Too Sexy For My Cert (announcing my L3 plans)

I'm about ready to further empty my wallet into the financial black hole of rocketry and start my L3! I wanted to do an L3 that was both simple and high performance. My plans have always jumped around. Initially, I wanted to do a 4in flying case on an N5800 or O3400. The price tag on those motors brought me back to reality. Next I began drawing up plans for a 3 inch minimum diameter to fly on either a Loki M3000 or CTI M2245 and aim for the M altitude record; more affordable, but still capable of racking up some serious altitude. However, I also wanted the capabilities to fly 4in motors without building a completely different rocket. My new design was one that could get great performance on 4 inch motors, and still get decent performance on 3 inch ones. It's basically a 4 inch minimum diameter, minimum length rocket with a simplified adaptor system for a wide range of motor options.

It's shown here with a 3in motor (top) and 4in motor (bottom).

Here is the Openrocket file with the CTI O3400 Imax

Project Goals: 

• Be flyable on all L2 and L3 motors (with the exception of 6in motors and the N5800)
• Meet all criteria for a successful L3 certification 
• Meet strength, stability and heat resistance needs for a Mach 3 flight with long 4 inch motors.
• Look pretty (before flight, not after.)  

Detailed Description: 

Nosecone: 

Let's start from the top! I will be using a Performance rocketry Filament wound fiberglass nosecone with aluminum tip. I've found these to be perfect for what I am trying to accomplish. They are both strong and easy to finish. The aluminum tips allows me to install an eyebolt and a shock cord attachment point in the nosecone. 

Coupler

The coupler will also be filament wound fiberglass. It will have a short switch band glued on that will butt up against the nosecone and body tube. The electronics bay will be housed in this coupler. 

Electronics 

I've picked out a Perfectflight Stratologger and Missileworks RRC3. In my experience, these are both highly reliable and will work great for what I'm doing. The Stratologger is rated up to 100,000 feet and the RRC3 is rated up to 40,000 feet. In addition, I may have a small "flip" camera onboard, looking through a small window in the switchband. A GPS or RF tracker will be used for particularly high altitude flights and will be stored in the nosecone along with the main chute. 

Body Tube 

Yep, you guessed it! Filament wound fiberglass. This is the best option in terms of price and strength. I have seen 4 inch filament wound fiberglass flown over mach 3 without any issues. I picked up 60 inches of it for only $70 at the Wildman Black Saturday sale. 

Fins

I'll start with 1/8 in G10 core. Those fins will be beveled, then be thickened and shaped by 3 layers of 5.7oz carbon fiber on each side, oriented at +-45, 90,+-45 for a quazi-isotropic laminate, then vacuum bagged for a high fiber content. The fins will be joined to the airframe with a high strength epoxy adhesive and filleted with a high strength epoxy. Extra reinforcement will be provided by 2-4 layers of 5.7oz carbon fiber tip to tip. The fin edges will be sealed with high heat epoxy to prevent delamination at high velocities. The entire fincan will then get a light coat of ablative to prevent excessive heat transfer and composites damage. This may need to be replaced after a particularly fast flight. 

Adaptor System 

The forward motor adaptor ring can be made of nearly any rigid material. The aft ring will butt up against the body tube and transfer all the stress from the motor onto the tube instead of the rings. This aft ring will be either made aluminum or fiberglass. The aft ring will also have short section of plywood attached to it with with a threaded insert. This will slip just under the body tube and a screw will go through the body tube and into the threaded insert, providing negative retention for the retainer. Adaptors will be made in all sizes 38 to 75mm. Cluster options are also available. The 38mm adaptor will have a shock cord anchor. 

Deployment system

As depicted in my layout above, I have different options regarding deployment based on the motor length, Motors shorter then a 98 6G will be able to utilize standard dual deployment with the drouge in the length between the coupler and the motor and the main in the nosecone. With long motors, deployment will have to be done with a cable cutter and main chute in the nosecone. 

I hope to complete this project sometime in the spring of 2015, however I still don't know where I will fly. My usual UROC field is has too low of a waiver for any M motor. My two very likely options are Springfest with Tripoli Vegas or Aeronaut with Aeropac. 

That's all for now, I will continue posting as building begins. 

--Alex Laraway