Look what the mailman brought me!

Aaaaah, a clean slate...

A quick word, as re-introduction.
As this is my second Unicorn, I have now the opportunity to see the progress and changes (if any)that
have been made in the production and packaging of our beloved 'Corn. Remember, my first 'Corn
was one of the earliest kits sold. At the time, as an introductory incentive, Mark was offering the 'Corn
with free postage within the US. Right about the time that the first Unicorn thread started at RCGroups!

Well, packaging has greatly improved. As you can see from the picture above, plenty of foam maccaroni,
and the balsa parts are wedged between the two EPP cores, as opposed to on the outside, as I received them
at the time (the balsa arrived split and broken then). So in all, a 10 out of 10 for packaging.
I wish the same could be said for the balsa. As was the case with my first 'Corn, I'm sorry to
say that I've seen better quality. The elevons may be slightly better then what I received initially,
but the balsa for the winglets is not grade A. Closer to Z it seems. It is not equaly thick all over,
very soft, and on closer inspection there is a split vein running along one side.

The elevons, I think I can live with. I was thinking of making some new elevons from a balsa and
carbon fiber strips sandwich, but I'll start with these and some carbon fiber tape across.
The winglets I will make from 2mm coroplast, so I will discard the balsa for this.

Sorry Mark, maybe you could consider dropping the balsa winglets, and cut some 2mm coroplast instead?

I really couldn't wait to get started, so after a close inspection, I removed the cores from the beds.
Another difference from #1 was noted. The wingbeds' LE is not cut, so I will have to cut them in order to be able to use the beds during construction.

As is tradition with EPP cores, I started with rubbing the supplied piece of EPP ove rthe wing cores
to get rid of the EPP veins. Since I will make this 'Corn a 42" I looked for (and found) the
relevant templates. All templates are in the rear of the manual, as opposed to the seperate pages I received with #1.
I don't think this is an improvement. Not really a big problem though. I just had to cut out all templates
with my X-acto knife.

The procedure is realy simple:
Put the wing on the relevant template

Mark where the cut has to be

and cut once

and twice

The manual lets you glue the wing halves together early on in the building process.
Since I have very litle working space (the diningroom table, which is shared with my wife
as a laundry folding table, a nail varnish/decorating table, and is also used as a general suppository
of our kids' junk), I will first do as much as possible on each individual wing half. It is also
easier (I think) to do all the measuring, cutting and slicing on one half, as opposed to
manouvering the whole 42" about.

Since I will be using PolyQuest 2600 3S1P batteries, I knew I had to deepen the battery bay about this much (=5mm):

What you can't see, is that I also enlarged the batterybay towards the nose by 10mm, to be able
to balance the CG beter.

On 'Corn #1 I had a coroplast battery cover. I will do that again, only this time the
cover will be flush. To do that I measured 3mm (the thickness of the coroplast) deep and 5mm
wide along the battery bay. Somewhat more on the nose, to get a good glueing surface for the coroplast

And obviously, then I cut it. No pics of that, because the white on white didn't come out.
But you get the picture... (pun intended)

Next, the Rx compartment. I will be using my trusty Berg, and she is this big...

And here she sits, rather snug, in her own compartment.

Later, when the winghalves are glued together I will make an EPP cover.

Next, the servo placement.

Not too close to the Rx, so I first played around with the positioning on the bottom of the wing.
Note the Rx bay proximity.

On the top it looks like this. Maybe somewhat too close to the LE.

So I'm planning to put the servos about here. Leaves me just with one dillema; servo arm away from the LE,

or towards the LE.

While mulling that over, I cleared my mind a bit by attaching a carbon fiber flatrod to the TE
with masking tape, and putting a few drops of thick CA on. Once the CA had cured I removed the
masking tape. This will later be covered by filament tape.

I figured, to decide the servoarm position, I would need to know the Golden-Rod position and bend.
To figure that out, I first measured where the inner most point would be of the elevon, using my
largest prop (a 7x4 Graupner CAM folder)

About 470mm, so the control horn on the elevon will be at about 235mm.

The blue line is paralel to the wing root and wing tip. The burried control rod should come out
of the wing along this line. Holding down the Golden-Rod on this line with one hand, I positioned
the other side near the servo with the other hand. So you'll excuse me for not having any pictures
of this procedure... Suffice it to say, the servo arm will be towards the LE, for easiest bend, and least friction.

