Sunday, December 19, 2010

Review - Public Enemy Ultra Fayboy (3")



The Public Enemy 3" Ultra Fatboy was my first high power rocket and was purchased for my TRA Level-I certification. I picked this kit primarily because of its sleek design and capability to fly on mid-power motors (adapter not included). There are quite a few rockets fitting the latter requirement so looks were the major factor. This kit turned out to be easy to build and extremely tough.  Unfortunately, Public Enemy is currently out of business.





Construction:
The airframe and motor tube are both paper. The four fins are plywood and extended through the airframe, the shoulder of the plastic boat-tail, and to the motor tube. Three fiber-board centering rings are provided. I don't know if I'd want this material on a large diameter kit but they worked fine in this application. The nose and tail cones are heavy-duty plastic. The recovery harness consists of a 2' section of flat nylon strap that is epoxied to the motor tube behind the forward centering ring. A 15' length of bungee is tied to a metal ring on the nylon strap and to the nosecone. The two 3/8" copper launch lugs are pre-cut at an angle. I don't remember the size chute that was provided as it has been assimilated into my range box. I remember thinking it was too small so I replaced it with a 36" chute from Giant Leap.

The instructions came on a single sheet but were sufficient for an experienced mid-power builder to follow without too much difficulty (hey - it was double sided). Being short and stubby, this rocket needs a lot of nose weight to fly safely. This was very clearly marked on the instructions and the CP/CG locations were provided. This was a big plus for the novice high power builder. As recommended, I filled the space between the motor tube and the tail cone with foam. This was a mess but ended up fine. The provided CP was at 22.75 inches. When run on Rocksim, I came up with 21.12 (Barrowman) and 22.25 (Rocksim). Being new to high power, I added resin, lead, nuts, bolts, etc. to the nose until I got the recommended one caliber of stability from the worst case figure of 21.12". I assumed the largest motor I anticipated using, an I211.

Finishing:
I simply gave it a coat of Krylon primer and 2 coats of a purple Krylon that I got on sale at the local hardware store. The kit came with lettering (Fatboy) and I added its name "Mini Mojo" which I cut out of silver metallic trim.


Flight/Recovery:
The recommended motors were basically any of the AT RMS 38 mm up to the J350, although the latter might require added reinforcement that I didn't provide. I used a Nomex® pad from Giant Leap in place of wadding and installed threaded bolts in the rear centering ring. I fabricated a motor retention hook from a coat-hanger and terminal lugs (normally used to terminate wire). My rocket flew twice on G80's and once on an H242-M for my Level-1 cert (Maryland Tripoli Eastern Shore Launch (ESL-29) on 11/20/99). The G80-7 makes for a relatively low, but straight flight. On the H242, it really moved out, with a predicted altitude of 2824'.


With the large amount of nose weight, my Mini-Mojo Fatboy weighs in at ~40 oz. It has recovered nicely from each flight. As mentioned earlier, I opted for a slightly larger chute than that which was provided. With the foam-filled boat tail impacting first, however, it would be hard to damage this tough little rocket.

On its 5th flight, I picked too large a chute on too windy a day and it was lost to a grove of trees. Then, on a bright sunny day in July, it reappeared. After about 2 years living in the trees, it had turned gray (something I am beginning to relate to). Anything cardboard was toast. The fins were rotten from the inside out. The plastic cone, tail cone, lugs and the chute were fine. The big surprise was that chute. I had patched it numerous times with self-adhesive rip-stop nylon tape. There was no sign of the tape lifting. Amazing! I only wish my 38/240 case was still in it. Very suspicious.

 
I stripped it down to the foam-filled plastic tail cone, removing the body tube, motor tube and fins. The fiber-board centering rings were in good shape, having been protected by epoxy (also amazing). I installed a new motor tube and reinstalled the fiber rings. The fin tabs were embedded in foam, so I ended up cutting and surface-mounting replacements. With the fins mounted so far from the base, they really don't have to absorb the shock of landing.


I decided to paint the Mini Mojo black. I first shot on a couple of coats of Kilz primer and then gave it three coats of Rustoleum (mainly because I had some from a garden furniture project).  It has flown several times since, most recently on an AMW G115-6.