Just a bit more work on the trailer

Trying to check off some more items from the to-do list.

Here are the new 316 stainless bolts with the UHMW spacers and the wedge shims as well.  I may have the wedges tack-welded in place.

I drilled holes for the wiring in the ends of the cross-members.  This is a low-stress location and the nearby welds should be sufficient support.  I was careful to deburr the drilled holes also to prevent from making a stress-riser of a sharp edge or a crack.  That has the added benefit of not chafing on the wires.

Here is a shot of the angle that will be welded to two of the cross-members, in order to support the end of the 4x8 plywood decking sheets butting together.  I'm confident in this supporting the plywood.

It's progressing.  Work remaining prior to welding:

• Drill holes for wiring to pass through the ladder rungs' webs.  It's much easier now than later.
• Mount the trailer tail-light brackets with a UMHW spacer for dissimilar metals.
• Buy & mount the amber side-lights.  This is probably fine after welding though.
• Make additional wedge shims and position those for welding

More trailer work prior to welding

The suspension is a small leaf-spring that attaches to a couple pieces of painted steel angle brackets.  It is this bracket that I will be bolting to the aluminum frame.  To avoid aluminum / steel contact, and to provide some spacers, I added UMHW plastic shims (white) that are rated for outdoor UV exposure.  

The axle needs to be positioned to give 10-15% tongue weight based on my extensive education watching YouTube (LOL), so the holes will be drilled after the whole trailer is assembled.  

There will be two holes in the shear web (less critical) and one hole drilled in the bottom structural cap.  Drilling in the caps is more detrimental to the structure, so I want to minimize those and put any in places that are less stressed.  For the trailer's loading, I expect the upper caps in tension to be more critical than the lower caps in compression, so I'll only accept holes in the lower caps.  Further, the overhang aft of the wheels seems more stressed than between the axle and tongue, so I'll avoid drilling into the lower caps aft of the axle.

I made some wedge shims to make any bolts going through the caps have a flat surface to tighten against.  These are cutoffs from the end mitering with a hole step-drilled up to the right M10 diameter.  Six were needed for the hitch bracket.  Thinking ahead, several more of these can be welded into the cross-members in places where I'll bolt down the decking (I'm still thinking marine / outdoor plywood to get over a couple seasons).

Thinking ahead for the decking, I bought some angle 6061 aluminum to weld onto specific cross-members so the plywood decking has somewhere to rest its edge (4x8ft, 4x4ft, 4x8ft).  These should be easy to weld in place.

I also bought new 316 stainless metric hardware to replace whatever was rusting on the old trailer.  The aluminum / stainless is unavoidable, but I am minimizing contact where possible to try avoiding galvanic corrosion.  Anyone have a suggestion for a grease or coating that I can spooge / spray over the area?

I did talk with a work colleague who is a professional welder, so one path toward completion is opening up.  There is some work on my end remaining prior to welding still, so no action other than making the contact at this point.

The tail light brackets were quick.  They do still need UHMW spacers between the pot-metal steel brackets and the nice aluminum frame.

Work prior to welding:

• Drill holes for wiring to pass through the ladder rungs' webs.  It's much easier now than later.
• Mount the trailer tail-light brackets with a UMHW spacer for dissimilar metals.
• Buy & mount the amber side-lights.  This is probably fine after welding though.
• Make additional wedge shims and position those for welding

Metal for a Goat trailer frame

The Goat saga continues!  I can never do something the easy way when it's quicker.  Instead, things must be done right.

I had the bright idea to build a custom trailer, which seemed the smartest way to transport Goat by Prius.  The caveat is that I have to design and build a trailer too.

A massive thanks to a friend with a sailboat trailer for spending a few hours helping me pick up the metal.  I bought four 20-foot sticks of 6061-T6 American Standard 3-inch by 1.4-inch by 0.188-inch structural c-channel.  It was going to be super sketchy to transport the 20-foot pieces on my tiny 8-foot trailer, so it was much nicer to use a trailer already set up for things of this length.  Thanks Sam!

