Upscale Goblin

[Landshark]

For whatever reason, when I first started building rockets again a few months ago, the old Estes Goblin kit caught my eye. From what I understand it was somewhat of a short-lived design that was actually a give-a-way at some point. The original was 24mm and all said, in such a small size, should have been quite the performance model (1400 + feet)

I decided to build a normal scale Goblin (mostly scratch with a few parts from Semroc) but went with an 18mm motor mount to allow for flights on smaller fields (before I knew about the 24 to 18mm adapters).

I liked the model so much that I thought it'd be cool to do an upscale... I settled on using BT-80 which will make this a 196% upscale. Not the most "extreme", but it's a start.

For power, I knew that I could probably do with just one 24mm E for its size, but since I also wanted to do a cluster, I went with a dual 24mm E mount setup. I'll be able to use twin "fat C's" all the way up to E's...

I compiled my list of parts and since I wanted "through the wall" fins, I contacted BMS for a custom slotted body tube. I found the BMS catalog to be very thorough (after deciphering the codes / order process) and also found the centering rings / engine tubes I need from them as well.

The tube arrived (cut and slotted exactly as I wanted it) from BMS and I then set about constructing the motor mount. The CR's were well-made (I chose wood for the material) and only required minimal sanding to position the motor tubes.

After I got the assembly together, I realized there might be a problem with the mount design in relation to my plans for TTW fins. Since there's only two tubes, this design doesn't allow for an even mounting surface for the fins to attach on all four sides.

Hmmm.... I thought about putting balsa ribs on the sides in between the tubes so the fin could mate to the surface. Seemed like it might be hard to do.

What to do? By chance, I tried some lengths of BT-20 I had laying around in the spaces and found that when fit against the BT-50 tubes, they made for a mounting surface that's the identical height as the BT-20's. Perfect! This meant that the four fins could essentially be the same size and I could still do the TTW design.

In this pic you can see the fin template, the body tube in the back and the mocked up mount...and don't worry, I actually used the right length BT-20's in the mount so I could glue all edges to the CR's.

 

[Landshark]

One tricky part of using the slotted tube and TTW fins was getting the CR's positioned correctly. Before gluing the motor mount up completely I made sure the rings cleared the slots and had the correct alignment.

At this point, I also added some kevlar cord for the shock cord mount (not shown). I ended up ordering cord that was too small in diameter so I ended up braiding three pieces together. Should be plenty strong.

With that out of the way, I began cutting the fins. After consultation with a friend, I chose 3/32" basswood for the fins. This should be light, strong and the grain should be very easy to deal with.

I used the original goblin fin pattern and enlarged it on a copier, then added the tab for TTW attachment. That took some trial and error, but with some scrap cardboard and the motor mount glued in place, it went very quickly. While doing this, I also started filling the body spirals with FnF.

Next, I cut / sanded the fins then glued them on. It went pretty well and looks pretty cool...(I think)....

After the initial glue had dried, I started filleting the joints with yellow glue to make a strong bond. The only trouble I ran into was related to the TTW fin slots. It appears that they're not supported real well and there's one or two spots that are "wavy" where it meets the fin. This is probably because of the filleting process. It's minor and not very noticeable, but does anyone have any tips for preventing that?

Here's a view from the back...

You can see the normal scale Goblin for comparison here in these pics:

I've still got to finish sanding the body tube and add the launch lugs. BTW, that beautiful nose cone came from Semroc. Not cheap, but it's a very nice part. Quality balsa and great machining work. From what I hear, I should add a hardwood dowel plug to the center of it before attaching the eye bolt.

I just found the correct decals from Excelsior the other day for both the normal sized and the upscale, so both will be finished as they should be.

More updates soon...

 

[sandman]

That looks great so far!

As most people here know I do custom nose cones.

For some obscure reason the "Goblin" it probably my most requested upscale nose cone.

I have made the Goblin cone in sizes from BT-5 all the way up to an 8.5" SONA tube.

I really don't understand the attraction the Goblin has...it's just four fins and a nose cone but it is popular.

 

[Micromeister]

Great lookin Build so far Landshark.