I decided to let the servo riddle rest for a bit, and have a look at some other stuff. The motortube for instance.
I dry fitted the center rod, slid the two wings together, and tried the fit of the tune. A picture paints a thousand words...

A fair bit of foam has to be removed from the battery bay area where the tube is. No biggy, but this isnot
mentioned anywhere in the manual. First time builders, beware!
After a little bit of carving the tube fits fine. I am contemplating though, to make a slight bend in the aluminum
bottom plate to get the motortube more in line with the wings horizontal center line. This will prevent the need
for different trim settings for powered flight or glide.

Back to the servos...
The blue pen lines show where the servo is going to be, not taking into account the servo arm.

Once the servobay is cut out, I carefully removed the foam for the servo arm. This will ensure a snug fit
for the servo, without slop.

Snug as a bug.

And the bottom. See? A tight fit=no slop.

Front view. The servo is completely flush.

Bottom plug glued in place. Later, when the pushrods are done, and the servo wire is routed, the top
will be covered as well.

I first taped the bottom wingbed to the working board, and on that I taped the wing half. I then
taped the Golden-Rod in position.

I drew a line along the rod, and cut out a shallow groove. This, so I will have an easy guide
for my soldering iron. The EPP I will use as a cover.

With a hot soldering iron I made a groove for the rod. Frequent test fits are necessary here.
I didn't want to take out too much foam!

With a few dots of hot glue I keep the rod in place.

I then put masking tape on both sides of the groove, with a Q-tip I slightly wetted the groove and rod,
and put a few small dots of polyurethane glue every 2.5"-3". The EPP I had cut out previously I then
placed on top, and covered that with masking tape as well. That I then covered with some weights.
This way the expanding polyurethane will go into the EPP pores instead of squelching out all
over my wing surface. At least, that's the theory. We'll see in about two hours...

There you are! Two wing halves with Golden-Rods pushrods flush in the wing. It'll need some
spackling and sanding. But that'll be done later, before taping.

And now the continuation of the servo-saga.

I like to "pot" my servos. So first I taped the bottom plug of the servo, to prevent seepage.

Then I wrapped the servos in clingfilm.

And I prepared some 5 minute epoxy mixed with Soda Bicarbonate (a cheap replacement of microballoons).
Please note, only the finest produce used. Real kosher Bicarb and clingfilm! The clingfilm is even Kosher for Passover...

I poored some of the mixture in both servo cavities, put the servos in sandwich bags.

And pushed them, like that, into the servobays.

Some pressure applied for a few minutes, and then I pulled the servos out.
And "Voila!" as they say in France.

I then glued the top and bottom wingbeds together, and put the top bed on the table. I had to
remove some foam, where the pushrods are, to have the winghalves lie flush on the bed.

I then maskingtaped of the root parts of both wing halves, and sprayed the roots with a healthy layer of 3M77.

The center carbon rod was inserted in one winghalf, and then in the other, taking care that,
when the halves touched they were perfectly lined up. Some pieces of maskingtape were
stretched along the root. I then placed some greaseproof paper on the bed, and placed the wing on top of that.
Some weights were placed on the wing, not really for pressure, but just to prevent anyone bumping
into the table from moving the wing bed and maybe throwing the winghalves off-line.

Note: This is not how the manual tells you to do it, but old habits die hard...
Also, I didn't glue in the motortube yet, that'll be after I had the opportunity to
drill lightening holes in the aluminum backplate. I want to bend the plate slightly, so the
motortube will sit lower, close to zero degrees up/down thrust. This will improve motor on/motor off trim.

Meanwhile, back at the ranch...

It was time to see to the carbon rods.
First the main rod, since it was already in place. I stretched masking tape on either side of
the rod cavity, to catch any "overflow". With a Q-tip I moistened the entire rod cavity, and
then squirted some Elmer's Pro-Bond polyurethane glue every 2" or so. I then covered the whole
length of the cavity with another strip of masking tap, and put some heavy books on it. For those
of you who don't know, polyurethane glue will expand about twice its' size, especially if the
area is moist or wet. Very usefull when you are glueing a "slippery" carbon fiber rod in a EPP
wing. The glue attaches itself to the carbon, and will seep into the foam pores, effectively
"anchoring" the rod in place. Ofcourse if too much glue is used, it wil go through the pores
right out the other side of the wing, and you will find your wing attached to the wing bed it was resting in...

Curing time is about 1.5-2 hours, so this stage of the build took up my whole evening. After the main
rod's glue had cured, I did the two side rods.

