Mach 2 Modification Sanity Check

[pyrrxa]

I just received my Wildman Mach 2 kit, and have been debating on modifying it to be a "zipperless," single break airframe. Essentially shorten and epoxy in the coupler to the airframe, and then run a cable cutter and chute in the nosecone. This would let me fit slightly longer motors (looking at the L1040) and would give me an easy retention solution (threaded rod from forward closure to AV Bay. My concerns are

1. Packing volume in the nosecone. I can use a centrifuge charge to avoid a big well, but it will still be a tight fit. Any experience on how a 36in thin mill chute and cable cutter would pack here? Currently looking at just over an inch of coupler in the nose cone.
2. The airframe stabilizing during drogueless descent. With a motor casing and not much mass in the nose cone, I don't want the first descent stage to be pseudo-ballistic.

Overall, the sims look like it should be fine, just wanted to get some second opinions before I do something irreversible.

 

[mikec]

I'm not sure how doing this allows you to use a longer motor than the HED config the kit is designed for. I'd stick with HED myself.

 

[pyrrxa]

I'm not sure how doing this allows you to use a longer motor than the HED config the kit is designed for. I'd stick with HED myself.

The extra space would come from shortening the coupler and not having to include recovery gear in the main airframe. To me, the big space saving is getting to double dip on using the AV bay for motor retention. I will probably build it as described and then order a second coupler if I decide to modify it.

 

[mikec]

Well, maybe. You could shorten the coupler and still use HED, fly drogueless with thin Kevlar shock cord, and use friction-fit for retention. But if you want to use the scheme you describe, I don't see why it wouldn't work. I find HED to have fewer failure modes than a cable cutter myself. The 36-inch thin mill should fit OK, you'd need the same for HED.

 

[Keener]

I'm a little late to the party here, so I wouldn't be surprised if you've already made your decisions or even flown your rocket, but I just flew my Mach 2 last month on a similar setup. I decided I wanted to cut out as much empty space from the kit as possible and fly on an L1000 with single sep HEDD from the nosecone. I ended up chopping off a couple of inches from the body tube and friction-fitting the L1000 in with blue tape. I wasn't happy with the fit of the nosecone onto the switch band of the AV bay so I decided to freehand it with an orbital sander and took probably a quarter to half an inch off of the nosecone in the process of straightening things out. I decided I would try and cram a 36" top flight thin mill parachute and a tiny spherachutes drogue into the nosecone along with both parachute protectors, redundant cable cutters for the main, and a 20 foot 3/16" tubular kevlar harness. The drogue was because I was worried, like you, about the much heavier body section weighing more than the nosecone at separation and restabilizing and pulling the nosecone behind it.

Once I ended up actually practicing packing the recovery gear I realized it was gonna be an extremely tight squeeze, especially with the redundant centrifuge charges in the tip of the nosecone. I ended up removing the parachute protector for the main and zip-tying the main parachute directly since I was using the exhaustless cutters from Tinder Rocketry and bundled the drogue and main in the same parachute protector. Even after that change it took several tries carefully packing and then another set of hands to compress and shear pin the nosecone on.

Things that went well:
-Centrifuge ejection charges in the tip of the nosecone
-Bundling the main and drogue together
-Tying the main only a few inches from the AV bay so the e-match wires would reach (get matches with longer wires if you can)
-Low-profile eyebolt
-Low-profile electrical connectors from Lab Rat Rocketry (these are absolutely awesome)
-Friction fitting, this saves room and weight
-Using a launch tower

Things that didn't work well:
-Using 20ft of shock cord... should have stuck closer to the rule of thumb of 2-3x body length, I had a couple extra feet I believe
-Using a drogue, the tiny drogue from spherachutes was beautiful but the nosecone caught more air than the chute and kept the body restabilizing
-Removing length from the nosecone shoulder area (many regrets lol)

There are 2 videos of the flight on my YouTube, the uncut launch and landing footage is linked below, and you can see multiple times during the flight that the shock cord is fully extended and falling under the nosecone rather than the drogue. I'd definitely recommend going drogueless and I would caution you to make sure you 100% have enough room for your motor, avionics, and recovery gear before cutting any couplers or tubes.

Video Link