Computing Fin Tab "Depth" in Thru_The Wall Fins

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BigRiJoe

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I'm working on a project that has a 3.0 PML Quantum Tube airframe strengthened with a coupler material. The Quantum tube has 4 slots that match 4 slots in the inner coupler material. I have the dimensions of the fin set, but how do I compute the correct "width" of the tab that will connect the fin to the motor mount?
 
Open Rocket will compute that automatically for you if you sim your rocket using it.
 
the good news is that Open Rocket has quantum tube in the data base, the bad news is it has incorrect info. the 3" tube has a wall thickness of .072", an outside dia. of 3.146" and an inside dia. of 3.002"(according to the PML website. the important data for fin tab depth is the outside dia. of 3.146"). good luck on your build.
Rex
 
TTW fin depth.jpgJust measure the thickness of each tube and add the center ring depth. Add about 1/32" to give you a little insurance that things fit right. You can always sand, but its a pain to recut new fins.
 
Rex: How are you figuring the outside diameter of the "3" Quantum Tube
 
3.002"(I.D.) + 0.072*2= o.d. of 3.146", I also plugged the figures into OR and got the same results(OR figures things a bit differently, you feed it an O.D. and wall thickness and it figures the I.D.(in this case 3.002")).
Rex
 
of course PML might have mis-labeled their tube spec.s...in which case all bets are off.
Rex
 
Quantum tube's specs change with temperature. It kinda makes things difficult...
 
I put the motor mount tube and rings in the body tube
Stick a piece of scrap plywood through the slot and draw a line on it
Repeat for other slots to make sure all is concentric.

M
 
Worst case, make them 1/8" longer than needed and trim / sand to fit (power sander).
 
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