So far on this fourm you seem to just want answers or to be part of something without truly doing much effort.

That’s a little uncalled for. And how am I relying on others? Is asking a question for my education a crime?

Your right your not but you still asked the question.

Yes but he was apparently thought that I was having the open rocket problem.

 

[cbrarick]

uggh. I'd never calculate barrowman by hand. there's absolutely no need and chances are I'll mess it up long before the computer would.

but, you do need to run it with the laundry, beeper and shock cord all the way down. There's also only one rail button, and that won't work.

as said above probably not stable. I'd let you fly it, but you might not like trotting out to the C rack. I wouldn't want it to return to the flight line.

 

[smstachwick]

Basically you’re recommending being a human open rocket, if it works for you I guess.

I learned how to do Barrowman by hand, even learning to pull square roots by hand for the project. The math isn’t super advanced but you should be confident with basic algebra and the order of operations for best results. Mind your groupings! I also got simple explanations of how the formulae actually work. Thread here.

If you’re curious I can walk you through it or provide an example, but I get it if you don’t. It’s a lot of steps.

To answer @ignisDei ’s question though, you need some measure of positive stability margin. Center of Pressure tends to move forward from the idealized, calculated position with any angle of attack and with Mach compression. 1-2 calibers is usually fine, more than that produces more weathercocking, less than that might produce unpredictable flight paths as the rocket moves in an out of stability. Negative margins will make the rocket skywrite.