Polecat Aerospace 3" Goblin
Polecat Aerospace - Goblin (3") {Kit} (27)
Contributed by Alexandra Eicher
| Construction Rating: | starstarstarstarstar_border |
| Flight Rating: | starstarstarstarstar |
| Overall Rating: | starstarstarstarstar |
| Published: | 2013-06-25 |
| Diameter: | 3.00 inches |
| Length: | 22.00 inches |
| Manufacturer: | Polecat Aerospace  |
| Style: | Sport |
Brief
This adaptable high power rocket is great for NAR Level One and Two Certifications. Its motor mount can support E motors to 6-grain J reloads. The kit comes with a fiberglass nose cone, a pre-fiber glassed and slotted body tube, a 38mm motor mount, and Baltic Birch fins and centering rings. I qualified for my NAR L1 Cert with this rocket. My certification flight was equipped with a 36" parachute and Cesaroni H125 "Classic" motor with a 9-second delay.
Construction:
Polecat Aerospace includes the following parts in its 3” Goblin kit:
- Fiberglass nosecone (11")
- Nose cone bulkhead
- Body tube – slotted (12")
- 4 Baltic Birch fins
- Centering rings
- 38mm motor tube
- Eye-bolt
- U-bolt
- 1/4” Nuts and washers
- ~10 ft Tubular nylon shock cord
- 2 Rail buttons with 8-32 screws
Tools not included but nonetheless necessary:
- 7/16” Wrench
- Epoxy (I used 5 minute)
- 1/8" Drill Bit
- Drill
- Sandpaper
Construction
The Goblin kit does not include a parachute or a motor retention system. I chose to create my own motor retainer by attaching two mirror clips to the bottom of the motor mount. I used a 36" hot pink chute and a 12" Nomex chute protector from www.RocketChutes.com.
The kit instructions were very good, and they can be found online at http://stores.whatsuphobby.com/catalog/goblin3instructions.pdf. The instructions include photographs that help guide the build process.
I started construction by sanding down the shoulder of the nosecone. This step took a very long time, much longer than expected, in order to get it to fit into the body tube. The nose cone also has a slight seam from the fiber glassing; however, it sanded off easily.
I then installed the eyebolt and hardware into the top motor mount centering ring, tightening the nut with a 7/16" wrench and securing the threads with epoxy. I used the 5-minute epoxy to assemble the motor mount. It is crucial to first check that the fins fit between the centering rings. I tied the shock cord to the eyebolt using a figure eight knot, and epoxied it in place. Then I tucked it inside the motor tube to keep it safe from any epoxy, as I installed it inside the body tube.
Next, I used 5-minute epoxy to attach the fins and smoothed out the glue that seeped out the slots. It was tough to judge what was symmetrical. I added fillets to the fins afterwards, ensuring that they would stay secure, although the kit instructions did not recommend I do so.
I connected the U-bolt in the to the nose cone’s bulkhead and then epoxied it in place inside the nose cone. I did not add any weight to the nose cone.
I installed the aft centering ring such that approximately ½” of the motor tube extended beyond it, which is the minimum to install an Aero Pac motor retainer; however, to save costs, the following supplies, obtained at a hardware store, were used to create a motor retention system:
(2) mirror clips
(2) 6/32 threaded wood inserts
(2) 6/32 round head slotted machine screws with nuts
I came across a very helpful video that shows how to properly install wood inserts: http://youtu.be/tIhEqoKE8Dc.
Lastly, I added the two rail buttons, each using one nut and two washers as spacers. The kit comes with two nuts. I drilled two 1/8" holes and then threaded the 8-32 screws. I drilled a pressure hole as well.
Finishing
After sanding and applying primer to the rocket, I spray painted the Goblin’s body tube with "Grape" Rust-oleum Ultra Cover Gloss and the nose cone with "Berry Pink."
Flight
I was qualifying with my Goblin for my NAR High Power Rocketry Certification at Lucerne Dry Lake, CA at a ROC launch in April 2013. I loaded the rocket with a Cesaroni H125 "Classic" and adjusted the motor delay to 9 seconds. The rocket screamed off the pad.
Recovery
Its 36" chute deployed perfectly, and I successfully retrieved the rocket far out on the lakebed. I was excited to earn my NAR Level 1 Jr. Cert!
Summary
PROs: Strong fiberglass body tube and nose cone. Quality fins and centering rings. Can fly on a wide variety of motors (from E to J). Flexibility to choose your own parachute. Reliable U-bolt attachment point and strong nylon shock cord. Clear instructions. Outstanding customer service from Jack Garibaldi of What’s Up Hobbies.
CONs: Nose cone fits very tight, so shoulder requires quite a bit of sanding.
Overall, the 3" Goblin is a great build. It has high quality parts and is impressive to watch as it flies off the pad and glides through the air. Additionally, it is an ideal L1 certification flight!
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