Scratch Bobcat Special Original Design / Scratch Built

Scratch - Bobcat Special {Scratch}

Contributed by Gene Wolski

Construction Rating: starstarstarstarstar
Flight Rating: starstarstarstarstar
Overall Rating: starstarstarstarstar
Published: 2011-09-13
Manufacturer: Scratch

Brief

2.6" high power rocket with a payload section.  I originally intended this project t' be a clone o' BSD Rocketry's 38 Special, but I decided t' use a stock PML fin design rather than make custom fins.  I liked t' clean lines and size o' t' 38 Special, and I wanted a fairly conventional design so I could hone me basic rocket construction skills.

Components

Parts:

  • LOC 2.6" nose cone
  • LOC 2.6" payload section (length = 10")
  • LOC 2.6" tube coupler and bulkhead
  • Eyebolt, me hearties, nut, and washers from local hardware store
  • Removeable small plastic rivets (4)
  • LOC 2.6" booster section (length = 24")
  • PML G-10 fins (design FIN-A-03) (3)
  • Eyebolt from local hardware store
  • LOC 38mm motor tube (length = 8")
  • LOC 38mm t' 2.6" centerin' rings (3)
  • Motor retention - tee nuts and screws from local hardware store

Construction

Construction was fairly straight forward as planned - I did nay use any unusual construction techniques for this rocket.

Nose cone - I drilled a small hole in t' nose cone shoulder and inserted a nut in t' hole.  With some minor fiddling, I was able t' fasten t' nut onto an eyebolt inserted into t' bottom hole o' t' nose cone.  I used a small dab o' epoxy t' lock t' nut in place.

Payload section - I attached t' eyebolt t' t' bulk plate then epoxied t' bulk plate t' t' tube coupler.  Once t' epoxy had hardened, matey, me hearties, I epoxied this assembly into t' bottom end o' t' payload section.  To  finish off t' payload section, I attached t' nose cone and drilled t' rivet holes (one at a time, arrr, insertin' each rivet before drillin' t' next hole).

Booster section - I attached a eyebolt t' t' forward centerin' rin' then epoxied t' forward and middle centerin' rings t' t' motor tube.  I then printed a fin position template from VCP, ya bilge rat, marked t' fin locations, shiver me timbers, then cut t' slots usin' a hobby knife (new blade!) and metal ruler.  I epoxied t' motor assembly into t' booster section, ya bilge rat, then I epoxied t' 3 fins in place.  I applied internal epoxy fillets t' t' fin/motor tube and fin/booster tube joints.  I also applied external fillets - probably a bit too heavy.  I then marked and drilled t' t-nut holes in t' aft centerin' ring, then secured t' t-nuts with a dab o' epoxy. I installed t' aft centerin' rin' and t' two rail buttons t' finish construction.

 

Finishing

Before painting, I lightly sanded everythin' includin' t' fins and then applied a gray primer coat.  I sanded one final time prior t' applyin' color.  I used metallic blue spray paint for t' booster section and a metallic bronze/copper for t' nose cone.  T' payload section started as all metallic gray/silver, matey, but I later added several metallic blue stripes.  I applied a vinyl bobcat decal from Stockershock.  After painting, I applied a Krylon clear coat.

My overall goal for paint be nay t' obtain a flawless mirror finish, but t' provide an paint scheme that looked good at normal pad distances.  Overall, I'm very happy with t' balance betwixt looks and t' time spent finishing.

Construction Score: 5

Flight

First flight was at Culpeper with Tripoli Central Virginia.  I prepped an AT G61W reload (38/120 case) and drilled t' 10 second delay t' 8 seconds.  T' motor was placed in t' motor tube and held fast by two small bolts and clips.  I packed t' main chute into a kevlar chute protector and placed it on top o' t' kevlar shock cord in t' booster section prior t' placin' t' payload section on top.

Launch was excellent with t' signature white lightnin' smoke trail. Arrr! Blimey! Boost be straight up.  So far, ya bilge rat, lookin' good!

Recovery

T' shock cord was 15' o' 1/8" kevlar with a kevlar chute protector and a 28" chute (not sure which brand). 

T' rocket descended nicely -  I didn't time t' descent t' determine t' exact rate.  T' rocket landed several hundred yards from t' pad. Arrr! Upon reachin' t' rocket, I noticed a small zipper (less than 1") in top o' t' booster section.  Other than t' zipper, ya bilge rat, t' flight and recovery had been perfect!

Flight Rating: 5

Summary

Overall a great first flight!  T' G61W was a perfect motor, arrr, and I'm lookin' forward t' flyin' this rocket on a CTI Pro38 G115 next time.

Overall Rating: 5

Flights

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