Sandman:
It has to be the Decals LOL!!! and the fact it was originally designed to fly on the OLD Estes D13-5 and 7's.
Regardless of size tho...micro to BT-101 5-D12 Clustered I still believe the thing should have been Orange & Black rather then Yellow and Black to more fit the Halloween theme.

Gotta show off just a little, It's such a KEWL looking model in the Air.

 

[RevKeith]

The Goblin is perfect for upscaling - Here's my BT80 2X24mm next to a standard sized Goblin - Now that Semroc has the nose cone and Excelsior decals its a piece of cake.

 

[Rocketcrab]

I agree with Sandman, et al, about the Goblin being so popular for such a simple design. I already had it on my "To Clone" list - now this upscale thread!! Inspiration for the coming winter!! But for now, back to building NARAM stuff....

 

[BobH48]

I agree, for a simple 4FNC rocket it sure is popular.

I made a BT-70 size upscale with a 2 X 24 mm motor mount and an authentic Sandman nose cone.

It really scoots on a couple of D12-5's

 

[hcmbanjo]

Here's my Goblins - all four!
My upscale was built for single 24mm engines, Ds through Fs. The mainframe is a Semroc LT-225, heavy walled tube.

But a favorite flyer is the Franken Goblin, the green one. It was built with parts pulled from other retired models and balsa scraps pieced together.

 

[sandman]

So...what your saying is, I should print mor Goblin decals.

 

[Landshark]

Update and launch pics...

I finally got the chance to finish the Super Goblin this past weekend. I chose the same "Bauhaus Gold" paint scheme as my normal scale Goblin and applied the decals I ordered from Excelsior. The decals went on easily and look great!

I took the advice of a more experienced friend and epoxied a hardwood dowel plug in the base of the nosecone so the screw eye would have something to "bite" into.

For the first flight, I decided to launch on two C11-3's since there was a bit of wind and just in case there were any unforseen build issues. Here's a pic of the SG on the pad. The pics really don't do justice to how big this thing is in person. Compared with the "real" goblin, the SG looks almost comical.

I chose the 24 inch parachute from my Big Daddy kit and also borrowed a clip whip from a buddy of mine for the cluster ignition. I had the pleasure of using my new Mercury Igniter Lighter launch pad (just got it last week). It's a great unit with plenty of cable and an audible tone for continuity.

Everything went like a charm. When I hit the button, the SG soared off the pad with both motors firing. A friend set up his video camera and caught these frames:

I like this sequence from the second camera that my friend was using to capture the entire flight...

Rocksim said the twin C11-3's would propel the SG to approximately 650 feet and I believe that's about accurate (two D's will net around 1000 feet and two E's apparently will push it to more than 1600 feet according to the sim).

The flight was straight and stable and impressive to watch. Unfortunately on the recovery, the rocket came down right on the park's gravel road and popped a fin. Although my plans for a second flight were scrapped for that day, the SG shall return another day!

 

[Landshark]

Finally had a great near-windless fall day to launch the SG on a pair of E9-6's.

Everything we had been launching that day had been coming down within 100 feet of the pad, so I figured drift wouldn't be such a large problem with the potential altitude. On the other hand, since we didn't necessarily want to wait 3 minutes for it to come down, I switched out the plastic 24 inch chute for a nylon 18" chute, packed it up with the twin E's and let it rip.

Both engines lit and wow... great long boost, terrific noise and a straight flight. Loved it. The sim says over 1600 feet with a max velocity of 400 feet per sec. I can't verify that it went that high, but it was very impressive. On any other day, the thing would have drifted for two miles...

All went well and we were set to recover the rocket about 50 feet from the pad until the "recovery crew" went to catch it and snapped off a fin (incidentally the same one that broke before). Not a huge deal, but I may have to break out the epoxy on that one.

This was a great project and is now one of my favorite rockets. It's got a place of honor on my display stand (ok, it's my dresser). I'll see if I can post some of the pics of that flight...

 

[JSW]

I’m about to build a nearly identical T-80 based Goblin,… (BTW, THANK YOU for this very informative thread.)

Main difference is: I’m considering a 4x24mm cluster setup in the T-80 tube.

I can’t find any posts with this type of setup, so wondering if there is a good reason not to do it?

