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Some fillet questions for high performance.
#1
A few questions in regards to fillets in high performance rockets:

1) When adding dye to epoxy (such as commonly done with RocketPoxy), wouldn't that in theory weaken the epoxy?  I'm thinking about a critical place such as fillets on a minimum diameter rocket (where the fins are just surface mount).

2) Is there an optimum size for fillets in terms of max aerodynamic performance?  I would assume that super big ones would create excess drag (and add unnecessary weight), but is there such a thing as "too small" as well?  In this instance let's not take into account sufficient strength; I'm interested here in aerodynamics at the moment).

3) With question #2 in mind, wouldn't it be nice if RockSim and OpenRocket had a way to plug in fillet dimensions?  

s6
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#2
(12-09-2015, 12:10 PM)stealth6 Wrote: A few questions in regards to fillets in high performance rockets:

Can't help with #2, and I'm only guessing with #1(unlikely to weaken) but can help for sure with #3
OpenRocket does have fillets, see pic below.
I've never used Rock$im so I can't help much there, but I'd be very surprised if it doesn't do fillets.


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AMRS #54
WARS #24
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#3
Open rocket allows for fillet dimensions to be added, although I don't know if they actually do anything in the sim besides add weight.

As for fillet radius, it should be 4-8% of the length of the root edge. That allows for the least amount of drag on the fillet. For example, a fin with a root edge of 6" should have a 0.24"-0.48" radius fillet. Or 0.5"-1.0" diameter PVC pipe.

NAR# 98194
Level 1: CTI I-216, 3,043'
Level 2: CTI K-740, 5,999'

Personal altitude record: 12,400' CTI L395
2014 total impulse: 9,018.2 Ns (76% M)
2015 total impulse: 7,171.7 Ns (40% M)
2016 total impulse: 18,664.2 Ns (91% N)
2017 total impulse: 8,281.1 Ns (80% M)
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#4
The drag for the fillets is simed also, though I have no idea how accurately. Try upping the fillet radius and see what it does to your altitude and speed. Though I haven't compared sims for equal weight fillets vs mass.
AMRS #54
WARS #24
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#5
Changing fillet radius on OR doesn't seem to do anything in terms of calculations. When the mass isn't changed but radius is (tested between 0.25" to 30"), the altitude stayed the same.

NAR# 98194
Level 1: CTI I-216, 3,043'
Level 2: CTI K-740, 5,999'

Personal altitude record: 12,400' CTI L395
2014 total impulse: 9,018.2 Ns (76% M)
2015 total impulse: 7,171.7 Ns (40% M)
2016 total impulse: 18,664.2 Ns (91% N)
2017 total impulse: 8,281.1 Ns (80% M)
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