With the material at home, it was time to start chopping and mitering to make the structure fit the way it needs to.

Here are some close-ups of making the miters for the ends of the center supports.

All of these cross-pieces are inserted as ladder-rungs into the uninterrupted c-channel side members. 

I chose to make a new tongue with the material (instead of more cross-members).  The tongue plate bolts on just fine.  This should work dandy.  The tongue pieces will be welded on the bottom of the frame, not exactly as shown in the mockup photo.

Tomorrow will be looking closer at the axle, and then prepping all the lights & wiring.  I can't weld aluminum, so it's either asking nicely for a favor from a friend or taking the parts to a welding shop.  The more prep-work I do, the quicker / cheaper the welding will be, so I'm going toward that welding as prepared as possible.

Comments welcomed.

Gap seals are all done (updated)

Not entirely sure why the time was right now to do the gap seals, but they're all done now nonetheless.

By the time I got to doing the last aileron, I finally had the wing gap-seal technique down...

• pre-shrink the cloth to 120C.  Its texture is mottled, but that's okay
• use a piece of blue painter's tape 6in in length for marking.  Find the attachment 2" on the wing side, and locate using the TE adhesion point as the alignment feature.
• hold the 2" fixed side in place with a thumb and flex the surface through its range, which will pull the loose end of the tape to reveal the end of the 6" strip.
  
• figure out the end of the adhesion on the control surface
• mark the ends and the adhesive contact point ends.
• pull a string or a flexible long straight-edge to mark down the length of the whole wing.
  

That isn't a complete description for marking, so ask in the comments if you want to use this method and need more.

• once marked, put adhesive on both fixed and control surface sides. Let dry.
• iron the fixed side on the wing.
• prop up the control surface at the angle of maximum stretch of the gap seal.
• pulling a 3" section at a time, iron the gap seal to the control surface side pulled taut.  There will be some wrinkles still, but get it overall pretty close.
• iron the control surface side of the gap seal
• increase temperature and pull the gap seal itself taut across the gap.  Flex the control surface occasionally to make sure you're not over-tightening.  If so, the Stewart Systems method allows the gap seal to be pulled off without penalty.
• second gluing and wiping (only on the glue joint).  Let dry.  
• iron at quite a warm setting, including tightening the gap seal to its final stretch.  Do this with the control surface propped up again.
• paint 2x coats of Glidden Gripper white primer diluted 3:1 paint to water ratio.  I do one coat horizontally, then one coat vertically with a foam brush.
• lightly sand with 220 grit the pinked edges and remove any boogers to make the skin surface smooth
• final coat of paint
• accept imperfection

Marked for the gap seal, ready for adhesive:

Just starting the fixed side pre-placement before ironing:

Flap gap-seal done, showing how it looks, with the aileron (foreground) ready for the fabric.

Aileron gap seal done & painted:

No word from the DMV yet on the trailer title & tags.  Based on previous timing, I'm not expecting anything in return until about November. (updated: it arrived the same day of this post!)

What else remains?  I pondered this recently...

• DONE - Get trailer title & tag
• Modify trailer to safely haul Goat
• Find an appropriate airfield to do the maiden
• Mount GoPro(s) for maiden flight documentation
  
• Backyard final assembly and thorough pre-flight check, including weight & balance
  
• Go do the first flight!
  

Some other things on the eventual list...

• add leather patch to wing tips where will rub the ground
• install leather patch guides for elevator control lines
• replace the nose tube (because the holes are twisted)
• Trim color paint
• Wing root kiss seal
• Wing tip dolly
• Wing wheel
• Strut fairings (after flying to figure out the right angles)
• Emergency parachute
  
• Real variometer (LXNav with a TEK probe is my intention, if it is sensitive at low speed...)
• Drogue chute
  
• Motor mounting revisit (need guy-wires that means some un-covering and subsequent repairs)
• Finding a "real" field for flying more regularly
  
• Place to store goat at home and/or at the flying field
• USHGA "hang 3" rating so I can fly at cooler sites??

