Adam Clarke LUNAR #

Nothing beats the heart stopping action of staging. (The heart stops in that half-second when you don't really know if that sustainer motor is going to fire) But if you are willing to take the risk, there is nothing like a sucessful staged ignition to make you feel like a rocket scientist. Gap staging just pushes the envelope a little bit farther...

Apogee Components produces an amazing rocket called the Super Centrix, it is an ultrathin 10.5mm gap stager capable of amazing performance. Unfortunately, this awesome product is useless to LUNAR members. Some government body (I think it is the big bad wolf) prohibits the use of Apogee's 10.5mm rocket motors in California.

My solution, don't fight city hall, bash the kit instead. This kitbash produces a really cool 13mm gap-staged rocket. Then we can put approved Estes motors in it and up we go. You will need the following:

Apogee Centrix Kit

Apogee Super Centrix Staging Unit Kit

Estes BT-5 body tubes

Estes Mini Engine Mount Kit

Estes NC-5 Nose Cones

Pratt Hobbies SL1-20 Kevlar Cord

Modeling Clay

Basically the kitbash is as follows:

Blow up the Apogee tube marking guides 125 percent on a photocopier.

Replace the Apogee tubes with BT-5 (13mm) tubes, cut to the same length

Replace the Apogee engine block with the one from the Estes mount kit

Replace the Apogee kevlar cord with a piece one foot longer

Replace the Apogee nose cone with an Estes one half-filled with clay

Then basically build the rocket as per Apogee's instructions, adapted to the new parts. Remember that we need to set the engine mount in a position 1.5 inches from the rear of the rocket, Estes motors are as Estes motors are only half the length of the Apogee motors.

Details

Nose Weight

Estes (45mm) motors are about half the length of Apogee (88mm) motors. As motors generally belong at the back end of a rocket, the CG shifts away from the nose, not good for stability. To compensate, I added 2gm of modeling clay to (half-fill) the nose.

Shock Cord Length

For their size, the small Estes motors pack quite an ejection kick. Combine this with the weight we added to the nose, and the fact that the engine block is further away from the nose (Estes motors are shorter than Apogee) and my first attempt kept overstressing the nose cone (it would separate at the glue joint) so we need a longer cord.

Estes Motors

Unlike the Apogee motors, Estes Motors do not need staging igniters. I think Apogee intended to use 3/4 inch scotch tape to mount the motors, since Estes motors are shorter, I use 1/2 inch tape, so the motors should extend only 7mm (Apogee used 9mm) beyond the tube.

Fin Position

Like the motor overhang, place the fins 7mm from the end of the tube, (Apogee used 9mm) and use 1/2 inch scotch tape to retain the motors.

Exhaust Ports

I place the exhaust ports further forward than Apogee, about 10mm from the end of the booster tube.

Stability

I calculate the CP for the sustainer to be 176mm (7 inch) from the nose, and for the complete rocket to be 235mm (9 1/4 inch) from the nose. Before launch, the CG should be at least 13mm (half inch) closer to the nose than this.

About the name

I believe that Tim Van Milligan named his Super Centrix after it's extraordinary 10mm (cent = 10) diameter. so, in tribute to the original design, I have named this 13mm variant Triskaideka, literally Greek for 10+3.