Mentioned earlier -
The instructions say to open up the small end of the tail cone until the yellow tube slides in.
Mine did, but just to double check I tried to slide a D engine in. It didn't fit!
Some 220 grit sandpaper was again wrapped around an engine casing and the hole made larger.
The edge of tail cone was now getting very thin. I could sand some from the bottom to widen the lip but that would effect the fit of the trailing edges of the fins.
Some Beacon Fabri-Tac glue was used on the plastic to tube joint.
If the space around the tube is equal, the tube should be sticking straight up, right?
This is as far as I could slide the blue tube in. It should probably be even with the end of the tail cone.
That was the problem. Sand and shorten the tail cone and the low end taper of the fin won't fit. If it were to thin the tail cone edges would be paper thin.
Friction fitting an engine in this assembly will be doable, but tricky.
> This is as far as I could slide the blue tube in.
ReplyDelete> It should probably be even with the end of the tail
> cone.
I'd say that the motor mount tube stopping short of the end of the tailcone is by design. The instructions do say to insert the motor mount tube as far as it goes without forcing it (which would otherwise crimp the end of the tube, likely making it impossible to insert the motor). If the motor mount tube was supposed to be even with the end of the tailcone, the instructions would've been worded as such. I would surmise this was done for aesthetic reason - in particular to avoid having an overly thick lip (which would be both the thickness of the motor mount tube as well as the thicker wall of the plastic tailcone).
Some thoughts on why I think gauging the size of the opening of the tailcone with spacer tube could be problematic:
* spacer tube may be slightly smaller diameter to make it less likely to be unintentionally glued inside while installing the forward thrust ring.
* even if it is the same outside diameter as (an empty) casing, an actual motor may be slightly larger diameter from the manufacturing process (i.e. casing may expand slightly when the contents are compacted).
* the casing may swell slightly after use (from the internal pressure) -- this isn't a problem when inserting the motor, but becomes a problem when extracting it. How many of us have noticed that even with the clip-type retention, the motor always seemed to be a bit more snug than when we inserted it? How many of us remember the headache of a stuck motor in a friction motor mount? Aside from the swelling, the tape adhesive seems to react to the heating by becoming rather gummy and more likely to leave residue.
My bad experience with stuck motors in friction fit mount was enough for me to swear off such rockets in favor of motor hook -- until someone showed me the method of using the tape on the *outside* (which works as long as you've got enough of the motor sticking out past the motor mount tube and enough motor mount tube w/o obstacles like fins getting in the way of applying tape).
Hi Naoto,
DeleteThe instruction drawings (old and newer) show the top centering ring even with the top end of the engine mount tube.
Regarding the removal of friction fit engines -
Fred Shector posted on a forum about this and I've found it to be true - Right after a flight it's easier to remove a friction fit engine. Something about the casing diameter slightly shrinking.
I also avoid friction fitting engines if I can help it. On this model you don't have a choice.