Semroc Micron Build 5

Greetings all! I hope both of my readers are doing well though perhaps it’s vain of me to assume that anyone other than my sweet wife Bridgid is reading these posts. And maybe even she isn’t reading them lol.

When we left off last night I had attached the fins using the Estes Fin Alignment guide. How did it turn out? Well, at first glance everything looked fine. Then I removed the little clips holding the fins:

On the left you can see the fins appear to lie flush against the little paddles. On the right, this one fin did not, when everything was all clipped and in place, as you can see. With its clip in place the guide pulled the fin off its alignment mark! So I had to let this one dry un-clipped.

I took Apogee’s advice to heart and only used enough glue to hold the fins onto the body. Sometimes I barely used enough and they were all actually wobbly. And during the drying process one of the fins slid up the body about 1/8” from the aft end, which made the whole rocket wobbly:

The loosely attached fins didn’t bother me because my next step was to fillet them. I’m using epoxy putty for the very first time to do this. Here’s what the tubs look like, with a little pellet already mixed up:

The idea is mix equal parts from each tub, pinch off a bit of the mixture and then roll that into a little fillet shape and apply this to the fin-body junctions. Standard for me, I used way too much for the first attempts, and was scraping the excess off with popsicle sticks. I did make manage to make each progressive fillet skinnier and more appropriately sized. Here’s the final result:

I apologize for the rotated photo, I don’t know how that happened. But in it you can see the rather, er, exuberant fillets along each fin.

Now, while filleting the fins a couple of them detached thanks to their tenuous initial gluing. So rather than repeat the glue-dry-glue routine I elected to put a few drops of gap-filling CA to stick these fins back on and rely on the fillets to definitively hold the fins on. Why gap-filling? Because it was closest to my hand lol.

The fins did end up looking pretty straight from an end view:

Doggone it, photo rotated again. But for me the jury is still out on using the fin alignment guide and the epoxy putty fillets. In the past I’ve had good luck just aligning my fins by eye and filleting with glue. Maybe the epoxy putty is better for mid and high power rocketry. And come to think of it, I tried putting all four fins on at once using the alignment guide. Next time I’ll try using it with the Baby Bertha (next project) but let each fin dry before adding the next and check them closely as they dry.

In the end, though, I’m afraid this little bird will never fly. I checked with an empty motor casing and the motor protrudes about 1/2” from the aft end when inserted. It’s only supposed to stick out 1/4”. This weight shift, along with the added weight of the epoxy putty fillets, may put the CG behind the CP and thus render the rocket unstable. So now I have to get RockSim 10 or whatever it’s called and see if that is the case. Gotta leave for work now - see you later!