25th February 2017, 06:35 AM
I want to say that what makes this thing a skill 5 is that its a serious Endurance Build. 27 detail fins, 9 stringers, 33 fin parts, 6 body tubes, 6 rings.....there's just a ton of pieces to prepare, fit, bond, and eventually apply a finish to.
As I mentioned yesterday in "What did you do today", I used TB Quick and Thick to add fillets to the detail pieces. 2 fillets per piece. 9 pieces per ring. 3 rings. 54 fillets.....The Q&T allowed it to be done in one sitting, but that was still a pretty long sitting. The cool thing about that glue is that it dries almost clear. Looking at it right now, I'm having a hard time even seeing some of them.
Today came the moment of truth: Mating the fins.
Since they were already sanded, It went pretty smoothly. A Bead of TBII on the bonding edges and press into place along the lines. The detail pieces were really useful for lining things up. When each piece was mated, I'd let it sit for 15 minutes while I did something else (dinner, dishes, Super Crazy Guitar Maniac Deluxe 4....etc).
All in all, I think construction is 90% done. See Leviathan below for scale (vv)
Still left is:
-stringers on the forward tube
-recovery (after painting....thats gonna be a chore)
I created a mock in OpenRocket and generated some flight speeds that this thing could see.
I used 150 ft/s as a design point for analysis. Running with an angle of attack parallel to a fin gave me CP results at ~27.47".
Once I get the noseweight sorted out, I'll get some engines and see where the CG tends to be. Based on a near complete weight with the clay in place loosely, the empty CG is just ahead of the forward ring of detail fins. That's a margin of ~11% of the rocket length empty, but I've still got more stuff to do on the front end plus recovery gear.
25th February 2017, 06:52 AM
And a side effect of the flow analysis means I got more Colors For Dollars to show off!
This run was with 150 ft/s air velocity (corresponding to a rocket flying 150 ft/s)
Here are some velocity contours. The surface represents all the points where air velocity is the same relative to the rocket. The colors are mapped by pressure (sorry, I set it up in a foot/pound/second system instead of inch/pound/second, so get lb/ft^2 instead of psi. Just divide by 144)
120 ft/s isosurface
And something cool, A slight region of air moving faster than the nominal airspeed
155 ft/s isosurface
Here are pressure regions. Notice the high pressure zones at the hollow front face of the rear fin half, and lower pressure regions contributing to the drag of the aft end.
Here's a pressure plot. greeny-yellow is ambient conditions.
Just another cool visualization of the aerodynamics on this unique rocket. There's a diffierence of ~.2 psi between the front and back of those rear segments.
(I kind of like how these pictures almost fit together)
And lastly some cool velocity cut plots. The wakes created by the odd geometry makes some pretty psychedelic patterns.
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