Forward fuselage skins and ribs deburring, fuel return path and bottom TAS antenna location

I finished deburring the remaining parts for the forward fuselage, and dimpled the ones that were already primed (the forward fuselage ribs):

Most forward fuselage ribs deburred parts

Dimpled forward fuselage ribs
I also did some work in planning for the fuel system. Since I plan to use the EFII System32, I followed the steps from others who have run hoses for it, and may end up getting the hose kit from Aircraft Specialty, so I followed their instructions, starting with enlarging the systems brackets holes - the original one is the right size for a 1/2" snap bushing (plus another which is meant for brake lines and thus much smaller), but I'm planning to use 3/8" fuel hoses with grommets, so I enlarged it to 5/8" for the grommet). I did this by transferring the holes to a backing piece, enlarging them to the right direction on the backing piece (away from the screw hole and away from the top bracket edge), then transferring back with a unibit:

Transferred existing holes to a backing piece

Enlarged holes in backing piece, to transfer back to brackets

Enlarged systems bracket holes

Systems bracket with grommets
Of course I did screw up and had to re-make two of those top brackets :)

I also enlarged the forward fuselage rib holes to 9/16" for the fuel return lines:

Enlarged center hole for fuel return line (before deburring)
I added a hole for those lines through the side skins and center section side plates:

Hole position on the side skin for fuel return line 
Enlarged fuel return side skin/side plate hole
Per the post on antenna positions, I made an antenna doubler for each tunnel section:

Antenna on aft tunnel doubler

Forward tunnel doubler for TAS antenna
I'm not going to install the forward doubler just yet - the aft tunnel is harder to rivet in (with the heat tee over the spot), so I'll just add that one for now).

Next up, a bit more deburring and then primer and riveting to complete this section!

Time lapse:


Total forward fuselage ribs and bottom skins rivets: 0
Total forward fuselage ribs and bottom skins time: 61.3h

More on antenna positions

For antenna positioning, I tried to put the forward tunnel parts around the place they'd go, and reailze it gets really crammed in there (plus, forward of the fuel valve goes the EFII pumps, filter, etc.):

The forward tunnel gets pretty crowded
Photos of the fully-assembled tunnel from others also seem to confirm that.

so I'm now reconsidering the TAS antenna position - putting it in the aft tunnel may be well worth the trouble of running the cables to it, and on the upside that'd bring it close to being aligned with the top antenna - so I checked whether there's clearance for the cables below the pushrod, and there seems to be enough:

Potential position for the TAS antenna in the aft tunnel

Just to give me some margin for decision, I'm going to add doublers to both places, and decide later.

Furthermore, I looked at the G5 installation manual and realized that it has an internal antenna - unclear if that'll be enough, but I'll be holding off on adding a third GPS antenna for the time being, and if I do I may add it to the top of the dashboard, just for some installation diversity.

Updated antenna positions

I had previously planned the antenna positions both disconsidering convenience of mounting the antennas, and assuming I'd have the MotoPOD on the bottom. Given this, I took some time to re-plan their placement taking both into consideration (click on any of these for a larger version - original file here). In these drawings, the solid circles are the ideal ground planes, and other circles are additional restrictions.

Top view - ELT, Stormscope, COM, GPS and TAS antennas
I no longer need separate UAT and transponder antennas. Given that Garmin requires a minimum of 3' of cable from the transponder to the antenna, I moved that antenna to the rear part of the tailcone:

Side view with all antennas

Bottom view - transponder, COM, NAV and TAS antennas

I added a third GPS antenna - one for the GTN, one GPS+XM for the G3X (PFD only), and one for the G5.

TAS antenna details - ideal and minimum ground plane plus distance to other antennas
I moved the bottom TAS antenna to inside the forward tunnel, since the aft part of the tunnel has no easy way to run cables to it, and very little clearance near the skin, with the elevator pushrod going through it. The distance between the top and bottom antennas is about 21", which should add a bearing error of about 0.2˚ for a target at 1 mile (perfectly acceptable, I doubt the TAS has that level of precision anyway):

Distance between the two TAS antennas - this introduces ~0.2˚ bearing error for a 9 or 3 o'clock target at 1sm

With the transponder antenna moved aft, I'll try using the original XPDR antenna hole for my bottom COM antenna. It's unclear what kind of performance I can get from the ground plane at that location, but since the ground plane area is only about 20% smaller than the top antenna's, I'll just plot the VSWR after the tailcone is attached and see (and if that doesn't work, I'll add another hole in the baggage area and plug this one).

COM ground plane area is ~1371sqin (ideal is ~1662sqin, ~20% more)
I was also briefly worried that the tailcone antennas might be too close to the ground in a maximum takeoff rotation position, but a quick measurement showed that's not the case (i.e. the tail would hit the ground first):

Tailcone antenna ground clearance at maximum rotation attitude

Given that none of these require any structural changes for now (only the top TAS antenna will give me trouble), I'm deferring any installation steps to later when I actually have the avionics - who knows what else may change until then.

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