Model Rocket Building Blog 
Model Rocket Building Posts
BIG GIRTHA Build Parts Part 1 (2010-08-18)
I've been building and flying rockets since 1969 and have never owned a Big Bertha or even a Baby Bertha. Over the years I've accumulated spare parts - lots of spare parts. It's time for a upgrade ... [Read More]
Big Girtha Build Engine Mount Part 2 (2010-08-19)I've already notched the 3" long engine mount tube 1/4" from the top. The 3" long XL EH Engine Hook is set in the notch and electrical tape was wrapped around the tube. In the picture at the right: ... [Read More]
Big Girtha Build Engine Mount Part 3 (2010-08-19)I'm using my rotary punch to make notches for engine hook movement. The hole is not centered but a little to the outside of the centering ring edge. This places more of the circle punch to the ... [Read More]
Big Girtha Build Fins Part 4 (2010-08-19)I'd forgotten how big the original Big Bertha fins were. That's a lot of balsa! I decided to trim them down a bit, it'll still be plenty stable. I didn't want to mess with the original shape, I just ... [Read More]
Big Girtha Build Baffle Part 5 (2010-08-20)To make the gluing of the baffle easier, I cut the 18" long 40mm Quest tube at 10" which left 8" for the parachute and nose cone. TIP: When installing a baffle, you want to keep it away from the ... [Read More]
Big Girtha Build Baffle Part 6 (2010-08-20)While it isn't necessary to fill the baffle/body tube seams, I wanted a smooth body on this model. You could handle the baffle joint like the Centuri Centurion model did. The seam was the color ... [Read More]
Big Girtha Build Shock Cord Retention Part 7 (2010-08-21)I'm not a big fan of the old Estes "Tea Bag" method of shock cord retention. This is certainly not a new idea, I remember seeing it in older Centuri instructions. This style of shock cord mount ... [Read More]
Big Girtha Build Fins Part 8 (2010-08-22)Now that I've cut my balsa template master, here's another old school method to transfer that profile onto the balsa. Hold the master on the balsa making sure the grain is running down the leading ... [Read More]
Big Girtha Build Papering Fins Part 9 (2010-08-22)Trace lightly (and wide) outside the fin edges. I'm using 20 lb. copy paper here. 24 lb. paper is better for covering fins. Flip the fin over (think butterfly wings) over the rounded leading edge. ... [Read More]
Big Girtha Build Papering Fins Part 10 (2010-08-22)The toughest part of papering fins is getting is getting a smooth roll over the leading edge. When spreading glue on the second side of the balsa, be sure to get a smooth glue covering over the ... [Read More]
Big Girtha Build Papering Fins Part 11 (2010-08-23)Cut the excess off close using scissors. Then shave off the paper very close to the balsa with a single edge razor blade. At this point I smoothed some thin CA over the edges to harden the paper and ... [Read More]
Big Girtha Build Papering Fins Part 12 (2010-08-23)Thinned Carpenter's Wood Filler is brushed over the balsa on the open edges. Sand down with 400 grit on a block and prime. I'll be priming these fins off the main body. Here's all four fins after ... [Read More]
Big Girtha Build Fin Positioning Part 13 (2010-08-23)I'm also going to prime the body tube with the fins off the model. The body tube has been marked for four fins. Look close at the picture and you'll see thin strips of masking tape on the fin ... [Read More]
Big Girtha Build Priming Part 14 (2010-08-24)Here's the rear of the body tube after priming and removing the tape from the fin location lines. This shows how much can be sanded off, leaving primer in what was left of the tube spiral after the ... [Read More]
Big Girtha Build Painting the Engine Mount Part 15 (2010-08-24)I decided to paint and glue the engine mount in now before gluing on the fins. It's easier to get paint in all the recesses before it's glued inside the main tube. With the long trailing fins of the ... [Read More]
Big Girtha Build Gluing the Engine Mount Part 16 (2010-08-25)The engine mount was glued into the main body with 1/4" of the engine tubes extending past the end of the main tube. TIP: Note on the back of the main tube, the fin alignment line is extended back ... [Read More]
Big Girtha Build Nose Cone OOPS! Part 17 (2010-08-25)The 1969 Estes catalog showed their Big Bertha paint scheme. It was one of the few full color pages in the catalog. The nose cone was simply painted red. I masked off the shoulder and sprayed it ... [Read More]
Big Girtha Build Masking the Engine Mount Part 18 (2010-08-26)This was a strange mask. First, small squares of masking tape were set sticky side out against the inside walls of the main tube with tweezers. Pieces of paper towel were pushed into all the ... [Read More]
Big Girtha Build Trim Tape Part 19 (2010-08-26)I'm trying to capture the Big Bertha paint scheme from the 1969 Estes Catalog. Not an exact copy - just the general feel. That barber pole at the top will be interesting to replicate. From the ... [Read More]
Big Girtha Trim Tape Part 20 (2010-08-26)As shown in an earlier post, I stuck tape strips on my glass patio door and cut them to the right width. Looking at the catalog picture, I'm guessing it's about 3/8" wide on all the strips. The top ... [Read More]
