MADCOW Jayhawk Nose weight question?

[AfterBurners]

So I'm plating around with some numbers in ROSKCSIM trying to get the correct amount of nose weight / ballast for this thing doesn't do anything weird like corkscrews out of control. According to the instructions on MADCOW's website the CG should be 19" from the tip of the nose. I'm assuming that would be loaded with the biggest motor you intend to fly.

https://www.madcowrocketry.com/content/pdf/jayhawk.pdf

So with an H250-14 ( not to say I would actually fly this) but with 12 oz of nose weight I come up with the following:

CG - 15.1623
CP - 19.5037
Margin - 1.64

For me this looks good, but nowhere near what the instructions are?

Next up the most practical motor I would fly in the Jayhawk more than likely a G64-8. Same amount of nose weight. I come up with the following:

CG - 14.2452
CP - 19.5037
Margin - 1.99

A margin of 1.99 for me is probably a little too high, I would like to stay within 1.50.175, but with this kit on a windy day well the extra nose weight might help.

So here's the dilemma. In order for me to get a CG 19" from the tip of the nose cone I would have to add only 2oz of nose weight. I come with the following:

CG - 19.0135
CP - 19.5037
Margin - 0.19

Attached is the ROCKSIM file with above specs of 2 oz of nose weight. View attachment Madcow Jayhawk AMQ-37A.rktView attachment Madcow Jayhawk AMQ-37A.rkt

And of course it fly's crazy as one would expect. So why does the instructions say to have the CG 19" from the nose tip??? This just doesn't make any sense at all?:confused2::confused2::confused2:

I think between 10-12oz of nose weight should be fine.

Any feedback is appreciated.

Another Note: I built the 4" Madcow Patriot. The instructions state that the CG should be 28" from the nose tip.

With 27.3000 oz of nose weight and a loaded J500-10 I get the following:

CG - 26.6366
CP - 32.4349
Margin- 1.45

Now I know that I'm at 26 instead of 28, but in this case I think it works to my favor. When I added the ballast and topped the rest of the cone with foaming epoxy, I didn't think it would add a couple oz. Anyway if you look at the velocity at deployment I'm at 0.00 perfect!!

Rocksim - View attachment patriot.rkt

I guess what I'm trying to say is sometimes the instructions are not always right and you have to trust your gut or a program you worked with before.

 

[Nytrunner]

I can't speak for the Jayhawk, but Rocksim has a decent representation of the Patriot CP. Better than OpenRocket at any rate.

The Jayhawk would also be hard to work the Barrowman Equations on since it has the finlet's and stuff. Did you create them properly in Rocksim?

 

[AfterBurners]

I can't speak for the Jayhawk, but Rocksim has a decent representation of the Patriot CP. Better than OpenRocket at any rate.

The Jayhawk would also be hard to work the Barrowman Equations on since it has the finlet's and stuff. Did you create them properly in Rocksim?

The file I used in RS was actually downloaded from Madcow's website. I think I'm going to stay with the 12oz of ballast. In most cases I would say 95% of the time RS has always been right on for me and I always used 1.0 -1.5 diameter of the tube for the CG. I guess it's a wait and see.

 

[dr wogz]

Personally, I think Madcow makes this confusing.

(anyone, please correct me if I'm wrong) but as I understand it, the CP is static; it's dependant on the design of the rocket. Unless you change the design, the CP won't change. The CG is dynamic; will, however depending on build style, motor use, payload, paint etc.. all that will affect the CG.

Fully loaded, in the "worst case" (laundry as far aft as possible, the largest motor, 17 layers of paint on the fins, etc..) the CG should be at least 1 caliber ahead (towards the nose) of the CP location.

All rocket kits should state the CP location. A seasoned / well versed rocketeer needs this one bit of info, and will balance accordingly.

Your addition of 10-12oz makes sense to me..

 

[AfterBurners]

Personally, I think Madcow makes this confusing.

(anyone, please correct me if I'm wrong) but as I understand it, the CP is static; it's dependant on the design of the rocket. Unless you change the design, the CP won't change. The CG is dynamic; will, however depending on build style, motor use, payload, paint etc.. all that will affect the CG.

Fully loaded, in the "worst case" (laundry as far aft as possible, the largest motor, 17 layers of paint on the fins, etc..) the CG should be at least 1 caliber ahead (towards the nose) of the CP location.

All rocket kits should state the CP location. A seasoned / well versed rocketeer needs this one bit of info, and will balance accordingly.

Your addition of 10-12oz makes sense to me..

Thanks for looking over it. I think I calculated it with H128 just in case I decide to fly it on one, but more than likely it will be a G64

 

[mikec]

Personally, I think Madcow makes this confusing.

Madcow computes the CP using Rocksim modified Barrowman and then tells you to balance the rocket at least 1 caliber ahead of that CP location using the heaviest motor you plan to fly -- that's what their CG number means. Sometimes (short rockets) they add a massless transition to simulate base drag.

I don't have Rocksim so I can't verify this particular file. OR can't handle the tip fins of the Jayhawk so I can't check it with that.

 

[dr wogz]

What I mean by confusing is this:

Madcow give a CG point in their instructions: 19" from tip / nose cone. No CP point.
That's somewhat vague. As: is that with the largest recommended motor installed? Single use or reloadable? Empty? What about when CTI / AMW / Aerotech release a new motor that's lead lined.. (They don't mention this in their instructions [with motor installed], so it's implied, and if you don't know..)
Is it then assumed that the CP is 1 caliber (2.6" in this case) behind this point: at 21.6" from tip? Is that just 1 caliber? Could it be more? or less?

This has come up in the past / other threads, and I believe Madcow do have both the CP and (recommended) CG points on their newer kits / instructions.

 

[AfterBurners]

What I mean by confusing is this:

Madcow give a CG point in their instructions: 19" from tip / nose cone. No CP point.
That's somewhat vague. As: is that with the largest recommended motor installed? Single use or reloadable? Empty? What about when CTI / AMW / Aerotech release a new motor that's lead lined.. (They don't mention this in their instructions [with motor installed], so it's implied, and if you don't know..)
Is it then assumed that the CP is 1 caliber (2.6" in this case) behind this point: at 21.6" from tip? Is that just 1 caliber? Could it be more? or less?

This has come up in the past / other threads, and I believe Madcow do have both the CP and (recommended) CG points on their newer kits / instructions.

I plan on using a bulk head plate and solid eye bolt, so I'll calculate that into the mass, but 10-12 should be fine, but I get what you are saying? I just rely on past experience, but never actually flown this kit.