Contests. What’s with all this contest stuff? Dual egg lofting? Ya gotta be nuts!

Okay, I’m not a hard-core contest competitor. But, just for fun, at one launch a couple of years ago, there was a contest with A motors—I don’t even remember what, maybe A parachute duration, something simple. So, I threw an A motor into my Alpha III, knowing that rocket based on BT-5 with an A3-4T or A10-3T would do better, and went to the front of the line…um, er, entered the contest.

And it was fun.

Then, Pipsqueak-1 came around, and I just wrote it off. Heck, I’ve got nothing that’ll fly on a ¼A motor. Streamer duration? Yipes, I’ve never done much with streamers! But, then I thought about it, and designed a little something on RockSim, and had fun.

Now comes Morning After 42. Parachute set duration: that should be simple. I probably don’t even have to build anything. Sounds like fun: I’ll enter. But those others? And a D dual egg loft duration? Skip it.

Hmm. D dual egg loft duration. D dual egg loft duration. What if…

I have a modified Big Bertha. 24mm motor mount, epoxy rivets to attach the home made basswood fins, Kevlar shock cord mount attached to the forward motor mount centering ring. She flies great on both a D and an E, and I can easily replace the standard nosecone with a clear payload bay, add a few LEDs, and fly her at night. But, that’s hardly an optimum airframe design. Yet, I don’t have time to start from scratch with a rocket built around an 18mm composite D-10 motor, small light weight fins, etc.

D dual egg loft duration. What would it take? I was hooked.

First, a caveat: I’m writing this before the contest, before we know the results.

Could I throw together a capsule that will hold two eggs and mate to my modified Bertha? Moreover, could I do this out of parts I already had in the garage? There certainly wasn’t time to order anything. I consulted the Pink Book online, and realized that straight BT-60—the airframe on Bertha—was just a few millimeters too small for a standard egg. I had no BT-70, but did have BT-80, and a BT-80 nosecone. With not even a week until launch, it was time to design and build.

Bertha’s nose cone, parachute, and shock cord are all connected to the Kevlar anchor with snap swivels, so it was easy to remove these. I built a transition from BT-60 to BT-80 using a couple of modified CR 50-80 centering rings, a piece of BT-60, and a tube coupler for BT-60. I found some software for printing transition shrouds, available at The Rocket Web (members.aol.com/_ht_a/rocketweb/resource/programs/archives.htm). I used Shroud Designer, though RocketCAD also works. To provide a place to anchor an eyebolt, I sanded down a BT-60 bulkhead to fit inside the tube coupler. The eyebolt, inserted through a hole drilled into the bulkhead, is anchored with a lock nut atop a fender washer.

The nosecone I had was among the least streamlined things I could imagine, but it’s all I had. Next issue, then: securing the nosecone. I didn’t want the nosecone popping off during ejection or recovery. Four #4 screws with nuts and lock washers, four holes through the BT-80 and the nosecone’s shoulder, and a little cyanoacrylate (super glue or CA) to hold the nuts to the inside of the nosecone took care of that. I cut away much of the bottom of the nosecone so I could glue the nuts in, but that’s easy with a Moto-Tool. For added strength, I also drizzled some thin CA down the forward part of the capsule.

The final construction task was adding new launch lugs. I like two launch lugs on a rocket like this, forward and aft, so I put one on the egg capsule, and the other out a bit on one fin, lined up with the one on the capsule.

A final question: how to pad the eggs. The egg capsule isn’t big enough for the eggs to sit side-by-side. The plan: cut some appropriately sized circles out of some closed cell high density foam for the bottom of the capsule, between the eggs, and the top of the capsule, and wrap each egg in this same foam to keep each one upright and intact.

The original parachute on this modified Bertha was a standard 18” Estes plastic chute. I replaced this with an 18” nylon chute; for the D-DELD competition, I’ll replace this with two 24” nylon chutes (one borrowed from my Saturn V).

Thanks to some late nights, I had time to paint the egg capsule like my Bertha: a simple black and white pseudo roll pattern.

How long will she fly? Who knows? This rocket is heavy, but still under the upper liftoff mass limit for a D12-3. I know what RockSim predicts; we’ll see how close that prediction is.

Think you can’t fly in a competition? Think it’s only for the serious folks who’ve done it before? Think again!

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C’mon: contests aren’t intimidating. Just give it a try!

Alan

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