The Payload Bulkhead interfaces between the Avionics Bay and the Nose Cone, and more specifically between the piston, the Avionics tower, and the Payload.
Rev. 1: Pathfinder
The Pathfinder revision was a basic flat plate with a centering ring welded on.
Rev 1.1: Pathfinder round 2
Thicker bulkhead to accommodate loads of main chute opening (based on analysis done below):
Sim results were good for 2000lbs and showed a displacement of ~.2mm.
Rev. 2: Hermes
All load from main and drogue parachute opening will go through the Payload bulkhead (whereas we expect all reaction load from piston separation to go through the Avionics bulkhead). While we are currently working to qualify an upper bound on deployment forces, we ran some simulations at 3000lbs (an over-estimate) in order to determine an approximate thickness. In these simulations, we applied the load evenly between the four bolt holes and fixed the lower surface of the upper lip as a fixed geometry. Part material was Aluminum 6061. All runs were performed under the finest basic mesh but we did not refine the mesh for bolt holes.
**A Note For Looking at Sim Results:** when illustrating part displacement, the magnitude you see in the screen shots is not the actual magnitude. It is greatly exaggerated. You have to look at the scale on the displacement page in order to understand the displacement results.
For our first run, we tried a Bulkhead with a upper and lower step thickness of 0.5" each. The results showed that this bulkhead would not yield under 3000lbs:
Then, we reduced the thickness to be 0.25" on each step and found that the bulkhead would yield, particularly around the bolt holes and at the contact point with the Avionics Bay coupler, but that overall displacement would be small (~0.2mm):
Then, we increased the upper thickness to be 0.375" (this is logistically easier to increase since it does not impose an increase on AV Bay coupler length), kept the lower thickness to 0.25", but added a piston seating cut of 0.125" depth. As one can imagine, results were generally speaking similar, with actually a slightly lower displacement:
We determined that this is an acceptable starting point for the bulkhead, even though it exceeds yield for a variety of reasons:
- 3000lbs is an over estimate. As of 4/23/2018, our highest estimate for main deployment force is 1187 pounds. This was using the old vehicle weight, which has surely decreased since we will now be flying on a smaller motor, so the main deployment force will have gone down.
- We will be using washers, which will distribute the load.
- A lot of the stress is concentrated at the bolt holes, which historically underperform in Solidworks simulations.
- Overall displacement is small and we expect to fly the part only once.