Sunday, January 10, 2010

Oh, Crap

Now that I've got all four fins glued onto the Quaddy - and it actually really looks like a Big Daddy - I'm starting the fillets. I did a little mental math, and I realized it's going to take some time...

[MMT is the Motor mount Tube that holds the motor in the center of the rocket. The 'walls' are the walls of the main (outside) body tube, and the rings are the cardstock centering rings that center the MMT inside the main tube.]

External fillets:
2 sides per fin * 4 fins = 8 fillets
2 launch lugs * 2 sides per lug = 4 fillets

Internal fillets:
4 fins * 2 sides * 2 places (wall-fin and fin-MMT) = 16 fillets
1 forward ring * 2 sides * (ring-wall and ring-MMT) = 4 fillets
1 aft ring * (ring-wall and ring-MMT) = 2 fillets

TOTAL: 34 fillets

Due to geometry, I can average three fillets at any one time. That's 10ish drying periods, or about 5 days of work. Double that if I add a second round of fillets, or use epoxy for some.

In other words, combine that with all the building I've got left to do, and I'll be lucky if the Quaddy is done building by the beginning of March.

However, there is good news in a few places. I managed to cut the one fin so there's no loss of strength from it being over the retention rod, and it's currently drying. I also talked with my mom and she's willing to make some more chutes for me, so I'm choosing the lightest nylon cloth I've got to make either an 18" or 24" chute, possible both, that'll bring the Quaddy down safely and still fit into the parachute space, which is very small:

2.6" [length] * {ϖ(1.5 [radius of main body tube])2-ϖ(0.6 [radius of MMT])2} = 15 in3

The good news is, I managed to pack a 24" nylon chute, with 8 lines (instead of the 4 these chutes will use), into that space, along with the nose cone. It's just tough wrapping it all around the motor mount tube.


Sascha Grant said...

I picked up an old nylon kids tent (cammo coloured!) a while back, think that having a cammo parachute will be neat :)

Good luck with the fillets!! Sounds like you've got your work cut out for you! Oh, 5 min epoxy would cut your fillet time down to an hour or so :) (Just don't mix up too much at a time)

The EGE said...

The only problem with epoxy is that I have to do the fillets with a finger. So I'd have to wear gloves and work *very* quickly. It's just easier to do it with wood glue.

Cammo 'chute.... easy to see in the air... absolutely invisible on the ground. You might want to have a beeper or radio tracker with those.