BIG GIRTHA Build Parts Part 1I'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 Big Bertha - a spare parts sorta clone! That's a Quest PNC-40 nose cone, a great buy at 85 cents each! ...
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Big Girtha Build Engine Mount Part 2 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: A 1/4" long engine block is started from the bottom of the engine mount tube. Push it in with an ...
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Big Girtha Build Engine Mount Part 3 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 outside and gives a little more clearance for the engine hook movement. The mount is finished and almost ...
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Big Girtha Build Fins Part 4 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 trimmed off 1/8" off all sides. The Bertha kit comes with 1/8" thick balsa fins, I'm making mine ...
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Big Girtha Build Baffle Part 5 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 engine mount, as far forward as possible while still allowing enough room for the parachute and nose ...
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Big Girtha Build Baffle Part 6 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 separation point between the lower white and upper black paint. Here I've simply painted the area with ...
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Big Girtha Build Shock Cord Retention Part 7 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 should only be used in bigger body tubes, BT-55 and larger. It won't interfere with parachute ejection ...
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Big Girtha Build Fins Part 8 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 edge. Take a pin and poke holes down the fin edges using the master fin edge as a guide. Cut out the ...
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Big Girtha Build Papering Fins Part 9 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. Trace wide again keeping plenty of clearance outside the fins edges. Cut the paper smaller, closer to ...
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Big Girtha Build Papering Fins Part 10 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 leading edge. Not too much, just enough for the paper to adhere over the rounded edge. You do have to ...
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Big Girtha Build Papering Fins Part 11 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 close up any gaps. This makes the edges easier to sand and ensures the paper wont lift up later on. ...
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Big Girtha Build Papering Fins Part 12 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 sanding down the primer. You can still see some balsa grain lines sanded through the primer. The root ...
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Big Girtha Build Fin Positioning Part 13 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 location lines. This will keep the primer off the body tube at the fin root gluing area. The thin strip of ...
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Big Girtha Build Priming Part 14 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 Carpenter's Wood Filler was sanded off earlier. After sanding the primer I noticed a shallow buckle ...
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Big Girtha Build Painting the Engine Mount Part 15 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 Bertha design, it might be hard to position the mount correctly after the fins are glued on. The ...
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Big Girtha Build Gluing the Engine Mount Part 16 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 over the rear lip of the tube. The fin's root edge will totally cover the alignment line. This is ...
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Big Girtha Build Nose Cone OOPS! Part 17 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 with Rustoleum Painter's Touch Gloss Apple Red. No problems. I decided to add a coat of RPT Gloss ...
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Big Girtha Build Masking the Engine Mount Part 18 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 recesses of the mount. A 1/2" dowel with an expended engine was locked into the mount for a painting wand. ...
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Big Girtha Build Trim Tape Part 19 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 picture, it looks like there is four or five red stripes spiraling up the tube. I'm going with four ...
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Big Girtha Trim Tape Part 20 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 stripe is standard black electrical tape simply wrapped around the top of the tube. The second white ...
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Big Girtha Decal Part 21 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 the red paint section would end. The middle white area was measured and a pencil center line marked. ...
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Big Girtha Finished! 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 wanted to concentrate on the tape trim stripes. I was happy with the way this one turned out. Lessons ...
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Big Girtha Recovered!
Two emails told me my Big Girtha model had been recovered after being lost in February at the Tampa TTRA field. One email said to expect water damage. The tube was swelled a bit, but it wasn't terrible.
There was some talk on TRF about why models are sealed and painted. After a ...
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Big Girtha Rebuild Part 1 Parts
To rebuild the Big Girtha I'll be using parts from a Quest Big Betty kit bought on Ebay. This kit is older, most all the parts are great quality. The die-cut fins were a bit rough, typical of most cut fins when the blades get dull. The nose cone has minor seams and the white plastic has some ...
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Big Girtha Autopsy If you missed the earlier post about my "lost" Big Girtha - The Big Girtha is a 2 engine cluster Big Bertha built from a Quest Big Betty kit. At the February Tampa TTRA launch it drifted away after a great boost on two Estes C6-5 engines. I had a video camera taped on and hoped to get a good ...
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Big Girtha Rebuild Part 2 Fins
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 balsa to add to the leading edge. A fourth fin was cut out. The Big Bertha has four 1/8" thick fins, the ...
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Big Girtha Rebuild Part 3 Papering Fins 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.
Only the leading edge of the fins was rounded. The 20 lb. copy paper covering was cut so it ...
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Big Girtha Rebuild Part 4 Papering Fins
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 could get a wrinkle you can't smooth out later.
The smooth barrel of a Sharpie pen was used to be ...
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Big Girtha Rebuild Part 5 Papering Fins 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 I used scissors. Careful - It's easy to cut too close and take off some balsa. On the top is a ...
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Big Girtha Build Part 6 Papering Fins
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 edges be sure the bottom trailing tips are square. When the model is finished you'll want all four fins ...
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Big Girtha Rebuild Part 7 Engine Mount
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 tube. Test fit both to check the engine hook movement. I turned them in to the center a bit for more ...
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Big Girtha Rebuild Part 8 Engine Mount
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 have to be filled or the ejection charge would exit out the rear.
Using the second centering ...
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Big Girtha Rebuild Part 9 Engine Mount
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 - no chance of the ejection charge blowing out the back. The two engine mount tubes fit close to the ...
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Big Girtha Build Part 10, Gluing Four Fins Evenly 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 root edge when gluing these fins on. You want the intersection of the root edge and trailing edge ...
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Big Girtha Build Part 11, Epoxy Fillets 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 decide on the fillet width. Taking a tip from Crazy Jim on TRF - I used a 1/4" dowel to mark the mask ...
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Big Girtha Build Part 12, Epoxy Fillets 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 Dowel (Clean and sanded smooth) Paper towels
Mix up the two part epoxy on waxed paper. You ...
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Big Girtha Build Part 13, Epoxy Fillets
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 they set up.
After the epoxy sets up for a few minutes, you can pull up the tape dams. While ...
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Big Girtha Build Part 14, Motor Mount Fix
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 as a little wiggle on the sides. The fit was good but not great. In the spare parts box I had a pair ...
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Big Girtha Build Part 15, Masking the Red
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 from red to white. (The front of the body tube is turned down in the picture.) This line will be ...
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Big Girtha Build Part 16, Trim Tape Placement
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 line with the launch lug. Be sure to overlap the tape strip ends by about 1/8". Over time the tape ...
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Big Girtha Build Part 17, Trim Tape Placement
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 with the upper marks, draw five more ticks for the bottom end of the diagonal stripes. Start the ...
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Big Girtha Build Part 18, Trim Tape Placement
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 bottom end of the diagonals. It looks pretty good like this and could be left as is.
The final ...
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Big Girtha Build Part 19, Odds and Ends
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 then having it "freeze" in the wrong spot.
It was dry slid into the tube using the end of my ...
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Big Girtha Build Finished
The re-built Big Girtha is ready for flight, ready for today's Tampa TTRA launch, June 15, 2013! Changes from the first version: Five red barber pole stripes instead of four A slightly smaller parachute so I'll get it back next time.
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The Big Girtha Saga!
My original Big Girtha was a two engine cluster built using most of the parts from a Quest Big Betty kit. I'd flown it a few times before losing it at a TTRA launch. On February 16 it was windy and I still switched out the two B6-4s for C6-5 engines. I had a new spy cam running, you can see it ...
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