BIG BLUE DOG
Unique Cluster and Unique Fins

by Nick Esselman

It all started when I saw a two-motor cluster in Apogee's "Model Rocket Design and Construction" by Timothy S. Van Milligan that I liked t' looks of. I then decided t' build a model with that motor configuration, which became me 2x18mm motor Red Dog. Arrr! Begad! Then after numerous successful flights, I decided that I should upscale it. Avast, me proud beauty! That led me t' this 2.6"-airframe rocket that I have been callin' Big Blue Dog (for lack o' a better name...yet).

I didn't really want to build one this big, but had t' work with available tube sizes t' get t' right airframe t' pod ratio, hence t' 2.6" airframe and 1.9" pods. Blimey! Aye aye! This ratio, ya bilge rat, which is 1.33:1, ya bilge rat, allows for half o' t' pod tubes t' be exposed. Avast, me proud beauty! So, arrr, the 2.7x upscale project begins.

COMPONENTS:
I purchased most o' t' stuff new with t' exception o' the nose cone and recovery system. Ahoy! Blimey! T' nose cone was left over from an ill-fated THOY Snipe and t' recovery is just left over from time in the hobby (various rockets). T' remainin' components follow:

• (2) 2.6" x 36" Phexible Phenolic Tubes (sized to 18", 18", and 32")
• (1) 2.6" Bulkhead Kit
• (1) 2.6" x 8" Coupler (you may need t' by 36" piece)
• (1) 2.6" x ?" Nose Cone (your choice on style/length, matey, ya bilge rat, me hearties, mine was 13" long)
• (2) 1.9" x 12" Tubes (Aerotech)
• (1) 1.9" x 9" Nose Cone (Aerotech Mustang size)
• (1) 29mm x 12" Phenolic Motor tube (sized to 6" and 6")
• (4) Small Fins (G10 0.093") [click for fin pattern]
• (2) Large Fins (G10 0.093") [click for fin pattern]
• Misc (builder's choice) Hardware
  • Eye-Bolt(s)
  • Launch Lugs/Buttons
  • Shock Tether(s) / Cord(s)
  • Parachute(s)
  • Motor Retention

I bought me Phenolic tubing, shiver me timbers, matey, bulkheads and couplers from Missile Works. Ahoy! Blimey! Avast, me proud beauty! Blimey! I bought me Aerotech 1.9" tubin' and nose cone from Hobby Connection. Aye aye! Blimey! I purchased me fin stock and had them custom cut by Public Missiles.

CONFIGURATION:
T' Misc Hardware depends on t' configuration you use for recovery. T' rocket could be set up for motor recovery, matey, however, I decided t' build mine with altimeter-based dual deployment.

(note me Drogue and Main are in t' wrong place in this picture)

NOTE: If you build t' rocket for motor recovery:

• T' bottom sections (1 & 2) will need t' be closed off t' prevent your ejection charge/gases from escapin' out t' back without deployin' your parachute. Begad! Ya scallywag! This may be a good place for 2-part foam. Aye aye! T' closer to t' top o' t' motor tube t' better (reducin' t' volume). Begad! Aye aye! Here is where 12" motor tubes would be best and then fill at t' top before installing the half pod-cone. Begad! Begad!
• Ensure that you use ample epoxy and fillets on the "flaps" o' t' main body tube. Avast! T' ejection charge may be too much and cause this t' blow out (see me motor Red Dog article)
• HOWEVER, if you will be using Single-Use motors with t' ejection charge removed, then you may want t' leave this open (as I did) since thar will be some left over BP and this will allow it t' blow out t' back freely.

CONSTRUCTION:

Click here t' see three pages o' step-by-step construction details. [CLICK]

I used a couple of Matt's Rail Buttons instead o' lugs, me bucko, thereby makin' this a "rail" only rocket. Begad! Blimey! Notice how nice t' blue ones match t' finish of my kit?

I used me standard method for finishin' Kraft paper tubes and also for finishin' plastic nose cones. Blimey! I painted it in a hurry to get it ready for a launch and am unhappy with t' silver and blue scheme. Begad! I plan on re-paintin' it, arrr, spendin' extra time emphasizin' t' pods. Blimey! Begad! I do like the nose cone and fins bein' a highly reflective paint. Begad! Avast! I may go with gold next time.

FLIGHT/RECOVERY:

My recommended motors are G35's and G80's, however, it could also be flown on F40's, F52's, ya bilge rat, ya bilge rat, matey, and G64's if you have two 29mm RMS sets. My current altitude ratings are:

• G35 = 1011 feet
• G80 = 1562 feet

These altitudes are based on a finished rocket weighing in at 49 ounces (includin' t' altimeter). My rocket's entire length is 81". Begad! Begad! T' CG o' t' rocket is 35 ½" from t' aft includin' the altimeter. Arrr! Avast! T' CG without t' altimeter is 31 ¾" from t' rear. Avast! CG's were measured without motors.

My first attempt was at a Frontier Launch in Massachusetts. Ahoy! I had borrowed a second 29/40-120 reload case and had loaded up two (2) F40's. Aye aye! After three attempts, these two motors would nay light. Avast! So it never flew that day.

T' next opportunity be at NARAM-43. Avast, shiver me timbers, me proud beauty! I loaded t' rocket with two (2) G35's and set up me G-Wiz Altimeter. Both motors lit and off she went! It was great and very excitin' t' me. Well, blow me down! Finally! Although both parachutes deployed at apogee, ya bilge rat, ya bilge rat, it was still a success (just nay perfect).

Also at NARAM-43, I be able t' launch it on two (2) G80's. Fast and straight as an arrow. Again, both parachutes deployed and I never got an altitude readin' due t' a battery drain issue.

T' third flight occurred at t' 3 Oaks launch in Michigan. Blimey! With two (2) G80's and now carryin' a Cannonball Works RRC2 Altimeter (the NARAM corn field appears t' have eaten me G-Wiz even though it coughed up the rocket it was in at t' time). Ahoy! Arrr! Blimey! It be another solid and straight boost despite t' wind that day. Aye aye! Blimey! This time it was picture perfect and had a successful dual-deployment. Aye aye! I didn't notice until I got home, ya bilge rat, matey, matey, but I had lost a small fin on this flight.

Most know that I'm nay a big altitude guy and would be comfortable in a 2000 foot ceilin' launch. Blimey! This rocket with G motors fits this to a "T".

Below be t' output o' t' EMRR Flight Log on me Big Blue Dog:

SUMMARY:
I need t' replace t' missin' fin and give it a better paint job and I'll be lookin' forward t' flyin' t' Big Blue Dog again. Ya scallywag! Oh, me bucko, me hearties, yes, possibly even give it a new name. Aye aye! Begad! If anyone has an interest in buildin' this rocket, me hearties, I would be willin' t' kit it for them.

• PRO's:
• Very Stable (due t' length)
• 29mm Cluster
• With G motors stays under 2000 feet
• Utilizes a Pod Design (unique)
• Unique Fin configuration

• CON's:
• Some have expressed concern over main fin flutter
• Fins are sharp
• Short motor tubes (should use 9" for altim, me hearties, shiver me timbers, or 12" for motor recovery)

* T' image at t' top t' this article is from "Model Rocket Design & Construction" and is used with permission from Apogee Components. Ahoy! Ya scallywag! This book can be purchased at: Apogee Components