Almost a Goblin

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Rocketjunkie

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I am building a Goblin upscale based on the new 7.5" Blue Tube 2.0. I'm calling it 'Almost a Goblin' as there are two deviations from scale. First, I'm using a PML nose cone that is the correct length but not quite the shape of an upscale BNC-55AO. Secondly, I'm increasing the scale 53" body length to 60" so I can use motors up to 48" long. The rocket will have a single 98mm motor mount.
 
First, I built an E-bay into a section of 6" coupler. The e-bay will vent into the main body and the main body will have vents a way down the airframe. I know I'm taking a chance that the apogee event pressure will effect the altimeter. From my experience, the Perfectflite MAWDs do not respond to an event that is shorter than the sampling interval. Do to the vent arrangement, I cannot just twist and tape the power wires so I built a screw switch that can be activated with an allen wrench through a hole in the airframe. The e-bay is my standard construction with a 1/2" threaded rod through the center and eye nuts on each end. The pictures show the inside of the e-bay, screw switch in off and on positions, switch wired to altimeter, and an overall view of the e-bay.

Nose02a.jpg

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Next, I modified a 7.5-6.0 centering ring to fit the nose cone and epoxied it into place, A 5/16" forged eyebolt was potted into the tip of the nose for recovery attachment. Then I installed a length of 6" body tube. There is plenty of room for wadding, shock cord, and 15' parachute. The e-bay inserts into the 6" BT and is held with 3 4-40 nylon shear pins. The entire nose assembly, complete with chute but without altimeter, weighs 8 lb.

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The Blue Tube main airframe has arrived along with the 3/8" baltic birch for the fins. I'll be working on the rest of the rocket gradually over the next couple of weeks.
 
I've gotten quite a bit of work done on the rocket over the last week. Fins were cut from the 3/8" plywood and the edges rounded. A 12" piece of body tube was cut and a coupler epoxied in. Then the fin slots were cut in this section. One centering ring was sanded down to fit inside the coupler.

Body01a.jpg

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Body02a.jpg

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I attach my recovery harness to the top centering ring so I added 3 layers of 7 oz cloth to each side. Then the forged eyebolt is mounted with fender washers to spread the load. After epoxying the forward 2 centering rings to the motor tube, it's installed first into the lower portion of the airframe, then the upper section is added.

Body04a.jpg

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The rear CR is removable so I can add fillets to the internal fin joints. To help prevent the front CR from ripping out in the case of a high speed deployment, a short section of tube was cut and slitted. This was epoxied in front of the centering ring. Next step - tack the fins in place. Finally, I put the nose cone on to see what it looks like :D The body section, including the shock cord currently weighs 10 lb. Now for the time consuming part - fillets, priming, sanding, and painting. I'm expecting the final dry weight to be about 25 lb.

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Hey, that does look like Almost a Goblin!:roll: Cool, Tom!:cool:75mm or 98mm motor hole?

Can't wait to see it in person! ;)
 
Is it done yest? Is it done yet? Is it done yet? :roll:
It's got a couple of coats of primer on it. Waiting for weather suitable for painting (on a day I'm not at work - beautiful weather the last couple of work days:()
 
First post here :)

I know this will date me but here's a reminder of the original paint scheme. By far one of my most favorite models. I think I know what I'll build for L2 :)

goblin3.jpg
 
First post here :)

I know this will date me but here's a reminder of the original paint scheme. By far one of my most favorite models. I think I know what I'll build for L2 :)
It was my favorite back in the early '70s when a D was a BIG motor. Mine will look like the attached picture but about twice the size of the large one (one black fin).

Goblins.jpg
 
:clap::clap::clap: That really looks like a Goblin Rocket Junkie.:cheers: I also like the last picture. Look at the size compairtions. One big and one small.:roll:
 
The e-bay will vent into the main body and the main body will have vents a way down the airframe. I know I'm taking a chance that the apogee event pressure will effect the altimeter.

Just to double check, is the inside of the altimeter bay completely shielded from the ejection gasses? I'm not clear on the venting arrangement.

The only reason I mention this is that I looked over one of my altimeters last week and it looks corroded. I know in the past I had one flight where I didn't properly seal the e-match wire through the bulkhead and I am assuming BP residue got in the bay and subsequently corroded the traces on the altimeter PCB. If that's not what happened, I am at a loss as to why that altimeter looks like it does.

Obviously you've been flying big stuff for a long time, so I am pretty sure you have it worked out, but I thought I'd mention it.

Looks great, BTW!

Sandy.
 
Awesome Tom!

This is one of my very faves! I did a 2.56 upscale back in '06 and have flown it many time with G80s and plan on putting a "H" in it this season...She needs new paint but still going strong! Gordan turned the nose for me and it was nothing less than perfect.
I have a 4" in the works and had always wanted to do something "ALOT" bigger and probably will one day. Yours gives me the inspiration to do so!

Anyways she is a beauty! And you did a FANTASTIC job on her!

Mike
 
Here is a shot of mine. It's seen many of flights with G's! But I had her prepped with a H128...She never saw the sky though...No Tripoli prefect there to watch my 4th Cert1!!!!:rolleyes: Thanks Walt! LOL

Anyways though you'd like to look at her...Gordon turned the nose for me back in the spring of '06...The cone is perfect! (well 'cept from scars and scratches) The rest of the rocket ain't so bad either!

Mike

Tripoli #5199

DSCN2245.JPG
 
Here is a shot of mine. It's seen many of flights with G's! But I had her prepped with a H128...She never saw the sky though...No Tripoli prefect there to watch my 4th Cert1!!!!:rolleyes: Thanks Walt! LOL
Lookin' good :D Sorry you didn't get to fly though :( Mine hasn't flown yet, planning on the May Orangeburg launch. I did mix up a 75/4800 L1100 for a second flight after the initial K700 :)
 
Nice job! I had a whole stable of Goblins, from micro-max to 5.5", love that rocket! I'm rebuilding my 5.5" one for the third time, I've broken fins twice on it. This time, it's getting 'glassed!
 
Lookin' good :D Sorry you didn't get to fly though :( Mine hasn't flown yet, planning on the May Orangeburg launch. I did mix up a 75/4800 L1100 for a second flight after the initial K700 :)

Hey Tom,
Your last name wouldn't start with a "B" and end with a "d" would it?
If it does i just watched some of my old Point 39 Productions LDRS tapes starring a "RocketJunkie"!

Mike
 
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