I'm finally building my BIG GOBLIN!


UPSCALE
GOBLIN
BUILD NOTES

PARTS LIST: Most all parts from www.Semroc.com
Body Tube LT-225220 Cut to 15.89"
Balsa Nose Cone BC-22588
Fin Material 2 sheets of 3/32" Basswood, Laminated to 3/16" thick
Screw Eye SE-12
Baffle Ring Set EBR–225T
Kevlar Cord SCK-418
Elastic Cord EC-236
2 Launch Lugs LL-320
Plywood Ring Set CR-9225P
1 Thrust Ring TR-9
1 Engine Mount Tube ST-950E
1 Engine Hook EH-38
1 Engine Spacer TS-9
18" Ripstop Parachute PN-18
1 Goblin Decal equivalent size from www.ExcelsiorRocketry.com


After having the parts for three months, I finally started the build on April 23, 2008.
All the main parts are from SEMROC. I am upscaling the original Estes GOBLIN from a BT-55 tube to a 2.34" Semroc (LT-225220) thick walled tube.
All upscaling was done to a factor of 1.766. The Original Goblin nose cone was 5" long from shoulder to tip. The Semroc nose cone is correct to scale at 8.9" shoulder to tip. The Semroc BC-22588 is a large scaled copy of the original Estes BNC-55AO Goblin nose cone.

PRE-CONSTRUCTION
I put a light bead (3/16" wide) of Super Glue inside the ends of all body tubes. I then smoothed the bead out with my fingertip. I followed by sanding (squaring up and cleaning) the ends of all body, baffle and engine tubes with 400 grit sandpaper on a block.

ENGINE MOUNT
My Goblin won’t have a removable engine mount. I plan to use single E and F engines. I used standard plywood centering rings (Semroc CR-9225P)

The rings were a little tight on the engine tube (ST-950E) and over the engine hook. (EH-38) It took a little light filing of the inside ring for a friction fit over the engine tube. I also cut a small notch in both rings to clear the engine hook.
The rings are glued 7/8" and 3 1/8" from the bottom of the engine tube. I made a white card stock “strap” over the engine hook. The strap measurement is 1" wide x 2 ½" long. It was cut from 110 lb. stock with a hobby knife and metal straight edge. I chose white card stock over the (usual) masking tape as the tape gets brittle over time. White glue was spread over the strap and it was rolled onto place. I centered the strap over the hook and between the two plywood rings.

That's it for now, that Semroc nose cone is BIG!
Chris Michielssen

Attached Images

YORFGoblinEngineMount.bmp (137.7 KB, 173 views)

Hey Chris

Sweet love the Goblin looking forward to your build thread.

The link below will show you the progress on my 196% Goblin since these photos were taken I have two more primer coats applied next comes paint and decals.

http://4hrockets.blogspot.com/searc...0&max-results=4


BAR
John

__________________
John

NAR #91135 L1
SAM #0037

Today's GOBLIN progress:

I Emailed Excelsior Rocketry about the Goblin decals. They had Goblin decals for many tubes but not the Semroc 225 tube. I asked which size decals would you recommend, the BT-70 or BT-80, which had close diameters? Excelsior immediately emailed back:

"I have upscaled the decal to fit the SEMROC tube, and have added it to the website, under the Upscale Decals page. The upscale decal is a full page and costs $9.00. The decal is ready to order via the website whenevr you are ready!!."

Phred

Talk about great service! Thanks Phred!


