Sunday, March 26, 2017

Assembly, because it's Spring!

I'm a fair-weather building for sure.  It was 75 and partly sunny on a Saturday, perfect for assembling Goat with the newly covered tail and seeing how everything is fitting together.  First, some wide-angle pictures...


The newly covered control surfaces (except that right aileron) look awesome.  Even in a light breeze, I could feel the aileron and elevator putting some slight control forces to work.  Sandlin's idea of "wind jamming," referring to balancing/steering with the control surfaces in wind, makes perfect sense now.  And if the wind direction is right, I can probably do this myself in the back yard with minimal risk.  That will help me figure out the stick deflections needed for positive control.  Coming from an RC background, my thumbs are used to moving, not my whole arm and both legs.  I also remember how the stick felt very heavy in roll and very sensitive in pitch in a Blanik, but less so in a Cessna 172 (well that was a yoke).  Wind jamming seems a great and safe way to get familiar with the Goat.  There is a good video of this somewhere, but this is the best I could find in a pinch.

The tail is all covered, but still needs to be painted.  There were no issues with assembly here with access being different ... with the wing, I tend to reach through the structure where covering will later prevent that access. 

Perhaps you already understood this from the drawings, but it seemed worth sharing a closeup of how the aileron cables route at the wing root while I was taking pictures already.  Several builders have replaced this arrangement with solid pushrods and torque tubes for the ailerons.  For me, this cable arrangement still seems okay.  The blue painters tape marks a tube I'm going to replace because of that stray hole.

I tried leaving the control surfaces, cabane, and strut on this wing panel to move it back into the garage.  It's quite awkward.  I normally find the balance point and hoist it over my head, using a good grip on the internal struts to balance it.  But, that won't be possible with the covering on, so it makes sense to resolve how to move it differently before covering.  I usually move the strut separately, and it does have quick links to support that.

The only new major lessons were that the wing control surfaces will definitely need to be held in place somehow prior to assembly and post disconnection.  I had removed the tail section and had the nose section balanced on the skid forward.  This large assembly caught some wind and rotated backward without me controlling it, with the ailerons streamlined (still connected to pushrods).  The ailerons were the first item to hit, transferring force back into the control pushrods, which both bent.  Those need replacement now.  I'm thinking a really long velcro strap to hold the control surfaces folded up against the wing.

Saturday, March 18, 2017

Rib attachment part 2

The leading edge fiberglass wrap has had a couple weeks to cure (ha, meaning I haven't been working).  Sanded down with a small block and 80 grit paper, it is great.  I'm pleased.  The rib seems firmly attached, which is the whole point after all.  It should also cover nicely.

I shifted the whole wing in the garage and bonded on the trailing edge.  An addition was a secondary support for the last rib, using the tip support.  It was bonded too, and lashed using a single s-glass thread.  Should be secure.

That's it for the ribs for now.  I really don't want to do them all before the load test, but wanted to see how that process was going to go.

Monday, February 20, 2017

Rib attachment

Not much work today, mostly experimenting with the rib attachment and leading edge shells. 

I attached only the outermost two ribs and used the method as described in the drawings.  I first pulled the fiberglass tape around dry, situated the fabric, and lightly marked the edges with a thin sharpie.  After removing the dry glass, a quick rough using 220 grit sandpaper within the lines gave some tooth for the epoxy to grab.  When I mentioned sanding aluminum to a colleague, he warned about removing the oxide protective layer and inviting corrosion.  With the epoxy sealing out the surface scratches, hopefully surface corrosion is no longer an issue.  Anyway, a good wipe with alcohol cleaned the surface and prepped for epoxy.  After adding the epoxy and clamping the fiberglass tape to hold it all in place, it cured for a few hours in the warm sun.

Several leading edge shells were added temporarily just to take another look at this process.  The outermost one had to be cut down an inch or so to fit the reduced width spacing, which was easy enough with a new, sharp Exacto blade.  After it was in place, here's a look at a few of the leading edge shells held in place with masking tape.

