(07/01/04) The Thrustline Aerospace Flux Probe is a "longneck" straightforward rocket that looks like an arrow. In fact, a 13 year-old that saw me fly it, said exactly that. Probably with some detail work, it would look exactly like an arrow.

What makes the Flux Probe "longneck"? It has a 0.734" diameter and is 36.75" long, giving it a 50:1 length to diameter ratio.

I purchased it because I liked the looks of the fins and perhaps because it did look like an arrow. It is my second Thrustline kit, after the Mighty Mick.

The kit includes two 17" body tubes and a 2.75" balsa nose cone to make up the 36.75" total length. There is a 2" coupler to join the two body tubes, two thrust rings, a Kevlar® tether (36"), an elastic shockcord (36"), a 12" mylar parachute AND a 2"x61" mylar streamer, and an eye-screw to attach to the nose cone. There is a balsa sheet to cut out the four fins from and single launch lug, which is cut in half to assemble.

CONSTRUCTION:

The instructions are printed on 8 pages (single-sided) of 8½ x 11" paper. There are color photos throughout to assist in the assembly of the kit. There is also a fin template and tube marking guide. The rocket is very easy to build and is probably not more than a level 2 kit.

There are a couple of things that should be pointed out in the build, otherwise, you are dealing with a very straightforward model rocket with four fins and a nose cone.

The Kevlar® tether is tied around one of the two thrust rings. This is done after a small v-groove is cut into the thrust ring. This is a good technique because it allows the thrust ring to fit nicely into the motor tube and prevents it from showing (denting tube outward). This is usually less important if the motor tube is smaller than the body tube, but in the case of the Flux Probe, the motor tube IS the body tube.

The next step was a first for me. Not really sure why the step is there, but it was described very well in the instructions. That is to glue the second thrust ring onto the first to make a double-length thrust ring with the Kevlar® sandwiched in-between. Perhaps Thrustline has determined that this protects the Kevlar® more.

The Flux Probe is not meant to be a person's first rocket. Why not? Well, because in the next step a used motor casing is needed! It is used to thread the Kevlar® back through and then the thrust ring assembly is glued and pushed into body tube.

The 2" coupler makes the it easy to have good alignment of the two body tubes. Thrustline does recommend rolling them on a level surface to ensure they are straight.

The fins are cut out using the template. My only complaint is that the template is regular notebook paper and it would be nice to have it printed on cardstock. I find the notebook paper is too flexible for me.

There is plenty of 3/32" balsa to cut out the four fins. The instructions indicate which edges could be airfoiled, but I chose not to. They are glued in place after using the wrap-around tube marking guide.

The 1/4" elastic shock cord is tied to the Kevlar® and then attached to the eye-screw that has been installed into the balsa nose cone. Then you choose (and I really like this) a parachute or a streamer. I chose the streamer.

Thrustline does give finishing guidance including using wood filler, priming, sanding, priming, sanding, then painting. There are no decals provided with this kit.

I used my typical multiple coats of Plastic-Kote Primer and sanding in-between. I then used Walmart Gloss Black paint to finish it off (additional comments about Walmart paint). I was going to add some prismatic paper on the fins, but just never did (so far).

Overall, for CONSTRUCTION I would rate this kit 4 ½ points. The instructions are excellent. I personally don't mind cutting out the fins myself, but would rather have a cardstock template verse a notepaper one. A nice bonus to have both a parachute and a streamer provided. The kit did not include any decals.

FLIGHT/RECOVERY:

Thrustline recommends the B6-6 for the first flight. They list the A8-5, B6-6 and C6-7 as recommended motors with altitudes from 200 to 1000 feet.

Thrustline indicates the rocket should weigh 2.0 ounces. My rocket weighed in at 1.8 ounces. My CG was at 22" from the nose cone.

Since this is a minimum-diameter rocket, the motors are friction-fit with masking tape. Also, since this is a small minimum-diameter rocket, it packing of the recovery system is difficult.

I decided to fly it for the first time on an A8-5. After loading in two sheets (each tore in half) of wadding, struggling to get the long elastic into the body tube and then sliding the rolled streamer on top, it was ready to fly.

The flight was straight as an arrow. A8-5, no way! The 5 is definitely too long of a delay. Perhaps I should have airfoiled my fins.

Also, the motor kicked out at the same time as the nose cone ejected, then this rocket came in for a core-sample. Perhaps this is why it is call a Flux Probe... probes into planets to take core samples for analysis? Perhaps it was because the motor kicked out.

The second flight was on a C6-5. Didn't have a C6-7, so thought it might eject early. However, after an straight liftoff it had turned and ejected at apogee. The rocket fell fine (not in core-sample position) until about 200 feet, then it lined up horizontally in the air and fell the rest of the way. It too had kicked the motor out, but this time the streamer was stuck exactly in half (the end had melted to the attachment point).

The third flight was on an A8-3 in our front yard. Nice flight, could have used another second of delay. Motor kicked (again) and it landed nicely. I had left the streamer stuck in half.

Fourth flight was on a B6-4 after unsticking the streamer. Nice flight, but again needed extra on the delay. It recovered fine, although I didn't see it land because it first bounced off our roof. No damage. Oh, yeah, motor kicked out.

For FLIGHT/RECOVERY, I would rate this rocket 3 points. The rocket is stable and will give you straight flights. I only tested the streamer recovery which is all that I think the rocket needs. I'm concerned that I could keep a motor from kicking out at ejection. I'm not new at this, but I think the minimum diameter combined with the amount of stuff (wadding, Kevlar®, Elastic and Streamer) that has to be stuffed in the top makes a lot of back pressure. I would recommend wrapping tape around the bottom 1/4" of the rocket body to the motor as well as the tape on the motor (friction-fit).

I give the rocket an OVERALL rating of 3 ½ points. It is a quick-to-build, steady performing rocket that is good for small fields. The streamer or parachute would let the flier experiment a bit. It does take some patience to get a nice finish with the balsa nose cone, but then again, that how is was always done prior to plastic molds. I'm going to produce a Comparison Article on 18mm Longnecks and include this one. Watch for it.

Oh, I finally did get around to RockSIM'ing it. Here are my results. Joe Policy's RockSIM shows it weighing 1.2 ounces, but I think 1.8 (as mine did) to 2.0 (as Thrustline says) is closer after all is said and done. The link to the RockSIM file above is mine. Joe's is in the RockSIM library.

Click to see my 18mm Longneck comparison article