Shadow Composites Shock Value
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Shown above is the official Shock Value graphic from the Shadow Composites website.
Shown above is my picture of the kit components with the Elvis CD for scale.
There is not much point in trying to design and scratch build a high performance single stage 54mm rocket as long as this kit is in the marketplace. It's design and materials represent the current state of the art. When I received the traditional long brown box from UPS, the box felt like it was empty. That is a good thing.
Everything but the nose is carbon fiber, and the components are exceptionally light. The ancillary items are good quality too; RocketMan parachutes, Kevlar shock cords, stainless hardware; it even includes high temperature epoxy and a floppy with the RockSim file. The instructions are thorough and easy to follow, the only drawback is the all-caps format.
The first construction step is to
bond the motor thrust bulkhead 14" in from the forward end of the main airframe
section. The bulkhead has a stainless eyebolt which anchors the drogue harness.
It is held in place by a one inch long split ring formed from carbon fiber
airframe tubing. Positioning of the bulkhead within the airframe is fairly
critical, since the rocket is designed for a single use K250W motor which has no
built-in thrust ring as is the case with the Reloadable type motors I usually
use. The forward end of the motor must rest against the bulkhead. The
instructions call for using a motor or spent motor casing to support the
bulkhead during bonding, and since none were available in the wake of the
Aerotech fire, I had to build a simulation using Giant Leap phenolic coupler
tubing.
To support and position the bulkhead and split ring during bonding from the front end, I had to fashion an 18" long epoxy brush and another section of phenolic coupler tube to use both as a "stuffer" and to mask the interior surface of the airframe from the epoxy. Since there is no ready access to the eyebolt once the bulkhead is installed, the Kevlar harness had to be tied to the eyebolt prior to bonding, so the result was having to thread the harness through the phenolic stuffer tube and keep it away from the epoxy while brushing it on. Quite a bear of a job and you've only got one chance to do it right.
After the initial epoxy had set up, another epoxy fillet between the split ring and the bulkhead needs to be applied. I used the same stuffer tube and another extended brush to apply the epoxy, and had my daughters roll the tube back and forth to evenly distribute the epoxy for the fillet. Shown is an action photo of the daughters doing this, and you can see by their expressions how thrilled they are to be able to help. Everything worked out well but I hope I never have to do this type of "deep depth" bulkhead installation again!
A Problem Arises...
Upon doing some dry fitting, I discovered that the tube cuts on the airframe sections were not true...off by approximately 3 degrees. The photo at left, if you look carefully, shows the problem. Both tubes side-by-side on a flat surface have a triangular gap between them. Uncorrected, this would result in gaps where the airframe sections are connected by couplers and a crooked rocket. That would be bad form in general and lead to higher drag and increased shred risk, as you probably know.
I gave all the tubes to Bob Hugo, my machinist, and explained the problem. After some consideration, he decided that the best way to fix them was to simply load them up on his lathe and use a diamond bit to square them up. Since I'm not a machinist, there are probably some heroics I'm leaving out, but after making some plugs to help with chucking, away he went and the results were dead-on, as shown in the photograph to the right (notice the gap between the tubes is now straight).
Onward and Upward...
The next phase is fin installation...if you have seen Dave's videos for attaching surface mount fins, he has an elegant method using two pieces of cutout foam board; each board having a circle cut out equal to the airframe OD with three slots each for the fins. The Shock kit includes templates for tracing your own cut outs on your own foam boards. The inner-mathematician in me knows that this is the simplest way to do this, but I could not execute. I bought many different styles and thicknesses of foam board, as well as two different circle cutters, but I could never get it precise enough to get the fins straight. I fell back on my usual habit of running to my friendly machinists to make a jig. I decided that I would be less of a bother to my machinist friends if we could make a universal jig once and for all, rather than having a new G-Job for them to do every time I had a new project. Here's what we came up with:
Fins placed and curing in the universal fin alignment fixture.
Shown above is the Shock getting
its fin reinforcement using the John Coker style tip-to-tip reinforcement jig. I
used three layers of cloth. The first layer is standard weave 2.4 oz. carbon
fiber, the second layer is also 2.4 oz. carbon fiber but with a bias cut (weave
is offset by 45 degrees), and the third layer is 2.5 oz fiberglass as a sanding
veil. Instead of using a bag of powdered mortar to supply the weight, I used
Ziploc bags filled with water, hoping to get better conformance to the surface
of the airframe. I was biting my nails hoping that nothing would burst or leak.
It took some practice beforehand to find bags that didn't leak. I tested six
bags in order to find three good ones. The pressure was 6" H2O (literally!)
which represents a relatively paltry 0.13 psi, but better than nothing.
Above left you can see the reinforcement results. Above right shows the fin-can after filling and priming.
