The Landviper


Parts, from the top:
Nose cone is a basic PNC-60 elliptical Big Bertha cone.

Upper body tube is 18" of BT-60. Same length as when you buy it from Estes so you don't even have to cut it.

Motor tubes are a convenient 18" of BT-20. Again you don't have to cut these.

Rear fin can segment of BT-60 is 3".

Fins are simple enough that I can describe them:

1. To make a pattern, draw a line 2.5" long; this is the root edge.
2. At one end draw a line 1 and 9/16" long perpendicular to the root edge; this is the trailing edge.
3. From the outer end of the trailing edge draw a line 7/8" long perpendicular to the trailing edge (parallel to the fin root); this is the fin tip.
4. Draw a line from the end of the fin tip diagonally to the front of the fin root and you have the leading edge.

Construction:
Glue two of the BT-20s together on a flat surface with a bead of glue down their length. When dry, glue on the third motor tube.

I used motor blocks in the motor mount end because I didn't trust the thin metal motor clips that Custom supplies. I used those clips for convenience, but I put the motor blocks/thrust rings just forward of the upper end of the clip where it protrudes into the motor tube.

Install the motor clips. I followed the instructions and placed them on the outermost side of the motor tubes so that they would be sandwiched between the motor tube and the fin can segment of BT-60. If I build a clone as you are about to do, I would place them on the side of each tube in the spaces that will exist once the fin can is placed on. In that case you will need to devise a way of securing the clip on its mid-point as Estes usually has you do with a wrap of masking tape so that the aft end is under tension as it is moved outward to insert or remove a motor casing. The problem with having them between the motor mount and the fin can is that it slightly deforms the fin can and is harder ensure a good glue bond between the motor tube and the fin can. I sent this plan description to another rocketeer who used wraps of tape to hold the motor clips in place and then ran into problems because the added thickness interfered with gluing the fin can on and also makes a problem when the motor tubes are joined together. The solution is to place the clips on the sides of the tubes as described and then use small rectangles of fiberglass cloth with epoxy to hold them in place at their midpoint. You don't want added thickness when gluing the BT-20s together or the fin can to the BT-20s.

The cluster of three tubes is inserted and glued 5" into the upper BT.

The 3" section of BT-60 is glued onto the aft end of the motor tubes flush with its bottom edge flush with the ends of the motor tubes.

The six fins (which look great, by the way, and sort of give it a mortar shell appearance) are spaced evenly around the rear tube with the forward end of the root edge right up to the forward end of the fin can tube. There is 1/2" of body tube at the rear of the rocket from the rear edge to the bottom of the root edge of the fins. Three fins are centered on top of the motor tubes and three centered on the spaces between.

A 3/16" launch lug about 1 1/8" long is glued on 2" forward of the rear of the upper BT and another between the fins 1 1/8" forward of the bottom edge of the fin tube.

I painted mine much like the kit art which is a gloss black nose, yellow BT-60 and grey BT-20.

The original came with an 18" silver mylar chute and I added a very long (2 or more times the rocket length) elastic shock cord. I have suffered two minor zippers of the main tube from using the recommended delays that were far too short. I was able to repair them and have since added a layer of fiberglass reinforced packing tape to the inside forward end of the BT (had to sand down the shoulder of the nose cone a bit so that it would go in) and this has totally prevented any more zippers.

There are no centering rings in the forward BT-60 so you must somehow fill the spaces between the tubes to prevent ejection gasses from escaping downward. I used the old method of making a putty of shredded bits of recovery wadding and glue and packing it into the intertube spaces. It's simple, but effective.

It's a great rocket and a real attention-getter. It goes like a bat-out-of-he** and is a whole lot of fun. It's a great way learn clustering and a good way to burn off a whole pack of motors! On three B6-4s it really gets up there and on three C6-5s it flat out rocks! Check out Kevin Nolan's Countdown Hobbies website at http://www.countdownhobbies.com/ which has an image of a Landviper at launch right on the homepage. Great looking flames in that shot, but I guarantee you that it takes off too fast to see them well in real life.