Here's today's work:

FINS
The original Estes Goblin used BFS-40 (1/8") balsa fin stock. This version is a (close) 175% upscale. For the upscale model I needed fin stock almost 1/4" thick. I really didn’t want cut 1/4" (through the wall) slots in the body tube. That’s a little too wide of a slot, and might compromise the strength and roundness of the tube. I decided on fin stock that was a little thinner, and would still give the right upscale fin thickness.
While I could have used thinner (1/16" basswood) stock, I was trying to replicate the look and fin thickness “ratio” of the original, only bigger.
The original:
1/8" (.125") X 1.766 (upscale ratio) = .220" thick fins.
Or, what I’m using:
3/16" thick basswood (Two 3/32" sheets laminated) = .1875" thick fins.
I couldn’t find 3/16" basswood stock so I decided to laminate two 3/32" basswood sheets together to reach the 3/16" thickness.
I squirted long beads of white glue on one basswood sheet, spread it out evenly and thin. I lined up the top sheet on the (glued) lower sheet and rolled a dowel over the two sheets. I applied pressure on the rolling dowel to evenly distribute the glue and squeeze out any excess. I put the glued basswood sheets under some heavy books to dry overnight.

Attached Images

YORFGoblinFinsDrawn.bmp (137.7 KB, 120 views)

Cutting 1/4" slots isn't a problem with strength, as the TTW design will give the tube all the strength it needs once glued. In fact, the tube strength will be about the same whether you cut a long 1/16" slot or a long 1/4" slot. In order to keep the tube round, you just cut the TTW part of the fin as two individual tabs with the back tab not going all the way to the bottom of the fin instead of making one long full length slab of a tab. That lets you leave a couple of bits of tube at the tail and in the middle of the fin making solid rings the full circumference, to keep the round shape. With 1/4" thickness, you won't miss the extra wood for strength.

I have a BT-80 based Red Max and Citation Patriot built this way, and will likely replace my trusty old surface mounted BT-80 based Goblin using the same build technique soon. I used balsa on all of these, because it's plenty strong at that thickness, and I didn't want to add too much weight. Rockets built like this are fairly light but nice and draggy, making them perfect for demonstration flights. Demos aren't much good if the rocket flies too fast or high for the kids to see much of the flight.

To TBZEP,
Thanks for the tips.
Getting back into the hobby after a 25 year absence I am new to TTW techniques. Your suggestion about two slots as opposed to one long one certainly makes more structural sense.
Years ago, I remember cutting slots into BT-20 and BT-50 tubes. Body tubes with a thin wall thickness could lose strength and roundness. I was going on my past experience.
That isn't a problem with this thick walled Semroc tube. As the fin tab and slot is not real long, for now I am going to stay wth my original plan.
I will incoporate the separated tab/2 slot technique on the next upscale model I build.

Thanks again for your suggestions.

Thirty years ago (toward the end of my involovement in rocketry) I launched by myself. With all the support the Forum offers today, I would have probably stayed in the hobby instead of just getting back into it now.

Hans "Chris" Michielssen
Old NAR # 19086

GOBLIN Upscale Build

Here's yesterday's progress:

The fins were quite thick and hard to cut out. I decided to cut the thru-the-wall notches after I squared up the fins. All edges were cut a little wider than the drawn lines to allow sanding to size. I also made the fin tang a little wider than necessary to allow trimming to size later on.
As the fins are large and thick, I wouldn’t be able to hold them together and sand all four square together.
I drilled three small holes near the outside edges and held all four together with straight pins. I squared the edges with 100 grit on a block. (See first picture.)


FIN SLOTS
I downloaded a fin marking guide from the free “Tools” page from the Payloadbay.com website. I simply typed in the body tube diameter and number of fins. Great site with great free tools.
I marked the fin slot ends 1" (slot bottom) and 3 1/8" (slot top) from the end. The slot itself will be 3/16" wide by 2 1/8" long.
I didn’t cut the body tube length yet. The tube comes from Semroc at 22" in length. If I happen to mess up the fin slots I can try again from the other side of the tube. Once I’m happy with the fin slots I can cut off the other end and throw the “bad” end away. The upscale tube length is 15.89".
Using the template, I marked the four fin guide lines. I drew a second line 3/16" to the left of all the lines. The bottom of the slot is 1" from the bottom. The top of the slot is 3 1/8" from the bottom.
I put a new #11 blade in my knife. Fin slot cutting has been a challenge in the past, trying to get the lines straight and clean. I tried something new this time, with great results. I actually taped my metal straight edge on the tube then used it to cut the straight lines. I made several lighter cuts until I got through the tubing.
I used a emery board to widen the slots (slightly) to match the fin width. I constantly checked by sliding the fins into their slots. As I fit the first fin, I marked the fin root with a “1", and the fin slot on the body tube “1". I continued marking the other three fins and tube slots. I wanted to keep track as there could be slight differences in the slot and fin tab lengths between the four fins.
The emery board even helped square up the corners of the fin slots. The final fit was great!
I sanded down the excess fin slot tang until the upper and lower root edges mated with the body tube. (See second picture.)

