Project Diamondback

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Jan 21, 2009
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Los Alamos, NM
The XRAAM Diamondback-75C is an HPR design/build project that will likely lead to my L3 certification. It is envisioned it to be a futuristic, eXperimental, hypervelocity, Ramjet powered, active radar guided, Air-to-Air Missile. The name “Diamondback” was chosen because there are several real air-to-air missiles that are named after snakes (e.g. Sidewinder and Python). The “75C” designation was chosen because it utilizes a 75 mm motor mount tube and I typically fly Cesaroni motors. It is an exotic, unique, and relatively complex design with 12 fins (4 larger semi-forward swept trapezoidal fins, 4 conventional sweep trapezoidal fins, 2 forward wing-like strakes, and 2 aft strakes) and 2 simulated ramjet intakes (with internal, nosecone halves surface mounted to the main airframe tube). RockSim version 9.0 was the design and simulation tool used to create the model.

This project is actually an upscale of a previous 3” airframe version of the same design called the XRAAM-54C Diamondback (former working title was "Bolaero Endgame"), which was documented herein at The original project served several purposes in the preparation for this project. The first build utilized the new Blue Tube airframe tubes from Always Ready Rocketry and provided familiarity with the product and experience building with it. I also used/tested some construction techniques that will be applied to the upscale. The previous project was also used to evaluate CG CP relationship/stability and performance of the unique design prior to spending significantly more $ on a larger one. Another major accomplishment of the former 3" project was the development of the artwork and production of a set of really cool vinyl graphics (done by Mark at Mark has made me an upscaled set of vinyl graphics for this project. The bird is essentially complete, although I still have to do some ground testing, apply the vinyl graphics, and complete my paperwork prior to cert attempt. Or I may just fly it first on a CTI K1200 for a shakedown flight prior to the cert attempt. This thread will document the build...

Here are a few more details...

75mm MMT with Aeropac RA-75 retainer
DD using 2 each Missile Works RRC2-mini Altimeters and
Dual RouseTech CD3s deployment system
Garmin Astro (DC-20) GPS tracking system
Top Flight 120" Crossfire Main Parachute
Top Flight 30" Crossfire Drogue
3/16th inch G10 fins
5.5 inch LOC nosecone PNC-5.38L

I took design cues and inspiration from three other designs in creating the Diamondback; two are real world missiles and one is an imaginary anti-alien missile from the model rocket designer Doug Schrock. Tandem fins penetrating through ramjet tubes was a design element gleaned from the Aerojet (GenCorp Incorporated) GQM-163A Coyote missile.


The MBDA Missile Systems BVRAAM Meteor which utilizes only two lower ramjet tubes inspired the asymmetrical two ramjet design of the Diamondback.


I took the forward swept forward fins look from the model rocket world, a Shrox designed, anti-alien missile called the Bolaero-Z.


The wing-like tandem strakes and the half-nosecone-in-cylindrical-tubes ramjets were my own original “tweaks” to the final design as seen in the RS9 3D graphic below.

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After reading the "how to" info on Vern Knowles site ( I decided to cut all my own centering rings for this project. I ordered a Jasper 400J Model Router Circle Cutting Jig from Turns out that just for this project alone, cutting my own centering rings (as compared to ordering them from LOC Precision) saved me over $100, enough to pay for the jig and a most of my router. A good investment...

I started this project by cutting all of the centring rings for the MMT, the bulkheads for the av-bay, and for mounting the DC-20 inside the nosecone. Here's a photo of the 1/2" plywood CR (made from 2 rings I cut from 1/4" baltic birch plywood) that I cut to go inside of the nosecone. I added 8 each 8-32 t-nuts to so that I could attach a removable bulkhead to it. I plan to mount the Garmin DC-20 to the bulkhead. The reason for the four notches in the CR is to allow the corners DC-20 (this will be shown in later photos) to pass through the ring...

