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SCP002 (Staging Cone).PDF

SCP001 (Staging Cone Base).PDF 

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Purpose

The Staging Cone serves as an attachment interface between the booster and the sustainer stages of Phoenix. After burn of out the booster motor, drag forces should be larger on the booster due to its larger freestream area causing the sustainer should passively separate from its resting position on the Staging Cone. Recovery soft goods are stored in the Staging Cone and are released when the piston separates the Staging Cone from the booster airframe. 

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The Staging Cone is designed to be able to attach by way of shear pins to the booster airframe and to the sustainer by a geometrical fit. The upper cone (henceforth the cone section) of the Staging Cone is to be the exact geometry of the sustainer nozzle (expansion section) so that it sits properly with no tilt and such that the entire wall area inside the nozzle is in contact with the cone. This calls for fine, and currently unspecified, tolerances. If manufactured correctly, the top lip of the base section of the cone Staging Cone should also be in contact with the bottom of the sustainer nozzle, dividing the weight of the sustainer between the base and cone sections of the Staging Cone. The number of bolts being used to attach the cone and base sections was derived assuming worst case tolerances and all of the sustainer's weight is on the cone section.  In the alternate extreme case where weight is only on the base lip, there is no force on the bolts.  

Hand Calculation Analysis:

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Output for 8 bolts:

Given: 

In progress

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Status: Completed

Actual machining plan used:

• Used slightly over-size round stock for both parts
• Lathe speeds were 800 sfm, max 1500 rpm
• Holes drilled at 400 rpm
• See drawing for hole sizes
• Base:
  • Faced both ends and turned the OD to create reference surfaces
  • Chucked stock from OD
  • Drilled out thru-hole on the lathe with Todd's largest drill bit
  • Ran a program to turn the inside profile on the lathe
  • Turned MPT interfacing-end to final dimension
  • Chucked part in radial indexer on mill
  • Drilled all thru-holes, tapped the holes that needed threads
  • Spot faced the forward-facing holes to allow for bolts to sit flush
  • Chucked part from the ID with the forward facing direction in the positive z direction on the lathe
  • Ran a program to turn the outer profile
• Cone:
  • Faced both ends and turned the OD to create reference surfaces
  • Chucked stock from OD
  • Turned Base-interfacing side to final dimension
  • Drilled several holes in the inner diameter of various sizes to get as much material out by drilling as possible
  • Turned half of the inner profile of the inside with a large boring bar that would not vibrate
  • Chucked part vertically in the mill
  • Used 3/4" end mill to drill all the way through the inner profile
  • Chucked part back in the lathe
  • Used a smaller boring bar to turn the rest of the inner profile
  • Chucked part in the radial indexer
  • Drilled and tapped all thru-holes
  • Chucked part from the ID with the forward facing direction in the positive z direction on the lathe
  • Ran a program to turn the outer profile
  • Drilled and tapped thru-hole on the lathe

Problems

• Inner profile hard
  • Inner profile was really too deep to be turned on the lathe
  • Not sure if that would work better using CAM and a large end mill on the milling machine
  • Could also just make the inner profile easier to machine
• Radial indexing
  • Radial indexer in the Deep not precise, after one or two full rotations the holes no longer lined up as precisely
  • Perhaps do all holes in the same rotation, or do all operations on each hole before moving to the next hole
• Fit check
  • Burrs from drilling/tapping made fit checking difficult
  • Could drill/tap holes immediately after creating reference surfaces, then the machining process would take off the burrs

Changes from Demo II

The main design change from Demo II is that the Staging Cone (Phoenix) will be made in two separate pieces. This was done for the purpose of making machining faster and more practical. It may also have the unintended (but welcome) consequence of making the part cheaper. This is due to the fact that there is less material that has to be cut away since the smaller diameter cone is made from a separate piece of stock from the larger diameter base (booster airframe retention). 

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