Build Thread Wildman Goblin 4

[Upsrocketman]

I already have too many projects to count, but Wildman posted a 4" Goblin kit a while back and I could not pass it up. I recieved the kit a few weeks back and decided to start building it so I could have it ready for LDRS in July.

First things first, all of the parts got a bath to get rid of any mold release or fiberglass dust that was left over.
Next up was prepping myself for lots of sanding...

Then I sanded the motor mount, and both centering rings and installed my aeropack retainer. Notice the difference between the sanded and un-sanded rings.

My forged eye bolts should be here today, I'll be installing two on the top ring before it gets glued into the airframe. My goal is to do internal and external filets this weekend.

 

[Dave S.]

Looking forward to seeing the rest of your build w/ the pics. Are you making this head end deploy or motor eject?

 

[ONAWHIM]

@Upsrocketman THANK YOU for starting this thread!
I also purchased the WM Goblin 4 for a future project and have this forum thread on my watch list.

Do you plan to sim and if so will you go from scratch or modify?

 

[Theory]

Watching : - ))

 

[TRWXXA]

Watching.

Got my Wildman 4" Goblin kit a couple weeks ago. Already got the switch band for HED, and am considering getting an extended motor tube.

 

[PATHFINDER]

Watching -Just started the same kit. I Added a Short AV Bay for HEDD with Blue Raven Alt, and, FW Tracker, Longer Motor Tube, Alum Thrust Plate / Flanged Retainer.

 

[Upsrocketman]

I put together a rocksim file tonight while I still had the rocket in pieces and was able to measure and weigh each piece. If you want a copy of the file send me a message with your email and I will send it over. I also plan on sending the file to wildman for them to review and post on the website.
I'm going to try and get some more construction done tonight. I'd like to have it ready for internal filets by saturday.

 

[Upsrocketman]

I got a chance this past weekend to do quite a lot with the goblin. I started by using the fins to make sure the top centering ring was in the right spot and I used 5 minute epoxy to glue it in place as I had a bit too much wiggle room for CA to effectively tack it in place.
As you can see, I decided to use two welded eye bolts rather than a kevlar Y harness glued to the motor tube. Normally with these I would use kevlar but I had a spare nylon 5/8 Y harness that I wanted to use.
While the epoxy was curing, I did the scariest part of this build and drilled holes around the fin slots so I would be able to inject my internal filets.

Hey guess what... it's time for more sanding!
I sanded the fin tabs and a bit up the fins as well to prepare them for internal and external filets.
Once the motor mount assembly was cured I put some epoxy inside the airframe right at the top of the fin slots and slid the whole motor mount assembly in.
I put a thin bead of CA on the fin root and slid the fins into the airframe.
I mixed up some west systems epoxy with a little chopped carbon fiber and injected it through the holes in the airframe. The internal filets only need to cover the joint between the motor tube and the fin. The first set were a bit thick so I used a little less carbon for the rest of the filets.
Once the internal filets were done and cured I took the opportunity to put the rocket together just to see what it looks like standing up. I will be doing external filets this week as well as building the ebay for head end deploy.

 

[ONAWHIM]

We live vicariously
Keep it coming

 

[Hobie1dog]

That's going to be a brute as good as you're building it.

 

[PATHFINDER]

Your build is looking really great. It’s a pleasure to follow along..

 

[Upsrocketman]

I finally got a chance to do the external filets this past weekend. They were all done using west systems epoxy with colloidal silica to thicken the epoxy so it doesn't run.

Once the filets had all cured, I sanded all the rough edges down to smooth out the epoxy and then covered all the filets in bondo spot putty.

It looks a bit rough, but once it had dried I began sanding the spot putty down to help smooth out the transition between the filets and airframe.

This is by no means necessary, I am just picky about my filets being smooth and level. The bondo helps fill any voids as well. Once I get everything sanded smooth it will be time for primer and more sanding!

 

[Dave S.]

Your work on the fillets where you used the Bondo looks just like what I do. I am a newbie myself w virtually no talent at all - I just learned a few things from these boards and asking around for tips. This rocket will look great when it’s painted.

 

[cflytech]

I put together a rocksim file tonight while I still had the rocket in pieces and was able to measure and weigh each piece. If you want a copy of the file send me a message with your email and I will send it over. I also plan on sending the file to wildman for them to review and post on the website.View attachment 585128
I'm going to try and get some more construction done tonight. I'd like to have it ready for internal filets by saturday.