Super random ---- I made it by the US National Sailplane Museum in Elmira, NY and found two of Goat's cousins:

Gap seals

Time flies when work is crazy.  Last post was in March...

Just about the last thing left on the build list is gap seals for the control surfaces.  To start, I used some blue painter's tape to determine how the gap seal worked relative to the hinge geometry.  The next sequence of photos shows starting from full deflection one way toward full deflection the other way.  There is definitely a point in the middle that is the, let's call it: "max stretch" where the tape is taut.  If there is any less material than that, the control surface wouldn't deflect all the way.  Good to know.  There will definitely be some slop in the gap seal material at anything other than the taut position.

I started with the rudder.  This photo shows mid-process with one side gap seal already glued to the rudder.  You see one side is bonded and the fabric ducks through the vertical tail (on the left) to rudder (on the right) gap; the flap of material is then similarly bonded to the vertical tail.

I did pre-shrink the gap seal fabric to 120C to make sure it didn't shrink during the adhesion phase (the covering glue joint is lightly ironed during this step).  It didn't work perfectly to pre-shrink, but it only has to keep out the air.

The horizontal tail was done using four pieces of fabric.  This was not quite as difficult since this fabric is just flat.

In related news, I took the motor system back off the nose section for some re-thought about how to support it with additional guy-wires or other structural member(s).  It won't be installed for the maiden, so it was going to come back off regardless.

I do have one piece of good news about the trailer.  It now has a VIN number.  Fourth letter to the DMV was the charm.  Each rejection cycle was about 3 months, so this has been quite the ordeal.  The final form has been mailed for a title and tags this time.  Keep your fingers crossed that the next mailing from the DMV is the actual tag.  With a tag, I can finally figure out final details about transporting Goat to an airfield.

Speaking of flying, if anyone has access to a good place for a maiden flight in the northern Virginia area some time late fall, I'm in the market and would love to make some new friends!  It'll be a whole sequence of low-altitude car-tows to start, so car access to the runway access is required.  A huge grass field with crops around is my thought.

Installed motor test run!

With a good friend, we did a few test runs of the installed motor & power system.  

Here is a very short run just to show you it spins.

Firstly, it is quite scary sitting that close to a spinning motor putting out 4.5kW.  Wearing a helmet helps, but it's just a LOT of power super close to your body.  Neither of us ran beyond 100A and we both kept our feet on the ground out of the plane of the propeller ... just in case.

At about 60-70A, there is a slight structural resonance in the nose tube assembly.  It's not present on either side of that RPM, so we just tried to avoid that.  Balancing the propeller would help.  Tightening things up more should help too.  Most of the play appears to be in the nose down tube connections, at either end, so I probably will start with getting the proper length bolts everywhere and snugging things up.  Replacing the nose tube with an aero strut would probably make a difference.

The throttle in the end of the control stick did not work for some reason.  It moves a servo just fine, but did not move the ESC.  I suspect the ESC calibration needs to be done using the same throttle driver.  For this test, I used a different servo driver that was the one used to set up the ESC in the first place.

The batteries and the ESC and the wires all were quite cool to the touch, even after a 60s run.  Rough math suggests about 10min run time at 4.5kW.

I did try balancing on the wheel to see if the thrust would roll Goat forward.  The ground is pretty soggy and the tire was partly flat, so there was no forward motion.  Howe er, it was a definite feeling of being pulled nose-down.  This is not surprising given the high thrust-line and low pitch rotation axis (here: the wheel axle), but it was nice to feel thrust as an external force, if that makes sense.

There is a fair amount of air movement along the structure, most visible in some vibration of the inboard edge of the flaps.  There was a little drumming of the lower wing skin covering.  The rudder tended to center up with the airflow, but the elevator had enough bungee that it mostly sat stationary.  Nothing was scary.

