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  #1  
Old 06-20-2013, 03:42 PM
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Bill Bill is offline
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Default Fin fillets for the Semroc Omega

The Semroc incarnation of the Omega features through-the-wall fins. But the tabs do not reach the motor mount tube. Furthermore, unlike most other kits with TTW fins, the motor mount is installed after the fins are attached. The aft centering ring butts against the rear edges of the fin tabs.

My question is: the instructions do not mention this, but is there any reason to not fillet the joints between the fin tabs and the inside of the body tubes? That would seem like a good thing to do, especially for the booster when flying with an E12-0.


Bill
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Old 06-20-2013, 11:28 PM
stefanj stefanj is offline
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"Slightly through the wall" fins were common at one point.

I always used internal fillets. I don't see a reason not too unless they interfere with fitting some part or another. (e.g., the Hawk Hobby Bandit upscale had tabbed fins; the fillets had to be kept neat and small so that the slotted rings of the interchangeable motor mounts would fit.)
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  #3  
Old 06-21-2013, 10:20 AM
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Chas Russell Chas Russell is offline
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Bill,

Why not add some same-thickness balsa strips to the fin tabs and sand until the strips touch the motor tube and the fin is flush with the tube. Then fillet at the motor tube, the strip/tab joint, and the tube.

Another trick I use is thin spruce on the trailing edge of swept fins to help prevent dings. No one knows the mod.

How about launch tomorrow....

Chas
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Old 06-21-2013, 01:11 PM
RWmarlow RWmarlow is offline
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Maybe it has something to do with "concerns" over the Booster "vents" getting clogged....I really have no clue...maybe Carl knows...
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Old 06-21-2013, 01:15 PM
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Quote:
Originally Posted by stefanj
"Slightly through the wall" fins were common at one point.


A lot of current Estes kits are that way.


Quote:
Originally Posted by stefanj
I always used internal fillets. I don't see a reason not too unless they interfere with fitting some part or another. (e.g., the Hawk Hobby Bandit upscale had tabbed fins; the fillets had to be kept neat and small so that the slotted rings of the interchangeable motor mounts would fit.)


The front centering rings are slotted to clear the tabs. If there was any interference, I can enlarge the slots a bit.

Now that you mention it, the Semroc SLS Laser-X is the same way with its interchangeable mounts.


Bill
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  #6  
Old 06-21-2013, 01:19 PM
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Quote:
Originally Posted by Chas Russell
Why not add some same-thickness balsa strips to the fin tabs and sand until the strips touch the motor tube and the fin is flush with the tube. Then fillet at the motor tube, the strip/tab joint, and the tube.


I am not concerned about the tabs not gluing to the motor mount tube. I was just wondering whether there was an obvious reason for not doing the "free" strengthening with internal fillets.


Quote:
Originally Posted by Chas Russell
How about launch tomorrow....


Planning on it...you?


Bill
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