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  #1  
Old 11-09-2023, 06:37 PM
PaulK PaulK is offline
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Join Date: Nov 2005
Location: WI
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Default Estes Great Goblin

This was a pretty basic build. I mostly followed the instructions, deviating only with a Kevlar shock cord through the top CR, reinforced with 2 layers of scrap CR material. To get close to the original NC aspect ratio and overall model length, I cut 1" off the BT, and painted the bottom 1" of the NC to match the BT. Even though it's 1" shorter than the kit design, since it's the same length-to-diameter as the small one, it'll should be plenty stable. Come to think of it, though, the current BT-55 kit does have a pat or two of clay in the NC...

I thought about doing some modest fin reinforcement, but simply didn't have enough time to do that and get it done for this weekend's launch. I'll put in at a 30" or 36" chute to reduce fin damage on landing. It certainly doesn't need plywood fins for flight, but the balsa is going to be fragile on landing.

Duplicolor Primer, Old Krylon base white coat, Ace Autumn Gold yellow, and Rustoleum black.

The decals are cut-your-own style, and are a bit on the thin side, so got a couple corners stuck underneath that I couldn't fix. As much as I like waterslide, once they get larger like this, they're definitely tougher to apply than vinyl.

Anyhow, it ought to be a fun flyer on the E16-4 & F15-6.
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Name:  GreatGoblinDecals.jpeg
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Name:  GreatGoblinMM.jpeg
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Name:  GreatGoblinPaint.jpg
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  #2  
Old 11-11-2023, 06:33 AM
PaulK PaulK is offline
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I created a quick RockSim, starting with a BT-55 Goblin rocksim (credit in the .rkt description), using the Scale feature, then adjusting all the components until I achieved mass & CG of my actual finished model, including a BT shortened 1" from the kit, and 1" longer NC when scaled from the BNC-55AO (shape isn't perfect, but good enough for a sim).

Anyhow, the CG with no motor is 20" from the tip of the NC, and with an F15-6, it moves to 22", with a 1.74 stability margin. No need for nose weight. I've attached the RKT file, feel free to improve, just update the .rkt description fields.

Fully finished weight is 14.2 oz (Estes website spec is 16.5 oz!), including a 30" 6-panel nylon chute, and a final coat of Future. It's first flight will be on an E16-4 today, which sims at 483'.
Attached Files
File Type: rkt EstesGreatGoblin.rkt (46.2 KB, 20 views)
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Last edited by PaulK : 11-11-2023 at 06:54 AM.
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  #3  
Old 11-11-2023, 04:37 PM
PaulK PaulK is offline
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The Great Goblin flew twice today, on an E16-4 and F15-6, from a 5' rod. The E16 flight was nearly flawless, until it came down on someone's car, dinging a corner of one fin, and the NC bounced on the street before the owner caught the model (thanks!), so it has a well-worn look now. Had the car not been there, the whole model would have hit the street, and had more damage. The F15 flight, really turned into the wind (about 5mph), so didn't achieve anywhere near the altitude I was hoping for, and worse, landing in a thick tangle of trees. It was about 20' high in a 4" diameter buckthorn. Fortunately, I carry a small Fiskars collapsible pruning saw in the car, and was able to cut down the Buckthorn (good riddance!), and retrieve the model, with the help of 2 friends in the club. The Great Goblin is ready to fly again. Even with the 30" chute, it came down faster than I liked, with those fragile fins, so I might go up to 36" next time.

It's little brother flew on a C11-5 for a flawless flight.
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  #4  
Old 11-11-2023, 05:12 PM
SolarYellow SolarYellow is offline
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A good guy on another forum has suggested keeping the balsa and just glassing them. Probably a good way to go.
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Old 11-11-2023, 09:36 PM
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erik442 erik442 is offline
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Sounds familiar. Years ago I had to climb a 20ft pine tree to retrieve my big Alpha.
Glad to hear your Great Goblin will fly again.
My vintage Goblin always flew best on a C11.
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  #6  
Old 01-09-2024, 01:40 PM
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astronwolf astronwolf is offline
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The Great Goblin is available at AC Supply. Just noticed this today.
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