Big Girtha Decal Part 21 (2010-08-26)It' still raining outside so I jumped ahead and applied the decal. I wanted it centered between the lower red and upper barber pole sections. Another black tape strip was temporarily applied where ... [Read More]
Big Girtha Finished! (2010-08-27)Here's the Big Girtha finished and ready for the next N.E.F.A.R. launch in Bunnell , Florida on September 11. I didn't get into the fin masks this time, my methods have been explained before. I ... [Read More]
Big Girtha Rebuild Part 2 Fins (2013-05-31)The Big Girtha fins were more of a Big Bertha shape. The kit fins were used but needed a little more on the leading edge to match the shape of the original Girtha. There was enough kit ... [Read More]
Big Girtha Rebuild Part 3 Papering Fins (2013-06-01)The first Big Girtha had paper covered fins. You could see some of the balsa grain through the paper cover. On this rebuild one coat of CWF was brushed on and sanded off before paper was applied. ... [Read More]
Big Girtha Rebuild Part 4 Papering Fins (2013-06-02)Work on the rounded edge first without letting the flat sides down on the balsa surface yet. Pinch and pull the paper down over the rounded edge. Concentrate on the leading edge first or you ... [Read More]
Big Girtha Rebuild Part 5 Papering Fins (2013-06-02)Cut the fin covering paper closer to the fins but don't get too close to the balsa edges. Let the fins dry overnight in a heavy book before trimming. You could use a sharp knife to trim the fins but ... [Read More]
Big Girtha Build Part 6 Papering Fins (2013-06-03)If the edges don't sand easily and fold over, chances are they aren't glued down. Slip a little white glue underneath the raised paper and spread with a blade. Before filling the ... [Read More]
Big Girtha Rebuild Part 7 Engine Mount (2013-06-03)I rarely use the yellow or blue engine mount tubes supplied in kits. They are usually too thin . The two substituted ST-7 engine mount tubes fit pretty well, side by side in the Big Betty's 40mm ... [Read More]
Big Girtha Rebuild Part 8 Engine Mount (2013-06-04)On of the Big Betty 18mm centering rings was glued to the top of the two engine tubes. The engine blocks and tube ends were sanded flat for a better glue bond. Those holes in the top center will ... [Read More]
Big Girtha Rebuild Part 9 Engine Mount (2013-06-04)Cut out the circles as best you can with a sharp knife. You can sand to the edges of the inside engine blocks using 220 grit on a dowel or back end of a Sharpie. Here's the finished mount - ... [Read More]
Big Girtha Build Part 10, Gluing Four Fins Evenly (2013-06-05)Three fin models stand on their own without wobbling. Four finned models that stand vertically on the fin tips require a few extra alignment steps. It's a bit tough to see the rear end of the ... [Read More]
Big Girtha Build Part 11, Epoxy Fillets (2013-06-06)This model is a two engine cluster and epoxy fillets aren't really needed. White glue fillets would be strong enough. But on a larger model the fillets could be wider. Before taping up the fins ... [Read More]
Big Girtha Build Part 12, Epoxy Fillets (2013-06-07)Before you mix up epoxy, have everything you'll need close at hand: Alcohol (to smooth edges and clean up) Disposable gloves (to protect your hands) Q-tips (to clean up ends and edges) 1/4" diameter ... [Read More]
Big Girtha Build Part 13, Epoxy Fillets (2013-06-08)Pick up any excess epoxy from the ends with a Q-tip dipped in alcohol. Set the model horizontal and let the two facing fillets start to set up. Epoxy will run! Be sure the fillets are level while ... [Read More]
Big Girtha Build Part 14, Motor Mount Fix (2013-06-09)Two ST-7 tubes side by side fit very well in the Big Betty 40mm tube. I thought I might get by with just the single, sealed centering ring at the top of the mount. When slid into the tube there ... [Read More]
Big Girtha Build Part 15, Masking the Red (2013-06-10)Here's the red paint after the first coat. A second heavier coat followed. After the Scotch tape masks were removed. Two fins were left white. The area above the fin can has a mask ... [Read More]
Big Girtha Build Part 16, Trim Tape Placement (2013-06-11)I started the colored electrical tape wraps from the top down. The strips were cut to 5/16" thick on my patio door glass. Use a new blade and a metal straightedge. The wraps were all started in ... [Read More]
Big Girtha Build Part 17, Trim Tape Placement (2013-06-12)Before laying down the barber pole strips - The name decal was set on dry to be sure there was enough space for it. Mark the five ticks at the top of the red strip. Directly below in line ... [Read More]
Big Girtha Build Part 18, Trim Tape Placement (2013-06-13)I used the same paper to trim the diagonal stripe ends. Wrap it around and trim along the edge. In time the tape will shrink some, you'll want to allow for overlap. Here I'm trimming the ... [Read More]
Big Girtha Build Part 19, Odds and Ends (2013-06-14)Normally a baffle like this would be used to couple two body tubes together. I had to install this one from the top. The fit was tight so I didn't feel good about putting glue into the tube first ... [Read More]
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