If a member knows what the CP is for Wildman's 5 inch Jayhawk I would be greatful if you could post the information. The only information I have found in the forums search is for a smaller Jayhawk.
Thank you
Thank you
CP For Wildman's 5 inch Jayhawk
- Thread starter BB Boomer
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Message WM they should be able to tell you. I didn't know WM had one.
I already tried talking to WM but all I got was " it should be in front of the fins". Not sure how that answer is supposed to help.
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If the fin shape / scale is the same you can get the Cp location from the smaller one and scale it up to 5” one.
(5”/OD of small one) x Cp location of small one.
depends on how true to scale they are. Sometimes the high powered versions are ‘sport scale’.
(5”/OD of small one) x Cp location of small one.
depends on how true to scale they are. Sometimes the high powered versions are ‘sport scale’.
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WM has to know they manufacture the kits
That's what I thought too but that was the answer I got and I talked to Tim.
I can't be the first one to build it so hopefully they have the info and see this thread.
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Only if they created a simulation file. My guess is that WM makes kits based on past experience or "that looks about right," hence the vague "in front of the fins" reply. Aerodynamic details come later, if at all. Nearly all the Rocksim files on the download page were worked up by Mark Koelsch. There is no Jayhawk file. So, the CP will not be known until somebody builds out a simulation.
Thanks Buckeye. That makes sense. I built his DC Twins and got pretty much the same answer. Some of the kits he has the Rocsim and others he doesn't. I don't think he is concerned about providing CP's in the future for his kits. Nice kits but no CP = pain in the butt.
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The center of pressure is a function of the geometry. If you assume it’s close to accurate scale model, you can scale up as a ratio of the body diameters.
This will not be as accurate as an actual simulation in RocSim, so take this with a grain of salt.
https://www.rocketreviews.com/unknown-mcr-jayhawk.html
This Jayhawk is 2.6” OD. CP: 21.1123 inches from front
(5.0/2.6)*(21.1123)=40.6 inches from the front.
I would probably measure from the aft end since it’s unlikely the nose cones are the same shape.
30.75-21.1123=9.6377
(5.0/2.6)*9.6377=18.63“ from the aft end.
The best thing to do is enter the dimensions into RocSim and see what it says. Of course the Jayhawk is tricky since it has the tip fins. You could take the file from the link above And modify it to the 5” version.
Hope that helps,
John
This will not be as accurate as an actual simulation in RocSim, so take this with a grain of salt.
https://www.rocketreviews.com/unknown-mcr-jayhawk.html
This Jayhawk is 2.6” OD. CP: 21.1123 inches from front
(5.0/2.6)*(21.1123)=40.6 inches from the front.
I would probably measure from the aft end since it’s unlikely the nose cones are the same shape.
30.75-21.1123=9.6377
(5.0/2.6)*9.6377=18.63“ from the aft end.
The best thing to do is enter the dimensions into RocSim and see what it says. Of course the Jayhawk is tricky since it has the tip fins. You could take the file from the link above And modify it to the 5” version.
Hope that helps,
John
Build your Jayhawk in Open Rocket or RockSim. Just the nosecone, body, and fins will show you the CP. Build up the whole thing with a motor, and you'll get the theoretical CG too. Have fun with it. I'm gonna "build" and "fly" more rockets in Open Rocket than I'll ever live long enough to really build and fly.
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That is awesome info, thanks!
I was going to try and write up a Rocsim like I did for the DC Twins but I didn't know how to go about entering the the winglets.
terryg
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Down scaled from the 5.5 inch file that I have for an unbuilt Polecat Kit. Uses an extra fin set to simulate the winglets. Do not use for CG calcs without updating materials and parts!
I took the Madcow file, kept the design, then changed the dimensions and materials used to the WM Jayhawk.
The rocket is 87" tall from the tips of the winglets that touch the floor to the tip of the nosecone. What I got from Rocsim is the CP is 61.69" with a margin of 3.27" The CG is listed as 44.97" but I think that has changed because I cut the body tube about mid-section and moved the AV bay there so I could have traditional dual deploy instead of head-end. Other than that, the rest of the kit is as how it came.
The rocket is 87" tall from the tips of the winglets that touch the floor to the tip of the nosecone. What I got from Rocsim is the CP is 61.69" with a margin of 3.27" The CG is listed as 44.97" but I think that has changed because I cut the body tube about mid-section and moved the AV bay there so I could have traditional dual deploy instead of head-end. Other than that, the rest of the kit is as how it came.
Just a quick correction. I had forgot to change the mmt from 54mm to 75mm so after doing that the listed CG is 47.6" and of course the CP is the same. Hopefully the new file has me in the right spot and I thank everyone so much for your input.
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