Gear Leg Fairings

So I started down this path years ago.  

First I tried to make aluminum gear leg fairings, and was not happy with them.  Made 1, never finished it.  I did not like how the two rode inside each other.

Then I thought about using the foam and fiberglass method.  The benefit to this is you can add a step.

When I had Langair make my extended gear legs, I asked them to machine a ridge into the gear leg for a step.  More on that later.

Then a member of the forum came up with a method to 3D print gear leg fairings.  I know (well knew) nothing about 3D printing and modelling, so I avoided this.  If I did not have the ridge on my legs for the step I could have just used the other members design.  Good old 'rule of 3's'.  Change one thing, need to change at least 3 more...

For months and months I have been thinking about and asking others what modeling software to use.  They all have their pros and cons... for now I am using OnShape.  It's free, with a catch.  Everything you model is public.  That is fine with me for now.

Then comes which 3D printer.... read lots of reviews, and finally decided on the Bambu Labs H2D (with AMS).  They had a Black Friday sale...

So now I have to learn how to model and print.  I gotta say this has been a fun journey.

The H2D is a BEAST of a machine.  I love it.  Works awesome.

OnShape is extremely powerful and fairly easy to use and learn.  There are tonnes of how to videos.

So I started off by printing a portion of the existing design from the other member of the forum.

Genius design.  Great job BS!

So I need to make mine a bit bigger.  I've modeled the first 9" of the fairing, as the gear leg is a consistent diameter that far down.

(Add OnShape pic here)

I had a bard time splitting the part in two.  The double curves got bisected, but I then learned that you can add parts together using the boolean feature.  That solved that problem.

Learning how to create screw holes... so far am failing.  Can't figure out how to locate the point on the curved surface.  I will get there... will just take some time.

So I took dimensions of the gear leg all the way down.  Next challenge is to determine the best method to narrow the fairing as it goes down.  The extrude function has a 'draft' feature.  Need to figure out the draft angle and I will try that.

I am used to AutoCAD 2D modelling (am passable at that... not great, but can make something look reasonable).  I am used to being able to specify exact distances.  You can do that with OnShape, but its not easy.  You freehand draw the feature, then add a dimension to it, then you can adjust the dimension.  Frustrating - but I am grateful to have a tool that I can use and learn.

First part of my design below.  Already seeing some problems now that it is printed.

It fits together perfectly... too perfectly.  There is zero slop.  Will be prone to crack.  This piece took 10 hours to print using PolyMaker PETG.  But the quality is outstanding.  Super impressed.  And I am getting the hang of OnShape.  Next step is to test fit and see what I need to change / learn.  Very excited by this entire process.

Test fit.  Fits very well... almost too well.  The two circles that hold the front together are just too tight.  They will snap together, but getting them apart is very difficult.

Version 2... redid the S curve that locks the two sides together... much better now.  Added the intersection between the fuselage and fairing.  Much better now, but could be a bit better.

The new model is about 80% done.  I am having a problem getting the loft as the S channel narrows to fully intersect as a surface.  Almost there.  Then have to add the screw holes, and lastly the internal donut for the step.  But its basically together.

So I finally plowed through and finished the model - only to realize I forgot the pins that interlock the top and bottom pieces respectively.  Print underway without the pins, but that will allow me to check the rest of the fit.  20 hour print for all 6 pieces (3 tops, 3 bottoms.

Very interesting journey to get to this point.  I am tempted to start over again (again) now that I am more fluent.  OnShape is so powerful, but you have to think like OnShape.  You can do so much with it... but you have to know how to accomplish a task.  Google Gemini (free version) has been my saviour.  I can ask it how to do something in detail, and it gives me step my step instructions.  You also have to think like the printer... and how it is actually going to make the piece.  Example... the pins and sockets.... easy enough to create... but the printer cannot print well a hollow with a flat interior end.  So I rounded them.  Hoping that will work.

First full size test print (without the pins and sockets) for general fitment.

