Center of pressure

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John Taylor

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Hi everyone, I am starting a build on an Estes Hi-Flier XL. I plan to fabricate 1/8th inch birch plywood fins instead of balsa. I will modify to thru the wall construction. This will add aft weight. I need the center if pressure location in order to insure stability. I do not have any way to access Open Rocket or Rock Sim. Can anyone tell me the CP location or figure it out?
I plan on buying a new Windows based laptop soon as soon as I can afford it. I don't want to just add a bunch of weight to the nose without knowing what I'm doing.
Can anyone help me?
Thanks very much!
John
 
Rocksim is 9.2951" from NC Tip

Barroman is 8.8692" from NC Tip

I always use the ratio between both of the above which is 9.082" from NC Tip
 
If you are keeping the fins the same size and in the same position, then there will be little change in the CoP location. You will of course move the CoG location aft. Here is a OpenRocket sim view of your model with the CoG and CoP locations.EstesHiFlyerXL_OR_Sim.jpg
Question is, do I have the right model?
Gary is measuring from the nosecone (NC) tip.
 
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This is for a XL? It's like 31" tall.
9" from the nose cone tip? Do you mean from the aft end?
Sorry to ask so many questions. I do appreciate your help.
Thanks

NOT the XL, I didn't notice yours was the XL, what I posted was for Hi-Flier its 11.8"
 
If you are keeping the fins the same size and in the same position, then there will be little change in the CoP location. You will of course move the CoG location aft. Here is a OpenRocket sim view of your model with the CoG and CoP locations.View attachment 397643
Question is, do I have the right model?
Gary is measuring from the nosecone (NC) tip.
I can't read the CP measurement, when I expand it, on my cell, it blurs out.
 
Estes Hi-Flier XL (3226)
Mass (Empty): 117 g
Stability: 4.24 cal
CG: 428 mm
CP: 604 mm

With plywood fins the figures are:
Mass (Empty): 156 g
Stability: 2.69 cal
CG: 492 mm
CP: 604 mm
 
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