Overview...The Bad Attitude from Hawk Mountain Enterprises (HM) is a standard kit. I built the initial configuration as Hermes 3 (H3) with a couple of options (75mm MMT in lieu of the standard 54mm and the larger (3/16") G10 fins). When I placed my order, I also ordered a second booster section that is 54" long that I used with an HM aluminum fin can in a minimum-diameter variant for Hermes 4 (H4).

Construction:
The booster section did not require much work other than finishing and bolting on the fin can.

Since the tube is rather long, I decided to take it to an auto-body paint shop for painting. The tube itself was in great shape with only a few pin-holes that required filling - I used some of the Bondo surface filling I mentioned in the Hermes 3 article.

After a wet sanding with 320 grit, I applied an initial primer coat with RustOleum Plastic Primer and filled in the few holes. A little touch-up with primer and another sanding, and the tube was ready for the paint shop. They applied two coats of white and a coat of acrylic gloss clear to protect the water-based paint.

I brought the tube back and applied some decals and pinstripes in a theme similar to that of Hermes 3, since the sustainer from that rocket will be coupled with the new booster. Back to the paint for a final clear coat (should have used two coats since some of the pinstripe pealed away during the initial flight).

Once painted, I cemented a Giant Leap Slimline 98mm motor retainer to the rear of the tube - having masked off the rear 3/4" of the tube prior to painting. The retainer comes with a flange that is normally supposed to sit in front of the rear MMT centering ring, but since this is a minimum-diameter application, I had the flange parted off in a machine shop to provide a more aerodynamic profile. I could have sanded it off on the bench sander, but I wanted a very clean result and was not sure I could achieve that on the sander.

I then assembled the fin can around the rear of the tube, just forward of the motor retainer. It is a relatively straight forward process and the included instructions from HM are clear.

I added a couple of rail buttons to the body tube with Loctite E120-HP super-strength epoxy and a couple of sheet metal screws that I ground down to make sure they did not protrude into the motor cavity - that only allowed about a half-turn of the screw into the airframe tube, but with the addition of a bit of the epoxy, it should help a little with the shear strength of the button mounting.

I used aluminum buttons since they looked nice, but I later learned they are really a no-no out on the range since they gall the rail. Uh-oh! I guess I will just have to apologize since the E120-HP works so well! I also had sanded the bottom of the buttons against a piece of sandpaper wrapped around a 4" airframe in order to make them more conforming to the booster surface.

A 1/4" vent hole for the recovery cavity and a couple 1/8" holes for the shear pins and the booster was set to fly! Since this is a minimum-diameter application, an eyebolt screwed into the motor's threaded forward-closure will provide the recovery anchor. A Fireball provides zipper control in the event of an early/late drogue deployment.

Everything else forward of the booster is the same as with Hermes 3.

Flight and Recovery:

The initial flight attempt utilized a AT M750W slow-burn motor. The loaded weight of Hermes 4 with this motor is around 35 pounds, so the M750 provides a 6+:1 thrust-to-weight ratio, which got it off the rail just fine. If the wind is up, then a better motor choice most likely moves to an AT M1939W which increases the T-W ratio something over 11:1.

I flew Hermes 4 on July 11, 2009 - the plan was to do a test flight on a small K805, but I found that my Aero Pack 98-75mm motor adapter would not fit into the rear of the Slimline motor mount...so, after checking with a couple of people and having them look over the construction on the new booster, I decided to go ahead and roll the dice and go with the big motor for first-flight.

After building up the Aerotech M750W moonburner motor (interesting construction requiring epoxying the grains together to keep the offset bores aligned), I hauled the rocket out to the pad. Launch was very straight and it roared and coasted to an altitude of ~21K' (average of the three recording altimeter readings).

The BeeLine GPS worked perfectly and I recovered the rocket downwind about 1.8 miles away - the rocket was in perfect shape except for some of the pinstriping that apparently didn't like the sustained time above mach, and one pyro battery that dislodged on landing (it hit a little harder than H3 - I used a Sky Angle 60" Classic II instead of the 10' Rocketman chute I used on the heavier H3).