Brief:
The Giant Leap Thunderbolt38 is a minimum diameter "almost ready to fly" high power rocket. By keeping the parts list as simple as possible, this rocket could be built and ready to fly in a single, rather short build session--especially for a high power rocket. However, despite the simplicity of the design, I would not consider this to be a good choice for someone just getting started in high power rocketry because this rocket is capable of extreme altitudes even on modest motors.

Construction:
I purchased the kit from one of Giant Leap's launch representatives at a recent club launch. It comes in a thick plastic bag with all of the smaller parts in a plastic bag contained in the packaging making it easy to locate and identify all of the parts of the kit. The bag contained the following parts:

• 1 48" long x 38mm diameter phenolic body tube
• 1 4" long heavy duty phenolic coupler tube with threaded rod insert
• 1 plastic nose cone
• 1 ACME fin can with instruction sheet
• 1 pair of ACME conformal launch lugs, 1/4"
• 16' tubular nylon shock cord
• 30" nylon parachute
• 1 heavy-duty swivel
• 1 peel 'n' stick decal
• 1 8.5" x 11" instruction sheet

I also purchased a 38mm Slimline motor retainer at the same time for use with this kit. What surprised me most when I picked up the kit was that the body tube is a single 4 foot long piece of phenolic. That means that mounting an altimeter--much less using dual deployment recovery--was going to be difficult, if not impossible, to implement without some serious modifications.

The instructions contained on both sides of a single sheet of paper are basic but are more than adequate enough for the build. Most of the first side of the instructions focus on the installation of the optional Slimline motor retainer. I chose to save the attachment of the retainer until after painting was completed. I dry fit the retainer onto one end of the lengthy body tube and made a mark on the tube so that I would ensure the fin can is forward enough for attachment of the Slimline at the end of the build.

Easily the trickiest part of the build is epoxying the coupler in the middle of the airframe. The instructions are a little vague as far as exactly where the coupler should be glued, but it does mention that you need to consider the length of the largest motor that you would ever want to use in this rocket. The threaded rod going through the middle of the coupler serves as an attachment point for the shock cord, so you also have to consider putting it towards the center because the shock cord, wadding/heat shield, and parachute have to fit forward of the anchor as well! I fly my share of H and I class motors but I hate to be limited in my motor choice even if it's one that I might not actually fly with any regularity (in this case, those long 38mm J motors). The instructions recommending the use of a long wood dowel for spreading the epoxy but also post a strong warning of not getting any epoxy inside the aft part of the airframe to impede putting a motor in the rocket. Aside from the issue of shipping such a long tube (had I ordered the kit), attaching the coupler/anchor poses quite a challenge. Instead I put some thought into the build and came up with a much, much easier solution: cut the airframe in half with a Dremel and then epoxy the coupler to rejoin the airframe. I made the cut exactly in the middle, which left 22" in the aft half in case I ever go insane with an AeroTech J570 and then left just as much room for all of the recovery hardware in the forward half. I made sure to do 2 things in the process of rejoining the airframe: 1) I made sure to have a large flat surface so that I could roll the tube to ensure that the tubes would be aligned straight, and 2) I used 15 minute epoxy so that I wouldn't have to roll the tube for half an hour until the epoxy cured!

After that, there is very little else left in the build--just epoxying the one piece fin can, attaching the launch lugs and tying the shock cord. The fin can needed some light sanding to smooth out the flashing from the mold. A palm sander with 220 grit sandpaper made quick work of smoothing out the flash ridges from the mold. There is a separate sheet of instructions with the fin can which states that the fin can is designed to be used with several different brands of tubing. There was a little bit of "wiggle room" on the GL phenolic. The instructions recommend that you put wraps of masking tape on the body tube near the forward and aft ends of where the fin can is going to be epoxied on. Once satisfied with the location of the masking tape, I slathered epoxy on the tube and slid the fin can into place then set it aside.

I waited until the next day to attach the shock cord. The instructions actually have you tying the shock cord onto the attachment rod before epoxying it in the body tube but I chose to wait because I wanted to us a secure but sliding knot that I could (with the aid of a long metal hook) extract the shock cord to periodically examine the shock cord for damage as well as easy future replacement if necessary. I tied a bowline knot so I had a loop in one end of the shock cord, put a little epoxy on the knot for security, fed the shock cord around the anchor, passed the untied end through the loop, and then pulled it tight. This will allow me to easily check the entire shock cord periodically and even replace it if need be. I tied the swivel to the shock cord, drilled a couple of small holes in the base of the nose cone, and tied the other end of the shock cord to the nose cone. It also took a few wraps of masking tape for the nose cone to fit and stay in place acceptably.

Next, I lined up the launch lugs by first using angle iron to draw a line running the length the body tube. I found that the included adhesive with the launch lugs to not be very reliable so I roughed up the conformal surface of the lugs with 220 grit sandpaper and stuck them to the body tube with dabs of 15-minute epoxy. One lug was placed just forward of the fin can and the other one is about 10 inches forward of the aft lug. And there was one last thing that I did that was not mentioned in the instructions: I drilled a vent hole in the upper half of the body tube. I did this to not only prevent separation from internal air pressure but also as a sensor hole for a barometric sensing altimeter, which would most likely only be used for recording peak altitude.

