Overview...The Bad Attitude from Hawk Mountain Enterprises (HM) is a standard kit. However, I ordered the 75mm motor mount tube (MMT) option. Since the rocket is to be used as my Tripoli Level 3 certification project, I need to be able to load an M-motor which are most typically found in 75mm or 94mm sizes. I also ordered an additional 94mm 54" booster section (stock, as used on Hermes 3 is 42") that I will use with a HM aluminum fin can in a minimum-diameter variant for Hermes 4.

The Bad Attitude is an all-fiberglass (FG) airframe. The parts are fabricated very well with minimum tolerances and nice finish - Alan Gorecki has done a very nice job with the kit. Each part was checked/fitted at HM before it was shipped, assuring there would be no issues upon arrival.

I plan to use most of the dual-deployment (DD) features that I worked out during the design and construction of Hermes 2. The Bad Attitude comes with an electronics-bay mid-coupler section for the flight computers, as well as an e-bay in the nosecone for recovery trackers. Unlike Hermes 2, the intent is for this rocket to achieve fairly high altitudes (my initial RockSim simulation suggests it will do 15K'+ with an M650 motor), so the Big Red Bee TX RF tracker and the Big Red Bee 70cm (ham band) GPS systems will probably come into play.

Construction:
Before I started any construction, I designed a totally new RockSim file (see above) since I could not find one out on the Web. I wanted to be sure that the goals I set out for performance after a discussion with Alan prior to purchase seemed reasonable. Additionally, I wanted to be able to do the Center of Pressure (CP) and Center of Gravity (CG) calculations, as well as flight simulations, for my Level 3 certification.

The all FG kit is straight-forward and contains a 4-1 Ogive style nosecone (with e-bay), an upper airframe, a 1.5" mid section/coupler for the ejection systems and a 48" slotted booster section. The fins are upgraded to the 0.187" variety and attach through-the-airframe to the 30" 75mm MMT.

Booster Section

Motor Mount Tube - The booster/MMT section utilizes a Kevlar strapping system for safety retention. Safety is the key mark in any rocket design, particularly for high flying, relatively heavy rockets such as the Bad Attitude. This Kevlar strap is provided in the kit already knotted and furnished with a large ball-bearing swivel - all components in the kit are first-rate and designed to tolerate large mach speeds and gee forces - no compromises at any level in this kit.

The kit includes three MMT-to-booster centering rings (CR). The forward CR is a 1/2" birch plywood piece that is slotted on the 75mm I.D. on both sides to accommodate the strap. I passed the ends of the strap through either side of the CR, and then folded each end and epoxied them to opposing sides of the MMT below the CR which I had previously epoxied to the front end of the MMT.

 I mounted the forward CR and strap to the MMT with Loctite Hysol E-20HP epoxy. This epoxy is an industrial grade epoxy with a shear of over 4500 PSI and is applied with a gun system that dispenses the 2:1 ratio ingredients perfectly through a mixing nozzle, eliminating the tedious task of measuring and mixing. I used this epoxy throughout the construction except for tacking the fins in place and creating the exterior fin fillets (see the fin section below).

For motor retention/safety, I am using a 75mm Aero Pack Quick-Change motor retainer. I had to pre-install (dry) the retainer in order to determine the exact location of the MMT within the booster airframe such that the CR's and the fins would align correctly with the slots of the booster section.

After marking the proper locations on the MMT and the booster, and taking care to sand all the FG surfaces on the booster and the MMT that would be subject to epoxy, I applied a coat of epoxy to the inside of the airframe for the forward CR with a small brush taped to the end of a long wooden dowel. I then tucked the Kevlar safety strap into the MMT to prevent getting any epoxy on it and installed the MMT by sliding it in through the rear of the booster. This allowed me to minimize the internal epoxy smear and create a small fillet on the forward part of the CR. I placed the aft CR on temporarily to keep the rear of the MMT centered in the booster while the forward ring's epoxy dried.

With the forward CR now firmly fixed, I made a special applicator extension for applying the epoxy for the middle CR out of a 12" piece of 0.25" aluminum tube - I crimped one end of the tube and drilled a series of small holes in one side and then taped the other end to one of a plastic mixing nozzles. By sliding the aluminum tube between the MMT and the booster, I was able to apply epoxy to the inside of the airframe and outside of the MMT, just ahead of the fin slots with a minimum of epoxy and mess.

After applying the epoxy, I pushed the middle CR up the rear of the MMT with a couple of small diameter dowels until it reached the marks I had made earlier for its final position. Again, the epoxy smear was minimized while still creating a good, uniform bond for the CR to the MMT and the airframe. Once that set, I was ready to attach the fins.

Fins - Copying the basic idea for a fin jig from Vern Knowles terrific web site, I set out to make one of my own. I added a couple of things that made the jig a little easier to true up the booster and the fins. By using a couple of stair-squares from a local hardware store, along with some fabricated straps and band clamps, I enhanced Vern's basic design slightly.

The squares keep the booster perfectly plumb relative to the jig's base. So, along with some carefully constructed L-shaped angles made from pine and composition board, clamping the fins into position for proper alignment and attachment became a relatively simple task.