Also, a weight check with a bathroom scale came in at 158lb including motor & batteries.  The motor itself is 5.6lb, so I am clearly below the Part 103 glider 155lb weight limit without the power system.  Adding propulsion essentially ups the legal weight limit to 255lb, so I'm also clearly below that.  Super.

 

What improvements are on the short list?

• Fix the throttle knob --- having throttle in the stick would be much nicer
  
• Improve the throttle wiring --- need a second look at the throttle wiring & battery location
• Tachometer --- having RPM would be really nice
• Move the wattmeter display? --- it was awkward looking down to the right for power readings
• Larger propeller --- the 30x10 just looks teensy.  May have to couple this with re-winding the motor for a lower KV, which is a much larger project
  

I'm also getting some hangar rash in the covering from strut or jury strut bolts poking into the covering.  Some of these looked avoidable.

Gap seal for the control surfaces is a necessary next step.  I really don't want to fly without gap seal.

Strut fairings is on the semi-short list.  It will fly fine without them, but I know the drag is unhelpful.

A trim color along the leading edge would be sweet too :-) 

Here's the battery tray installed.  It works.

Here is how the motor tube mounts.  It's sturdy in itself, but the nose tube seems like what is vibrating.

More work toward a motor-Goat

A test assembly outdoors was necessary to get the thrust angle to match with what I picked for the starting visual.  I suspect that some thrust-line changes will be needed based on cruise attitude and the pitch coupling (noting the Romanian Goat said it took a lot of up elevator in this mount location), but for now I simply set it parallel with the bottom of the wing and match-drilled.

Mounting the battery is the next major task.  With 25ft of 8AWG wire tripled over for an ~8ft extension, I was able to reach from the motor, down the nose tube, back along the nose side rail, to beside the seat.  Like most others, I'll mount the battery beside the seat.  Instead of mounting to the struts, I decided to extend the seat tubes to make a little shelf of sorts. It did take removing the seat and destroying a couple torque seal marks to get it all, but that was a fun afternoon.

Seat off!  You can also see the final structural mounting for the motor and see the wiring runs.

New little shelf.  In retrospect, I should have put it on the left side so my right hand can stay on the stick, but maybe next version.

And here's the first mock-up of the battery tray.  The ESC is going here also.

Let's talk a bit about the battery tray.  I watched several videos about the e-help and related DIY systems (this one was particularly useful) to decide a rough plan was to make a u-shaped tray with Velcro loops to secure the batteries.  The other major decision was to place the ESC directly on the battery tray.  The battery to ESC leads apparently need to be short due to inductance issues, and let the three phase AC lines be the long runs (EMI and start-up routine are potential issues).  

I ended up making a small aluminum bracket to hold the ESC.  This was the first time I bent up a complicated sheet metal bracket, and it went pretty well.

 

Here's how the ESC is held in its bracket.  It will be riveted (or bolted) to the bottom of the battery tray.  There is lots of metal surface area to help with heat transfer.

The battery tray itself was fabricated in a similar manner, bent from sheet metal.  The cylindrical bosses are handles.

And here are the batteries and a watt-meter (this model) mounted in the tray.  I still need to put slots for the Velcro straps to hold the batteries in place.  There will also be a couple switches in the panel for ESC arming and the throttle power.

The last major component to solve is/was the throttle actuator.  For this ESC, I need a PWM signal going from 1.0 to 2.0ms and bringing its own power (the ESC is opto-isolated).  The awkward part to me was that no small servo driver had a convenient remote-mount potentiometer.  I ended up buying a $7 servo driver, de-soldering the rotary potentiometer, and remote-mounting it in a custom 3D printed mount that will fit in the end of the control stick.  I stuffed the servo driver inside the same 3D printed mount, so I only need to run it power and get back the PWM signal.

