Sunday, February 5, 2017

Ch 9.5: MLG / Fuselage Intersection Fairing

Now that the MLG fairing is done, there needs to be an intersection fairing that makes a smooth transition between the fuselage and the MLG.  The key here is that it has to allow for movement between the two.  With weight on the gear and on landings, the gear strut will flex up so the fairing has to allow that without breaking anything.

I really liked Wayne Hick's solution.  See his instructions here for details.  I will only summarize my attempt at it below.

 For starters, I crafted the fuselage side of the fairing out of left over 3/8" PVC foam.  This will form the curvature to the fuselage.  I used the large end of the Eureka CNC MLG fairing I had trimmed off as the template for the airfoil shape.  In the pic, you can see the before and after shaping the contour.

I glued the top side of the fuselage faring to the fuselage using scrap pieces of 3/8" foam to ensure the necessary clearance between the fairing and the MLG.  Afterward, glue the bottom portion to the underside including the MLG cover.  Don't worry, this will become a permanent part of the cover but it will stoll be removable when done.

Now I used other scrap Last-A-Foam approximately 2" wide to serve as the transition from the fuselage-side fairing to the MLG fairing.

I glued it to the MLG fairing butted up against the fuselage-side fairing.  I used expansion foam to fill in the gaps and began sanding to match the fuselage fairing and gently fair it into the MLG fairing.

Here you can see the both starboard (left pic) and port (right pic) from the nose looking back after being sanded to shape.  I'm not sure how I did it but I seemed to be able to shape them almost identical without the use of any templates.

Not shown (sorry) is the shaping of the back edges curving into the fuselage.  See pics below after glassing.

Once I was happy with the shape, I glassed the bottom of each fairing with 2xBID.  I wrapped the leading edge up past the center point and left an overhang at the back supported with card stock.

Here you can see the back edge after glassing the bottom and some trimming and sanding to blend into the existing MLG fairing.  Once I had it the way I liked it, I used a piece of card stock to form a template so I could get the other side to match.

I removed foam from the aft edge and used micro to fill the wedge where the top glass would meet the back edge.  It worked pretty well.

After all the glassing was done, I used an xacto saw and a Dremel with a small saw to carefully cut along line separating the PVC foam from the white Last-A-Foam.  I used a sharpie to help mark it.

After cutting the fairing loose from the fuselage, I used folded over sand paper to clean up the cut line for a nice look.  I also removed the gear and painted the exposed foam inside the fairing with micro to protect against water intrusion.  I also wanted to ensure water could not get trapped anywhere in the gap so the smooth micro finish helps ensure the water drains out the bottom cut line.

MLG Cover on the bottom with
Intersection Fairing mods
I uncovered a problem after separating the MLG cover on the bottom.  I found that I would need to make a few adjustments to accommodate where the corner screws landed for my cover.  I didn't see that coming.  I couldn't move the fasteners without causing a conflict with getting the gear in and out when needed.  So I made adjustments to the intersection fairing on the bottom.  I think it turned out fine.

Main Gear Fairings & MLG Cover Complete!

Sunday, January 22, 2017

Ch 9.5: Gear Strut Fairings

Pick'in up Some Knots

Top View of Eureka CNC Fairings
Side View of
Eureka CNC Fairings
Although the MLG strut has an airfoil shape to it, it's formed in way that puts it out of alignment with the air stream when it's in cruise.  That creates unnecessary drag which reduces speed and fuel efficiency.  Several builders (Wayne Hicks, Kevin Walsh, and others) have formed fairings over the strut to realign the aerodynamic shape which reduces drag and increases speed. Kevin and Wayne did it slightly different but the result is very similar.  Kevin worked to have his made available through Eureka CNC.  These are what I used.

The fairings come in two long straight pieces that won't bend around the curvature of the strut so you have to cut it into pieces.  I cut it into 8 pieces, larger widths toward the top and thinner widths where the strut curves sharper.  I positioned the top piece about 3/8" gap from the fuselage side and went down to about the top of the brake heat shield.  I'm assuming that some of this will end up being trimmed off when the wheel pants are built and installed.

Test Fitting
Then I tested the fit by taping the pieces on each leg.  I numbered each one to ensure I put them on in the proper order.  Note that the closer to the bottom you get, the foam get's very thin and hard to keep from breaking.

Vacuum Bagging
To the left is my poor man's vacuum bagging technique with a small shop vac.  It worked well enough to keep the pieces all together and aligned while they cured.

To the right...taken after the foam has been micro'd and glassed with 2xBID. Notice the white trailing edge.  I glassed the bottom side first and then removed foam from about a 1/4" or so on the top at the trailing edge, filled the gap with micro, and glassed 2xBID on top.  This gave it a nice solid sharp edge that should be able to survive a minor hit without permanent damage.

The bottom was trimmed off to be level while sitting on the ground.  Next there needs to be a fairing built for the intersection of the MLG fairing and the fuselage side.

Onward, cab