 

[cflytech]

I would like a copy of the sim file if you still have it, I jut got the kit in and open the box , Looks lik I am going to have to get another one for my daughter so we can race.

 

[ONAWHIM]

@Upsrocketman, for the head end deploy what did you choose for harness sizes?

I would think that the primary harness gets the greatest stress and therefore sizing while the HED could safely take a thinner harness since the rocket has lost most of it's energy at the second deployment, maybe 3/8" primary and 1/4" secondary (or even 3/16").

I'm thinking packing the nose cone with less harness and more parachute , thoughts?

 

[Pinetree]

What size eyebolts did you use?

 

[ONAWHIM]

What size eyebolts did you use?

@Pinetree if the question was directed at me I'm sorting that out now.
I have a number of 1/4" lifting eye type eyebolts, that's 1/4-20 thread with an eye I.D. of 5/8"

Edit: Look at the pics in post #8, similar to those. 316 stainless

 

[Pinetree]

Thanks.

 

[Upsrocketman]

I used 1/4 eye bolts all around and ordered the 4 inch harness from wildman which is 1/4 kevlar for both harnesses.

 

[ONAWHIM]

@Upsrocketman for Wildman's 4" set I am seeing 3/8" for both harnesses?

 

[Upsrocketman]

Quick updat for those following this build thread...

The goblin is was finished on July 6th, I have no pics of the painting process as most of it happened at night due to the fact I was knee deep in LDRS prep and couldn't paint while the sun was still up and dad duties were the priority.

Here is a pic of it on the pad at LDRS prior to its first flight...

Special thanks to Mark Hayes from Stickershock23.com for the awesome Goblin Decals. He included a Wildman logo that can be seen in the photo.

Liftoff on a J415 in my drag race with @ECayemberg, rocket boosted to a little over 4800'.

Flight was perfect on the way up, great drogue separation and then I lost sight of it on the way down and when I found it I discovered why...

Main chute never came out so we fell on a toasty drogue chute and cracked 2 fin filets. Luckily it broke the filets and not the airframe, so repairing it shouldn't be difficult.

 

[Upsrocketman]

@Upsrocketman for Wildman's 4" set I am seeing 3/8" for both harnesses?

My bad, they are 3/8".

 

[ONAWHIM]

Wow! The boost must have been awesome!

What did you have for the head-end deploy?
3/8" x 25' harness if I understand, what was the parachute? How did it pack in that volume?

I'm sorting this out now.
Thanks

 

[Upsrocketman]

Wow! The boost must have been awesome!

What did you have for the head-end deploy?
3/8" x 25' harness if I understand, what was the parachute? How did it pack in that volume?

I'm sorting this out now.
Thanks

I was running the 3/8 harness with a 50" top flite parachute. Everything packed ok and had no problem coming out when I tested it but I cut one of my charge wires short and didn't have a backup so I couldn't run a charge in the tip of the nose like I had planned. When my charges went off they shoved the chute up in the nose cone.

 

[KyleMurdock]

I had the exact same problem with my 5" Goblin and HED. Came down under drogue only and cracked a fillet on the fin that stuck into the soft ground. Have since launched it 3 times with a charge in the tip of the nosecone with great results. Glad you have an easy repair as well.

 

[MarsLander]

@KyleMurdock and @Upsrocketman did either of you get any max velocity data from your flights?

Could you share motor and max velocity? Interested for some flutter analysis I'm doing.

Thanks!

 

[Upsrocketman]

@KyleMurdock and @Upsrocketman did either of you get any max velocity data from your flights?

Could you share motor and max velocity? Interested for some flutter analysis I'm doing.

Thanks!

I only had an rrc2+ on board, so I have no data other than max altitude.

 

[mathrules]

I put together a rocksim file tonight while I still had the rocket in pieces and was able to measure and weigh each piece. If you want a copy of the file send me a message with your email and I will send it over. I also plan on sending the file to wildman for them to review and post on the website.View attachment 585128
I'm going to try and get some more construction done tonight. I'd like to have it ready for internal filets by saturday.

 

[mathrules]

I would love the sim file. I finished putting the last glue on my Goblin and am curious about how it sims (comes in at just under 7.5 pounds all told).