Last thing I did that evening was routing the servo wiring. I used a 5mm drill bit to make a
whole through to the wing's bottom, and with an X-acto knife I cut the route.

The plan for the antenna was to have it easily removable, so I can share the Rx with other planes.
For that purpose, I first drew a line where the antenna would be.

Then I made a cut along that line, and sank a pushrod sleeve in place.

But try as I might, I could not get the antenna to go in (and out) easily. So I decided to resort to an
old stand-by: the Micro Deans Plug.

How does the saying go? "A place for everything, and everything in it's place."

Back to the rear end then... (That woke you up now, didn't it?)

The bottom plate looked a bit too solid (=heavy) for me, so I had a friend drill some lightening
holes with his press drill. I had made little indentations where I wanted the holes. However,
in his enthusiasme to realy lighten the plate, he also drilled out the holes for the nuts & bolts!
Luckily, the washers are slightly larger then the lightening holes...

I lightly sanded the motor tube, and put some fibertape on the stress points; the area around
the main rod, the area around the bolts, and the rear-end, where the motor will be.

Sanded it again, and sprayed a light coating of 3M77. While that dried, I cut out a piece of
the glittery stickyback paper. When the glue felt tacky, I stuck the glitter on.

Because I want to get the motortube in with as little up incidence as possible, I am going to get
the foam under the motortube to bend somewhat. I got the idea from a post on the RCGroups Unicorn thread
(thanks Lono!). I placed the wing upside-down on the table, and placed equal weights on either side of the centerline.
This is how far I want the foam to bend:

By carefully heating the area with a covering iron (tried it on a piece of scrap foam first!) I managed to get the foam to bend without melting.

Due to the bending, a small opening was created along the centerline. This needs seeing to
before I glue on the bottom plate.

A small piece of EPP was cut and glued into place.

Then, using a technique I'd never used but read about, I fixed a few strips of carbon fiber
on the area, to strengthen the foam. Very simple realy. I cut the strips to size, placed a
piece where I wanted it and put a few drops of thin CA on top. Then, with my hand in a plastic
bag, I gently squeezed the CA into the CF strips, waited a minute, and did the next strip. Piece of cake.

All that needs to be done now, is bend the aluminum plate to fit the contoures of the wing.

I taped of the area on the wing where the aluminum plate will go, and sprayed some 3M77 on it.
I then lightly sanded the underside of the plate, cleaned it with some alcohol, and sprayed that
as well with some 3M77. 10 Minutes later I put the plate in place, and weighed it down to let the glue cure.

While it was curing, I fashioned a cover for the Rx cavity, and glued it in place after the
plate's glue was cured.

The next step will be glueing in the motor tube. Since I will be using the wingbeds for storage
and transportation, I hollowed out the top bed in the areas where the motortube and the pushrods
will be (with a hot soldering iron).

Motortube gooped in place.

And the bottom plate nuts & bolts in place (after much fiddling to get both the nuts and rings inside the tube).

From some EPP cut-offs I made two servo plugs, and glued them in place with a tiny dot of goop.

Time to spackle!

I'm not going wild. Only the servos, servo wiring, antena, and cf rod areas will be covered lightly!

Looking at the previous pictures, I realised the foam is rather thin in the batterybay area.
So, some CA'd CF strips were called for.

I gooped the front part of the coroplast batterybay cover in place, and gave a light misting of
3M77 on the bottom, LE, TE, and tips. I used a mix of 1" wide bi-directional, and slightly lighter 1/2" regular fibertape.

A close up of the bay. You can see the two rare earth magnets that will hold the flap down.

Flap closed & flush.

Another light 3M77 misting on top, and two 1" strips of bi-directional tape from the wingtip's TE to
the opposing LE, each.

And some on the nose. Note the servos are not covered by tape, and the servo arms are not covered
by EPP. This way I still have fairly easy access to the servos, if (and when) necessary. Naturally,
they will be covered with Oracover.

The makings of a carbon sandwich ...

I started preparing the elevons. I CA'd carbon fiber strips on to the original elevons, and cut
two more from 1mm balsa.

I placed the cf strippyfied (note, new verb) elevon on some greaseproof paper, then mixed some
5 minute epoxy, spread it on the elevon. The I put the 1mm balsa on top, and covered the whole
ensemble with more greaseproof paper, and weighed it down with some heavy books. The key here is to
use too much epoxy. The excess epoxy wil ooze out by itself, and once cured, can be sanded of.
You can see that I followed my advise with the top one, less so with the bottom one...

