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  #21  
Old 02-28-2019, 09:27 PM
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teflonrocketry1 teflonrocketry1 is offline
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I also updated the Semi-Scale Saturn V Estes K-39 with separate engine fairings and both the plastic and balsa fins. Be sure to only include whichever set you are flying with. This simulation contains pods so it won't work in OpenRocket.
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  #22  
Old 03-02-2019, 07:55 AM
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Quote:
Originally Posted by teflonrocketry1
I also updated the Semi-Scale Saturn V Estes K-39 with separate engine fairings and both the plastic and balsa fins. Be sure to only include whichever set you are flying with. This simulation contains pods so it won't work in OpenRocket.
Thanks, this will come in handy when I build mine!
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  #23  
Old 03-02-2019, 08:12 AM
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If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.
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  #24  
Old 03-02-2019, 01:05 PM
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Quote:
Originally Posted by mojo1986
If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.


I remember reading somewhere sometime someone said with "stock" scale fins, if you balance it at the front of the second stage, it'll be stable. I can't recall exactly where or when I read it nor by whom...

Later! OL J R
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  #25  
Old 03-02-2019, 08:31 PM
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Quote:
Originally Posted by mojo1986
If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.


For the Estes Semi Scale Saturn V K-39 kit RockSim calculates a CP of 11.7602 inches from the tip of the nosecone on the escape tower with just the scale fins in place, an unstable situation by -0.50 calibers with a C6-5 motor installed. I had to put 1.5 ounces of weight into the BT-52 section to get a margin of 1.13, see attached RockSim file. I tried to create a simulation with the 5 x BT-5 motor tubes installed and using 2 centering rings; RockSim calculates a margin of stability of 1.11 calibers with 5 x A10-3T motors installed and 1.75 ounces of weight installed at the top of the BT-52 tube at the bottom of the balsa section. Since there is some uncertainty in this simulation, I urge you to use caution when making this flight for the first time, 1.75 ounces still might not be enough added nose weight for a stable flight especially on a windy day.
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File Type: rkt oop_Estes_Semi_Scale_Saturn_V_K_39_2_paper fins.rkt (97.7 KB, 3 views)
File Type: rkt oop_Estes_Semi_Scale_Saturn_V_K_39_5A10_s.rkt (94.6 KB, 2 views)
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  #26  
Old 03-02-2019, 08:42 PM
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Bruce, that's just super! Thank you!


Joe
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