Brief:
The ATTABOY is a boattailed FATBOY with 24mm upsized motor mount that can be flown in two different configurations--both with and without upper payload tube.

Modifications:
I was inspired by Michael Bade's "Big Bad V-2 Daddy", Kevin Johnson's "OY!FATBOY", and David Fergus' "Boattail FATBOY".

I applied similar techniques to those that Michael Bade describes for his "Big Bad V-2 Daddy" MOD but used two FATBOY kits in place of Big Daddy kits.

The supplied fins must be replaced with slightly larger ones to fit the curve of the boattail. To keep down the weight on the tail end of the rocket I decided to stick with balsa wood. To begin, I made the new fins by tracing one of the stock fins on a piece of paper and then, placing a nosecone on the paper and lining it up to the top of the traced fin, I held a pencil straight up and down against the nosecone and transferred the curve of the nosecone onto the fin pattern. I added 1/2" at the bottom to the length of the outside edge then drew a new trailing edge line up to meet the nose cone line. The span remains the same on the fins but they are 1/2" taller on the outside edge. The added height and the additional fin area where it curves in at the bottom of the boattail give the fins a slightly larger surface area. I reasoned that would move the center of pressure back slightly, offsetting the increased weight of the boattail and larger engine. I added tabs to the fin template for through the wall fins and left them long. I trimmed them to fit after I installed the 24mm engine tube and centering rings.

After making the new fins, I began the boattail by first cutting slots in one of the nosecones for the through the wall fins. I did this by inserting the nosecone into the bottom of one of the body tubes and using the fin slots (that would later be filled) on the body tube, I lined up a flexible ruler to the slots and marked the location of the new fin slots on the boattail. Then I cut them out carefully with an X-Acto knife and sanded until the tabs of the 1/8" balsa fins fit snuggly but not too tightly. I measured the bottom of the boattail for the engine opening (actually the top of the nosecone) to find where it was 1 1/2" in diameter. I marked it, placed it in one of the body tubes temporarily, and used a miter box with a hacksaw (because it has relatively fine tooth blade) to cut the bottom off the boattail for the engine opening. I then marked the same boattail nosecone at the halfway point (3/4") of the section that fits into the body tube and cut it carefully with an X-Acto knife. I kept the part that has the lug for attaching the shock cord and parachute to use in the bottom of the payload tube when the rocket is flown in its payload tube configuration.

Next, I used a 24mm engine tube and traced enlarged openings in two centering rings and cut them with an X-Acto knife. Then I trimmed and fit the outside diameters of the centering rings until they fit into the boattail--one above and one below the fin tabs. I did this by trimming and test fitting until they fit. The diameter of the bottom one will be smaller than the top one. Since I had two engine clips I put them both on the engine tube in the standard Estes manner but one would probably do the job. I tend to error on the side of caution and I figured if one was good, two was better. Then I added an engine block made from a 1/4" piece sawed from a spent D motor and epoxied the centering rings onto the 24mm motor tube. Now, I epoxied the assembled motor mount into the boattail. NOTE: It is possible to misalign the motor tube so I suggest using 1 hour Epoxy for this step to give enough time to get it aligned properly. (I used 5 minute epoxy and almost ran out of time.) Finally, the fins were glued into the boattail and epoxy fillets added.

The fin slots in both body tubes were filled as Michael Bade did on his "Big Bad V-2 Daddy, by epoxying strips of balsa on the inside of the tubes, taking care to leave room at the bottom (just below the slots) for inserting the boattail on the lower body tube and the part that has the lug for attaching the shock cord and parachute in the upper payload tube. After the epoxy dried I glued small strips of balsa in the fin slots and sanded flush. The small gaps that were left were filled with automotive body putty and sanded smooth.

I added a launch lug, epoxied the boattail and fin assembly into one of the body tubes and the epoxied the piece leftover from the bottom of the nosecone that became the boattail into the other tube which becomes the payload tube. I used 48" of 1/2" elastic purchased from a fabric store for $1.75 and attached it 2" below the top of the bottom body tube. I used the standard Estes "3 fold" technique. The unaltered nosecone can be taped for a snug fit and placed on the top of the payload tube with the shockcord and one of the 18" parachutes attached to the bottom of the payload tube or you can eliminate the payload tube (my preference) and attach the shockcord and parachute to the standard nosecone and fly in the shorter configuration.

Construction:

• Two Estes FATBOY Kits
• 1/8" Balsa for Larger Fins
• 4' of 1/2" Elastic for shock cord
• 24mm x 2 3/4" motor tube
• 24mm engine block (made from spent D motor)
• Total cost of the project was:
• 2 Estes FATBOY kits - $20 (I found the Estes FATBOY kits on sale at Toys R Us for $10 per kit)
• 1/8" Balsa - $3
• 1/2" x 48" elastic - $1.75
• Primer and Metallic Paint - $10
• 24mm motor tube - Had on hand
• Pinstripe - Had on hand
• Total = $34.75

Finishing:
Finish preparation included body filler between the seam of the boattail and the body tube and on the spirals of the body tubes. Lots of primer and sanding. I finished the "ATTABOY" using Red DupliColor Metalcast Anodized Paint which I purchased in the automotive section at Meijers. This is a 2 part paint system with a reflective ground coat and a transparent color top coat. When applied correctly it turns out beautifully. I added a ring of Chrome auto pinstriping to the bottom of the payload tube to enhance the metal look of the rocket, Following the lead of Kevin Johnson and his 2 stage OY!BOY, I thought about what name I could conjure using two sets of FATBOY decals. I came up with the "ATTABOY". I kinda like it.

Flight:
Like a lot of BARs, I like FATBOYS. Can't tell you why, I just do. But like many things I like, they have some irritating features. In the case of the FATBOYS, they weathercock too easily. When I conceived the ATTABOY I knew I would be adding weight to what I I believe is an already underpowered rocket so I chose to increase the engine diameter to 24mm to allow me to use C11-3 and D12-5 motors. I wanted the added trust to overcome the weathercocking tendency and to carry the added weight of this design.

To date, I've flown it 4 times. The first flight was with the payload tube on a C11-3. It was a somewhat gusty day. It launched straight up off the pad and arched gently into the wind. It did weathercock, but not nearly like my other FATBOYS that seem to do 90° turns into the wind. I estimated it's altitude at 150-200'. Ejection was right at apogee and recovery was slower than I expected on the 18" chute given that I had the mass of almost two FATBOYS on one 18" chute. It landed just before the rocket eating tree line that borders my launch field for a successfully first flight.

Next, I launched it without the payload tube, again on a C11-3, but this time, I cut a spill hole in the chute. Beautiful straight up flight to and estimated 200'. Very slight arc into the wind. Ejection at apogee and safe recovery.

A couple weeks later we got a wonderful early spring low wind day. That's a rare event in Southwest Michigan in spring so I had the chance to try it on D12-5s and I took it. Surprisingly, the flights were very similar. With the payload tube, it arched gently into the wind. Without the payload tube it went virtually straight up. Again using my height calibrated altitude guesstimater, I'd say they reached 400-450'.

Recovery:
While I like the thrill and the height of the D motors, They push the limits of my flying field. Both flights on Ds recovered way too close to the tree line for comfort. I think I'll stick with the C11-3s except on a dead calm windless day.

Summary:
I think the larger motors, boattail, slightly larger fins and slightly taller height make a huge improvement over a stock FATBOY's flight characteristics. I also think the design is very elegant. I guess the only cons that I can think of are the price and the time spent filling the slots in the body tubes. But it is a pretty unique rocket so to me, it was worth it. It helped to find the kits on sale.