Finishing:
The phenolic airframe has marked spirals, but not the worst I've seen. Reading the instructions, I was pleased to find that they were exactly how I finish my rockets. I applied diluted Elmer's Wood Filler to the grooves and sanded it smooth then a coat of Krylon gray primer was sprayed and wet sanded with 400 grit sandpaper. I had to do this process twice to ensure that I smoothed out any traces of the spiraled grooves.

I'm a big fan of Krylon paints and they recently released some new line of metallic spray paints called X Metals. It is designed be used directly on metal, but there is a special base coat spray that will allow you to use it on non-metal (or as the label says, "pre-painted") surfaces. Be careful to read the directions on both X Metals cans as you have to wait 5-10 minutes between recoating with the base coat and the color top coat must be sprayed 30 minutes after the last base coat. I found that it took 2 passes with the base coat to get full coverage and that the translucent purple top coat didn't initially allow much of a metallic shine right after spraying it, but within an hour it had the awesome sparkly finish I was looking for!

The last steps were to apply the smallish peel 'n' stick Thunderbolt38 decal and use JB Weld to permanently attach the Slimline motor retainer. The decal isn't going to earn much in the way of style points, but with such a long, skinny rocket, fancy decals would hardly be worth the effort of being put on this rocket anyway. The Slimline retainer hardly affects the overall aerodynamics of the rocket but I would be lying if I didn't admit being slightly disappointed that Loki Research motors cannot be easily retained with the Slimline. The motor fits inside the retainer but there is too much casing aft of the motor's thrust ring to get the retainer snap ring on. Perhaps the threaded version of the Slimline would have been a better choice...?

PROs: Definitely lives up to the advertised "almost ready to fly" billing as it was completely built in under 2 hours (and could have been faster if I'd used faster curing epoxy!) Excellent quality components make for a nearly bulletproof rocket. With such few parts and thorough instructions, it's difficult to botch the build.

CONs: For those maximum performance freaks like me, the finished rocket is on the heavy side for its size (it weighs almost twice as much as the comparably sized LOC Weasel). Building per the instructions can be tricky when it comes to the shock cord attachment and would make shock cord inspection and replacement difficult. I spent more time filling and sanding the body tube spirals than actually building the kit! (Although some people might think of this last comment as a pro.) Slimline retainer and Loki motors aren't a good combination.

Construction Rating: 4 out of 5

Flight:
For a shakedown flight, I prepped a G61W-M. The Slimline retainer held it adequately in place. I clipped a Nomex heat shield to the shock cord and packed the shock cord and chute using the shield to wrap them up like a burrito. It was a snug fit but not so much that there were any potential concern about it being pushed out at ejection. The winds were a steady 15-20mph. Not my ideal rocket flying weather, but I felt it was still OK for this motor-rocket combination. The motor lit and the rocket came off the rail to battle the intense winds. It weathercocked but not as bad as I had anticipated as it coasted to apogee.

I followed up a month later with a G67R-M flight. The weather was quite the opposite of the previous month--light breezes that never seemed to exceed 5mph. In a word, idyllic for flying rockets. Boost seemed quicker and altitude was noticeably greater than the first flight due to better field conditions.

Recovery:
The 30" nylon chute is a very bright neon orange for easy tracking. Since this kit is pretty much intended to fly on motor ejection single deployment for recovery, I wish the chute was a little smaller. The 30" chute might be great for those flying this rocket at higher altitudes, but a 27" or 28" flat or 24" hemispherical chute would be a better choice for those of us at sea level, especially when I attempt to get some serious altitude. I just don't want to be chasing it any further than necessary. The nylon strap shock cord is adequate although it has a slick feel which allows knots to become easily untied. I definitely make sure to check the knots in the shock cord before every flight. I haven't ruled out upgrading the shock cord to some tubular Kevlar either.

Ejection for the first flight came on the early side (it was more like 6 seconds than 10), however, that wasn't necessarily a bad thing as it kept it in the air less time to drift. The 30" chute brought it down safely but a little slower than what I like. The nose cone appeared to have smacked against a fin, taking a chunk of paint off the nose cone. Nothing a little sanding and painting wouldn't take care of...

The second flight ejected right at apogee and I again wished for a slightly smaller chute. The Thunderbolt seemed to hang up there a while even though it came down relatively close to the pad.

Flight Rating: 5 out of 5

Summary:
There is no disagreeing that Giant Leap Rocketry Thunderbolt 38 is an easy to build high performance rocket. What it may carry around in weight, that extra heft directly corresponds with the robust choice of components making up the kit, which is built to last. The only modification or upgrade I would recommend for this kit is adding a Slimline retainer to resolve any concerns about motor retention.

Overall Rating: 5 out of 5