(1) Was concerned if the centering rings would have enough remaining material to retain integrity and strength. BMC offers a T-80 4x24mm centering ring, so it must be ok?

(2) normally I’d probably launch on just 2 of the 4 motor tubes. I guess I’d need to figure out how to plug the other 2 unused motor tubes so that the ejection charge doesn’t leak out the back?

(3) another reason for 4x cluster was to make through-wall fins easier to mount. i would extend the fin tabs to the joints where the motor tubes meet. Should be stronger and easier than using two extra T-20 tubes like Landshark shows?

(4) is clustering a PITA? Maybe just set up with a single 24mm motor?

Thanks again for any feedback. Much appreciated.

(Sorry for bumping this old thread,… seemed like the right spot for this question. )

 

[kuririn]

I’m about to build a nearly identical T-80 based Goblin,… (BTW, THANK YOU for this very informative thread.)

Main difference is: I’m considering a 4x24mm cluster setup in the T-80 tube.

I can’t find any posts with this type of setup, so wondering if there is a good reason not to do it?

(1) Was concerned if the centering rings would have enough remaining material to retain integrity and strength. BMC offers a T-80 4x24mm centering ring, so it must be ok?

(2) normally I’d probably launch on just 2 of the 4 motor tubes. I guess I’d need to figure out how to plug the other 2 unused motor tubes so that the ejection charge doesn’t leak out the back?

(3) another reason for 4x cluster was to make through-wall fins easier to mount. i would extend the fin tabs to the joints where the motor tubes meet. Should be stronger and easier than using two extra T-20 tubes like Landshark shows?

(4) is clustering a PITA? Maybe just set up with a single 24mm motor?

Thanks again for any feedback. Much appreciated.

(Sorry for bumping this old thread,… seemed like the right spot for this question. )

1.Plywood centering rings and epoxy should be plenty strong.
2. Use expended engine casings. Plug the nozzle hole with glue if you feel like it.
3. Correct.
4. It's more of a PITA than a single motor, but more exciting as well. Also 4 motors = 4 X $.
A clip whip will come in handy.
Cluster Cables : Rocketarium Model Rocket Kits, parts and launch supplies

Have fun!

EDIT: PS remember to re-check your CG with all that extra weight in the back. Add more nose cone weight if needed.

 

[JSW]

1.Plywood centering rings and epoxy should be plenty strong.
2. Use expended engine casings. Plug the nozzle hole with glue if you feel like it.
3. Correct.
4. It's more of a PITA than a single motor, but more exciting as well. Also 4 motors = 4 X $.
A clip whip will come in handy.
Cluster Cables : Rocketarium Model Rocket Kits, parts and launch supplies

Have fun!

EDIT: PS remember to re-check your CG with all that extra weight in the back. Add more nose cone weight if needed.

Thanks for the feedback. I'm definitely doing the 4x cluster now!

 

[Rocketjunkie]

I built a 7.5" Goblin in 2010. So a N motor would fit, I put the main in the nose cone. Build thread https://www.rocketryforum.com/threads/almost-a-goblin.8709/ This is the reason I built it this way. My Research N800. (Fits AT 98/15360 case.)

 

[RobertH3]

It works great, you may want to hang the motors out the back a bit even if you need a little nose weight - mine got a little charred and damaged the paint a little.

Cheers / Robert

 

[JSW]

It works great, you may want to hang the motors out the back a bit even if you need a little nose weight - mine got a little charred and damaged the paint a little.

Cheers / Robert

How did you set up the engine retainers for a 4x cluster?

I’m using a T-80 tube with 4 x 24mm 29mm motors. There isn't hardly any material left in the centering ring. The traditional metal hook will probably break the centering ring. (I already broke the other centering ring just by pushing on it too hard).

I was thinking of a wood screw centered between the motor tubes holding a washer against the back edge of the engines.

Is there a better way?

 

[kuririn]

You mean 4X24? I don't think a BT-80 tube has enough room for a 4x29.

I was thinking of a wood screw centered between the motor tubes holding a washer against the back edge of the engines. Is there a better way?

