Quantcast

Upscale Goblin

The Rocketry Forum

Help Support The Rocketry Forum:

Landshark

Well-Known Member
Joined
Apr 27, 2009
Messages
86
Reaction score
0
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

Well-Known Member
Joined
Apr 27, 2009
Messages
86
Reaction score
0
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

Well-Known Member
Joined
Jan 18, 2009
Messages
10,468
Reaction score
5
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.:cool:

Golblin8.JPG
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
38
Location
Washington DC
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.

150-a_Hobby Goblin on Pad_05-14-94.jpg
 
Last edited:

RevKeith

Well-Known Member
Joined
Jan 19, 2009
Messages
413
Reaction score
0
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.

Big Goblin flash.jpg
 

Rocketcrab

Well-Known Member
Joined
Jan 18, 2009
Messages
855
Reaction score
0
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....:eek:
 

BobH48

Well-Known Member
Joined
Jan 18, 2009
Messages
3,370
Reaction score
1
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

Goblin_BT70_3.jpg


Goblin_BT70_4.JPG
 

hcmbanjo

Well-Known Member
Joined
Jan 18, 2009
Messages
2,295
Reaction score
100
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.

GoblinFamily4OnFloor.jpg


Goblin&F.Goblin.jpg
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,468
Reaction score
5
So...what your saying is, I should print mor Goblin decals.;)
 

Landshark

Well-Known Member
Joined
Apr 27, 2009
Messages
86
Reaction score
0
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

Well-Known Member
Joined
Apr 27, 2009
Messages
86
Reaction score
0
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...
 
Top