Saturday, January 29, 2011

Reviews: Two Cognis Aerospace kits

This post reviews the Cognis Aerospace Lunar Lander and Eenie Meanie. Cognis is long since OOP.

Lunar Lander

This is review (circa 2002) of a pre-production version the 24mm Cognis Lunar Lander, the LLV 201. Its unique design is based on a 6" Styrofoam ball, legs made from wooden struts, and circular fins. The Cognis Lander was manufactured and distributed in the U.S. by LawnDart Rocketry. I won the kit as a prize for the Boink rocket contest. When EMRR heard my kit was tied up with production problems, he offered this pre-production version. A real class act - thanks Nick!


1. One 6" Styrofoam ball, pre-drilled for the 24mm tube
2. One long 24mm body tube
3. Six short 24mm tubes
4. Six spruce stringers
5. 15 balsa stringers
6. One sheet of balsa fin stock
7. One nosecone (resembles a 24mm - 13mm transition)
8. One eyehook
9. One 24mm motor block
10. Two launch lugs
11. A long piece of Kevlar® twine
12. A section of elastic shock cord
13. A 12" Mylar chute kit from Aerospace Specialty Products

Since this was a pre-production kit, the instructions consisted of only a drawing of the kit, shown in two views. The changes from 18mm to 24mm was indicated with hand written annotations. I had to figure the details out on my own. The good part was the drawing provided full-scale templates for the struts and circular fins.

Construction details:

1. I used white glue throughout. (I built it in the kitchen not my rocket workshop, was too lazy to get wood glue from basement)
2. Tie the Kevlar® twine to the 24mm motor block and install it. I also added a metal engine hook (not provided).
3. Glue the side tubes together in pairs, and then to the bottom of the main tube, just like a tube fin rocket.
4. Cut spars for leg structure per templates. Mark root and tip edges. Each leg consists of two pieces of spruce and two balsa supports. Note that all the stringers are the same length and are cut to fit.
5. On a flat surface covered with wax paper, glue the main leg structures together.
6. Cut small triangular pieces from the scrap basswood to fit the joint between the basswood leg sections. I used the legs as a template. Add this to the leg assembly.
7. The original 18mm version included a piece of balsa along the root edge of the leg assembly, which fit between the 24mm side tubes. Since the side tubes on the 24mm version touch at all points, this component was not provided. However, I decided to add pieces of balsa along the root edge of the leg anyway. I used one spare balsa spar, and made the remaining two from balsa stock I had lying around.
8. Install the leg assemblies one at a time. Find stuff to support them while the glue is setting.
9. Cut all cross members per the templates. For a better fit, I also sanded the inner faces where they touch the main leg sections.
10. Install the cross members. I didn't mark the position of the cross members on the main leg sections before they were glued onto the body. This was a mistake. Do this in step 4!
11. Cut out, seal, and install the circular fins. I placed mine such that the grain is perpendicular to the leg. This should keep the edges from breaking off on landing.
12. Add liberal fillets everywhere.
13. Install the Styrofoam ball. I wrapped masking tape around the body tube near the top to make the fit snugly and glued it to the body tube with white glue. To allow the ball to sit on the outer rim of the side tubes, I also cut a small conical section from the lower end of the ball.
14. To install the launch lugs, I ran a 3/16" launch rod along the joint of two of the side tubes and up through the ball. I glued one lug in the top of the Styrofoam ball and the other at the bottom of the side tubes.

Haven't decided on how to finish the kit, so for now I will fly it nekkid. One thing I should have done is seal the balsa spars before installing them. At least I had the forethought to seal the fins prior to installation.

I chose a D12-3 for the first flight. On this motor, the rocket weather cocked into the 5+ mph wind and there was some wobble. The boost was nice and slow - everyone at the launch took notice. I used my home made 12" nylon chute and a combination of Estes and dog-barf wadding. A 12" chute isn't enough for this kit and one of the legs broke on landing.

I also flew this rocket on a E15-7, another D12-3, and two E9-4's.  The latter were great motors for this draggy rocket.

This was a unique looking rocket. It took a bit more work than the average LPR kit, which is a good thing. It was just challenging enough to be fun.  The rocket boosted great but sustained damage on every flight.  Status: junked.

Eenie Meanie

This is a downscale of the popular long kit by another, un-named vendor. It flies on 13mm mini-motors and uses a streamer for recovery.

The kit included:

* Two BT13 tubes, with a white glassine coating and almost no spirals
* One tube coupler
* One 2-part nose cone (instructions referenced a different type)
* One engine block
* Two launch lugs
* 1/16" balsa fin stock
* One Mylar streamer, 2" x 12"
* 54" of thin Kevlar® twine
* 3" thin Kevlar® twine

This OOP kit was manufactured in the U.S.A. by LawnDart Rocketry. The instructions are seven pages long and with many color photos--it is almost more than you really need for this simple rocket. However, there were changes to the US version of the kit that were not consistently reflected in the instructions. The changes are that the US version uses a streamer in place of a chute and that it uses Kevlar® cord exclusively, whereas the foreign kit uses a Kevlar®/elastic combination. In addition, the last page looks to be an add-on by LawnDart, which includes a nice break-out drawing, a fin template, and an alignment guide. It also presents several notes, including an alternate placement of the top launch lug and a note stating a concern about 'possible references' to that un-named kit and vendor. Of course, 99.9% of you immediately knew what kit it was--and the rest of you have homework: search EMRR and find the mystery kit :-)

I decided to build the kit using the new Perfect Glue-1, by Liquid Nails. The Perfect Glue series has three glues. The #1 glue is for wood/paper, so I thought I'd give it a try. This is a clear, rubbery glue that reminds me of a thinner version of the standard Liquid Nails.

The balsa was very light and cut easily. The fins and lugs went on easily, but I could tell that this glue is not good for fillets. The Perfect Glue says to spread the glue on the surface to be bonded, separate the parts to ~five minutes, and then re-attach them. I do this same thing with white and carpenter's glue anyway. Oh, I'm glad LawnDart added an alignment guide on the last sheet, as the one in the main body of the instructions didn't fit the 13mm tube.

The motor block and coupler were a bit snug and the joint between the two tubes was damaged, but filling and sanding too care of this.

Assembly of the nose cone was not discussed in the instructions. I first bored two small holes in the base of the shoulder and inserted the small piece of Kevlar®. I tied it so that the knot was inside, added a large drop of the glue, and pulled the loop down from the outside. Finally, I spread some of the glue on the inside of the cone and slid in the base.

The shock cord is attached to the tube using the tri-fold paper method. I generally don't use this method but decided to give it a try to further test the glue. A cutout wasn't provided. That's a minor item but sloppy. The other end is tied to the Kevlar® loop on the nose cone.

Despite the numerous issues with the instructions, this was an easy rocket to build. I would be more critical on a more challenging kit. I also was disappointed the fit of the coupler and the two part nose cone. The latter may be personal preference, but I don't like this type cone.  It cracked during one of the rocket's many relocations within the Dungeon and  I replaced it with a similar Estes plastic cone.

Finishing was easy because the spirals were almost non-existent. In fact, I couldn't detect any gaps although the spirals appeared to be slightly raised from the tube. I filled the gap between the tubes, sealed the fins, and made fillets with fill-n-finish. I then gave it one coat of white primer. Since it was launched in October, I painted it Halloween orange and black.

I flew it on an A10-3, which was held in with masking tape. I used cellulose wadding and found the streamer, which was corrugated. It had a nice respectable flight, similar to my Skinny Mini. I had packed the streamer a month earlier and didn't repack it. As a result, the streamer didn't open. Still, it fell on grass and there was no damage.