I cut the bottom off the nosecone so that I could use the internal volume to hold the Garmin DC-20 GPS transmitter. I sized the nosecone CR such that it can be inserted into the nosecone "sideways" and then rotated into postion where it's a nice tight fit and it sits on the internal lip that is formed at the top of the nosecone shoulder. I epoxied it in place, although it probably was not necessary...

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This shot is the NC bulkhead before I mounted the lower disk that supports the DC-20 GPS unit. The white nylon spacers (combined with the back side of u-bolt) provide a flat surface on which the lower disk rests...

Because I read about the DC-20 (in the latest issue of Sport Rocketry) causing interference that lead to an unplanned discharge of BP ejection loads, I added a thin layer of aluminum (cut from a Coke can and spray mounted to the plywood disk) to act as an RF shield between the av-bay and the DC-20. The article I read indicated that locating the DC-20 greater than 6 inches away from the altimeter proved to be failsafe. So, the shield is not really necessary, but I figured that it couldn't hurt. In my current setup the DC-20 is more than 2.5 ft away from the altimeters. I'll have to add that issue to my preflight checklist, to ensure I don't turn on the altimeters untill av-bay is secured to the forward airframe anchor bulkhead and the DC-20 is turned on first and is secured in the nosecone with the shear pins installed. Here's a photo of my RF shield disk before and after drilling the mounting holes...


Here's a shot of the Garmin DC-20 mounted to the nosecone bulkhead. It is held firmly in place between a couple of smaller bulkheads that slide down the 1/4-20 allthread rods and is secured with wingnuts for quick removal/install. The upper end of the allthread rods will be used to attach additional nose weight should it be required (at this point I'm guessing that the weight of the DC-20 and associated hardward in the nosecone bulkhead will be sufficient noseweight...

Okay, I started from both ends and worked toward the middle. On the other end of the rocket is the Aeropac retainer. It is flange mounted with threaded inserts and 12 each 6-32 hex head screws...

Back up to the other end for a moment... Here's a photo of one of the three brass shear plates that I added to the shoulder of the nosecone. I use a small sanding drum on my Dremel tool to grind out a shallow spot so that the brass plate will be flush with the surrounding surface of the nosecone shoulder. I also cut a slot in the shoulder and put a 90 degree bend in the upper end of the brass plate, rough up the back side of the plate with 80 grit sandpaper, apply JB Weld and insert the brass plate into the slot/trough and tape it down with painters tape until the JB Weld sets up. I use #2-56 nylon screws as my shear pins and a 5/64ths drill bit for the holes. If you happen to use this technique be sure and drill the holes with the nosecone installed in the airframe as it will be during flight. After you drill the first hole install a shear pin before you rotate the assembly to drill the next hole. Similarly, after you drill the second hole install another shear pin before you proceed to the next hole. That way you keep everything properly aligned. This same setup has worked flawlessly on 8 of 8 flights of my Nuclear Stonebreaker (which is also a 5.5 inch airframe rocket with DD).

Here's a shot of the av-bay sled all loaded up with the Missile Works RRC2-mini altimeters. The two red connectors held down with zip ties will connect to key switches that will be mounted on the av-bay band so they can be armed when the rocket is on the pad. The other half of the connectors will also be secured with zip ties (that's what the extra two holes in the G10 sled are for) to make sure nothing moves during flight...

The key switches will be placed on the av-bay band as shown in the photo below. You can also see one of the three altimeter static vent ports (.25" diameter per the equations recommended on Note also, that you can see the RouseTech hardware (green cylinder) mounted through the aft av-bay bulkhead. It holds a 12 gram CO2 cartridge which will deploy the drogue chute.

Here's the aft av-bay bulkhead. Note that the wiring to the e-matches is color coded so that the port altimeter output wiring is orange and the starboard altimeter output wiring is green...