Once the fins were tacked to the MMT and the back of the middle CR with the E-120HP epoxy, I was ready to apply strengthening fillets to the interior portions of the fins. I taped off the resulting fin-slot gap on the outside to keep any epoxy from running through to the face of the booster (the E-20HP is relatively thick/viscous and not much of a problem in this aspect). I taped off the rear of the MMT to keep it clean and created a rear dam for the epoxy with some pieces of closed-cell foam which sort of wrapped up slightly forward of the rear of the fin so I did not have to worry about being able to attached the rear centering ring up against the rear of the fin later on (once the fillet epoxy was almost set, I removed the foam pieces).

I made another tool for getting the epoxy up between the MMT and the airframe, this time using some tygon tubing taped to the end of the epoxy mixing nozzle. Before pushing any epoxy out the end of the tubing/mixer nozzle, I ran the tubing up against the middle CR.

I then laid a line of epoxy as I drew the tubing out. The tubing size was such that drawing the tubing down between the MMT and the airframe created a nice fillet to both sides. After the epoxy set, I epoxied the rear CR in place.

The exterior fin fillets were then applied using Aeropoxy, mixed with some West System 406 Filler to give it a more thixotropic consistency - I used a heaping teaspoon of filler per ounce of mixed epoxy. I also found that I needed to let the mixture of epoxy and filler sit for just a few minutes after mixing for it to reach its final working consistency (the "mayonnaise" state, as suggested on the 406 box). I basically followed Vern Knowles' method using a short section of PVC pipe to smooth and shape the fillets.

I used tongue depressors to initially apply the epoxy to the fin joint which gave me a nice applicator and also started the shaping process, then used the pipe piece to form the final fillet.

       ...dried fillet...

...sanded fillets/fins...

Once the mess of the filleting was over, I attached the fixed piece of the two-piece motor retainer to the MMT with JB Weld, a high-temp, strong two-part epoxy, along with the rail launch-buttons included in the kit, which were contoured to the airframe by sanding and then secured to the fore and aft CRs with #8 screws and some epoxy.

Upper Airframe and Nosecone

There is little to be done to these pieces save for securing the e-bay to the nosecone and the finishing, and later, application of some shear pins and plastic rivets (see below). The nosecone is pre-fabricated by HM and includes a retention strap. It will house both of the Big Red Bee trackers in its e-bay. I cut a friction-fit sled from a long piece of basswood and attached the RF and GPS trackers with a tie-wrap.

The nosecone seams required a bit of work to scrap/sand down in order to get a smooth finish prep for painting. In retrospect, after getting things smooth by scraping, I realized I should have probably filled/sanded the seam gaps rather than shave it in order to achieve the most rounded final form.

Mid-section Coupler/Avionics-bay

Since I had already built a fully redundant dual-deployment (DD) CO₂-based recovery system electronics bay, I really only needed to "port" the devices and concepts over to the HM FG e-bay. Rather than use the smallish sled provided in the kit, I fabricated a larger 3.5" x 9.25" sled from some .125" G10 plate. Getting all that gear into the 4" x 8" e-bay of Hermes 2 was a challenge, so I wanted a bit more room this time out. In addition to the room afforded on the larger sled, I also will be mounting the on-off switches for the flight computers and the e-match shunts to the mid-section airframe, rather than the sled itself which will free up some room.

                         ...planning the layout...

                                        ...nearly finished...

I am using a G-Wiz HCX as the primary flight computer/altimeter and a Ozark ARTS2 as the secondary. In the event that one of the manufacturers may have a software bug, having to totally different computers should alleviate any related issue and allow deployment from at least one of them. In keeping the two systems totally redundant/isolated, I am incorporating a pair of C&K P2011U2WM03NQ2 (similar to the switch included in the HM kit, but the DPDT version) ON-OFF key-switches from Newark Electronics to connect each of the CPU and pyro batteries to each computer individually. As with the Hermes 2 design, I used a pair of audio-jacks (also from Mouser) wired to provide 4-point shunts for the Rouse-Tech CD3 CO₂ ejection systems e-matches.

                   ...the other side...

I used a 12-gram CO₂ system for smaller cavity of the booster section with the drogue chute and a 16 gram system for the upper airframe section housing the main chute.

Finish

I first went over all surfaces to be painted with a wet-sanding of 320 grit. I initially sprayed on a coat of RustOleum Plastic Primer, then sanded/primered again as needed. After the initial primering, for the exterior fin fillets, I filled in the air bubbles and such with Bondo filler, sanded and then primered again.

I then applied three coats of gloss white, wet sanding in between with 320 grit as required. I finished it off with some various widths of blue and black striping tape (Hermes 1 and Hermes 2 were of a red-white-and blue theme, but since the upper section of Hermes 3 will be used with Hermes 4, I needed to change the scheme a bit since Hermes 4 will be using a black anodized fin can). I added a few some custom decals, and then a final coat of protective clear gloss.

Flight and Recovery:
I plan to test fly the new rocket prior to going for the Level 3 certification flight. I normally prefer to fly long, slow-burning motors, but since the Bad Attitude is fairly over-stable in design, I want to be sure the early initial velocity is sufficient to get it flying before it leaves the rail. So, I will use a K1499N for the test flight.

If all goes well there, will assemble an M1550R for the cert flight. Once at the launch site, I will use my prepared Hermes 3 Checklist during preparation and pre-launch. The Checklist can be downloaded here: Hermes 3 Pre-flight Checklist

Summary:My Level 3 certification flight was flown in June of 2009 at the ROCStock launch at Lucerne Valley. Perfect up, perfect down - recovered fully intact about 1/4 mile from the pad after attaining 13K'+... ahhh ...an L3!

Level 3 Certification Flight - June, 2009 Lucerne Valley, CA