rocketry

One of the reasons I stalled on my L2 build was because I had to make some key decisions about the recovery system and was looking for some guidance from a more experienced builder. I thought it would be easiest to corner a friendly L2+ flyer and pester them with questions until they cried “uncle”.

A couple of weeks ago, I organized my questions and posted to the LUNAR Google Group looking for a volunteer. The general response was, “Just post the questions to the list, someone else might benefit from the discussion.” So I did, and the response was awesome.

My questions concerned deployment redundancy, shear pin use in a cardboard/paper airframe and ground testing. You can view the full thread here on the LUNAR Google Group. This is what I took away from the discussion:

1. Altimeters fail. eMatches fail. Redundancy is a good policy. Just how far you want to go is a decision you need to make for your project. I’m taking that principle and designing my av bay and deployment system with flexibility in mind. It will have the potential to support two separate altimeter systems and two separate deployment charges for each parachute.
2. Shear pins aren’t strictly necessary for lower power, lower altitude flights as long as you can get a tight friction fit. Drill vent holes to relieve the pressure differential that increases with altitude and can cause airframe separation. If you do use shear pins on a cardboard/paper airframe, treat the holes with CA glue and re-drill. This provides enough strength to prevent too much damage during deployment.
3. There are eMatch options for folks who don’t want to go though the hassle of holding a LEUP. Bay Area Rocketry carries them.
4. Ground testing is absolutely essential to confirm the size of your deployment charge and work out any other bugs in your system.
5. L2 certification does not require redundant electronics. When testing for L2, go for a simple, predictable approach.

I’m sure there’s going to be many more questions as this build progresses and the I approach my first flight. Looking forward to the next step of the build.

Here is a quick look at the fin alignment jig I made for my L2 rocket build. I wasn’t keen on the standard approach, where you eyeball down the fin to make sure it aligns with a printed template – that always seemed hokey to me. This was a relatively quick build. I drew it in Illustrator and cut it on the Epilog laser at TechShop. It’s made from 1/4″ birch plywood and some dowels I had lying around the shop. Total cost was about $5.

The jig has some nice features. First and foremost it ensures the fins are aligned in all planes: they are evenly spaced around the airframe, they are attached perpendicular to the airframe (no lean), and parallel to the rocket’s primary axis (no twist). I used this jig to tack them to the motor tube with epoxy. The triangular shape provided a nice way to rotate through each fin placement. There’s a small margin at each attachment point so I didn’t accidentally glue the fin to the jig with squeeze out. After these were dry, I removed the jig and followed up with solid internal fillets. I like this design and will use it again.

Here is a link to the Illustrator file in case anyone would like to modify and use it for their own purposes.

It’s been several years since I attended a launch. Back in July 2011, I experienced my first major launch failure when my first L1 rocket shredded at high speed during ascent (more on that later). It was only my third high-power flight, and I was bummed by the setback. But I picked up the pieces (literally) and resolved to get the rocket back into working order.

At the time, I had already started on my next build: a Binder Excel that I planned to use as my gateway to dual deployment and L2 certification. I had the kit, I had the altimeter and I began running simulations in RockSim. And then everything went on hold…for a bunch of good reasons. I picked it up for brief periods and assembled some components, but it’s been in a partially done state for four years now.

I don’t like leaving things undone, and I’m ready to finish this project and get this bird in the air. I still have a lot of questions and plenty of work to do. I’m going to use this site as a place to document the build. Maybe it will be helpful for someone else, or maybe it will just be a good way to organize my thoughts. Posts related to build will carry the hashtag #journeytoL2 and everything related to this as-of-yet-unnamed rocket will carry the hashtag #LEA-6