Brief:

Modified Estes Ranger - a three motor cluster rocket with a payload section. My version includes a baffle and uses motor hooks that were not part of the original kit.

I was looking for a kit or a plan that would be suitable to fulfill the NARTREK Silver cluster flight requirements. This look alike to the Big Bertha would be a great addition to my fleet if painted in a similar scheme to my venerable Bertha. The plans were available from the Jim Z web site in Adobe format. I was already placing an order for some parts for another project from the Balsa Machining Service, and added the correct nose cone and balsa bulkhead to the order. The rest of the parts were found at my local hobby shop.

• Parts:
• 1 Nose Cone: BMS BNC60MS, balsa
• 1 Main Body: Estes BT-60 cut to 11 inch length
• 1 Payload Body: Estes BT-60 cut to 7 inch length
• 1 Bulkhead: BMS balsa block, 2 inches long
• 3 Motor tubes: Estes BT-20 cut to length of 3 inches
• 3 Motor blocks: Estes CR2005 Rings
• 3 Motor hooks: Estes hooks
• 4 Fins: cut from 1/8 inch balsa stock
• 1 Shock Cord: 1/8 inch elastic strap, 2 feet long
• 1 Shock Cord: 100# Kevlar® string, 5 feet long
• 1 18" Parachute: Estes
• 1 Inner baffle tube: Estes BT-50 cut to 3 inches
• 1 Outer Baffle tube: Estes BT-55 cut to 3 inches
• 3 balsa strips: cut from scrap to center a BT50 on a BT55
• 1 centering ring: card stock, centers BT-50 in a BT-60
• 1 centering disk: 1/8 balsa, outside matches inside diameter of BT-60

Construction:

The three motor tubes fit snugly toghether in the BT-60. Harry Stine mentions in his Handbook of Model Rocketry that the BT-60 was designed specifically for using three BT-20s in this manner and it's easy to believe because they fit so nicely. The motor hooks work OK in the small gap between the tubes. Simply glue the three tubes together, add the hooks and fill the space with scraps of balsa and sand to a round profile.

An ejection baffle fits in above the motor mounts. Let me add a paragraph here about that since it isn't standard. Baffles protect the parachute from hot gases, burning powder, and hot bits of the clay cap from scorching and burning holes in the chute without requiring wadding. It works by changing the direction of the ejection charge. There are many ways to do this, but I prefer a tube in a tube. In this rocket it's done by centering a BT-50 inside a BT-55 with the ends offset. The two tubes are held in the rocket with a pair of centering rings at the top and bottom that seal them at the same time. The center is left in the top ring and CA was used to fix it there permanently. The BT-50 is joined to and centered in the BT-55 using some strips of scrap balsa. The ejection charge goes through the lower centering ring, up the BT-50, and runs into the disk at the top of the BT-55. It is now forced downward between the BT-50 and BT-55 where it runs into the lower ring. It's now forced back up between the BT-55 and the airframe wall. It passes out into the recovery system bay through slots or holes cut around the outside edge of the top ring.

The payload section and nose cone fit together easily with a little bit of sanding to get the cone to match the airframe perfectly. The plug was glued into the other end of the payload bay and a screw eye was used to attach the assembly to the shock cord.

The fins aren't difficult to cut, nor is there a lot of sanding involved since the original kit called for a simple rounding off of the leading and trailing edges. Gluing them on is standard - marking the tube is easily accomplished using Harry Stine's book, and gluing the fins on with yellow glue isn't tricky either. Rating 4/5 - this is a fun rocket to build, but not overly challenging.

Finishing:

The original paint scheme is fairly complex and would require at least three masks and hits of paint to complete. The results would be very rewarding, but I wanted the rocket to match an existing Big Bertha. The result is a very simple paint scheme that was very quick and easy to realize - the primer coats took much longer than the final ones.

Rating 3/5 - This could be a tricky rocket to finish and decorate, but I chose a non-challenging scheme.