Tomorrow I'll tackle the ejection baffle.

Hans "Chris Michielssen
Old NAR # 19086

Attached Images

	YORFFins pinned, ready for sanding.bmp (215.8 KB, 126 views)
	YORFFins and Tube Slots.bmp (217.6 KB, 113 views)

EJECTION BAFFLE
The Semroc Ejection Baffle set (EBR_225T) consisted of two plywood rings and two “8" series tubes. The tubes were 4 ½" long.
The main Goblin body tube is just under 16" long.
The engine mount assembly will take up 5" of room in the lower main tube. I would also need at least 6" of space above the baffle for the parachute(s).
I decided to cut down the baffle tubes to 3", the same length of the baffle tubes in my Semroc Explorer kit. Considering the 6" for the parachute “space”, this should place the baffle 2" above the top of the engine mount.

I had to figure out all the internal structure placements to guarantee all would fit in the “short” main tube.

From the rear of the main tube forward:
5" for the engine mount
2" open space above the engine mount
3" for the baffle
+6" open space for the parachute and nose cone shoulder
= 16" total main body tube length.

I wanted to coat the tubes with white glue to protect them from the ejection charges. To coat the inside of the 8 series tubes I used a ½" dowel to spread the glue. I put glue on the end of the dowel, laid the dowel in the tube then “rolled” the glue in place.
It make an even, smooth, fully covered interior of the tube. I will also spread glue on the outside and the exposed areas of the plywood baffle rings.
At the moment I’m not able to finish the baffle, I misplaced the plywood rings! I know they’ll show up sometime, but it gave me the excuse to order extra parts, two Golden Scout kits and another baffle from Semroc. On the positive side, while looking for the rings, I had the chance to clean off my work area and consolidate all my building supplies.
The Semroc order, with baffle rings, will be picked up on Monday, May 4.

More tomorrow,
Hans "Chris" Michielssen
Old NAR # 19086

FILLING BODY TUBE SPIRALS
While I waited for the order to arrive, I filled the body tube spirals. I used thinned Elmer’s Fill and Finish and followed sanding with a block using 400 grit sandpaper. The spirals were very shallow and required a second fill in a few spots.
I even filled the spirals in the launch lugs. The Goblin will use two 3/16" x 1 ½" long launch lugs.

FINS
I rounded the leading and trailing edges of the basswood fins. I left the root and outside edges square as directed by the old Estes Goblin instructions. I rounded the edges starting with 100 grit on a block and then finer grades down to 400 grit. I sealed the fins with two coats of sanding sealer.

DRY FIT
I dry fitted the engine mount, nose cone and fins. The TTW fins lock the engine mount perfectly. The model is really starting to shape up now. It's over 2 feet tall with a fin span of around 10 inches.

Attached Images

	YORF Dry-Fit Side View.bmp (211.2 KB, 115 views)
	YORF Dry-fit full view.bmp (210.8 KB, 117 views)

__________________
Hans "Chris" Michielssen
Old/New NAR # 19086 SR

www.oddlrockets.com
www.modelrocketbuilding.blogspot.com
http://www.nar.org/educational-reso...ing-techniques/
Your results may vary
"Nose cones roll, be careful with that."
Every spaceman needs a ray gun.
Look out - I'm the Meister Shyster!

Chris, was this finished?

If you didn’t know, there is a link from eRockets site to this build thread on this page:

ERockets page