TL;DR:  This is a builder's kit.  I created it months ago and debated whether to rewrite the description.  There's some useful stuff in here so parse it as you like or just print it and launch.  

Enjoy!

Introducing the BetaMax Mk4 Model Rocket Kit!  

This was inspired by another full kit I downloaded and printed for my wife.  We had such a great time with it, that I wanted to share the fun with some updates.  Unfortunately, the original author did not allow derivatives for his kit.  Not wanting to impinge, I built this one from scratch in Tinkercad.

This is a full kit.  It contains everything you need to print, build, and fly outside of the recovery system, motors, and launch pad.  I will explain the variations and everything you will need to source below.  

I have tried to make this guide as thorough as possible.  If you have experience building rocket kits, then this shouldn't be anything new.  If you are new to model rocketry, WELCOME!  You will never be the same.  I would suggest watching some build videos of rockets by Dr. Dave Thomas on the Rocketry Education and Research (R.E.A.R.) channel on YouTube (https://www.youtube.com/@REAR_rockets) before starting out.

Disclaimer:  I make no assertions or guarantees with this model.  Use and enjoy it at your own risk.  Please follow the NAR safety code when using this.  They can be found here: [https://www.nar.org/safety-information/model-rocket-safety-code/](https://www.nar.org/safety-information/model-rocket-safety-code/)

Overview:

The BetaMax is a similar-sized kit to the Estes Alpha III from which it was inspired.  The Alpha was the first rocket I built and launched when I was a teenager.  It was the classic TFN (three fins and a nose cone) design and capable of flying A-class through C-class Estes rocket motors.  

BetaMax has some differences.  The obvious change is that I have modified the booster section to include four fins.  Why?  Dunno… I like the look.  I have beefed up the motor mount so you can easily print with any PLA family of filaments, ABS, or PETG.  I had great success using PLA+ on multiple launches without heat deformation.  Just let the rocket rest for a few minutes before launching again.  The third feature of the booster is a motor sleeve, which is optional, but worth finding the body tubing.  The reason for this is that the body tube serves as a heat sleeve to insulate the motor mount from the motor's hot exhaust and ejection charge. It also serves as a platform to install the motor retainer ring.  This is also optional but makes replacing motors easily and eliminates the need for a retention hook or taping your motor.

The baffle is an optional addition that is included because it eliminates the need for recovering wadding.  It will trap the hot ejection gases but still pressurize the body tube.   It is sealed so nothing is to be done once it is glued into place.  It has both a recessed retaining loop and a small hole on the forward side to affix an eye hook if you choose.

The motor retaining rings are also optional but I have included them because I find them so useful.  They give the model a nice, clean look, and make installing/removing motors very easy. You will have to include the motor sleeve if you wish to use this feature.

A Launch Lug is provided if you decide to use your own body tube (recommended).  It is oversized, so you can size it to taste.  It is not used with the fully 3D-printed kit.

The nose cone is of an Ogive design.  I do not know what the ratio is.  I sized it for looks and performance.  It has a retaining rod recessed within the shoulder to attach your parachute/streamer and altimeter.  The top half is solid to help with your center of gravity (more on that later).

Put it all together and you have a rocket!

Things you will need:

There are a couple of things you will need to complete this project.  I recommend not using the body tube included.  It is thin and you will need to sand the nose cone shoulder so you have a loose fit.  I have included it in case you cannot find the body tubes.  Links to everything you need can be found below.  Now for the assembly requirements:

• Adhesive - You can get as serious with this as you want.  I do not recommend wood glue or modeling cement.  Neither will give you the bond you'll need.  If you are just starting out, I recommend 5 or 15-minute epoxy.  It's a little messy and more involved but gives you lots of working time. Just use gloves and do it in a well-ventilated area.  If you're a pro, then thick or medium CA glue will work.  I would also recommend some CA debonder, so when you glue your hand to the booster, you can remove it without a trip to the hospital.  
   
• Parachute/Streamer - Make one or buy them at a hobby store
   
• Shock cord - typically this is a thick,  elastic band to absorb the shock of the nose cone being shot out of the body tube.  You can also use Kevlar thread (~ 4 lengths of the body tube or about 500mm / ~18-24 in. ).  If you use the baffle, even good kite string should work but Kevlar is the best.  You can also use elastic.
   
• BT-50 Body Tube (24mm I.D) - 120mm length is ideal.  Less than that makes for a dangerous and unstable rocket!!
   
• BT-20 Body Tube (18mm I.D) - Heat Sleeve for motor and motor retainer
   
• Rocket Motor - Estes A8-3s are great first-flight motors.  I have flown this with C6-5s without issue but test your rocket first with something tame.
   
• Launch Pad/Launcher - devices for kicking your rocket to the sky… see: Google
   
• Paint, stickers, friends, lunch… and lots of water.

Assembly:

First off, if you have never put a model rocket kit together before, maybe you do that first.  Many of the concepts are the same.

  Preferred method

1. Assuming you have printed all the parts and given them a general sanding, grab the booster (aka fin can, the part with fins). 
   1. Cut your BT-20 body tube to 80mm or just over 3in.
   2. Slide the tube into the motor mount at the back of the booster to check for fit.
   3. Once you're happy, pull out the heat sleeve and apply a few drops of CA inside the motor mount.
   4. Insert the heat sleeve, twisting to help spread the CA but do it FAST because if the CA kicks and you're not seated, you have a mess.  It's called modeling.
   5. Find the threaded motor retainer (receiver) and dry fit it onto the heat sleeve until it is up against the booster, checking for fit
   6. When you're happy, slide the ring back a bit and put a drop of CA on the sleeve, and slide the ring back up until it makes contact with the booster.  DO NOT GLUE YOUR FINGERS TO THE BOOSTER!
   7. After a few minutes have passed and the CA has cured, you can cut the heat sleeve flush with the retaining ring.
   8. Test the fit of the retaining screw cap.  If you have a motor, you can test the fit but do not push the motor all the way in just yet.
2.  Cut your BT-50 body tube to ~120mm or 4-¾ in.  This length with the other parts should provide you with a stable rocket, that will fly straight up.
3. OPTIONAL - The included launch lug is provided to give the rocket additional stability off the launch rod.  It is not necessary but it is recommended.  If you use it:
   1. make a line down the BT-50 body tube.  
   2. Then on that line, make a mark about 5-10mm from the bottom of the tube.  This is where the bottom of the launch lug will be glued.  
   3. Put a couple of drops of CA glue on the launch lug and glue it in place, making sure to line up the launch lug on that line. and let the glue cure.
   4. If you want to use the optional baffle, there is a tie-off at the top for the shock cord.  You should really only use Kevlar, and get it tied off before insertion.  If you use elastic, glue that in the body tube 1.5 inches below the top of the body tube.
   5. Test fit the baffle into the body tube just above the booster but don't push it all the way up.  You will need to pull it back out.  The baffle will absorb all the ejection gasses yet still allow your body tube to pressurize and blow the nose cone off.  The farther up you push it the longer life it will have (based on your filament type), but don't push it up more than 2 inches from the bottom or you will change the Center of Gravity for the model
   6. When you are satisfied with the placement, put a little adhesive in the body tube near where the bottom of the baffle will rest.  With a stick, dowel, or screwdriver, push the baffle into place.  If you use CA and it grabs before the baffle is seated above the shoulder of the booster, you will have to get another BT-50 tube and print another baffle.  Ask me how I know. :P
4. Have a moment to reflect… You are building a rocket!  How cool is that?
5. Take your booster and dry-fit it to the body tube with the optional launch lug nearest the booster
6. Make a small mark with the edge of some masking tape, or a marker to indicate where the body tube line is.
7. Line up the launch lug on the booster with the line on the body tube. 
8. If you sight down the body tube, through the launch lug, you should see through the launch lug printed on the booster.  Just make sure both lugs are lined up and make “witness” marks on the tube and booster so you know when the two are aligned.
9. Make sure you are lined up on your witness marks.  Let the assembly cure for a couple of minutes.
10. With your booster in place in the body tube, and your lines for the launch lug are lined up with the fin launch lug, pull the body tube out, and place a small amount of adhesive at the bottom of the body tube.  Then press the fin can all the way giving a twisting motion when you are seated so as to spread the glue around.  Let your adhesive cure.  Take a break.  Drink a 7-Up.  Eat a Moon Pie.