Ch 10 - Canard - Part 13

Top skin (12.5 hrs)

Now that the VOR/LOC and GS antennas have been permanently mounted on top of the canard, I can finally apply the top skin consisting of 1 UNI, 1 BID, and 2 UNI.

As usual the manual is overly optimistic about how long this process should take. It specifies 2 hrs for 2 people. So, I took it to mean 4 hours for one person. From prior experience I learned to at least double that to 8 hours, a long day, but doable. 

I was very disappointed when I was nowhere near finished at the eight hour mark. Twelve hours after I started, I finally rested squeegee and paintbrush on the table, and went to bed with enough aches to keep me awake most of the night. Getting old sucks!

Let’s see how it went down…

In Part 8 I showed how I was able to get a very clean 1/2” (1.3 cm) of bare fiberglass at the trailing edge. This is a structural requirement and it is very important to the overall strength of the canard. I marked an half inch line along the trailing edge to make sure I would not encroach on this limit.

The trailing edge had been peel-plied, but it got sanded anyway as a precaution.

I then masked off every bare fiberglass surface that I did not want to contaminate with the micro-slurry I’d be using next, and started patching up dents and holes in the fiberglass with dry-micro.

Masking to keep micro balloons at bay

The process of removing the trailing edge peel-ply described in Part 8 left a step in the foam that needed to be smoothed out. I made a popsicle tool for this job which worked okay, though not perfectly. Nevertheless it proved sufficiently useful to be pressed it into service.

A little dry-micro fillet is needed near the trailing edge (hence the tape).

I had high hopes for this popsicle tool

It was designed to extrude the perfect fillet

Popsicle tool in action

Before and after popsicle tool use

Then it was slurry time!

Nothing new here, if not for the amount of surface to be covered.

It’s amazing how much surface there is on a canard. I bet the wings are going to be a real tough job!

Anyhow… I removed the tape, and revealed a perfectly preserved trailing edge and spar-cap just begging for some pure-epoxy, but first a little more masking would be in order to keep epoxy off the metal pipe, and from running back under the bottom of the trailing edge.

Trailing edge and spar-cap peel-ply removed

More trailing edge masking

After obliging the bare fiberglass requests for epoxy, I started laying up UNI. Glassing solo, the UNI laid up nowhere near the way I had intended, so I had to straighten up every individual fiber by tugging at it from other ends of the canard, and did my very best to keep the cross-fibers in line as well. This necessary attention to details ate up a lot of time.

First ply of UNI

Fibers straightened and edges trimmed

Seen from the other side

Next it was BID time! Laying BID solo made me wish I was back doing UNI again. This stuff really has a mind of his own, but I eventually wrestled it straight again. However, I had to do this four times due to the small pieces that get laid at a 45º bias.

BID took forever to straighten back up

This stuff gets skewed just looking at it!

Piece #2 of 4

The front edge gets wrapped around the leading edge of the canard

Working the far end pieces of BID

To avoid a surface bump, these BID pieces are butted not overlapped.

Even then, I did get a tiny bump that I'll have to take care of during finishing.

I was glad to get back to UNI again, and worked on layup #3 and #4 next.

Approaching hour 9 I'm back to UNI (ply #3 of 4)

Hour 12, (ply #4 of 4) declaring a truce.

Mostly finished canard

After the last ply of UNI I peel-plied the ends since some tips will be added at a later date. I then copied my buddy Wade, and applied some dry micro to smooth the small kink on the trailing edge my popsicle trick hadn’t completely eradicated.

Dry micro fillet over the still wet fiberglass

Peel-ply will help when the tips get mounted.

I was pleased at how the cables exit from the canard turned out.

This spot is not aerodynamically active since it is buried into the nose

All fiberglass cloths were wrapped around the bottom of the leading edge of the canard for a distance of about 2” (5.1 cm). This effort was helped by the clear directions on the plans to overhang the canard off the bench, but hindered by having to be on one’s knees for a long time, working a paintbrush loaded with warm epoxy uphill, while the stuff runs over one’s gloves and onto the arms.

Time for curing at last

The last hour was certainly the hardest, and when it was over I left the shop without even cleaning anything up (a first on this build).

