Tow-release from a car hitch

One hobby deserves another ... a TIG welder and necessary accoutrements are on the way to me from somewhere in China (surely!) and from New Jersey (seriously).  It'll be a few weeks for all the stuff to arrive.  And I'll likely have to figure out a 220VAC plug in the garage.  And burn some metal practicing.  Lots of practicing.  But then, I'll be able to start the trailer welding.  Don't take the sarcasm wrong!  This is exactly what the hobby is all about for me: doing something independently because I can, not because it's the quickest (or least expensive).

In the meantime, I started up a small project that will leverage the welder, and clear a nagging infrastructure equipment issue.  For the auto-launching, I really want a release mechanism for the tow vehicle.  The same Prius that tows the trailer can double as the launch vehicle.  The trailer's tow hitch will be pulled out and a new one inserted, which has the release mechanism already attached.

The main two requirements for the release mechanism are:

1. Allow the line to be pulled in various directions and still transfer the towing force safely.
   
2. Allow the driver to pull a release handle that opens the line.

Personally, I've made a few release mechanisms for RC applications that all worked mostly fine.  The ones that didn't work usually jammed because the pull-pin was side-loaded.  This leads me to reconsider those exact mechanisms.

After some looking around online, the Tost release mechanism is standard in nearly every sailplane.  RC hobby aero-tow folks and hang-glider winch-tow folks have different typical release mechanisms, likely owing to their lower load cases.  In-between is something akin to the Schweizer release, with a simple hook on a rotation pin, and a small lever-arm to release the hook end.  I found the Schweizer release is sometimes used on the back of the towplane to release the sailplane or a banner.  Time to copy the good idea...

I started with CAD to draw up my impression of a Schweizer release and printed a few 3D plastic parts.

An assembly with the 3D printed parts is a wonderful way to understand the mechanism and check its functionality.  This always feels like a wasted day as I impatiently watch the printer print, but ideas and tweaks always come from spending the time staring at a single part as it prints.

With a total assembly, I went to the back of the car to see how it all fits.  And yes there is snow on the ground right now.  I'm not 100% sure how the rope will route to the driver quite yet, but I can confidently say this mechanism will release cleanly once the line is pulled.  The large 3/4" bolt will also let the release mechanism rotate if Goat gets off of the runway centerline.  Seems plausible so far.

With all the fit-checking done, I printed 1:1 scale drawings, pasted on 6061-T6 aluminum with 3M Super 77, and started cutting, drilling, and filing.  Two hours later, it's starting to come together. 

It's working great so far.  Once it's all assembled from metal, I'll weld both the left line-guide tab and weld the release housing sides to the bottom plate.

Hopefully my next post will be of burning metal.

Probably the last trailer work before welding

I had a nice holiday break.  It was mid-60's at times and so it was wonderful to be in the garage.

I drilled small a hole for the tail light wires and routed them through.  It occurred to me at this point that the UMHW plastic spacer between the aluminum frame and the steel bracket would electrically isolate the ground line.  Doh.  I'll either remove the spacer entirely (and add dielectric grease), replace the plastic spacer with a sacrificial aluminum shim, create a jumper, or maybe just see if the stainless steel bolt does fine.  Thank you for the grease suggestions D.

While doing wiring, I did try out the wiring holes through the holes in the cross-members.  Here is a close-up shot of that, and you can also see how the c-channel mitering works.

As cleanup, I made sure that all seven cross-members had the same fit and exact same length (under a 1/16th).  It's overkill for a trailer, but why do something just half-way at this point?

I also cleaned up the 16 wedge shims with a center mark (no pic, sorry) and figured out where to mount them on each cross-member.  This is prepped for welding.

The amber side lights will wait until after welding.  I do have marked out places for 5x each side, thinking ahead that I won't want someone to merge into a dark space behind my car at night.  It should be hard to miss the giant white wings, but I'm not going to count on that.

I think that may be just about it for the trailer prep.  Welding is next.

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.