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!

Sunday, July 3, 2016

Covering order prep

I'm pretty sold on Oratex at this point.  The process is essentially like covering a model airplane and there is no painting (and associated spray equipment) required.  So all I need is the covering, glue, tapes, and rib-stitching stuff.

How much covering is the big question to answer.  A standard Oratex roll is 71 inches wide (or 34.5 in, but that seems less practical) and cut to length by the meter.  Measuring out the components yields the cut-list:

  • Wing bottom: 48 x 228 in (2x)
  • Wing top: 54 x 228 in (2x)
  • Aileron: 15 x 122 in (4x)
  • Flap: 15 x 94 in (4x)
  • Rudder: 28 x 48 in (2x)
  • Stab, Elev: 40 x 100 in (2x)
  • Vertical: 36 x 88 in (1x split into two triangles)
  • Nose: 40 x 78 in (1x)
  • Cabane: 24 x 52 in (4x) and 24 x 20 in (2x)
I originally had the aileron and flap as one-piece, instead of top/bottom, but this way will fit a wing top/bottom and an aileron/flap top/bottom in the 71 in of the roll.

I drew up a roll in CAD and tried to fit the cut list on top of it, tetris-style.  What came out was a total of 33m to cover all the pieces with 2" edge distance between parts.  It's 82400 in2 onto 92244 in2 of covering for a utilization factor of 89%.  The extra will likely be useful in lieu of anti-chafe tape.  For reference, that 10% overage is worth about $350 in 2014 prices, so it was worth the hour of CAD time.  I'll round up to 34m to be safe.

The price list I have from is from Feb 2014, listing $109.95/m.  With the US Dollar strong against the Euro for the past year and a half, there is no reason for 2014 prices anymore, aside from whatever stock the distributor purchased at old prices.  The other option is TLAC in the UK (the Pound is really down against the Dollar right now after the Brexit vote), and their online price list is from May 2013.  Oil is also down 50% over the 2014 time period, so everything points to this being less expensive than it appears on paper.

For the adhesive, I read on another Oratex covering blog (here's another good one) that 1 gallon of adhesive matched up to 36 yd of fabric, so it's probably about the same for me.  It only comes in 1L or 5L increments, so I'll probably buy 3L and get more if I run out.
  • 34m ($109.95/m) Oratex UL600 ($3738.30 from Feb 2014 price list)
  • 10m (1 roll, $39.95) rib-lacing cord, colored-matched ... or 500 yd white for $45 from Aircraft Spruce
  • 25m x 25mm (1 roll, $89.95) straight-edged tape, color-matched
  • 3L ($61.95/L) hotmelt adhesive ($185.85)
  • 7 x 10cm felt blade ($11.95)
  • 2m release paper ($4.95)
  • Total: $3986
The 82400 in2 also should give a clue of covering weight.  82400 in2 is about 53 m2, and at roughly 100 g/m2 for the covering, gives 5.3 kg (11.7 lb) of fabric.  Last time I weighed Goat, it was right at 100lb, so still well within the 154 lb Part 103 limit.  Adhesive will certainly add some more, and I haven't re-weighed after adding the 4lb seat, but it's still well within the ballpark.

Workin' at it.  What am I missing?

Sunday, June 19, 2016

Tons of work accomplished

New bolt to support the forward cable guides:

Tail skid now more roundy.  All I did was rotate it 90 degrees and round it over slightly.

Rivets for the ailerons:

Added a tube to mount the seat:

Added the slots to mount the aileron crank plates.  I'm a bit sketched out putting slots into a tube like this, but was willing to give it a try because I can always remake the tube if I need to:

Working to replace this sketchy wing bracket.  This is the before picture.  Note the small distance between the bolt and the edge of the bracket on the left of the picture.

While I was replacing the strut bracket, it was time to work on the main load path in general.  The base tube (strut attachment though the nose) had holes for the strut brackets that meant I had to twist the struts during assembly to get the main pins to slip through the holes.  I remade the base tube (again) and mounted it to the nose.  It only took practically taking the entire nose section apart to get the old one out.  And then I spent a solid hour in the back yard aligning the struts and marking the holes before match-drilling the four holes one at a time.

After the strut carry-through was done, I put the seat back on.  Boy it looks good.  

And of course I sat in it and made airplane noises :-)   With the high edges, my hips are well supported, but I also can't get my feet on the ground anymore.

That's pretty much everything prior to a structural load test.  I'm debating a few options for what's next for that prep.  I can stay local and build a giant gazebo rig, or I can work on transportation to a large swingset a few hours south.  We'll see.

  • DONE new cabane aft tubes with sleeves
  • DONE cabane compression braces (some are loose after the cabane rework from G3 to G4 design)
Control surfaces:
  • DONE glass the right aileron ribs
  • DONE flip fwd aileron control horn bolt to other direction ... and switch to AN3-13
  • DONE rivet aileron crank tube to trailing edge (G4S4)
  • DONE aileron crank tube slots
  • change control stick axis bolt to drilled with cotter pin (will have to remove the torque tube)
  • sidewalls in forward nose section (G4N13) 
  • make a nose skid (G4N10)
  • DONE AN3-26A bolt into the forward line guide bracket, replacing a rivet (G4T14)
  • DONE round off the tail skid to be more roundy than pointy
  • DONE swage aft cables (4x remaining) 
  • replace lower horizontal strut to tail connection bolt with a longer one
  • check all bolts are appropriate grip lengths
  • DONE remake the wing strut bracket marked "replace" 
  • glass the ribs to LE and TE
  • stiffener for aileron control line 
  • leading edge shell (G4S9) ... the Colombian Goat uses a piece of sheet aluminum instead of foam
  • wrap every pulley with tape and heat shrink to hold stiff and straight
  • threadlock on every quick-link
  • check every quick pin for elastic retainers are both present and correct length (several are just singles)
Buy list:
  • covering and adhesive
  • (1x) 1/8" SS quick-link

Wednesday, June 15, 2016

Removing blue tape

I'm marking known tubes or brackets or bolts that needed to be replaced with blue tape.  I knocked 5 off with the work last night and tonight: trimmed the tube to length and sorted out the mounting to the other end.  Also trimmed the lower cabane compression strut and added the two washer + rivet retention onto the new cabane.  I'm debating to not add the upper compression strut. 

The new u-bracket is 1-1/4" channel instead of 1" channel, and thus the cabane fits within the bracket without any ovalizing.  I'm trading a little bump in the covering for a lot less pain. 

For now, feels like it's done.  Done tonight anyway!

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