Competitor 4 Significant Progress

After attending URRF 2 in Potter NY last weekend as a spectator (a big launch with a lot of high altitude and large rockets), the "bug" struck me and I am in "rocket mode." I resumed work on my Competitor 4 rocket, which I've had since I bought it at LDRS 31, which was 2 years ago.

Fins

The first thing I worked on was the fins. I've been hesitant to attach them without a decent way of aligning them but I decided to go for it anyway. The problem is a lack of a large, flat surface. I ended up using the combination of the floor in one particular spot, and the coffee table. After some simple math, I figured out the spacing required to exactly place the fins at half the height (radius) of the body tube while laying horizontal. I used 5 minute epoxy at the root of each fin and used the body tube slot to align it and glued it to the motor mount tube. It's nearly the same technique that I used for Positive Ascent, although I had some nice, flat counters to work from. I believe what I came up with will be ok. If it spins while flying, at least it's still flying.

Fin number 1 initial alignment checks.

Fin number 1 glued in place.

Fin number 1 tacked in place (1 of 2)

Fin number 1 tacked in place (2 of 2)

Same idea for fin number 2, but using the coffee table to allow clearance of fin number 1.

All 3 fins tacked in place and awaiting some internal reinforcement.

The gray is JB Weld to create internal fillets. The blue is tape to keep the JB Weld from getting where it could interfere with a clean motor can insertion into the lower body tube.

Electronics Bay

Next, I finished the electronics bay. I had to install the black powder charge holders (PVC caps) onto the bulkheads of the electronics bay. I did this by roughing the bottom of the PVC caps with sandpaper and epoxying them to the bulkheads. I had drilled 2 holes in each charge holder to allow the epoxy to ooze up through and spill into the bottom, effectively creating an epoxy rivet. This should help keep them from breaking off.

Bulkhead with both (primary and backup) charge holders installed.

Close up of the epoxy rivets.

Main Recovery Setup

While waiting for the JB Weld to set on the fins (8 hours or so), I figured out how to rig the main recovery gear. 

Background on the Use of Deployment Bags

I am using a deployment bag for the main parachute, which essentially is exactly what it sounds like. It's a Kevlar (flame resistant) bag to contain the main parachute. It also provides elastic bands to neatly and systematically bundle all of the shroud lines of the parachute. The idea is to protect the parachute and provide a clean, structured method to deploy everything in the right order. 

Deployment bags are normally used with a pilot chute, which is a small parachute that opens as soon as the nose cone comes off. The pilot chute pulls the deployment bag free which then allows the main parachute to open up and the rocket to descend in its final configuration.

The question then is, what happens to the pilot chute and deployment bag?

There are 2 normal ways of handling this. The first method is the integrated method, which is what I did for every flight except one of Positive Ascent. This method is to attach the deployment bag and pilot chute directly to the apex of the main parachute. This allows the pilot chute and bag to dangle harmlessly above the inflated main parachute, and the nose cone would be attached to the main harnessing, under the main parachute.

The other option is to freebag it. This means that the pilot chute pulls the bag free and descends separately with the nose cone. Then you have 2 pieces to recover.

Figure illustrating the two methods of deployment bag use. Courtesy of Giant Leap Rocketry.

Deployment Bag Setup for the Competitor 4

I prefer the integrated method, simply because the tracker is in the nose cone, and I don't want two pieces to look for, only one of which can guide me to it. 

The main parachute that I have for the Competitor does not have an attachment point for the pilot chute. Instead of trying to make one, I believe I figured out a different way to deploy everything. Basically I am attaching the pilot chute directly to the nose cone and deployment bag, but allowing those pieces to descend under chute, and remain attached to the main Kevlar harness. 

By leaving just the right amount of slack in the right places, I can neatly bundle some of the Kevlar harnessing into the deployment bag keepers, causing that cord to come free at the same time and same rate as the main parachute shroud lines. This further reduces the chance of anything tangling.

This figure shows the Kevlar harnessing that needs to stay out of the way of the pilot chute and the main parachute when they are opening up.

This figure shows little cord there is to deal with now that all the extra is bundled. I have to be careful to ensure that the Kevlar does not pull tight when the gray cord does. The gray one is what pulls the bag away from the main parachute. I also intentionally rig it so that the parachute shroud lines get some tension before the Kevlar line does, assuring as much energy as possible goes into getting the main parachute free.

I put together 2 demonstration videos to show that it works, at least in a controlled environment.

 VIDEOS

Full Deployment Sequence Demonstration

Deployment Bag Operation

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Next

The next items I will be focusing on are:

• Rail button (launch guides) installation
• Selecting final shock cord lengths and installing additional parachute protective blankets
• Finish fillets on the motor mount centering rings
• Installing the completed motor mount/ fin assembly into the lower airframe tube
• Creating internal fin/ airframe tube fillets
• Creating external fin/ airframe tube fillets
• Installing motor retention
• Ground testing the ejection systems
• Paint? Maybe.

I hope to get all this done and get a first flight in this year.