Clustering is a popular technique in high power rocketry, but it's not as common in model rocketry as it once was.
Before motors of D power and higher became widely available at reasonable prices, the only way to launch a large rocket was with a cluster of 18mm motors. Estes' Saturn V and Saturn IB were two examples of rockets which required either a three-motor or four-motor cluster for a safe flight. Clustering was made even more difficult in those days with the old nichrome igniters, which required significantly more current than the current Estes, Quest and MRC igniters.
Model rocket company catalogs have little in the way of clustered rockets. Estes offers clusters only in their "Pro" Series. But the Custom Rocket Company has brought clustering back to the model rocket set.
Custom's Landviper flies on three 18mm motors. Recommended motors are B4-2s and C6-5s. The design is novel, featuring six fins and three long, exposed motor tubes. The rocket reminds me a little bit of the Saturn IB (the real one), which clustered eight engines, had several fins and exposed tubes.
The kit features balsa fins, which you cut out of a pre-marked sheet of balsa. The nose cone is plastic. Three long BT-20 tubes are glued together in a triangular configuration. This group of tubes is then glued into a length of BT-60. A short length of BT-60 is glued to the motor end of the rocket. The fins and lower launch lug are glued to this BT-60 tubing. Two 3/16-inch launch lugs are used.
Hooks are provided for each motor tube. The shock cord is elastic thread. A bright silver parachute brings the rocket back in one piece.
Construction is fairly simple. It is very important to stuff some sort of glue-soaked tissue in the upper BT-60 between the motor tubes. Otherwise, the ejection gases will leak out and the parachute won't be ejected. Alignment of the two launch lugs also is important. I find it easiest to glue on one launch lug, let it dry, then use a launch rod to align the second lug with the first one.
I attempted to match the yellow, black and gray color scheme shown on the package. Decals include two large "Landviper" logos, some "experimental" and "USA" type and some smaller decals that mimic the instructions stencilled on the outside of real rockets.
The most impressive feature of the kit is the inclusion of six micro-clips and wire to assemble clip whips for the engines. This saves the rocket builder from having to buy a large package of clips and a roll of wire. I thought this was a nice touch and showed much consideration for the rocket flyer.
The Landviper's first flight was at a Dallas Area Rocketry Society launch on May 15, 1994. Because of the large size of the field, I felt comfortable sending it up on three Estes C6-5s. Before launch, I carefully attached the clip whips to the igniters. It's critical that the two micro-clips attached to each motor have different polarities.
As I waited to put it on the pad, the rocket caught the attention of another rocket flyer, who said he was impressed with the appearance of the rocket and asked if it was a scratchbuilt or a kit rocket.
Then it was on to the pad, where I attached the pad clips to each clip whip. The DARS launch system has the required 12 volts and plenty of juice.
Ignition was instantaneous and all three motors ignited. The rocket accelerated so fast that in a photograph of the launch, taken at a fast shutter speed of 1/1000 second, showed a blurred rocket.
The recovery system operated properly, but the rocket flew extremely high and a slight wind blew it several hundred yards from the launch pad. The silver parachute made the task of finding the rocket much easier, as it glinted in the bright summer sun.
Several months later I got around to painting the rocket and flying it again. I used the recommended B4-2 motors. The ejection appeared to be too soon after motor burnout and the shock cord broke, possibly as a result of high-speed ejection. The booster spun down and was crimped slightly on one motor tube. I repaired the rocket the next morning by putting a piece of Kevlar® cord through the wall of the body tube, knotting it on the outside and using cyanoacrylate glue to keep it in place. I attached the Kevlar® cord to about 14 inches of one-fourth-inch wide elastic thread, using a knot and white glue to secure the connection.
I launched the rocket again, but used B4-4s. The ejection was about at apogee and the rocket had a safe recovery.
It would be hard to improve on this kit. You could ask for die-cut or pre-cut fins, but cutting fins out of balsa isn't very difficult if you have some rocket-building experience. Actual motor blocks in the motor tube would provide a backup for the motor hook. The instructions were nicely done and illustrated in a clear, straightforward manner.
This rocket serves as an inexpensive introduction to clustering. It's impressive in flight, with three motors roaring away. The Landviper looks nice when displayed.
There's no practical reason to cluster three 18mm motors, but then, this is a hobby - it's not supposed to be practical! If you're interested in expanding your rocketry skills or want to try something out of the ordinary, get a Landviper and get into clustering. A 12-volt ignition system is required and I do recommend B4-4 motors instead of B4-2s.
Type: Three-motor single stage cluster rocket
Skill Level: 3
Length: 33.5 inches (85.0 cm)
Diameter: 1.637 inches (41.6 mm)
Weight: 2.9 ounces (83g)
Engines: Three B4-2 or three C6-5 recommended; reviewer recommends B4-4 engines instead of B4-2s. Engines must all be the same type when launched. 12-volt launch system required.
Likes: Decals, appearance, inclusion of clip whips