Bit to snug in the middle around the donut for the leg step, and slightly to snug at the bottom as well.  Hoping that will be an easy fix to both.

Fixed.  Printed a test piece out where it was tight (around the ridge for the gear step).  Has a little bit of play, which was the intent.

Deciding on when or not to print a full test piece of the latest design, or just go for it.  Probably a full test piece.

Nope... printing a test piece with new settings and new filament.

• Using Polymaker ASA filament.
• Changed layer height to .15 mm
• Changed wall setting to outer, then inner
• Slowed outer wall print speed to 50mm/sec
• Slowed inner wall print speed to 200mm/sec
• Changed to 3 wall loops
• Sparse infill density to 8%
• Sparse infill pattern to adaptive

8.5 hours print time for 4 pieces.

I am getting some stepping on the ellipse.  I need to figure out how to smooth that out.  You can see it in the onshape model.

Progress!

• Changed the export settings from onshape and have almost completely eliminated the stepping.
• Printed test pieces with ASA.  Significantly lighter.
• Printing the starboard gear leg in its entirety in one shot.  30 hours.  Reduced layer height from .2mm to .15mm.
• Ordered some TPU.  That should make it a bit 'bendy' but printing it 9" tall will be a challenge.

First leg printed out of ASA installed.  30 hour print.  Weights 1 lb, 4 oz (565 grams).

Both gear leg fairings in place (temporarily).  Still needs to be silicon'ed in place.

I redid the fairings out of TPU-95A.  They have been primed and painted.  Installed today.

Main gear toe

5 years ago when i drilled the gear legs, I used a method on the forum to align the gear legs.  It was not the correct method.  I knew it as soon as I put weight on the gear.

At the time, I did not see any point in trying to fix it as there was a lot of weight to put on (engine, wings, etc).

I've checked the gear toe a couple times and knew it was out (toe in).

After consulting the gurus, today was the day to figure out how many shims need to go in.

Measured the toe in a 3 point attitude.

Rolled the aircraft into the hangar, and left the tail sticking out the door.

String line from the tailwheel, plumb bob on centerline of fuselage at firewall.  Taped the string to the floor.  Yard sticks on the tires and centered.  Measured from yard stick to string line.

Results:

Shims ordered from Aircraft Spruce.

Sims installed!  Had a delay as the axle bolts were not long enough anymore, so had to order and wait... done now.

Miscellaneous 'STUFF'

Have been diligently working away on a number of items.  So this is a real grab bag of things that are underway.

Headset Jacks

In my package from Advanced, I received a harness for all of the audio jacks.  4 phones, 4 mics, plus a hardwired music input.  I did tell them how long to make it :-).

I was debating on where to put the jacks.  There were a number of options:

1. Overhead cable cover (right behind the pilot / copilot's heads)
2. Overhead console (from Fibertech composites).  I have my tailwheel lock and light installed in here.  Could use the sides, but they are not terribly strong.

So after a bunch of debate I decided to put them where Glasair does.... in the aft center of the cable cover.  Most just drill holes and seat the jacks.  I decided to get a nice little engraved and painted plate to mount there.

I had been looking for an excuse to try Front Panel Express. They have their own design software, and give you a price.  Below is my final design using their software.

For small stuff, you can print to scale.  Below is a previous version of the design that I printed and checked.

I ordered the plate on a Friday afternoon.  It shipped the next Tuesday (I ordered 5 business day turn around, but they shipped it in 2).  Delivered Wednesday.

Cost:  $88 USD, $96 with Tax.  Shipping included.

Once received I cut the hole in the cover.  The panel will fit through the hole sideways if needed for future removal.

To secure the wiring, I took some standard plastic tie wrap mounts and ground off the sticky backing.  Took as much off as I could with a knife first, then use the belt sander on the rest.  Then I epoxied the mounts to the inside of the cover after sanding and cleaning the target area.

Then it was just tie wrapping the harness in place (taking note to ensure that the cables will not rub).

The cover easily slipped in place.

