Sunday, September 15, 2019

Musings about transportation

There are not a whole lot of physical things left to do on the aircraft, so I'm looking at transportation as the next big task.

A trailer is the obvious choice.  I already have a 4x4 trailer base that could be stretched and a new top made to haul Goat, and I could enclose it to store the aircraft in the trailer outdoors.  The major downside is that I don't have a good place to store the trailer when not at the airfield.  It can't stay on my street for more than 10 days.  I could push it into my back yard, but don't want to be "that" neighbor.  The trailer is even too long to store inside my garage.  And the vehicle I have to tow is a Prius, which I have seen towing a Sunfish sailboat on a trailer, but towing isn't approved.

Here is a flatbed trailer that I was looking at pretty hard:

Here is the Yando Goat trailer, which would be similar to my plan for a home-built enclosed trailer:

The other option is a rooftop system.  A Prius is also not the ideal rooftop vehicle.  The Thule roof rack only spaces about 27 inches between bars, and the Yakima roof rack spaces 34 inches.  For a wing panel that is 18 feet long, there should be more support.  And I have to drive about 60 miles at highway speeds to either of the two places targeted for a maiden flight, so it needs to be well secured.

This guy had a narrow roof rack for the long Goat wing, so maybe it would work for me.  It just looks sketchy for highway use.

This guy has a forward support mounted somehow under his hood, but which gives a lot more support to the length of the wing panel.

The Prius does have a pair of screw-in eyebolt locations in the front bumper, typically used for towing.  These might be okay bolt-points for mounting a support frame.  But how about something on the rear bumper?  Apparently you can get these kayak/canoe bed extenders that plug into a hitch:

The combination of a roof rack and support T-frame would let me strap the wings to the roof rack, and slide them reasonably far aft to leverage the support coming off the hitch.  Would it look weird?  Probably.  But that just might be the best option I have!

Saturday, September 14, 2019

Some to-do items checked off

From lessons on the first fully-covered assembly, here is my to-do list:

  • DONE flip aft cabane bolts to avoid hitting the aft pins.
  • DONE aileron pushrods are hitting bad. Need to free up.
  • DONE permanantly mount the aileron pushrods?
  • DONE install missing cotter pins:
    • DONE left aileron x3
    • DONE left flap x2
    • DONE right flap x2
    • DONE right aileron x3
    • DONE rudder pedals x4
    • DONE control stick x1
    • DONE forward sweep cable attachment to nose x1
    • DONE left cabane x2
    • DONE right cabane x2
  • BOUGHT velcro straps to keep the control surfaces up on the wing before assembly. 
  • DONE add bungee to hold the struts against the cabane?
  • DONE replace the forward nose tube (it is twisted)
  • Adjust aileron line tension and re-center by moving the knots.
  • Weigh.
  • Trim color paint.
  • Wing root kiss seal.
  • Gap seals... ailerons, flaps, rudder, and elevator.
  • Wing tip dolly.
  • Wing wheel.
  • Strut fairings.
  • Jury strut fairings.
 Here's what I did with the aileron pushrods ... crimped over the thin aluminum support plate embedded in the covering, and also switched to a bolted pin (per the drawings) that is lower profile.  Turns out the other end of the pushrod can be clipped to the aft strut bungee during transport.

First ever painted & covered assembly!

It's just all white now, but my Goat is officially covered and assembled in a flight configuration!

The aileron pushrod exits from the covering bind with the linkage, so the stick did not move the ailerons without excess pressure ... I'll fix this first.  Hopefully I can just bend the flange over all the way to clear.

It was nice to see that the aileron lines did line up nicely with the inspection panel access to connect the crossover cable.  I had no issue sticking my arm inside to make this connection.

I did not have terrible problems assembling the pins with the covering installed.  It worried me a little this would be tougher not being able to reach through the structure, but concerns were unrealized.  All the cables and pins and things were okay, save for a couple places where the covering made a little "tent" over a nearby bolt head.  Nothing stood out as an actual problem.

The covering and paint definitely added some weight to the wings, which showed up as a bit more aft mass.  When sitting in the seat, I used to be able to lean forward and pick up the tail.  Now the mass is far enough aft of the CG that I really need a person to step on the nose to get the tail off the ground.  It still balances with my mass forward of the wheel when in a flying attitude, so the simple CG check still passes.

I definitely need some trim color, but Mr. Goat looks happy :-)

Sunday, September 8, 2019

Goat painting

The wings have been slow progress, but are about to be done later this morning!  I switched away from using old chairs as sawhorses and brought up my workbench table from the basement so I could flip the Goat wing upside down and paint the bottoms.

