Photo from Sunward that enticed me to purchase the Interplanetary Shuttle™

The Sunward Interplanetary Shuttle caught my attention despite the unfinished look of the advertisement. I thought the center tube looked really interesting. The overall look was unique with the the fins wrapping around the center tube and extending the entire length of the rocket.

The rocket kit comes complete with the 0.976" diameter body tube (central) and the 2.1" diameter center tube that gives it the unique look. The plastic nose cone uses clay nose weight. There are four laser-cut balsa fins and two laser-cut centering rings that are used for the center tube. The kit includes an 18mm motor mount with a retaining hook. It also includes the plastic parachute that needs to be assembled.

Construction:

The instructions are printed on six pages of 8½ x 11" paper which include a Launch Prep section and both the NAR and CAR safety codes. There is a fin marking template that needs to be cut out from page 2 of the instructions. They include illustrations to assist in the build.

Sunward calls the kit a Skill Level 2 and we agree. It is a fairly easy kit to build, however, with the fit of the center tube and the fins around that tube, attention to detail is required.

The motor mount is assembled first and it seems that Sunward has standardized this portion of the kit.

I decided to cover the fins with newspaper to help in the finishing process. So before gluing them in place, I coated each side with Modge-Podge and placed a piece of newspaper over them. Then place them between wax paper and under heavy books. They will warp if you do not do both sides at once and place it on a flat surface with heavy flat surface on top.

I really want to spend a little time on the central tube because this is probably the most challenging portion of the build. What makes it a little more challenging (and in my opinion unnecessarily so) is that the top and bottom laser-cut balsa caps used for the center tube are exactly that... caps. In other words, they do not fit inside the center tube to ensure that it is centered, they sit on the outside and the center tube has to be aligned to be even with these caps. I believe that if they were used as centering rings (fit into the center tube) the build would be better.

The instructions have you mark your body (central) tube at 5 5/8" then glue the first balsa cap in place. Then they have you glue the center (larger diameter) tube to that cap, followed by the second cap. I was uncomfortable with this approach for three reasons: 1) I didn't know which side of the 5 5/8" line I should align to; 2) I didn't trust myself to get the first balsa cap perpendicular/even with the central body tube, and 3) I didn't like the "floating" center tube arrangement. Next, I'll tell you what I did, however, it should be noted that following the instructions will work.

I took two of my fins, both caps and the center (larger diameter) tube and test fit them all together. The cut on the fins are so perfect that this allowed the assembly to be "held" together without glue. I then was able to slide the center tube and caps up and down to align the fins to the body tube. The fins are slightly longer than the body tube. (The placard shows that extra portion extending above the body tube where the nose cone would go. If you look closely at my finished rocket, I ensured that extra was at the bottom of the rocket.)

Once I had the assembly and fins where I wanted them, I touched the upper cap in several places with CA. I then removed the fins, bottom cap and center tube. I then applied a nice fillet of glue to the underside of the top cap (pictured right).

After that dried, I put glue on the top and bottom edges of the center tube and placed it onto the upper cap. I then slid the bottom cap down onto the center tube. I used the two fins to check alignment and while they were in place, touched the bottom cap in several places with CA (pictured below). I then removed the fins and set the assembly aside to dry.

Once the CA was dry, I added a fillet of glue to the outside of the top and bottom caps.

All the fins fit nicely around the central tube, however, I had to sand the root edges to ensure that they set "down" onto the central tube. This took a bit of work to have them fit nicely. Once done, each fin was able to be glued into place.

Before gluing them into place, I cut out the tube-marking template and wrapped it around the body tube. There were only three fin lines to be marked. I looked at the placard and it looked like the rocket had three fins. I re-checked the instructions thinking I did something wrong. The instructions said four fins and therefore I went ahead and marked the tube using my Estes Tube-Marking tool with four fin lines. (Sent a note to Sunward and they were aware of the problem and was surprised that my kit came out with the wrong template).

