All --Gotcha gotcha, thank you for the article on that. I'll look into it for a more accurate G value. My plywood thickness is 0.25 in, and the fins are trapezoidal.
According to my sim, my rocket weighs about 54 oz with motor, and I'm planning on launching with a J357 motor.
Adding TLAR to my analytical toolbox! Never knew such a handy tool had a name.
What a great thread !
Thanks !!
@ParagonRocketry --
Thank you for the link to the Apogee "Peak of Flight" Article: How To Calculate Fin Flutter Speed By Zachary Howard.
I am going to try to follow the calculations with all the info provided here and maybe write a Q&D script wrapper around the calcs ...
I am also following @Adrian A's related TRF thread: Counter-intuitive AeroFinSim Lite result
Now that I know about Zachary's Article, I want to try the calcs for myself.
I was able to make a simplified OpenRocket SandHawk.ork File by starting with a RockSim file for an Estes Sandhawk, scaling and substituting LOC Parts for Estes Parts.
At least I didn't have to hand enter the fins ( as long as they scaled properly for the LOC Kit from the freehand fins for the Estes model )
The Dry mass of the scaled and edited Sandhawk is 0.87 Kg / 31 oz.
Sees to be close enough for this purpose since all I need is the fin geometry, as long as they scaled correctly ...
Q: Is a J357 Motor a Cessaroni Pro-38 5 Grain 658-J357 ?
If so, using my q&d Sandhawk.ork, OR came up with launch mass = 1.521 Kg / 51 oz ( a little less than your 54 oz launch mass but I didn't bother with laundry nor links, etc ).
And OR says the Apogee Altitude will be 4552 ft with a max Velocity of 1127 ft/sec ( Mach 0.98 at 95F Launch Site Temperature ).
But this should be close enough to try Zachary's Fin Flutter Speed Calcs.
Thanks again for this info !
Full Disclosure:
I just learned TLAR this week from @Rschub in his VERY interesting Level 2 Cert thread: Minnie-Magg drag mods for Level 2?
And now, @tsmith1315 shared BTDT here in this thread -- these are two very important techniques for HPR or for life in general
Good luck with your Level 2 Cert, @ParagonRocketry !
Please let us know how it goes !
-- kjh
@ParagonRocketry -- I just noticed that you edited your original post:
EDIT: Thank you guys so much for the information, I really appreciate all the good advice here and in my messages. I think the primary problem I had was that my fin thickness was off; for some reason, it was in my OpenRocket sim as 0.118 inches, while LOC and people who had experience with those fins said that it was 0.25 inches. I checked and they were right- which lead to a much more reasonable necessary G of 16,422 psi. I also thought I should post the article where I'm getting my calculations from, so here that is: https://apogeerockets.com/education/downloads/Newsletter291.pdf
Interesting, when I first converted the Estes .rkt to a LOC .ork my fins were also 0.118 inches thick which I changed to 0.25 after reading this thread ...
Last edited: