Edit August 8th 2020 Added 29mm and 32mm versions with 6mm rod for Anixie

Edit October 23rd 2019 Added 50mm version for Mr_Phelps

Edit July 20th 2019 - Flight testing resulted in successful launches of 1 x F (CTI Pro24 3G), 1 x G (CTI Pro24 6G) and 1 x H (Aerotech) motors - overall the design worked well however there was one breakage due to weakness where the two screws hold each of the carbon fibre tubes. Carry some spares and you'll be fine

Edit July 7th 2019 - Version 2.4 is uploaded to fix minor config issues. Solidworks source is moved into the zip file.

Edit July 4th 2019 - Version 2.3 is uploaded. Each size of rail guide now has two files for A (top) and a B (bottom) containing two pieces each - you'll need to print one of each file (4 pieces total). If you printed this prior to July 4th then you have the "A" version - download and print a "B" file to get a complete rail guide

OVERVIEW

This is a new and stronger fly-away rail guide for medium power and high power model rocketry. It's used to launch sport rockets as an alternative to gluing on launch lugs or screwing rail buttons directly onto the rocket body.

The guide fits around the rocket with two sets of rail buttons that engage in the launch rail (rails are usually 1010 extruded aluminium). On launch, the guide provides stability as the rocket travels up the rail - as soon as the rocket clears the launch rail the flyaway guide springs open and detaches from the rocket body to reduce drag in-flight.

PLEASE READ THE INSTRUCTIONS CAREFULLY

• You're on your own to ensure this rail guide is OK for your rocket and launch rail as your mileage may vary
• I recommend you take a couple of spares to your launch site (its easy to swap the hardware) as we've shattered the hinges on the previous version under high impulse from launch
• please follow the high-power safety code for your country
• there are lots of places to find tips on printer settings for higher strength

There are four versions here:

• 2.75" / 70mm ID (for 6.35mm tube)
• 2.1" / 60mm ID (for 8.4mm carbon fibre tube)
• 1.7" / 44mm ID (for 8.4mm carbon fibre tube)
• 1.6" / 42mm ID (for 8.4mm carbon fibre tube)

Many thanks to Idaholion for contributing a version with integrated 3D printed rail buttons. I've not tested it as yet - if you do then please let us all know how it goes in the comments below!

All are slightly over-size to allow for a little shrinkage when printing - use some electrical tape, foam or similar on the inside to fit the guide securely to your rocket, making sure it's tight enough so that it won't slide down the rocket body when launching, but not so tight that it causes the rail buttons to bind. If the guide doesn't readily spring open, try adding another rubber band and testing it in your launch rail until you have the tension right for your setup.

I'd be happy to adjust the .stl model for other diameters if you'd put the exact dimensions of your rocket body and carbon fibre rod in the comments. All I ask is that afterwards please post a photo of your launch!

PARTS

• each size of rail guide has an A and a B file containing two pieces each for top and bottom. You'll need to print one of each file (4 pieces total) to assemble the guide properly
• 3 x 8.3mm OD carbon fibre tubes - 300mm or longer for larger size rockets and around 200mm for the smaller sizes. These tubes are available online from suppliers of drone parts.
• 4 x delrin or nylon rail buttons
• 4 x M4 x 15mm screws with M4 nuts to secure the rail buttons
• 8 x M3 x 12mm countersunk screws with M3 nuts to secure the outside carbon fibre rods
• 2 x M3 screws to physically secure the centre carbon fibre rod (optional / just-in-case)
• 4 x 80mm rubber bands (2 each for top and bottom for redundancy)

ASSEMBLY

• first add 4 x rail buttons secured by M4 x 15mm screws with M4 nuts
• slide the three carbon rods into the holes each end to create the rail guide assembly. If the hinge formed at top and bottom falls apart, turn either the top or bottom pieces upside down so that it all holds together
• as the rods slide in, pass the rubber bands around each rod as shown in the photo to create a spring
• secure the rods with 8 x M3 x 12mm countersunk screws and M3 nuts
• add a thin layer of electrical tape, foam or similar on the inside of the rail guide to provide grip on the rocket body and to protect your paintwork.
• its ESSENTIAL that the two halves open freely - if there is any sticking or binding disassemble and sand or file away any rough spots / add a lubricant such as dry graphite to ensure the assembly opens with minimal friction

A word on filament:

• we've been printing test versions in PLA and had successful launches so far
• settings were 1.75mm PLA, 0.2mm layers, 30% infill, support is required, no brim or raft.
• fully assembled weight was around 120 to 150 grams, however, the guide is discarded immediately after the rocket clears the rail
• through testing it seems a thicker wall is the key to higher strength prints

The finished product is quite strong .... BUT....

• our experience is that PLA is very poor for long term use as it is quite hygroscopic and becomes brittle after a few months
• for long term use, definitely use one of the newer high strength filaments that are stable in high humidity and provide greater shock resistance
• even using polycarbonate we've shattered the centre hinges launching G and H motors (the rockets themselves launched fine / just the rail guide ended in pieces). Recommend take some spares to your launch site