The harness is then tie wrapped to the vertical risers on the aft side (again, keeping them away from the cables).

Previously I had cut, fit and finished the overhead console that houses the cabin light and tailwheel lock.  Need to wire it...  

The ACM has an output for cabin lighting, that can either be 'always on' or switched.  I am going for the always on option.  2x22 gauge wires run along the upper beam and tie wrapped.  There is a 2 position connector inside the overhead console for easy disconnect if / when needed.  Have not terminated on the ACM yet, but that will be soon enough.

Temporarily wired to a 12 power supply to check connections.

Lastly, I finally decided to ditch the trike gear legs (ditch = remove from fuselage).  I had been leaving them on as it make removing the main gear legs super easy.  All the final hardware is installed on the main gear legs, so it was time.

Back to wiring... going to work on the rear first.  Belly strobe, elevator trim, etc.  Ordered all the RG400 I am going to need, so will get that soon hopefully.

Gear leg fairings

The build manual gives to options for gear leg fairings.  Aluminum or Fibreglass.

For aluminum, the fairing is two pieces (an upper and lower due to the flex in the spring gear), and  wrapped over the leg, with a foam support structure to keep its shape, with a piano hinge on the aft side to hold it together.  The brake line runs down the aft side of the leg, and holes are drilled in the foam for it to run through.

For fiberglass, the brake line is bonded to the aft side of the leg, and then foam is glued over top and shaped into an airfoil shape (using the front side of the leg as the leading edge).  Fiberglass is layed up on top of the leg / foam, and then finished.

The kit comes with material for both options.

The below describes my 2nd attempt.  The first didn't work out quite right.  Close, but not close enough.

The trick here seems to be that you need the piano hinge to line up exactly the same on both sides.  I accomplished this by laying both pieces of aluminum on the edge of a bench (leftover from my wing jigs).  Clamped it down, and then laid the piano hinge down and drilled it in one piece over both sides - with the intent to cut it later.

I predrilled all the holes on the piano hinge, then clamped it down to the table as well.

Once I had drilled everything I could, I drilled some extra deep holes into the wood and clecoed to the bench.  Then I could remove the clamps and drill the last couple holes

To put the bend in the skin, the manual recommends wrapping it around a broomstick.  On my first attempt, I wrapped it around an axle, and it worked OK.  However, the RV guys use a trick to bend their ailerons and flaps.... Make a channel slightly wider than your bending form (AKA broomstick), and then lay your material down, and force the broomstick into the channel.

I raised my tabletop up off the bench to get clearance.  I had some scrap MDF strips laying around (about 3" wide) and clamped them to the top.  Again, needs to be a hair wider than your broomstick.  Mark the centrelines on your piece, line it up, and push the broomstick down.

I used clamps to force the broomstick down.  In the past I had glued / screwed this contraption together, and then you can just straddle the piece and step on the broomstick.  Clamps work once you get them aligned.

This also worked out nice for taping the trailing edge.  Leave the piece in the form, apply tape (I used Gorilla brand duct tape) to one side, then aligned and pinch the trailing edges together and push the tape over the top.  Worked out real nice.

And voila!  Bent and taped...

The above is both pieces (upper and lower).  I fed the lower down through the top to check the overlap.  I need to take about 3/32 off the lower piece before drilling the other half of the piano hinge.

You can see my first attempt the lower part of the gear leg.  Also, you can see the mounts I have made...

After trimming the lower leg to fit inside the upper, I marked and drilled the 2nd half of the piano hinge using the same method - but with the 2nd half of the piano hinge clecoed in place.

At this point, the piano hinge is still one piece.  I figure this is the best way to make sure it lines up.  Need a small gap between the two halves so there is room for it to wrap around.

Two halves joined with the piano hinge.  The alignment is pretty good.  The lower half needs a small trim on the trailing edge for them to line up perfectly.  The nice thing is its super easy to see now.  Will take it to the sheer in a couple days.

Overlap detail.  No real way around this.

