Final Flight Design Comes Alive!

Today the team is presenting their flight design of the seatback and headrests to NASA engineers Christie Sauers, Jeff Fox, Dustin Gohmert, and Rick Ybarra.  These images were created in ProE (also known as Creo). This provides visualization of the design, allows the team to verify that the parts will fit together correctly, and provide a computerized model for performing stress analysis.

Bottom view of seatback.

Top view of seatback.

The curved seatback and curved headrest will be made of Aluminum 2024 and the remaining parts (rails, ribs, shoulder bolsters, brackets, etc.) will be made of Aluminum 7075.

Second Design Concept for Seatback

Seatback design #2, also rejected, is show below.  The curved surface of the seatback would be achieved through shape rolling aluminum plate.  Bracing plates made of sheet metal would be used for stiffness, and attached to frame using L brackets (as shown) and rivets/bolts.  Slots would be milled into the frame to aid in holding the bracing plates in place. The frame would be made of aluminum square tubing.  The curved seatback would rest on top of the frame.

Conceptual sketch of seatback design #2.

This design was rejected because the team became concerned about excessive vibration between parts that are not completely secured and potential problems with tolerances stacking up. 

First Design Concept: Manufacture by Casting

The design team initial saw casting as a possible means of economically manufacturing the seatbacks. The current Lockheed Martin prototype of the main body of the seatback would be used to create an investment casting mold, and the seatback would then be cast in Aluminum. The brackets required to attach the seatback to the pallet would be separately machined and bolted on to the cast part. After casting, the final part would be machined to the exact dimensions needed.

Conceptual sketch of Design #1.

However, the size of the seatback caused the cost of investment casting to be too high and the design team rejected this idea.

First PDR!

The UT Tyler NASA team had a preliminary design review yesterday.  Present at the meeting were the design team (Valerie Morgan, John Bogdanich, Luke Onderko, Travis Rhea, and Jared Stroud), their faculty advisor (Dr. Sara McCaslin), machine shop manager (Jim Mills), and NASA engineers Jeff Fox and Christie Sauers.  Joining us by teleconference from JSC was NASA engineer Rick Ybarra.

The purpose of the PDR was to present a preliminary conceptual design to NASA for feedback, direction, comments, ideas, etc.  Once the concept for the final design is approved, the team will move on to prototyping, analysis, and testing.

The next three posts will discuss the different design concepts the team explored.

Head Rest Issues

One of the major discussions at the PDR (Preliminary Design Review) involved redesign of the headrest.  Below are some of the images we took when visiting NASA Johnson, and they are re-posted here for the convenience of the team as we start brainstorming.

We need to increase the stiffness of the headrest without adding additional weight.

Headrest - note guide rails.

Note the four bolts, where the headrest assembly attaches to what we are calling and end plate.

Backview of headrest as attached to seatback.  Note the pins for removal, and the attachment brackets.

Again, a back view showing how the headrest is attached to the seatback.

Head rest attached to seatback.  Note the rivets attaching the bow-tie headrest base riveted to the adjustment rails.

Note the shape of the adjustment rails.

Pro-E model of the Lockheed Martin design.

Prepping for NASA PDR

The student team has been prepping the their preliminary design review (PDR, in NASA-speak) scheduled for November 1 when Jeff Fox and Christie Sauers from NASA Johnson come for a quick visit to Tyler, Texas.

You can view their slides below through Slideshare.

Seatback Materials

The current flight model of the Orion seatback is manufactured of Aluminum 7050-T7451, with a tensile strength of 75 ksi and a yield strength of 64 ksi. 

The 7000 series of aluminum alloys is commonly used in aerospace and are referred to as wrought aluminum alloys. This series of alloys is known for their high strength and additional strengthening available through heat treatment (in this case, preciptation hardening).

According to Alcoa Aluminum, the 7050 alloys are usually preferred because they combine strength, resistance to stress corrosion cracking, and its toughness. Al 7050 allows are available in both plate and sheet, making it a good choice for applications requiring a thickness greater than 2 inches but less than 6 inches, like frames and bulkheads. Remember that the flight model of the seatback is machined from a solid block of aluminum, which means that it will require a thick block of stock.  Machining from a large block is expensive and time consuming -- just look at the image below and imagine using a CNC mill to generate the ribbing and curved geometries!

Full-scale model of Lockheed Martin Seatback design used for testing.

Note that the material is listed as Al 7050-T7451.  The T7451 is a temper designation which describes the type of heat treatment the material has undergone.  The T means heat treated (as opposed to strain hardened, H, or fully annealed, O) and the 7 means that it was artificially aged and then solution heat treated.  If you are curious about what all these terms mean, try vising aluMatter's page of heat treatment of aluminum alloys.

Detailed specifications for this type of aluminum are available from Alcoa, the original developer of Al 7050.