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.

Sunday, July 17, 2016

Reinforcement patch time

Thought I'd post a picture of the reinforcing patch around the rudder control horn.  Went smoother than I thought by brushing a layer of adhesive and placing a pre-cut patch into the wet adhesive using the ends of the brush.  Then, I brushed more adhesive on top and immediately wiped off the excess.  Repeat all over the patch and give the weird overlaps extra attention, and use a little heat to help tack where needed, and viola!  I do have a couple of wrinkles around the perimeter that I can do better to remove next time.  For a first time using this covering system, I think this is pretty successful.

And that completes the covering (as far as I can tell) of the rudder.  Here is a picture of it mounted to the vertical tail structure.  It's certainly a different look not being able to see through the structure.  I suspect that covering will turn this Goat from a collection of tubes to a real airplane :-)

I'm thinking of a painting scheme similar to the "Irish Mountain Goat" of white and lime green leading edge trim:

Saturday, July 16, 2016

Covering the next task

I received a "current" price list from dated March 2015, with unchanged prices from Feb 2014: $109.95 for a 1.8m width, per meter.  That's just bonkers considering the changes in the world economy in the last year alone.

Direct from is 69.96E ($77.30 at 1.11). I did contact them asking if they updated their price list each year, but did not ask about exporting directly, since they already have a US distributor.

From a UK distributor named G-TLAC, the price list from May 2013 from their website lists 60.42 pounds ($77.94 at 1.29), though I am unclear if/how VAT plays into the price.  They emailed back and said they are unable to sell to the US.

All this is to say that the price from BAF is high and I don't get it.

Another couple Oratex blogs:

So after all of this back and forth trying to find a good price for Oratex, it was time to research some other options.  I've read internet posts about using the normal polyester process and then latex house paint.
The covering option that looks good to me is Stewart Systems.  It is water-borne and has no real smell.  Looks like Ecobond is the same as 3M Fastbond 30NF.

Looks like the Ekofill layer (the filler and UV blocker) is made from coal ash, according to this guy.  It only gets about 300 ft2 of covering per gallon, and so would take around three gallons at $180/gal from spruce, that adds up quickly.

After all this research, I've decided to go with the the 3M 30NF and sprayed latex primer/paint.

I ordered a quart of 3M 30NF from Amazon for experimenting by covering the rudder.  Turns out their quart quantity only comes in neutral color.  No matter as long as I'm careful to get the right coverage.

 I started by cleaning the structure very well with alcohol.  It was mostly dusty from sitting in the garage.  This part was originally built in Feb 2009!  Next I took cloth tape and covered over all the sharp edges, to include the rivets and exposed ends of the tubes.

The uncovered rudder with cloth tape weighs 537g for reference.

I trimmed a piece of polyester fabric a couple inches large and it weighs 45g.

The first step was to brush adhesive on the structure around the perimeter and let it mostly dry.  Then I laid the fabric over the rudder (slitting for the control horn) and hand-pressed it against the semi-tacky adhesive, all the way around.  A small heat iron set to 250 deg F helped set the adhesive around the edges.  I brushed another layer of adhesive around the perimeter, wiping the excess off, and let that mostly dry.  A quick trim of the excess and ironing down the inside finished the first side.  Trimmed first side weighs 588g.

Flipping it over and doing a gentle 250 deg F shrinking pulls the fabric taut enough for doing the second side.

Repeating for the other side using pinking shears to keep the edges clean, and it's ready for patches.

If I'd known it was this easy to cover with polyester, I wouldn't have put in all the effort on acquiring Oratex.  Maybe I'll be singing a different tune while painting, but only time will tell...

I have not forgotten about the load test.  I wanted to get myself spun up for covering as a way to encourage myself to do the math for the load test.

Other than that piece of business, I cut out the rest of the leading edge shells.  Whew that was some CNC time, but tolerable using the variac to help knock down the noise levels!  I also tried to cut the strut fairings on the CNC.  The fairings would be much easier to cut using a hotwire, which I don't currently have.  But I can see the shapes and cut templates for borrowing a hotwire from a friend.

Monday, July 4, 2016

Leading edge shell cutting

On a rainy Independence Day holiday, I spent some time cutting the leading edge shells on the CNC machine.  First I cut a piece of cardboard the size of the stock (6 x 1 inch) and then traced the airfoil profile onto it.  This was laid onto the ground and a photo taken from directly above.  The image was imported into CAD, sized, and a spline used to trace the airfoil curvature.  After extruding, some other features were added to the ends to fit the ribs and make reliefs for the rib angle brackets.  That solid file was imported into CAM and I set up a cut sequence, primarily chordwise, with some extra attention around the edges.

Cutting the first part out of some scrap identified some minor changes to the part.  After making the adjustments and a quick trip to Home Depot for more foam, I set up the machine for running back-to-back parts.  The 20 minute time between parts then became a rhythm of hearing my watch beep, going to the garage to service the machine and index to the next part, hit run, reset the timer, and walk away.

I taped a few of the pieces to the wing leading edge between ribs.  It fits really nicely and supports the ribs as well.  I'm thinking of glassing the back of the foam shell pieces and then also glassing the front once the pieces are all bonded to the wing.  That should provide some extra ding-resistance and robustness.

Another minor change, I finally tried adding a variac to limit the voltage input to my router (poor-man's spindle).  Previously, it ran full 1.75 HP continuously and was rather loud at 30,000+ rpm.  Now I'm running about 50% voltage, which still appears to cut foam quite nicely at the lower RPM, and quiets down the router below the noise level of the shop-vac dust-collection system.  Didn't even have to turn up the TV in the living room, which shares a common wall with the garage.

Happy Independence Day!

Locations of visitors to this page