Phoenix Sustainer FRR

Design

The forward retention ring serves 2 main purposes:

• It retains the forward closure from sliding past the end of the motor casing.

• It couples the motor casing to the airframe.

In order to accomplish this, certain design considerations were made.

The forward closure presses upward on the FRR. The force it applies is equal to the chamber pressure times the ID of the motor casing. The FRR must be able to withstand the load of the peak pressure (given by the Propulsion Sub-team) with a safety factor of 2.

Working with Propulsion, we decided that the FRR will have 1 row of 12 ¼-20 holes that interface with the motor casing. This was based on calculations that Prop did for the motor casing.

Using FEA, I decided that this cross section worked under the following conditions:

• 4,330 lb from the forward closure

• 3 ft-lb preload on the bolts (this puts 960 lb tension in the bolt)

• FRR made of 6061 T6 Aluminum

In this design, the wall thickness is only large where the bolt tension is acting, saving quite a lot of mass. This also gives the bolts lots of thread length to engage with. The safety factor is 2.27. 

For the forward part of the FRR, which is designed to interface with the airframe, the design was much simpler. This is because the weight of the airframe rests on the fincan (which rests on the nozzle). The main job of the forward-most screws are to restrict rotation about the central axis of the rocket. There are no major forces that apply this kind of torque on the airframe. These screws also hold the airframe on during the descent back to the ground, but there are no major forces associated with this, either. 4 8-32 screws were used for this.

Manufacturing

TBD - waiting to return to campus

The plan is to use one of the semi-CNC lathes in The Deep as well as a radial indexer.

Testing

Static Fire?