Scratch - uTrident {Scratch}

Descon uTrident

Scratch - uTrident {Scratch}

Contributed by Bill Westfield

Manufacturer:

µ-Trident
(Contributed - by Bill Westfield)

µ-Trident

This model looks like an Estes Trident downscale, about a 1/2 scale, at first glance. It uses BT5 for the motor and "passenger" compartments, and 1/4 inch dowels for the duct tubes. Obviously, dowels are not tubes, and 1/4 inch tubes would probably not be adequate for ducting ejection gasses anyway, so another scheme is used for ejection the parachute. The bottom tailcone (which is a small cork in the prototype) and forward nosecone of the passenger section are both mounted on a thin dowel (bamboo skewer), so that the assembly can slide entirely out of the forward section of body tube. The dowel extends past the tailcone and ends in a hook. When in launching position, a rubber band(s) is looped over the duct pods and engages the hook, and a small burn string is threaded through the exhaust ports in the motor pod to hold the assembly in place until motor ejection.

The ORIGINAL Trident, which had three BT-5 sized ejection ducts. Later, there was the "Trident-2" or somesuch, which only had two pods of BT20 and is sometimes insultingly called the "bident." The u-Trident is a downscale of this original three tube trident, with a twist.

Fins are attached in between the duct pods rather than ON them (for a stronger joint.) Small tubes were fashioned that are a slip fit OVER the BT5, and the duct pods were fastened to this rather than direct to the body tubes. This allows easier construction, as well as clearing any over-diameter of the nose cones. Both nosecones are missing their base, and the forward nosecone has the shoulder trimmed as well to make more room for the recoevry system.

The ejection ducts are actually drilled THROUGH the shoulder of the motor pod nose, to make for greater strength there.

uTrident Instructions

Section A - "Strutwork" - See diagram A

Create the slip tubes of the strutwork. Wrap a layer of waxed paper around a 7inch piece of BT5, and then make short tubes using 1.25x4 inch strips of paper. After the glue is dry, remove the short tubes and waxed paper

Shape the dowels. Rounded at the front and pointed at the rear, sort of like an airfoiled fin. (see the photos.)

Mark the long BT5 for three equally spaced "fins" using your favorite tube marking method. Position the short collars 4.25 inches apart and glue on dowels along the marked lines (glue the dowels to the collars only. The front of the dowel should be approximately even with the end of the collar, while the rear should extend past the rear of the rear collar.

After the glue has dried, the struts and collars should slide off of the BT5 as a single unit. Fillet liberally.

Cut two pieces of body tube, 2.75 and 3.25 inches long. glue the longer section into the front collar, so that it extends behind the collar about 0.1 inch.

Short sections of launch lug are glued along one of the strut/collar junctions.

Section B - motor pod - See diagram B

For the motor section, start by punching three 1/4 inch holes (using a hole-punch) about 3/16 inch from one end of the 2.75 inch body tube, along the marked lines.

Omit the bottom part of the short nosecone, and glue the noscone into the motor tube. The shoulder of the cone should cover the punched holes (this is OK.) When the glue is dry, melt through the shoulder with a hot skewer or equivilent. (make the holes in the plastic the full 1/4 width of the holes in the body tube.)

Glue the three fins onto the shorter body tube as shown, and allow to dry (one at a time, unless you have special equipment!)

At this point, the fin unit should slide into the bottom collar in the strutwork assembly, with the fins coming up against the collar between the struts just as the end of the motor tube reaches the forward end of the collar. Use your hot skewer to put holes in the collar that match up with the holes in the body tube/nosecone.

For no particularly good reason, the fin/motor unit is never glued in place. It should fit relatively tightly in its collar, but since the only "load" is borne by the fins pushing foward against the collar, it needent be TOO tight.

Section C - Recovery Piston - See diagram C

The recovery piston should be assembled carefully, based more on test fitting than on measurements.

Start by gluing about 3/4 inch of the end of the dowel onto the inside edge of the long nosecone. When dry, stuff the nosecone with tissue and glue the outside layer so as to form a hard surface cose to flush with the bottom of the nosecone.

Burn a dowel-sized notch in the edge of the cork, using the hot skewer again. Fit the nosecone into the forward body tube (the dowel should lie along the inside edge of the tube.) Position the cork so that its forward surface is just inside the rear end of the body tube, and mark the position on the dowel.

Remove, and glue the cork in position on the dowel, taking care to keep it aligned with the nosecone.

At the rear end of the dowel,twist a fairly stiff wire (like a paperclip or a piece of the wire closure on a box of food from a chinese restraunt) and form into two hooks. The hooks should face the OUTSIDE of the rocket when assembled. (See the detail drawing) Glue in place.

Parts-List

1 BT-5 body tube, approx 7 inches long. (or one section 2.75", one 3.25", and one longer section for temporary use during construction.)

1 NC-5 "short and round" nose cone.

1 NC-5 "Long and pointy" nose cone.

1 Dowel - 3/32 inch diameter by 6.75 inches long.

3 Dowels - 1/4 inch diameter by 8 inches long.

1 #2 cork.

Balsa, paper, wire, assorted glues.

- Completed Rocket -

- Rocket Components -

All images and designs are protected by the author's copyright
RMR DesCon 5 1999

uTrident Flight Report.

First, the choice of recovery system is a bit critical. There's only about three inches of BT5 tubing for it to fit it, and it has to fit loosely enough to be deployed by rubber bands. I made an eight inch (8") parachute from a grocery produce bag (of the thin, MDPE variety, I think. Thin and rather soft. 1/4 mil mylar might work fine too.)

Pre-flight prep is a pain with this model, a bit worse than the average model that uses a burn-string. The piston is inserted partway into the recovery bay, and then the chute is folded and wraped a couple times with its shrouds to keep it folded. Then you insert the chute over the bottom of the piston, followed by all the shock cord and additional shroud lines, trying not to get them tangled about the piston's dowel. I used a piece of larger dowel to push them in (lightly.) Finish insterting the piston and seat the nosecone.

Now, thread the burn string (a piece of dental floss worked well - strong but with a low melting point) through two of the exhaust ports and knot it tightly on the piston's hook. (if you learned any fancy knots, you may have a chance to use them. You want something that can be tightened, but won't loosen on its own.)

Finally, attach the rubberbands. I used a #16 rubber band, knotted in the middle - the knot engaged the hook, and the two ends looped over two of the "pod" ends. Don't position the rubberband in a way that it will block the launch lugs. (note that the rubberband is disposable used this way.) Hopefully the tension of the rubberband won't push the nosecone back out (when your burn string knot wasn't tight enough. Note - perhaps a longer nosecone shoulder would help with this!)

Insert motor. Use an external tape thrust ring, and enough tape so that the motor probably won't be kicked out. (Unlike most parachute models, this is more esthetic than important. Even if the motor ejects, the burn string will probably be burnt through!)

It's a relatively heavy model for it's size, so I picked an A10-3 for the Launch. This sent it up a good distance, straight and true. The recovery system deployed successfully and the rocket recovered fine, drifting a "typical" distance and landing on the parking lot (the eight inch chute seemed to be just about right.) Upon recovery I noted that the piston had fully deployed, as it was supposed to. Pretty much a perfect flight!

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