dford
Tada
- Joined
- Apr 23, 2016
- Messages
- 330
- Reaction score
- 2
I was just about to suggest a paper shim for the centering rings. That should work well.
Great minds think alike
I was just about to suggest a paper shim for the centering rings. That should work well.
I like to do the final adjustment of the fin slots until after the fins are ready to install(fins and slots are indexed), I like to leave the slots just tight enough to hold the fins in place. easy enough to adjust slot width with a dremel sanding disk.
think most folks radius their fin guides at the tube fin interface so as to reduce the chance of glueing the guide to the rocket .
Rex
I still have the hardest time remembering that myself......Don't forget, your launch guides go on before you paint .
Rex
use the MK 1 eyeball(which is probably how I got one fin leaning on my 'jart', which given Murphy & Finagle...that fin will stay firmly in place till the end of time ). think most people use 1/4" foam board for 'fin jigs'.
I don't use a dremel to cut the slots in the tube(angle aluminum and hobby knife). I suspect that you didn't have the mmt glued in place when you fitted the fins/slots, and when the glue dried (and shrank) it distorted your tube a bit (search for 'coke bottle effect' for more info), this is less of a problem with heavier walled tubes. or the tube might have swelled due to a change in humidity, such are the joys of using Estes type thinwall tubing. some people use; emery boards or popsicle sticks wrapped with sandpaper to sand slots(which works nicely for paper tubes, rather slow going with fg tubes).
main thing is to remember that this is a hobby, its' supposed to be fun, and that most rockets look good from 10' away . also you get a fair amount of slack for your 1st few scratch builds as you get some practice doing new things(we were not born knowing how to build rockets). you will likely get better the more you build.
Don't forget, your launch guides go on before you paint .
Rex
Interesting build. Minus you motor mount issue, it looks pretty good. I will say, this looked like anything but keeping it simple! I was expecting this to be a basic scratch build from all store bought parts with little (if any modifications), as opposed to buying a kit.
The tear drop on the leading edge of the fin is new to me.
1/8" 3=ply Baltic birch will do fine for centering rings if you wanted to cut your own with a fly cutter / drill press. Scroll saws work too if you have a circle cutting jig that you rotate the wood on a pin. I've made some sloppy centering rings with the scroll saw free hand.
do you have(or can take) any photos of the fins post flight that you could post? I would guess that the bond between the fin tabs and the motor mount tube failed 1st, then the mount moved. been my experience that, when built properly the centering rings carry very little thrust load with TTW fins. the fins transfer the thrust load directly from the MMt to the airframe. I have used cardstock/foam/cardstock sandwich rings w/ TTW fins(1/8" balsa w/cardstock skins) and everything moved as a unit at launch. I will grant that they were small impulse motors, but they were lightweight rockets .
Rex
p.s. my bad, should have stressed the importance of securing the motor hook before launch. a couple wraps of masking tape or safety wire will keep the hook from being forced open and allowing the casing to be ejected from the mount. sorry about that.
Rex
Sounds like a shred. The motor mount probably would have gave away right on the pad and slammed up into the nose cone.
A G76 is a pretty good powered motor. Un-reinforced BT-60 / Estes is a bit weak for that power on a very light rocket. Try a LOC 1.52 w/ nose cone. That is a thick tube as it is also the 38mm motor mount tube.
I'm guessing some people here may have the skill / technique to pull it off. I do not without fiberglassing the tube.
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