Use a small bolt, wing nut and washer instead of a wood screw. Drill a small hole for the bolt, epoxy the head in on the forward side of the aft CR. The washer only needs to be big enough to overlap the edge of the four engine casings.
Or, you can cut notches in the four holes for engine hooks, like the cluster mounts from Uncle Mike's:

Note the placement of the notches for the engine hooks.
Good luck!

 

[RobertH3]

I used the Rocketarium 4 x 24 mount and thought it was "OK." Like Uncle Mikes above. The rings were lite ply, would have preferred plywood. The mount also has a 3d printed motor hook holder now - looks like a red 4 leaf clover with notches. That was better.

I did a 3x24 Estes Phoenix back in the 90's and made my own rings. I think a dowel centered between the 4 tubes would hold a T-nut / hurricane nut for a screw and washer also.

Lots of ways - give at least 3/4" motor oveerhang if you can swing it. I'll take a pic of the butt end of my Goblin. Roasted!

Cheers / Robert

 

[JSW]

You mean 4X24? I don't think a BT-80 tube has enough room for a 4x29.

You're right. It's 4xT50 (24mm) tubes in the T80 made of light ply - from Balsa Machining. Even then, the T80 barely has enough room. The centering ring only has ~2mm of material between the T50s and the outside edge. Too delicate to cut notches. I'll go with the bolt/washer approach. Thanks!

 

[JSW]

Rail buttons or Launch Lugs?

I'm continuing on my build of a BT80 Goblin with 4xE engine cluster. Built with 1/4" rail buttons. For flexibility, I'd like to also put launch lugs on it.

Two questions:

(1) 1/4" launch lugs seem big? I guess it's the right size. post above of the BT70,... looks like 1/4"? https://www.rocketryforum.com/threads/upscale-goblin.4995/post-41784. And DER BIG RED MAX has 1/4" for about the same size rocket as what I'm building.

(2) Does something exist to allow convert rail buttons to launch lugs (as needed,... then screw rail buttons back in )? I picture a couple options:

• 3d printed part that would be able to screw into the rail button hole and have a 1/4" opening for a launch rod.
• I could glue a launch lug to a piece of plywood, and find a way to mount with a screw to the rail button hole.
• Or maybe a ring bolt? That might be easiest? https://www.amazon.com/Eowpower-5Pc...+bolt+8+32&qid=1631288094&s=industrial&sr=1-2

Thoughts?

Thanks.

 

[DigBaddy]

I'm building a 3" Goblin now. I just glued on some lugs in addition to buttons. Yeah, not pretty. I'll just not look at that side of it.

 

[JSW]

Finally finished my 2x Goblin upscale. First full custom rocket.

Appreciate the answers to my earlier questions. ESPECIALLY appreciate the info from first build in this thread. Invaluable for me.

Planning to launch it 10/31 as part of our Goblin mass launch. Likely will start with 4xC11 and see what happens. OpenRocket says 4xC11 only 360ft?! (478g without motors. It's a little heavy, but surely can't be right?)

 

[JSW]

I decided to build the matching “normal size” Goblin.

 

[smstachwick]

I love the Goblin, always a great performer. Top 10 rocket designs, easy.

 

[JSW]

I decided to build the matching “normal size” Goblin.

View attachment 487871

Sad weekend for my Goblin rocket family:

(1) The normal sized Goblin lawn darted on first launch due to failed ejection on the Estes D12-7 engine.



(2) The 2x Goblin has a snapped fin (birch ply) because I underpowered it. I was too chicken to put in 4 engines thinking I’d lose it. I put in 2 D12-5,… chute came out maybe 2 feet from the ground. Lesson learned.

 

[user 35280]

The normal sized Goblin lawn darted on first launch due to failed ejection on the Estes D12-7 engine.

File a Mess report on that faulty motor,

MESS Reports (MESS)

 

[smstachwick]

The C11 is a fine motor in a Goblin. Good for test-flying without having to worry about underpowering it.

In fact, I have yet to fly mine on a D.

CORRECTION: I actually have flown it on a D12-5, one of several extras I’ve had lying around for years

 

[JSW]

File a Mess report on that faulty motor,

MESS Reports (MESS)

I submitted the MESS.

Also emailed Estes about the problem. Estes is sending a replacement Goblin kit and motors!