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Les Kramer's L-3 Certification Project
 
ALTIMETER BAY ASSEMBLY
The following parts make up the Altimeter Bay assembly:
• (1) 16" x 7.5” diameter section of Flexible Phenolic Tube Coupler
• (1) 7.5 x 15" section of Concrete Form Tube PIC
• (1) 4" x 7.5" diameter section of Flexible Phenolic Body Tube
• (2) 1/2" 9-Ply Outside Bulkheads PIC
• (2) 1/2" 9-Ply Inside Bulkheads PIC
• (3) 18" x 5/16" Threaded Rods PIC
• (6) 5/16" x 1 1/2" fender washers
• (3) 5/16" wing nuts
• (6) 5/16" lock washers
• (3) 5/16" hex lock nuts
• (3) 5/16" T-Nuts
• (3) 3/8" U-Bolts
• (4) Sections of barrier strips PIC
• (4) Schurter On/Off Switches
• (2) 1/2” PVC Pipe Caps PIC
• (2) 3/4” PVC Pipe Caps PIC
All parts are assembled with West Systems epoxy (105 resin / 205 hardener / 404 filler) where required. PIC
Note: Design and construction of the electronics associated with the altimeter bay can be found in the "Recovery Systems - Electronics" page.
Inside Tube Construction
The altimeter bay is a 7.5" x 16" flexible phenolic tube coupler. Concerned about possible failure of this item, it was decided to strengthen the coupler with an internal tube made from concrete form tubing. I found the concrete form tube at a local Lowes hardware store. The tube comes in 48" lengths and 8" (nominal) diameters. I looked around until I found a tube that was close to 7.5" in diameter. This tube must fit inside the forward tube coupler so I knew that I would have to modify the diameter.
I first had to cut a 15" piece of the form tube (coupler is 16" and both ends have a 1/2" bulkhead). Next, I removed a 1/2" section of the tube by cutting it lengthwise. This allowed me to "squeeze" the tube to form the inside diameter of the tube coupler. The final product was a very thick walled coupler. The inside tube was joined to the tube coupler using epoxy.
Bulkhead Assembly
The bulkheads on both ends of the altimeter bay were constructed from (1) 1/2", 9-ply outside and (1) 1/2" 9-ply inside bulkheads. The two pieces were joined together using epoxy.
I marked the location of 3 - 5/16" holes on the face of each bulkhead and drilled each hole. I used the fin guide from earlier steps to ensure a proper location. I also located the holes for the U-bolts and drilled these as well. The aft bulkhead gets one u-bolt and the forward bulkhead gets two u-bolts. The U-bolts were attached to each bulkhead and the excess threaded stock cut off. PIC 1, PIC 2, PIC 3
Threaded Rod
The threaded rod keeps the two bulkheads in place and creates the internal structure to support the weight of the rocket during recovery. It also acts as a "holder" for the electronics.
I cut 3 - 18" pieces of 5/16" threaded rod and tested each in the altimeter bay. Two 5/16" hex lock nuts, two 5/16" T-nuts and two 5/16" x 1 1/2" Fender Washers secure each rod to the forward bulkhead. These rods will not be removed from the forward bulkhead. The aft bulkhead is secured by using a 5/16" x 1 1/2" Fender Washers, 5/16" lock washers & 5/16" Wing Nuts. PIC 1, PIC 2, PIC 3
Ejection Charge Holders
The face of both bulkheads from the altimeter bay were used to mount the hardware to secure the ejection charges. Each bulkhead has two charges and two sections of barrier strips for connecting the wiring from the altimeters. The "holders" are simply PVC caps used for water pipe. The forward bulkhead gets 3/4" caps and the aft bulkhead gets 1/2" caps. This is based on the estimated size of the ejection charges needed. They are screwed to the bulkheads. A small hole is drilled in the side of each cap towards the bottom for the e-match wire to go through. These caps will hold the ejection charges which are made from 1/2" & 3/4" PVC water pipe with wooden dowel plugs in one end. The barrier strips were attached using #4 sheet metal screws. Holes are then drilled next to each strip all the way thru the bulheads for the wiring to pass through. PIC1, PIC2, PIC3
Center Section
The center of the altimeter bay has a 4" wide piece of body tube for installation of altimeter swtiches and to drill static ports. I wanted this section exactly in the center of the altimeter bay, so I measured from each end and made a mark. The body tube section was then slide into postion and temporarily held in place with masking tape. Next I determined where to monut the swtiches and drilled 1/2" holes. The body tube section was then removed and the holes slightly enlarged so that the switches would mount flush with the outside of the body tube. I then mixed a small amount of epoxy and let it soak into the marked location on the altimeter bay. Next, I simply "slid" the remaining larger body tube section into place being careful to line up the switch holes and wiped up the excess epoxy.
Static Pressure Ports for Barometric Altimeters
The altimeter bay needs to be vented to the outside to equalize pressure so that the apogee and main deployment events are as accurate as possible. I have always used the calculation provided by MissileWorks in the RRC2 documentation. Using these calculations, the (4) static pressure ports will be 1/4" holes spaced at 90 degree intervals around the switch section. I used the fin layout template to mark the locations on the switch section and drilled (4) 1/4" holes. All the edges both inside and outside of the altimeter bay were sanded smooth. PIC
Completing the Altimeter Bay
The final step in this assembly was to test fit the pieces. The alignment of the threaded rod was checked as well as the fit of the bulkheads into the tube coupler. I had to slightly enlarge the holes in the aft bulkhead to allow the threaded rods to slide in and out easily.
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