Final Details
I wanted to use shear pins to hold the nose, so I decided to go with a non-stock nose cone. Tom Rouse has a nice modification he does with Curtis Turner nose cones, so I went with that and Tom was nice enough to machine it for me on his lathe. The modification consists of slicing the fiberglass shoulder from the cone, and machining a new shoulder and removable bulkhead plate from aluminum, and then attaching it all with epoxy. Finally, I filled the empty volume of the cone with two-part foam and drilled out a 1/4" cylindrical space to add weight if I needed it. Here is a photo of the components before epoxy:
I chose an RDAS "compact" flight computer for this project. I mounted it on a narrow fiberglass board and added a separate power switch and safe/arm screw type switch from Aerocon Systems, similar to what I did with the M-Python project. Below is a photo of the electronics board:
I used the RocketMan parachute main that was included with the kit, but went with a streamer for the first part of the dual recovery system. It was a RocketMan 10 foot orange streamer, and my wife Lisa sewed in a Walston transmitter using Kevlar thread. As an experiment for future high altitude use, I also used a new CD-3 carbon dioxide deployment device for the streamer, which was designed by Tom Rouse and marketed by Aerocon systems. I helped Tom with the sizing guide (CO2 cylinder size vs. compartment volume), so I have an emotionally vested interest in the system. I decided not to paint the rocket quite yet, since I thought that some modifications might crop up after the maiden flight. I left it with a full coat of the two-part epoxy "UV Smooth Prime" primer.
Launch
The first opportunity to launch was at the "Hellfire" 2003 launch at the Bonneville Salt Flats Speedway in Early September. My friend Steve was kind enough to volunteer as the crew, and we set out in my wife's trusty Volvo wagon for the 10 hour drive to Wendover. The final approach to Wendover happened at sundown, and it was one of the most beautiful desert scenes I've ever witnessed. Lightning was all around and semi-violent rain storms cropped up...not good for rockets but nice to look at. Steve and I checked in to the Silversmith casino, had a nice dinner, and before nodding off, listened briefly to the most hilariously bad jazz cover-band ever created.
As
I feared, the previous night's rain had created havoc with the flats. At left is
a picture of the temporary shallow salt water sea created around the entrance to
the speedway. It was 5" deep at the entry, and gradually faded out beyond
a five mile radius.
There were plenty of brave souls from the Utah rocket club that decided to go out through the salt water, and it was entertaining to watch some of the folks go out, but I decided to turn around and go home. I just couldn't do that to an automobile, especially one that I planned on living with for a while.
The big plan was to use this launch as a solo test for the Shock Value, and then use it as a sustainer (second stage) in "Project Tupelo" at the XPRS launch at Black Rock in late September. But, since the Bonneville launch didn't happen for me, the solo test would have to be at XPRS. Many thanks to Steve for accompanying me on this fruitless endurance test, but I think the "road trip" aspect of it was fun in its own way.
My friend Keith volunteered to crew for me at XPRS (late Sept. 2003). I've been thinking that a VW camping bus would be good for a one or two person Black Rock playa-mobile, so I rented one from California Campers in Redwood City. They specialize in mid to late 80's models...it was kind of scary with the mismatched tires and excess heat from the radiator which sits 12 inches in front of the driver...WHERE THE AIR BAGS SHOULD BE!, but Keith helped calm me down and we ended up having a lot of fun with it. Here's our camp in the photo below:
Following is a photo essay of the
flight. Beginning with the traditional pose and ending with the scrambled
letters on the identification stickers that used to say "JRockdale.com" but were
translated to Korean by the aerodynamic drag forces. Final altitude on the K1050
single use motor flight was 16,583 feet, less than Rocksim's predicted 18,900
feet, probably due to launching 15 degrees off vertical and the partial
delamination of the aluminum tape that secured the altimeter bay to the main
parachute bay. Let me add that the rocket rapidly disappeared after burnout and
I never would have found it without the Walston transmitter. I acquired the
signal at apogee deployment
and was able to find the downed rocket one mile
due
south of the launch site.
Here is the RDAS plot of the flight. Since I used the timer back up function as well as the "smart recovery" (apogee plus 685 feet AGL), I needed to enter a main deployment time. The maximum value of main deployment time is 254 seconds, so the main ended up deploying a little early at the 254 second mark, while the rocket was still at 2,000 feet above ground level. The main parachute and nose cone separated well; a little too well... they ended up separating from the main airframe parts. The remainder of the rocket came down on streamer only, but since the empty rocket is so light, no harm was done. I either tied the tether knot incorrectly or didn't cinch it enough. Since the K1050 motor has such a short burn time, it isn't optimized for highest possible altitude but it does provide plenty of speed. With that in mind, I entered this flight in the XPRS speed contest, and ended up winning with a mach 1.99. Huzzah!
This was the last time that I'll fly the Shock Value as a stand-alone vehicle. In the process, I learned about the RDAS, gained confidence in the CD-3 CO2 system, and pre-prep for the next flight will be easier. I also learned that the fins and airframe will stand up to higher speeds and acceleration than will be experienced with the K250. Next steps are to remove the rail buttons and paint it in preparation for its return as the second stage of Project Tupelo.