I'm considering to put a layer of fiberglass on the back of the foam prior to bonding it in place.  If I also add a layer on the front (after sanding), that will stiffen the foam tremendously, providing some ding resistance and hopefully keeping the foam from getting cracked from any poor handling.  Sandlin calls out for a layer of epoxy seal coat for the foam. The Stewart Systems process I'm using to cover does not eat foam like Polyfiber adhesives, but it is a good idea anyway.  I have a bunch of 2.75oz/yd2 cloth that is probably a bit light.  4oz unidirectional fiber seems about right.

Remaining covering is the right aileron, the cabanes, the nose, and then the wings!  I'll be stopping for a load test prior to beginning the wing covering.

Saturday, February 18, 2017

Tail covering

The vertical tail took quite literally all day.  I cut separate left/right pieces.

The first half went reasonably well.  It wasn't hard, just a lot of bolts to go around near the trailing edge in particular.  The cutout for the control linkage was a particularly challenging area.  I ended up making a grommet using a piece of thin metal roof flashing.

The flashing was bonded onto the skin and then a larger patch put on top.  Perhaps the slit could have been shorter, which I'll know after a full reassembly.  With the long slit cut, the grommet deformed a bit relieving the tension in the aft portion of the covering.  Meh, it'll be okay.

 After an evening of covering the second side, I got to the point of match drilling the new tail bracket to fit the tail on.  It's now fixed in place and fully remounted.  The controls have been re-rigged as well, and they work fine.  It's weird having the skins attached.  Just different.

To another day...

Saturday, February 11, 2017

A little more covering

I knocked out covering of the two flaps.  They were quick, being rectangular.  Took just one evening each, and that was just enough time between getting home from work and needing to head to bed.  I forgot how the covering task wasn't hard, just takes some time.  Here's a mid-process shot.

The ailerons are now on the bench awaiting covering. Those should take a couple evenings since they're just a bit larger and also have the nice long curve near the tips.  But I'll get to those later.

The tail needed some cleanup work before covering.  It was dusty from sitting in the garage and was easy enough to wipe clean.  I took off the flying wires, control cables, and brackets in preparation for installing the covering.  Then I took a closer look at the foam spacers during this cleanup and just wasn't happy with them.  The epoxy was cracking off the aluminum in places and just wasn't carefully applied back in May 2010.  Instead of covering over this, it made more sense to take care of replacing it now.

After a punching out the foam and a bunch of scraping to remove the flaking epoxy, and some additional clean-up with isopropyl, the tail section looks much, much cleaner, and almost ready for covering.

This part needs to be replaced.  It might be fine, but there is no reason to stick with a part I'm not satisfied risking my life on.  I built this bracket to the specifications in the drawings, but apparently the hole in the horizontal stabilizer didn't align perfectly.  Adding a shim washer made the fit work, but, yuck.  I'll order some more aluminum channel and match drill the holes next time to not need the washers.

That's all for today.

Sunday, February 5, 2017

Some simple covering

I took a long break from working on Goat to do other things.  Life.  The EC Goat guys beginning to cover helped encourage how far behind I have gotten.

One elevator half was prepped for covering a long while ago.  Unfortunately, I put the adhesive onto the surface and didn't do the covering.  After months of sitting, it seemed prudent to remove it and start over.  It took a LOT of rubbing with my fingers and some scraping to remove it all. Hours of work.  Don't leave work half completed...  Interestingly, the adhesive is like a very sticky goo.  You can get it off the surface of aluminum one little bit at a time.  It appears the adhesive works by being in shear and having ample overlapping surface area.

After clearing the old adhesive yesterday afternoon, I started anew this morning.  Put cloth tape over the sharp corners of rivets, tube edges, and bolts.  Add adhesive around the perimeter and let dry.  Place the fabric down gently into the dry adhesive on the first side and smooth out all wrinkles.  Iron down (~225F) around the edges, working out wrinkles.  This is the stage of the first photo.  Add adhesive around the edges again, letting dry.


Come back and trim the excess, then iron it down inside the perimeter.  Flip to the second side.  Add adhesive about 1" around the perimeter of the first side, let dry.  This is the second photo

Once that perimeter is dry, pull the fabric around and start working carefully to remove all wrinkles, using the iron to help shrink the edges.  Come back with pinked shears and trim to that same 1" overlap.  Iron down, and definitely remove all wrinkles.  Finally, add another layer of adhesive and wipe off while still aggressively wet.  Let dry, then do a final ironing over the overlap to set the adhesive, and do a final shrinking over the whole thing.

