Honest John fins

[jpaw33]

I'd like to make the k-27 honest john,but with a bt-55 body tube,like the Estes kit #1919 honest john. I have all the parts but when looking at my semroc fins it dawned on me the the k-27 is bt-50 based and the fins were to small.I really like the look of the k-27 fins and would like to know if anyone can tell me how to figure out how to upscale the k-27 fins to fit the bt-55. Any help would be great!Thanks
Jpaw

 

[sandman]

Divide the final tube size BT-55 (1.325") by the original tube size BT-50 (0.976).

1.325/0.976 = 1.357 or 136%

Copy the fins or fin pattern on a copy machine and blow it up by 136%.

Done!

BTW, I have the decals for the kit #1919 on my web site for both the olive drab operational round and the black and white test round.

 

[rocketguy101]

...and if you don't feel like sanding the diamond cross section, try built-up fins. see this discussion about the technique

 

[jpaw33]

Thanks guys,I'll do that today! BTW...I already ordered 2 sets from you.Thanks alot.
Jpaw

 

[sandman]

Thanks guys,I'll do that today! BTW...I already ordered 2 sets from you.Thanks alot.
Jpaw

Oh, that was you? OK, nevermind.

 

[powderburner]

Copy the fins or fin pattern on a copy machine and blow it up by 136%.

Or, go to: https://www.rocketryforumarchive.com/showthread.php?t=2175
get the Excel spreadsheet from the bottom of the big post by the long-winded guy, input the geometry numbers for the basic fin, and input a 1.36 scale factor (in cell F7)

The spreadsheet will scale the fin up or down for you