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Reposted from apawood.org:

An engineer recently asked me about the Exterior and Exposure 1 classifications of plywood. Specifically, he wanted to know if APA Rated Sheathing Exposure 1 plywood panels could be used outdoors.

Wood structural panels may be produced in three bond classifications: Exterior, Exposure 1 and Interior. The bond classification relates to adhesive bond, and thus to the structural integrity of the panel. By far, the predominant bond classifications are Exposure 1 and Exterior.

Exterior Plywood Panels are bonded with fully waterproof glue and are suitable for repeated wetting and redrying or long-term exposure to weather or other conditions of similar severity.

Exposure 1 Plywood Panels are suitable for uses not permanently exposed to weather. Panels classified as Exposure 1 are intended to resist the effects of moisture due to construction delays, or other conditions of similar severity. These panels are manufactured with the same fully waterproof glues as used in Exterior plywood; however, because of other compositional factors that may affect bond performance, only Exterior panels should be used for long-term exposure to weather. Exposure 1 panels may, however, be used where exposure to the outdoors is on the underside only, such as at roof overhangs.

APA Rated Sheathing Exposure 1 plywood, commonly called CDX, is oftentimes confused with an Exterior plywood panel and misused in applications. It is important to understand the difference between these classifications in order to select the best panel for your project.

On the APA trademarks shown here, the bond classifications are described as Exposure 1 (left) and Exterior (right).

I spoke with a decking expert named Chris at our local Home Depot today over lunch.

Chris had a couple of statements:

Joist hangers are stronger than nailing from the other side of the board

The joist hangers are more for anchoring the joist in a fixed position as explained here.

Gluing plywood between two sistered beams makes it a lot stronger

I researched this one a little because it made some sense to me and wouldn’t be hard to do but this article really puts it in perspective (the main point is that only some of the plies are oriented in the correct direction making a lot of it potentially wasted).

Nails have more sheer force than screws

Follow this link for an interesting debate. Apparently, as long as the design load isn’t exceeded, the withdrawl force needed to pull a screw out is greater. However, screws are more brittle so if they are “overdriven” or subjected to a lot of repeated stress (wood warping, foot traffic) they will break whereas nails will bend and bend.

Finalized the framing design last night. I already purchased (7) 2x8x8 joists and am anxious to get cutting!

Also wrapped up the port interior framing and ready to start the front interior framing.

Broke down and obtained Project 2010 through MSDN. Much more solid than OpenProj although I see where OpenProj got their inspiration.

So I am all set up now and can see what I need to do and when I need to order what. No progress this week as I have had sick child (my son) today and I had an allergy attack yesterday.

Started the framing for the port interior wall yesterday.

Switching from GanttProject to OpenProj due to some bugs I can’t work around.

The original base frame was made of 2×4’s sandwiched between 3/4″ plywood. I hired a structural engineer to estimate the uniform load capacity for the 7′ length of a sistered 2×4 beam and it was only rated for about 500lbs. Since then I have gone back to the drawing board and determined the relative strengths based on Moment of Inertia:

2×4: 5.36
4×4: 12.505
2×6: 20.8 (almost 4x as strong as 2×4)
2×8: 52.73 (almost 10x as strong as 2×4)
2×10: ~115 (more than 20x as strong as 2×4)

After seeing Aliens for the hundredth time this morning (thanks in part to my son) it dawned on me that they don’t have a conventional power quadrant (thrust levers).

I drew on my professional experience flying jet aircraft – manual manipulation of the engine output is dwindling. There are basically 5 modes (detents) on a modern day thrust lever (FADEC):

• Takeoff / Go-Around (TO/GA)
• Flex/Max Continuous Thrust (FLX/MCT)
• Climb (CL)
• Forward Idle
• Max Reverse

Is it possible to map this control to the flight stick? Because of the VTOL nature of the Dropship don’t we need some kind of fine control? Like in hover – to climb or descend?

I can envision a “auto-hover” which will reduce the pilot workload but what about landing on a grid reference? Using pitch trim in VTOL mode? Not sure what else it would do.

Got it 50% mounted this evening.  One of the bolts has no access and the other was off by an eighth of an inch!

The project is getting a little complicated – I am always waiting on a bolt or nut and I stare sometimes for what feels like half an hour before I figure out what I can actually do in a given session. I remember my project managers used Microsoft Project (MSPROJ) years ago and the Gantt chart it produced seemed like it would do the trick. I found a free version online that can import/export MSPROJ files called GanttProject. Here is an example of the current items and their dependencies.

While we are on the subject I started looking around for acrylic sheets. My first inclination was to get a large sheet from Home Depot and then cut it. Somehow I landed on Professional Plastics where they will cut to size and deliver for the same price or less. I am currently working up an order for the 1/8″ thick inner window panes for the six (6) monitors.

After cleaning all the saw dust up I felt confident to do some metal works (grinding). My son thought I looked pretty funny!