N254MR

When the WxWorx XM receiver finally showed up about two months ago, it presented a new problem. Originally, the two EFIS's required only a single point-to-point crossover cable between them to talk with each other. Although I had originally expected the WxWorx receiver to be an RS-232 serial device, the receiver version that AFS decided to support uses Ethernet connectivity instead of serial. It's a sound engineering decision, because of the data rates involved. However, because there are now (3) separate Ethernet devices, an Ethernet switch is required. Although any Ethernet hub or switch would work, AFS recommended the Linksys SD205 switch, because it's very small and one of very few designed for 12VDC power. In addition to mounting a yet another gizmo, the requirement of a switch raised issues of how and when to power its 0.5A maximum current draw.

I decided that if the panel is in the battery only, E-bus mode, where current loads must be minimized, and I'm not normally using either EFIS 2 or the XM receiver, I will not need or want the Ethernet switch. So it would seem that powering it via the main bus will suffice. However, I have planned to be able to selectively keep EFIS 2 up even when in E-bus mode, which may be the case in IFR, or marginal VFR conditions, for example. There is already an EFIS 2 alternate feed toggle switch, to power it from the E-bus, just for that reason. Further, if the second EFIS is up, I want the EFIS's to be able to talk to each other, so the switch also needs to be up. Consequently, the switch needs to be powered from the main bus or from EFIS 2's alternate E-bus feed. Bottom line, two wires will go to the switch's input power, with an inline diode in the main bus wire to prevent cross feed when the main bus is OFF.

The photo below shows the power harness for the Ethernet switch. At top right is the 5.5mm "M" style coaxial connector for the switch. The black wire is ground. The white/red wire will be spliced into the EFIS 2 backup power wire of the same color code, which is switched at the panel to selectively power EFIS 2 during E-bus operation, if needed. The red wire will be spliced into the red main bus feed to EFIS 2, and is diode protected to prevent back feeding of the main bus when powered is applied via the red/white wire in E-bus mode.  The Ethernet switch draws about .35A, with three ports active. Because EFIS 2 has a minimal complement of functions (no engine monitoring, no external gear, etc.) the additional .35A current requirement of the switch should fit within the limitations of EFIS 2's planned 3A fuse. Of course, that will be tested. All wire splices use RayChem solder sleeves, covered with heat shrink.

No rain (yet) today, so the shed, which will liberate the hangar, got some more work. Upper wall windows and front door header got framed, a few previously missing studs were added, and half the upper plates are done. When the upper plates on the 10 ft. high left side wall are done, it will be ready for rafters.

Wow! The latest edition of the task list shows only eleven build/install items remain before first engine start, and three of those are at least 70% completed! The biggest item yet to go? Completing the panel.

There are innumerable ways to get overwhelmed building a project like this. Of course, thinking ahead to what remains can be daunting. However, lately I've noticed an increasingly common feeling of exhaustion just looking at all that has been completed. For example, sitting in the cockpit, I'm glad all those hundreds of wires are in place already, but it's pretty heavy to recall all the painstaking work it took to get it done. Gazing on the firewall forward area, it's astounding to realize I've worked on mounting & wiring all the gizmos and plumbing there for over a year. There are dozens of such scenes throughout the airplane now... lots of hard work about which I'd just as soon not be reminded. Somehow it seems that only looking forward could be overwhelming, not looking back... but it is. Closing up and covering the stuff that's done does help.

Well, after much hemming & hawing, musing and modeling, Mike and I have committed to a design for the lower cowl framing. It will be similar to RogerHoffman's beautiful cowl but with a wider, trapezoid shaped bottom beam, connected to a rectangular, tig welded aluminum frame under the firewall. The latter will be approx. 16" wide by 4.5" high which, with the additional triangle areas in the corners, will provide about 115 sq. inches of outlet area, which is roughly three times the total of inlet area at the front of the nose bowl. The wider beam will allow the exhaust pipes to pass through this beam area, instead of through the doors. Mo' bettah! Best of all, when modeling these dimensions we found that the lines from nose bowl to firewall in the lower area will be very clean -- virtually no dips or bulges at the nose bowl-to-door junctions -- so it should look pretty smooth as well. The photo shows a wood mock up profile of the bottom rear cowl frame.

It's been a bit over a month since posting the last project task list, but a new one is now up. Several things checked off, more items nearing completion, and... a few things added.

It's the time of year we have to take advantage of good weather when we have it, and the last couple of days have been spent laying down plates and framing a new utility shed on a 12X17 concrete pad that was poured for this purpose a whole year ago. It won't be long before I'll have to move the airplane for tests of various kinds (fuel, engine, etc.) and there's so much equipment in the hangar I couldn't even move it out right now. The power and garden equipment now clogging the hangar will go into the shed so the hangar can function like... a hangar. The forecast is for rain the next 3-4 days, so I'll get back to the inside work on the airplane tomorrow.

This evening Mike and I got the top nose bowl secured in three dimensions... and I do mean secured! The first of two photos below shows the top metal cowl frame clecoed in place. It's eight inches wide in .032, which adds considerable lateral stability. The front edge of the frame is slightly rolled in the center, between the two center clecos, to match the bubble on the nose bowl.

In the second photo, holes for screws that will connect the nose bowl to the side frames have been carefully located to match the center line of the Camlocs™ that will hold down the top doors, then drilled and clecoed. Holding the nose bowl at the front end, I'm able to firmly wag the entire fuselage side to side with no perceptible movement in the the nose bowl framing. It's über solid. Yea! (Mike was unfamiliar with the proper operation of this venerable camera, which may explain how a number of odd spacial distortions got into this pic, including the curved hangar door frames, and right above my belt. :-) However, the nice clean line across top of the nose bowl as it transitions to the top frame and back to the firewall is accurate. 

It turned out the there wasn't enough room behind the EFIS's for the full depth of the original plastic defroster vent inlet tubes. The EFIS itself would fit, but not the EFIS with D-sub harness connectors. The interference affected only one D-sub on each EFIS, but... it was necessary to cut the original vent inlet off at an angle and create a smaller, right angle side inlet. Because there will be significant heat on this assembly, and the ABS plastic is problematic to bond, I didn't want to rely on silicon or epoxy adhesives for structural strength.

The photo below shows the remodeled defroster vent from a side angle. The black plastic down tube (up here) was cut at an angle, to shorten it at the aft, panel side, while still leaving enough structure to insert a 1" dia. aluminum tube to function as a right angle side inlet. An .025 circle with tabs extending outward was formed to cover the bottom of the now slanted original plastic inlet tube. Two tabs will be riveted to the sides of the original plastic tube, and two wrap around the underside (top here) of the new side inlet tube, and will be riveted there. The second photo shows a profile view. The assembly will be sealed with high-temp RTV or firewall sealant.

Completed defrost vent with side inlet:

Tonight, work on the top cowl metal frame has begun in earnest. In the picture below, the front edge of the frame has already been lightly rolled to match the "bubble" in the top of the nose bowl. The front edge of the frame has been shaped (hand filed, mostly) to match the edge of the cowl. (Because the rear edge circle of the nose bowl is not vertical, but leans back just a bit to echo the line of the firewall, the forward edge of the top metal frame has a concave line.) The four corners of the frame have been carefully marked on the frame, nose bowl, and firewall. What's really nice is that after reshaping the top nose bowl there is now a beautiful straight line from nose bowl to firewall -- no more "dip" at the rear edge of the nose bowl.