I also added reinforcements over the hinge eyebolt penetrations through the covering.  These were a circle traced onto fabric, cut out with pinking shears, and a small slit to slide over the eyebolt.  First slid this into position and traced the outline, then added adhesive to the skin fabric, then pushed the patch down into the wet fabric, wiping up excess.  After that dried, ironed down the patch into the adhesive, then add adhesive and wipe away excess.

This now completes the horizontal tail to include both the fixed and moving portions.  These need to be painted and they'll be ready to go.

Next up is probably the flaps.  Those should be easy, since they're just large rectangles.  Next is probably the ailerons, again because they're mostly just large rectangles.  No formal plans beyond that, lest I get ahead of myself!

Sunday, July 24, 2016

Thinking about other purchases

After effectively saving a bunch of money by not going with Oratex, I'm looking toward the other expenses.

Check!  :-)  Works great for skiing too.

Video camera
GoPro, is a requirement for proper documentation. :-)  Check!

Yaw string
I have some red yard hanging around somewhere...  Check!

Airspeed sensor
Long, long ago I received a Hall wind meter sensor as a gift.  Check.  I still need to make a mounting/clamping bracket for it.

Can go two distinctly distinct ways: hang-glider specific, or sailplane specific.

There are hang-glider variometers, like the FlyTec units, which are designed for the same operating regime of Goat.  Airspeed sensors should be set up for the low airspeeds and vario calibrations should be tailored for slow aircraft.  However, few have total energy compensation, which I consider a requirement for a vario (lessons learned from using RC variometers).

There are also equivalently priced sailplane variometers, like the LX Nav units, among others.  These almost all come with full total energy compensation, and I can find total energy probes and mounts that should work (ILEC).    But, these units are not tailored for the low airspeed range of Goat.  Some units offer customizable vario averaging, so the response can be tuned for slow flight.  However, if the pressure sensor selected is set up for handling much higher airspeeds, the low speed range will be exponentially worse.  If anyone has experience trying to use a "real" sailplane vario on a hang glider, please let me know how that went!

Seems like the hang glider guys like the ICOM radios.  The A14 looks good enough.  What I can't find online is if I need some kind of FCC license to use it for aviation.  Maybe you used to?  Doesn't look like anyone checks on a license when you go to purchase the radio, so maybe not?  I already have an air-scanner radio for a third party to listen.

Sandlin recommends a hang glider style parachute in a throw-bag for emergencies.  All my online research says these are only good for altitudes above a few hundred feet, so this purchase will hold off until getting past the initial ground-effect flights.

Tow Setup
There is a lot of setup to do here, more than I realize now.  The glider side is pretty straight-forward, with the quick release and weak link.  The car towing also needs a release and should also have a tension meter of some kind for better safety.  The rope itself seems to generally be polypropylene from 1000 feet to much longer, if it fits the takeoff area.  Found rope for what seems to be less expensive than I expected:

Uhg, now we're getting into the less fun details.  I do already have a 4x8 trailer kit which is currently disassembled in the basement for storage.  A friend once adapted the same trailer to carry an 18ft homebuilt sailboat by buying a really long steel square tube.  As it seems others do, I'll probably start by making a flatbed trailer and then figure out how to cover it.  I don't have a great place to store the trailer except filling the garage or parking it on the street.  We'll see.

Flying lessons ... sort of
I'm building Goat as a trainer, so it seems ironic to get training to use my trainer.  That being said, just Friday I went out flying in a Cessna 172 with a friend and he let me practice being at the controls.  He configured the plane in slow-flight (~70kts) thinking that would better emulate the control feel of Goat.  There was certainly a difference in the need for and authority of the rudder that I felt.  I also did several turns around a point and turns to various headings.  If the opportunity presents itself again, I'd like to do some stalls to understand the buffeting feeling and the change in control authority leading to the stall.  General Aviation teaches spin-avoidance now instead of spin-recovery ... wonder if they also just teach stall-recovery?  Anyway, Aaron's comment was that I flew fine and should have no problems learning on Goat.

Uhg, that's a lot of things.

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