Finishing this rocket was tough! The spiral-groove in the center tube was very deep and I ultimately had to fill it with an automotive filling glaze. After several coats of Plasti-Kote. I then used the new Krylon paint I had left over from another build. I used the green as the base. The next day I covered the fins and attempted to coat with Krylon red. Oh, it didn't work out. Some wrinkles and some paint stuck and pulled off with the tape. I was out of time and needed to box it to get it mailed to Maryland for NARAM.

The kit didn't come with decals. Interestingly, this could be a really neat looking rocket if it was painted white with black fins. Then if there were some port-hole decals on the center tube. You get the idea.

Overall, for CONSTRUCTION I would rate this kit 3 points. The rocket is fairly easy to build with the only challenge being the alignment of the center tube to the body (central) tube and fins. Had the one little issue with the 3-fin template when it was supposed to be a 4-fin template. The instructions are just okay and no decals.

FLIGHT/RECOVERY:

Sunward recommends the following motors: A8-3, A8-5, B4-2(first flight), B4-4, B6-2, B6-4, B6-6, C5-3, C6-3, C6-5, C6-7

My rocket weighed in at 3.2 ounces with a CG at 6" from the nose cone.

I shipped this rocket to NARAM since I was only going to be there a day or so. This plan included buying motors at the site. When I arrived on Thursday afternoon I was able to buy some C6-5's and planned a flight on this rocket.

I used cellulose (dog barf) as wadding and I replaced the plastic parachute with a 12" RocketChutes.com Tie-Dye nylon parachute which barely fit. The parachute change may have not been a good idea.

The C6-5 flight launch was... interesting. The rocket took off and did two or three flips before landing next to a pad on the opposite site of the launch area (within 30 feet) and rejected. Definitely not stable.

So was it the parachute, the weight added due to my finishing techniques or is the rocket unstable on C6's?

I did successfully create a RockSIM for this rocket. It was a fairly challenging RockSIM to build. I had to create three sets of fins to simulate the single fin. I set it up to match my weight and CG with the nylon parachute. The flight simulations showed the rocket to be marginally stable on A8, B6 and C6 motors. The margin of stability per RockSIM is below:

Interestingly, here is was the Rocket Glossary says for Marginal Stability: "Rockets with a static margin between 0.5 and 1.0 caliber are considered to be 'marginally stable'. These rockets may fly fine, but extra attention must be given to the wind conditions, thrust-to-weight ratio, and launch rod velocity. For example, short stubby rockets with a length-to-diameter ratio of under 10 typically will be stable with under one caliber of static margin."

Another interesting observation is how the A8-3, B6-4 and C6-5 simulate in RockSIM. Notice in the clip below (here is the full size AVI) how each of them fly (in order). The C6 (third flight) comes off the pad at an angle verses the A8 and B6 straight flights. (Note: The conversion to YouTube made it blurry, so you can look at the AVI above... but you get the idea from the clip)

So, my gut says that the design is not robust to handle some of the finishing techniques I used; covered the fins with paper, plenty of primer, glazing and paint. I have asked for anticipated finished weight and CG from Sunward but have not received that. Another clue that I over did it was that Sunward indicates on a "C" motor the rocket would get about 1000 feet. But truth be known, I could not get it to reach 1000 feet in RockSIM even cutting the weight of my rocket in half.

Well, I removed the nylon parachute and put in the Sunward parachute. I then attempted a flight on an A8-3. That flight took off the pad and did a large arc into the soft ground and then ejected. Not enough power perhaps?

Reloaded the rocket with a B6-4. It came off the pad, did a flip and land-sharked. Unstable.

This rocket is now retired.

For FLIGHT/RECOVERY, I would rate this rocket 1 points. Unfortunately, I have to rate this kit very low. I have built many, many rockets using my finishing techniques. It is clear to me that either this design is not robust enough for my build and finish techniques, or it may, in fact, not be a stable design.