How it was...

The figure above is taken directly from the instructions:

• item B is the main airframe
• item C is a coupler halfway inserted into item B
• item A is a very short coupler about 1/2" long that works as a retaining ring for D
• item E is the shock cord

Item D is the most important: in this case it consists of 3 2mm birch plywood pieces laminated together using epoxy; a srew-eye is then inserted in its center point and all the sub-assembly is finally slid into item B against A (in fact item D OD equals item B ID). The coupler C is then epoxied in place against D and another length of airframe is then joined to B.

... how it should be.

• it is not necessary to place D where two airframes are going to be joined: simply cut a length of coupler to make a retaining ring A [usually more than 1/2 " is useless], slide it into the airframe as deep as needed (determine the parachute volume and/or coupler/nosecone shoulder clearance) and epoxy it in place;
• make a bulkplate of Your choice: thickness may vary depending on many factors (final mass of the rocket, airframes OD, deployment stresses...) but it should have some holes if You're asking the engine to eject the parachute;
• replace the screw-eye with a U-bolt (again size my vary) and bolt it onto the bulkhead tightly as it won't be accessible as the sub-assembly is permanently glued;
• epoxy the bulkhead sub-assembly in place making sure that it is tightly against the retaining ring;
• consider another length of coupler [around 1" long] and epoxy it against the previously glued bulkhead sub-assembly.

This design offers a great way of taking the loads of a deployment without putting the airframe under stress; it is also a better deal than bolting the attachment harness directly to the most forward centering ring; it finally can be used with almost every rocket design (one airframe, payload section/s, dual deployment...) and can be easily retrofitted to already finished models.