As I had to go to work early the next morning, it wasn’t until a week later that I was able to rip the canard off the jig, and trying it on the fuselage for a photo op. 

Canard pulled off the  jig

Trying the canard on for the first time

It's amazing just how big the canard really is

Ch 10 - Canard - Part 12

Antennas (9.8 hrs)

To make a long story short, I decided not to mess with success, and go with a proven setup. 

As many before me have done, I will bury my Localizer/VOR and Glide Slope antennas under the top skin of the canard. Being that fiberglass is transparent to radio waves (carbon fiber is not, mind you) this is a perfectly acceptable practice, and it is indeed a smart thing to do. I will also bury two COM antennas in the winglets, and perhaps a spare VOR antenna into one of the wings.

All antennas on the plane will be made out of a roll of very thin copper strip I purchased from RST engineering, and have to be assembled. Jim Weir ships a CD with very thorough instructions, but it can also be downloaded for free on his website.

Jim's kit is not expensive and includes enough copper tape and ferrite baluns to make all the antennas on the plane. The length of each antenna is determined by the frequency at which it is trying to receive/transmit, and its aspect ratio (length/width) determines the bandwidth. The wider the copper foil is in relation to its length, the larger the bandwidth. 

The 22.8" (57.9 cm) length of the VOR/LOC antennas corresponds to the middle frequency of the VOR/LOC range 113 MHz, and the width of the copper strip allows it to stretch its reception to both ends of the frequency spectrum (108 MHz to 117.95 MHz). The GS dipoles are only 7.5" (19 cm) since the center of its frequency band is roughly three times higher.

The one thing that cannot be substituted in this installation is your typical home coax cable. Home coax is a 72Ω cable, and will not work well with aircraft radios. The correct choice of coax is 50Ω cable, with the most popular being the cheap RG58. I chose to go with the more expensive RG400 for upward compatibility, just in case my future radios might required it, and found a reasonably good deal on eBay on 100 feet of it.

One hundred feet of RG400 coax cable

Cutting one of the two dipoles of the VOR/Localizer antenna to the proper length

Getting the geometry of the antenna fixed

Before soldering

Voilà! One VOR/LOC antenna completed.

These antennas are mounted with a 10º to 30º angle in order to negate the null reception zone at the tips. I used an angle as close to 30º as possible for the VOR/LOC antenna, but only 10º on the GS antenna since the Glide Slope station is always in front of the airplane during an approach.

Getting the antenna and cable run situated

I stole the toothpick trick from my builder buddy Wade

Glide Slope antenna finished

More toothpick action

To separate the shield from the inner wire, one might unbraid the shielding, or pull the inner core out through the shield.

I started by pushing the outer conductor back...

...and used a pick to open up a small window...

... then bent the cable...

...and helped myself again with the pick...

The inner core was out in no time

The baluns sole purpose is to keep reflected power from traveling down the outside of the coax braid and radiating or reflecting into the rest of the airplane’s electrical system along the way. Three of them are able to stop 99.99% of this energy, and like the wires they get buried into the foam, then microed over.

I picked this 0.25"x0.25" tool from the Dremel box

This foam is no match for any tool

Cable, baluns, and soldered ends were sunken into the foam.

Another look at the VOR/LOC installation

Here's the Glide Slope installation

GS antenna from above

I made my antennas exit the back to the canard about 3” left of centerline since the radios will be on the left side of the instrument panel.

A panoramic view of both antennas from above

Using dry-micro to cover the GS installation...

... as well as the VOR/LOC

Coax cables exiting the canard from the trailing edge

For the coax cables to exit the canard I took the unusual step of creating a "flox blob" through which they would exit. This way skinning the top of the canard would be easier, and I won’t have to cut holes in the fiberglass in order to thread the wires through while glassing. Think of it as a big flox corner with coax wires running through the middle of it.

Building up a structural cover for the coax

As seen from the leading edge

Flox blob sanded down to a nice transition

Fiberglass will make a structural bond here without the need to cut holes in the cloth

Next time I will glass the top of the canard, thus the main canard build will be over. Non structural tips will get added later on.