...and the forward av-bay bulkhead is shown below. Note that the main parachute is deployed using a 16g CO2 cartridge which rides in the gold anodized hardware. The three 1/4-20 all-thread rods (secured to the aft av-bay bulkhead with acorn nuts) pass through the av-bay and the forward av-bay bulkhead which is then secured to the av-bay tube with wingnuts. Note that I use JB Weld to glue the washers to the bulkhead (that's three things that I don't have to worry about keeping track of or dropping in the wheat field). The rods extend a little more than an inch beyond the wingnuts and will be inserted through corresponding holes in the av-bay anchor ring which will be epoxied inside the forward airframe tube. The entire, fully assembled av-bay will be secured to the anchor ring/forward airframe tube by another set of wingnuts. A 4-conductor locking connector allows the forward av-bay bulkhead wiring (to the two e-matches that fire the forward CD3 unit) to be securely plugged and unplugged from the av-bay sled. This allows disassembly of the av-bay without the need for tools...

Given the large number of fins on this design, cutting the fin slots is a bit more time consuming. I cut the slots using a flex-shaft Dremel tool and a cutoff wheel. I measure and mark the tube, then outline the slots with painters tape and cut them by hand (no jig) using the edge of the tape as my guide. Here's a before and after shot of the slotting activity...


After I make the first set of cuts on the slots, I use a stack of cutoff wheels (equal to the thickness of the fins) to clean up the slots. This pic shows the technique...

Here's a couple of shots of the MMT during construction. Because this design has lots of long fin slots, the slots themselves weaken the airframe considerably. I used a couple of "extra" centering rings for several reasons, 1) to re-enforce the airframe where the slots are extra long and 2) because of the tandem fins and long fin slots it is difficult to add internal fillets through one end or the other. I intend to add balsa strip "troughs" to the MMT that allow me to poor a generous amount of epoxy through the fin slots into the troughs, then I will insert the fin into the slot/epoxy, slide on a fin alignment jig, and allow the epoxy to set up. This forms fairly beefy internal fillets on the MMT. I will then add fillets at the outer fin/airframe junction. In both cases I rough of the surfaces to be joined with 80 grit sandpaper and use two-part Aeropoxy with a heathy dose of milled fiber added in. Because this design has so many fins I want to avoid trying to do tip-to-tip glassing (also the reason I used 3/16" G10 fins).


Last thing I needed to do before I installed the MMT and start on the fins was to take care of the rail guide attachments. I'm using the PML linear rail lugs, just because they look a little more like the lifting lugs you might see on a real weapon system (as compared to rail buttons). For the aft rail guide I added a small hardwood strip attached to the aft centering ring and installed a couple of t-nuts that allow me to attach the lugs through the airframe wall with 6-32 allen screws. The forward rail lug was attached toward the forward end of the booster section (where there are no centering rings). This is the section of airframe which holds the drogue and aft shock cord. I needed a "low profile" means of mounting it so that no hardware on the inside of the airframe would snag the drogue or shock cord. I cut out a small rectangle from a scrap piece of Blue Tube 5.5" coupler, added two t-nuts (attached with JB Weld), and using a belt sander I sanded the edges of the the coupler section to make a smooth transition so the drogue/shock cord can slide over it on deployment...


And here it is glued in place inside the booster airframe...

Here's a shot showing one each of the four types of fins on this design. I have to give credit to Mike Fisher at Binder Design for my custom cut fin set for this bird. I'm not equipped to cut and bevel G10 fins, so I sent the RockSim file to Mike and he did a great job creating these for me. Thanks Mike. Mike you will notice that I did modify the tabs on the long strakes to accommodate the two forward centering rings and open up the forward end of the aft airframe tube to make more room for the drogue/shock cord.

This is my favorite part of any new build... puttin' the fins on and seeing the design start to take shape. Here's a shot showing the beginning of that process. The fin on top is this the only one with epoxy on it at this point. The other two are just there to balance it out and help square up the alignment of the fin jig...


and one more...


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