Left hand gear leg fairing installed.

I am fairly happy with this one.

Now I just have to replicate it one more time...

Extended Heavy Duty Main Gear

 The gear truss upgrade done earlier in 2021 was in order to be able to handle larger main wheels - specifically 31" Alaska Bushwheels.

Ordered the legs from Langair in January, and the arrived early April.  I had a shoulder added to the leg to be able to add a step at a later date.

Drilled a small hole from the top of the gear socket down through the fibreglass (with a very long bit), then opened it up with a unibit, then a small drum sander on the end of a drill.

There was some corrosion in the sockets, and some overspray.  So again, with a drum sander I very carefully cleaned everything up, and then cleaned out the socket with some WD40, a rag, and a long screwdriver to push it through a few times.

They are REALLY tight.  Had to pound them in the last inch with a rubber mallet.  Hopefully they come out again :-)

I bought two 100" lengths of 1.5 x 1.5 x 0.25" angle for levelling the legs and setting the toe.

Next step is alignment.

There have been a huge number of posts on this subject.... but here are the goals:

1. Level the legs.  Each leg needs to be within 1/8" of the top of the socket, and the gear legs need to be level from side to side.
2. Set the toe.  For tail drawers, we want somewhere between 0.5 and 1 degree toe OUT.

With the fuselage level (by adjusting the tire pressure), I inserted the legs.

The manual states to grease them, which I did.  They move steadily with the liberal application of a heavy rubber mallet.

My original plan was to clamp the aluminum angle to the outside of the axles.  Yeah, bad idea.  Using the forum, turn the axle around (temporarily) and bolt them to the INSIDE.  Trimmed the aluminum angle down, and presto

After lots of frustrations with clamps and blocks of wood, I decided to make a platform that the aluminum angle sits on.  using various shapes and sizes of wood I had laying around, I lifted the angle into position against the axle.

I achieved the initial goal of having the fuselage level, gear level, and 0 degrees toe.  However, I am slightly out on the pilot side gear truss.  It needs to be within 0.125 of the top of the socket, and currently it is .142.  I need to move BOTH sides up slightly.  8 whacks of the mallet on both sides brought the left side into .121, and the right side is slightly proud.  Level shows that the gear legs are 0.05 degrees.  I am good with that.

(NOTE:  The below procedure did not work.  Follow up on the end about what to do to fix it.)

Inserted an .030 shim on the INSIDE of my turned around gear leg on both sides.  Bit of mallet work, check level on everything again, and that should give me a little bit less than 0.5 degree of toe out.  I am gong to work the math tomorrow to validate, plus I have emailed the forum for double check guidance.

I haven't done much trig in years, but with the help of google I figured it out.

Radius of the tire = 15.5" (31" bush wheels)

Axle length = 4"

At 0 degrees toe (which is 90 degrees for the triangle formula), the hypotenuse is 16.008".  Adding shims to the hypotenuse, then solving for the to angle.

0.030 shim = 0.43 degrees / 0.23" of toe (per wheel - 0.46 total), 

0.040 shim = 0.6 degrees / 0.32" of toe

0.067 shim = 1 degree / 0.54" of toe

I drilled everything, and pushed it outside, put on the tires and measured the toe.  Definitely toed IN (not desired).

Rough toe measurements with tired on (I am going to repeat this again with angle on the ground.

Front:  102"

Back:  104"

Toe calculator (inches to degrees):  https://robrobinette.com/ConvertToeInchesToDegrees.htm

According to this, I am about 3 degrees toe IN, which is bad.

With everything apart and back in the garage and levelled, the legs are again slightly toe OUT.

The only good news is the legs are exactly level.

I am going to stop working on the gear at this point.  I think once the wings, engine, panel, interior, etc are all installed the toe measurements will again change.  So there is no point fighting this now, just to fight it again later.  My gut says that once there is weight on the gear, the toe will go out, but I don't know how much.  Shims are available to change the toe angle, but I don't know which ones to buy.

Moving on to something else...