I have a little tupperware for keeping the mixed paint fresh.  When more is needed, I pour 120 grams of paint into the tupperware, pour in 40 grams of water, mix with a popsicle stick, and then start painting again.  It takes about 3 minutes to cycle a new mix.

The foam brushes have been a bit kludgy.  The 87-cent brushes from the local Home Depot are soft and tended not to last one coat before a cut appeared in the foam.  The 1-buck brushes from Michaels are a bit stiffer and tend to last much longer, but eventually start to come apart and drop foam debris into the paint.  Maybe I'm just trying to use a throw-away product longer than it should be used...

Freshly mixed paint goes on a bit watery, which is awesome for coverage.  As I get deeper into the mix, the paint feels more sticky and takes more effort to spread nicely.  It probably could get thinned back out with more water.  Usually 120 grams of mix is not too much for being sticky if I'm using it all that same day.

The first coat on fabric tends to absorb about twice as much paint as subsequent coats.  Surely this is because the paint is going through the pores and putting coverage on both the outside and inside.  After that first coat dries, the subsequent coats only put paint on the outside and thus stretch much farther over more surface area.

I estimate that painting Goat has been about three quarters of a gallon of the Glidden Gripper white primer paint.  Some of that mass certainly off-gasses and does not count toward the final airplane weight, but this is still roughly 10 pounds of mass for paint.  Recall I'm using three coats total on every surface (except the bottom of the wings that will not see the same UV load).

Between coats two and three, I have been using 180 grit sandpaper (lightly!) over most of the surface area to knock down any dust or bumps in the paint layer.  It takes extra special care at any hard corners to not sand through the fabric -- basically, don't sand at corners. 

The last coat is drying now, then I'll do an assembly with the whole of Goat covered later today.  Stand by for a cool photo!

Saturday, August 31, 2019

Wing covering, Part 3

The final item on the wing covering to-do list was the aileron linkage cutouts.  Similar to the elevator linkage area, I added a piece of thin sheet metal with a slot in it to stiffen the cutout.  Lesson learned with the elevator area though, the covering has a LOT of tension and can distort that piece of thin material.  So I bent a lip most of the way around the cutout to stiffen the part from bending like a potato chip.

From previous marks (before adding the top covering) of the centerline and ends of the travel, I knew where to place the reinforcement.  The pencil marks show the outline of the metal reinforcement.

Next is a coating of adhesive on both the fabric and the back of the metal reinforcement.  I never quite figured out the best amount of time to wait before sticking these two together -- the Stewart Systems videos on Youtube say to do this wet, but it is easier if it is dry.  At any rate, I stuck it on and then used an iron to encourage the adhesion.

I then drew another pencil outline and put a healthy coat of wet adhesive inside the lines, including over top of the metal part.  The cloth patch now goes on, pushing it with the brush into the wet glue.  It is visible in person to see when it is completely wet out and without wrinkles.  Another coat of wet glue is spread on top and wiped off when it is still "aggressively wet."

After drying overnight, I went back over the edges with an iron set to 250F to smooth down the mini frayed edges as the pinked cut, and to stick down any little bubbles.  I also shrunk the whole wing to 275F so the covering was all set and putting tension into the patch.  With a committed sigh, I cut the inside covering slit and was relieved the metal reinforcement did not distort when taking the tension!  A little clean-up around the covering edges, some more coaxing of the bend with the pliers, and a final trim of the covering to the edge, and this task is done.

These wings are now ready for paint!

Oh man there is a LOT of surface area to paint with a 4 inch wide foam brush...

Thursday, August 29, 2019

Wing covering, Part 2

I'm really quite pleased with how it turned out!

It took (only) five straight days of roughly 8 hours each to (mostly) finish the wing covering.  Maybe I am detail-oriented and couldn't leave a wrinkle, but I think it just takes this long to do it reasonably well.  But it's (basically) done!

The qualifiers are for the cutouts for the aileron linkages and to check over that nothing else is left to do.  Oh I do need a second shrink, going to 300F instead of the 250F initial shrink that you see.

Alrighty, here is the second wing up on sawhorses and ready for some air-proofing...

Here is a closeup of the trailing edge attachment with the bottom covering partially attached.  This was the method I found best covered this area, which leaves the lower angle bracket exposed.

The leading edge root area is similarly covered except for the bottom angle bracket.  This seems logical.

The bottom covering is shown here completed, and preparations for the top are ready.  Around the trailing edge tube is roughly 2 inches of adhesive for fabric to tube.

Starting not long after sunrise on day number five is the last of the four wing skins.  It is still interesting to see where it starts before even working the perimeter.