Here's the final servo driver and remote potentiometer arrangement.

The bracket fits inside the control stick tube (ignore the holes --- same size tube from the scrap bin!).

That's all for now.  I'm still working on tidying up the wiring for the panel and then will need another beautiful spring day for a test re-assembly and run in the back yard.  Stand by for more...

Motor mounting comparison to other eGoats

I've decided not to mount the motor in this traditional location behind the seat.  That location is closer to the CG, so it makes sense for very heavy engines to have a smaller impact on balance.  That location is also large enough to eat a reasonably sized propeller (~49in).  But, it is almost entirely shielded by the pilot's body, meaning there is a lot of turbulence that the propeller has to eat.

Here's the Lima Goat (Pelican) with the typical motor mount location.  From what I can find, this setup is ~20kg according to Alex Ferrer in a YouTube comment (6.4kg motor Freer 202/80 27, 1.9kg KBL ESC 72V-144V/400A, 6.68kg six CNHL 6S 8.0Ah =1kWh, ~2kg wood prop 49x30in == ~30kg thrust, ~6min WOT or 10min sustain for 170kg TOW)

Instead, I'm going out front on a post ahead of the forward nose tube.  This is a traditional location for human powered aircraft (e.g. MIT's Daedalus), and the Romanian Goat was the first Goat that I've seen to do it.  It puts the prop in the cleanest air possible, allowing getting the most out of the propeller efficiency (prop selection matters too, but so is getting the most from that installation by putting it in clean air).  A typical downside is the forward location doesn't match well with heavy internal combustion engines without a long driveshaft.  Even human-powered aircraft usually have a long driveshaft arrangement to make it work.  For me, I went for a minimally sized motor, so the balance works out just fine, and I really need to maximize the propeller efficiency.

Here's the Romanian Goat with the forward motor mount.  From what I can find, this setup is 28kg (4.44kWh battery, 20kW motor (2350rpm, 78kg thrust), 1.3m Helix 3-bladed prop, 45min runtime).

Here's the first mock-up of my selected mount location.  The motor is mounted on its tube (yes, the prop is on backwards) and clamped very roughly in the right place.  I'm planning to pin the mount to the nose tube and support it up from the nose tube roughly parallel to the prop.  If it does not feel sturdy enough, I can add guy wires from near the motor to the leading edge of the wing, which should be more than sturdy enough.

Key weights so far come to 9.3kg (2.5kg motor, 0.4kg ESC, 3.2kg for four 6S 5Ah = 0.4kWh).

What about a motor?

I visited the two local (hour and forty-five minute) grass strips to the West that almost certainly will not allow a car to drive on the runway.  So, what's plan B?

I found two local paved runways (about an hour and a half away) to the East that are in Class G airspace and look to be very low traffic.  Assuming I can't get a car on those either, what's about some power, cap'n?

Came across the E-Help Student system on YouTube, built for ground launches of a hang glider.  With the similar wing loading of the Goat to an old hang-glider, this seems like it'll be just about right to be a sustainer.

Cue some pictures...

Mounting the Rotomax 150cc motor to a 2in tube took some sheet metal brackets.  Not much sheet metal work on a typical Goat, so went out to buy a small sheet metal bender from Harbor Freight to bend these two.

The wiring harness was not the most glamorous task, and I'm still going back to look at the XT90 connectors once I take some measurements of the current during ground runs.

First test runs were literally on the bench in pusher mode.  The ESC needs some settings tweaks for softer start, and the brake needs to be on, but she does spin.

Next is figuring exactly how to mount the motor.  The two main options are behind the seat, like most powered Goats, or on a post ahead of the seat forward of the wing leading edge.  That'll be tomorrow's game before the big game and snow.

Other to-do's:

• Gap seals for the control surfaces
• Trailer tags (paperwork in the mail for the fourth time)
• Carrier cradles for on the trailer (started)
• Line and release system for auto-launch