Fin Thickness

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Digit
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Fin Thickness

Postby Digit » Sun May 14, 2017 1:15 pm

Hey all, I am about to enter the world of all fiberglass rocketry for my L2 build and would appreciate some assistance on selecting the correct thickness for fins.
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Re: Fin Thickness

Postby OverTheTop » Sun May 14, 2017 4:47 pm

More details needed I think. Diameter? Length? Motor maybe? Top speed?
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Re: Fin Thickness

Postby Digit » Sun May 14, 2017 4:53 pm

Of course.
sim design is 1.5m long, 3.9" dia, top speed mach 5.2, 4 fins roughly 200mm long by 100mm tall.

Thanks.
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Re: Fin Thickness

Postby Digit » Sun May 14, 2017 7:03 pm

Digit wrote:mach 5.2


:shock:
Try .52 lol
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Re: Fin Thickness

Postby SpaceManMat » Mon May 15, 2017 9:35 am

Digit wrote:
Digit wrote:mach 5.2


:shock:
Try .52 lol


Thought for a second they'd come out with some new Utra Vmax propellant"...

Off the top of my head 1.6mm would do the job.
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Re: Fin Thickness

Postby OverTheTop » Mon May 15, 2017 12:58 pm

Run your sim with the biggest motor you can put in it and see what top speed you get. Never hurts to allow for going harder...


I would think something like 3.0-3.2mm would be OK for that bird as it stands. If you want to push it harder you could go up to 4.2mm, depending on top speed. The 3.2mm might even be ok.

An alternative is to consider carbon fiber sheet. No different to G10 to work with IMHO. It is quite a bit stiffer than G10 so you don't to be as thick to get the same stiffness.
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Re: Fin Thickness

Postby drew » Mon May 15, 2017 5:46 pm

Yea, what OTT said. 1/8 inch thick G10/G12 will be perfectly adequate. Make sure you use a healthy fin fillets and you'll be fine, no need for any FG or CF T2T work.
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Re: Fin Thickness

Postby OverTheTop » Mon May 15, 2017 5:54 pm

Make sure you use a healthy fin fillets and you'll be fine, no need for any FG or CF T2T work


+1

If you want to go the "whole hog" (as the pig farmers say) you could build it like I would. MD motor mount to take the thrust (keep the tail in tension) and slot the airframe for the fin attachment :) .

Maybe something like this build, but bigger
viewtopic.php?f=6&t=4758&p=58844

Remember you can always adapt down, or wish you had built it bigger :D
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Re: Fin Thickness

Postby Digit » Sat May 27, 2017 6:54 pm

Thanks for the advice guys, I might even look into CF as you suggest OTT.
And I've simmed it at mach 1.02 with the biggest motor I can shoehorn into it.
OverTheTop wrote:bigger

Assimilated! :lol:
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Re: Fin Thickness

Postby OverTheTop » Sat May 27, 2017 9:47 pm

Orange Revolution went to Mach 1.8 with surprisingly little damage to the paint. The worst damage was a scrape from the rail on the way up. Not even any Mach rash on the automotive two-pack :(

It's not too difficult to go Mach+. Just build well and relax. M2+ is a different kettle of kipper...

BTW, remember going transonic already means some of the airflow around the bird is supersonic :)
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