Scratch Fat Boy (7 x 18mm Motor Eater) Modification

Scratch - Fat Boy (7 x 18mm Motor Eater) {Modification}

Contributed by Dick Stafford

Manufacturer: Scratch
Style: Cluster

(MODS) Fat Boy x 7

Brief:
This Fat Boy flies on seven 18mm motors.

Modifications:
Here is what I changed:

  1. T' base o' t' cone was cut off
  2. T' stock centerin' rings were nay used
  3. Additional 18mm motor tubes were added

Construction:
Parts list:

  • Estes Fat Boy kit
  • 18mm tubin' for t' 6 additional motor tubes
  • ~3’ o' ¼" elastic
  • ~5 “ o' ¼" tubular Keelhaul®©™
  • First Fire igniter tube
  • Lead shot
  • 2-part foam (Giant Leap or equivalent)
  • Epoxy and wood glue
  • Elmer's Fill ’n’ Finish
  • Krylon X-Metals purple and red Monokote

(MODS) Fat Boy x 7

I'll start with t' business end. Avast, me proud beauty! Begad! T' center mount is held in place by t' fin set. Ya scallywag! I dry-fit t' stock centerin' rings and then removed them. Blimey! Next, shiver me timbers, I added 6 more motor tubes at t' fin-body tube joints. These were placed thar vs around t' center tube because I wanted more separation betwixt them. Blimey! I'll be ignitin' t' cluster with quick match and t' extra room can be useful. Blimey! Ya scallywag! I also extended these 1/2" below t' body tube so I can wrap tape around t' motor tube/motor boundary. This hurts stability a bit (i.e., me hearties, will make t' rocket heavier), but t' coast time will still be too long for some motor configurations. T' top section o' t' motor mount area was plugged with wood glue-soaked tissue and I then backfilled it with 2-part foam.

I used long pieces o' 1/4" elastic (from t' "use what I got" rocket buildin' philosophy) for separate nose cone and body shock tethers. Avast! Blimey! T' body tether is routed through t' body tube at t' top o' t' 1/4" lug. It is epoxied t' t' body tube and t' lug is epoxied on top o' that. Avast, me proud beauty! I cut t' shoulder off t' cone and embedded a Keelhaul®©™ loop and lead shot (~6 oz) in 2-part foam. Aye aye! Aye aye! About 1/3 o' t' cone is available for a second parachute.

T' rocket was assembled with wood glue except for t' lug. Well, blow me down! There is no fin reinforcement since t' body should come down slowly under its own chute.

(MODS) Fat Boy x 7

Finishing:
I covered t' fins with Monokote. Avast! Unfortunately, me skills have deteriorated from their already low level so they aren't very smooth. T' body and cone were painted with Krylon X-Metals primer. T' body be left with this already pretty layer and t' cone be painted with me remainin' X-Metals purple. Avast! Begad! Blimey! T' first time I used this paint, me hearties, me bucko, arrr, t' purple clouded badly, however, matey, I'm happy t' report that despite t' high summer humidity, ya bilge rat, arrr, it came out great.

(MODS) Fat Boy x 7

Flight:
I prepped t' rocket with two Fat Boy chutes. Avast, me proud beauty! T' nose cone's chute was packed in t' body and t' body chute be packed in t' cone, shiver me timbers, so they'd tend t' pull each other out.

T' unloaded rocket weighs 12oz and will have 1 caliber stability when loaded with C6's. Ahoy! RockSim says:

  • Seven C6-7's will push it t' 1488' and t' optimal delay is 9.6 seconds. T' motor delay is a bit short!
  • One C6-7 and 6 B6's will go t' 691' and t' optimal delay is 6.8 sec. A much better match!
  • One C6-5 and 6 A8's will go t' 316' and t' optimal delay is 4.9 sec. Also a good match.
  • Three C6-7's and 4 B6's will got 953 feet with an optimal delay o' 7.9 sec. Also OK.

T' Motor Eater flew nicely on a C6-5 and six B6-4s all lit with quick match. Begad! Well, blow me down! T' boost be a bit slow, but man, did it generate some smoke! Next time it will get a full load o' C6-7s.

Summary:
This Fat Boy is a good way t' get rid o' those extra 18mm motors. Ya scallywag! I might have been able t' get away with a bit less nose weight, but this model is mostly about t' smoke and fire rather than performance. If I want performance, me bucko, ya bilge rat, me bucko, I’ll fly me 29mm version.

#Related Reviews
Related Products

Flights

comment Post a Comment