The wing tips were another neat area.  The lower surface wraps all the way to the tip bow piece, so the upper merely wraps around the one tube.  Curvature here is pretty tight.  I was able to work the fabric around with gentle heat so there were no wrinkles at all.  Maybe this is why it took five days to cover the wings, but it all seems worth the effort and patience.  Obviously the next step from this picture was to mark and trim to the line, then the covering was locked in with another application of glue-and-wipe.

Done!  The hole for the aileron cross-thru is much larger than it probably needs to be, but I saw no downside being able to stick my whole arm into the hole.

As a final act on Goat for the near-term, all of the parts and pieces have been brought back into the garage together.  It feels good to have everything back in a single pile.

Next up is paint.

Tuesday, August 27, 2019

Wing covering, Part 1

Whelp, it took amazing weather, (effectively) weeks of making sure I'd cleared all the to-do items, and a job change for me to make time to tackle covering the wing.  But here we are with the right wing completely covered and preparations for the left wing underway.

This isn't going to be a comprehensive how-to post for covering.  I just shot images of the highlights, mostly for my own recollection if (when!) I do this again, and enough shots of what is now going to be really difficult to inspect.

I ended up adding foam spacers to the compression ribs, as a way to support the lower surface covering.  This trick was not on the drawings (that I saw), but was done by Alan of the Yando Goat (IIRC).  Making these foam spacers is easy enough by hand, though I knocked them out on the CNC router.  The outer surface that touches covering has a layer of fiberglass tape and has all edges sanded smooth.  The spacer height roughly matches the bolt brackets or leading/trailing edge tubes as appropriate.  Here is a close-up:

Starting the covering with the first drape looks fairly sad and wrinkly.  This first pull showed the areas where I'd need to trim for eyebolts or brackets to pass through.  The root was quickly identifiable as a tough area.

Using the Stewart Systems process, I worked around the leading and trailing edges.  The root area definitely was the toughest.  I wrapped the covering around from the bottom (no extra spacer rib) to the upper tube of the root rib.  This gives continuity, but means the wing attachment brackets are a massive pain.  Instead of going over those, I ended up trimming the corner on the bottom and leaving those brackets exposed.  This photo is also before I poked holes for the aileron cables, or trimmed the trailing edge fabric.

After a few hours, I had the lower surface ready for shrinking.  It wasn't that terrible if I'm being honest.

And the lower surface after the initial shrink to 250F was looking really good!

I put in several inspection rings, including in places I don't plan to cut open, but now have as an option (e.g. for cable tensioning).  As noted in the Stewart Systems instructional videos, these ring locations are MUCH easier to mark from the inside of the wing after the bottom covering is on, but before the top fabric goes on.

This is a medium shot showing the inspection ring located below the aft aileron cable pulley.  This location should allow me to inspect the pulley and re-tie the cable knot if that is ever needed.

The bottom covering also had some challenging covering areas, such as around the tip handles.  Following someone else's process (Brady Butterfield??), I removed the tip handles, added two slits to the covering, added reinforcement patches, and reinstalled the handles after covering.  This worked rather well, and leaves the whole area with a continuous fabric.

Next up was covering the top of the wing, which was a bit trickier with respect to the curvature, but was overall easier due to fewer protuberances such as bolt heads.  Here is a shot after going around the perimeter for the first time, with only basic wrinkles pulled out.

With further cleanup of the perimeter, the upper surface was ready for the initial tensioning to 250F.  As every online instruction suggested, I started in the middle, and worked to bisect the remaining sections, moving back-and-forth to stay balanced.  Shrinking took maybe 15 minutes and was very satisfying!

Here we are after tensioning!  The lighting and wide-lens makes the sagging between ribs look worse than it actually is.

Finally, I added the reinforcing tapes.  The roll of Ceconite tape was a much heavier cloth, so I ended up cutting four strips of 2 inch wide fabric from the trailing edge cutoff (sooo much cutting with pinking shears).  This reinforcement on the leading edge puts the upper surface fabric in double shear, in addition to its overlap to the lower fabric of three inches.  I thought about doing the same tape job on the trailing edge (I think this is typical), but the fabric overlap is already over three inches there, despite only needing to be overlapped by one inch.

That's where she stands right now --- I'm actually partly through the other wing half already, and will most certainly do an assembly in the back yard once both are completed.

One random note: the wing panels are much more difficult to handle once the covering is on.  I was used to picking up the panel by myself by holding onto the internal structure.  Now, instead, I have to pick it up differently, and that makes the panel seem much heavier and/or more awkward.  It sure seems like this will be a two-person assembly process.

If anyone sees anything questionable about my process or of the structure itself, please, please leave a comment.  Your five minutes of typing just might save my life, or maybe saves me hours of repair work later.

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