This may be overkill, but there's hardly any weight added with this.
I found with my first 'Corn that the wingtips were slightly "soft" and could bend under stress.
To add some strength I cut two carbon fiber flatrods to size.

To cut a slit in the foam, I taped the blade of my knife at 5mm, so I wouldn't cut too deep.

I pushed the flatrod in the slit, and put a few drops of thin CA over it.

Before covering, I sanded both sides with some 600 grit paper. Especially the tape, since there
is an oily film on top of the tape, to prevent the tape sticking to itself on the roll. After the
sanding, a good wipe with a clean cloth, followed by a light misting of 3M77. I found this Solarfilm
much easier to apply then Oracover. It also needs much less heat.

The other side was slightly more tricky, because of the batterybay and the metal plate, but in the end
it turned out ok. I still had the templates, so the bottom decoration was soon done.
Don't you get that sense of "deja vu"?

The top still looks boringly white, but we'll fix that tomorrow. Guess what I'll put there...
The right answer gets a turn to fly my 'Corn (but you have to come overhere first...)

and.....
a roll of the drum.....
tadaaaaaaah! A touch of patriotisme here; our national flag.

In the past I struggled to get the six pieces of covering to stay in place and to iron them without
moving them. Many a naughty word was utterred, not allowed on RCGroups, to get something looking like
this. But I at last the lightbulb clicked on last night...
I had a template to get the right size. So I cut the six strips, and removed the back covering.
I then laid them out on the template, and with a miniscule bit of paperglue (the sort my daughter
uses in school) I fixed the two triangles. After that it was easy to iron on first one triangle, and then the second one.

And to add a bit of colour, I added a Unicorn decall on the other side.

I sanded of the excess epoxy, and bevelled the LE of the elevons. I found that the easiest way
to do this, is to tape the elevon to the edge of the worktable, and tape a metal ruler to the top
of the elevon, 4mm back. This way you can only sand of so much, and you end up with an even bevel.
I also slightly rounded of the elevon bottom towards the elevon's TE.

I then cleaned the elevons with some alcohol, a light mist of 3M77, and covered with Oracover.

Some "racing" stripes (at least she'll look fast...)

Oops. Cut a few red strips too many. Oh well, some more stripes. After all, I am a corporal...

Marked where the control horns should go.

Drilled two 2mm holes.

And screw in the control horn. Piece of cake...

Piece of cake? Did you know that the holes on the control horns of a set are on opposite sides,
so you should use the left horn to measure the holes on the left side, and the right one on the
right side. Guess what I did...

After my previous Unicorn's crash I pulled out all equipment and bench tested the servos, ESC and motor.
All seemed fine. So to my unpleasant surprise, when I had installed the pushrods and tested them,
one servo was making a horrific clicking sound, and did not work properly. On opening up the offensive servo
I found this:

Yup. A bad case of missing teeth! A new set of gears was ordered from Aircraft-World.
(including postage, still 2/3 of the local price...). Replacing the gear was a bit tricky,
since I did not want to remove the servo from the wing to do the job. That would have meant to
dig up the servo wires, and that would have meant removeing part of the covering. So with a little
extra effort and some choice swear words I managed to replace the gear. When previously trying the
servos I thought I detected some binding. So before sliding the pushrods back into place, I ran a
piece of cotton material through the pushrod sleeves, to remove any dirt/dust from the sanding and building.
I also rubbed the pushrods themselves with a piece of 800 grit sandpaper very lightly, and only once.
I then wiped the pushrods clean with a bit of alcohol.

Another source of concern was my attempt to keep the pushrods low for a clean wing profile.

I needn't have worried. The servos work cleanly, and the elevon moves just fine. I did have
to attach the pushrod on the lowest hole on the control horn, so I had to reduce the servo throws
quite a bit. Low rates are at 35% to get to the recommended 1" throws!

I had a friend transform a piece of aluminium into this motormount.

I bend the "wings" back

Screwed the motor on the mount, and slid the motor into the motor tube. Two zipties will keep
the motor and mount in place.

Due to the bad quality of the supplied balsa for the winglets, I cut out two winglets from some
2mm coroplast. This is the way I like to attach my winglets:

A whopping 932 grams (32.9Oz)AUW!!!

Including 63 grams (2.2Oz) of lead on the nose to get to the recommended CG of 9.75" from the nose!

I hope I can take some of that nose weight of after the maiden...

Well, I did try a maiden flight. Didn't go very well. Read all about it over here...