Flight/Recovery:

A couple of weeks later I launched it with a set of B6-6 motors for another very nice flight.

It's been launched on three other occasions with A8-3s and B6-6s, and has made the NARTREK Silver flight it was built for, so it's all gravy from here. I haven't had an opportunity to launch it with C6-7s yet, but I'm planning to in the near future if the weather will cooperate.

Rating 4/5 Cool rocket

Overall:

Specifications: Diameter: 1.6 inches Length: 24 inches Weight: 3.5 oz (no 'chute or motors) Recommended Motors: A8-3 or 5; B6-6; C6-7

Rating: 4 out of 5

Brief:
I received these plans from NAR and built this as part of my NARTEK Silver achievement. In addition, this was my first cluster rocket. During the construction I made one modification, replacing the payload section with plain BT-60 body tube. The paint scheme represents the classic struggle of good vs evil--I will let you decide which team represents good and which evil. Our family is divided.

Construction:
The kit includes:

• 1 BT 60 - Body Tube (18" Long)
• 1 Nose Cone (Plastic)
• 3 Engine Holder Tubes
• 2 Centering Rings
• 2 1/8" Launch lug (7/8" and 1-1/4")
• 24" of 150# Kevlar®
• 24" Elastic Shock Cord
• 18-24" Plastic Parachute
• 0.125" Balsa Fin Stock
• Nose Cone Weight (~40g)

This was a pretty simple build. Body tube, nose cone, 4 fins, and engine mount. The paint scheme actually took longer to paint then it took to assemble the rocket.

Engine Mount: I used the 3 18mm engine tubes glued them in a triangular shape, gluing each to the other. I traced this triangular tube shape on to centering ring material and then traced the outer tube diameter. I cut out 2 engine mounts. I mounted the 3 tube sub-assembly and bulkheads. I choose not install engine hooks and use tape to hold the engine in place.

Fins Construction: I used the templates included in the plans and cut the fins from 0.125" fin stock. I rounded the leading edge and filled the flat surfaces with thinned Elmer's Wood Filler. I sanded the fins with 220 grit sandpaper, filled, and sanded again with 400 grit sandpaper until smooth.

Main Body Tube Assembly: I mounted the engine subassembly into the main body tube leaving the engine tubes sticking out about 0.375". Next, I mounted the fins 90 degrees apart and added fillets to the fin tube joint.

Finally, I used the traditional Estes shock cord mount to attach the shock cord to the main body tube. If I had to do this over, I would attach this to the engine bulkhead.

Nose Cone: I added ~40g of nose weight to ensure the rocket would be stable.

Finishing:
After the rocket was complete, I then applied a few coats of gray primer. I then painted the entire rocket white, once this was dry. I masked the rocket and painted the yellow, let it dry and masked it for the orange. Once the orange was dry I masked it for green and then blue.

I found the images on the internet and printed these on to Expert's Choice Decal Material. After the decals, I applied 3 to 4 coats of clear coat.

Construction Rating: 4 ½ out of 5

Flight and Recovery:
The flight prep was your basic rocket prep. Engines installed (taped in place), dog barf added, and put in the folded parachute. I installed the igniters. After reviewing the wiring diagrams, I chose to make a 2 jumper sets (basically 3 wires with alligator clips, twisted together).

I used 3 C6-5s for the first flight. Launch was nice and straight. It went a lot higher than I anticipated. Ejection was a little early, but overall it was a very nice flight for my first cluster rocket. The next flight was on C6-7s. This flight seemed to fly much higher and it took about double the time to land.

Flight Rating: 4 ½ out of 5

Summary:
This is a great rocket especially if you have not attempted a cluster. I would highly recommend making jumper wires to attach the igniters rather then twisting them together as shown in the wiring diagram.

I would make two changes if I rebuilt this rocket: replace the nose weight with an engine baffle and change the shock cord mounting attachment method.

Overall Rating: 4 ½ out of 5