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Aileron Bell Crank Rib Brackets

We mounted the two vertical C shaped channels behind the aileron bell crank assembly.  There are little right angle peices that connect these channels to the skin.  All this extra structure is to stiffen the rib where the bell crank is.  The plans show to make the top face of the angle peices flush with the curvature of the rib flange, since both are riveted tot eh skin.  This took me more time than I thought it might because the rib flanges are not perfectly square, some are a little over bent, so it is hard to tell where to mount this angle bracket vertically.  Dan had a good solution to clamp a long piece of aluminum angle extrusion to several ribs on  either side of the bell crank rib.  The angle extrusion is stiff enough that it won’t bend so it will lay like the final skin on the ribs.  With the extrusion on the ribs, I could see the gap of the over bent rib flange, and mate the angle bracket to the under side of the extursion.  We think when the skin is riveted on it will pull the rib flange up a little.  Once we had the top ones done we moved the extrusion to the bottom as can be seen here :

Locating Bottom Skin Bracket For Aileron Bell Crank
Locating Bottom Skin Bracket For Aileron Bell Crank

Celco-ed Bell Crank Brackets:

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Top Skin Brakets Mounted
Top Skin Brakets Mounted

We took the wing structure apart do deburr the parts for priming.

Ready For Deburr-ing
Ready For Deburr-ing

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Aileron Bell Crank Assembly

Dan assembled the aileron bell cranks.  The bushing holes in the angle brackets were matched drilled, in the drill press, a little under and reamed to final size.  In case you don’t know bronze bushing are designed to be press fit onto bores but this casues the inner diameter to collapses a tiny bit.  We could just start the bronze bushing in by hand until it stopped.  We then checked the fit of the rotating steel bushing.  Dan polished the outside of teh steel bushing on the Scotchbrite wheel.  We thought it was good so used the arbor press to insert the bronze bushings.  There is a peice of phenolic to space the angle brackets.  We had to use a shim of paper on either side of the phenolic to get the rught feel.  (I would really prefer ball bearings  but given the limited motion of the bell branks this seems like a good design, but we both wanted a good smooth feel the rotation.)

For some reason our aluminum angle has a big inside radius so the head of the angle clamp bolt and the nut did not sit flat.  We machine a little spot face so they sit properly.  We will sand this area really smooth.

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Aileron Bell Crank Parts

We have been working on the Aileron Bell Crank parts.  Used the scan/print spray glue method for the parts that had make to print size on them.  After the root rib trim episode we looked at the how these parts are assembled.  For example the U channel parts are stiffeners on the rib behind the bell crank assembly.  The length should be accurate but it is position so there is clearance between the end and the skins.  So there is no need to be right on the 1/64 dimension, which might save a little time for making four parts.

Aileron Bell Crank Parts
Aileron Bell Crank Parts

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End Trim of Aileron Skins

April 30, 2012

Dan marked and trimmed one edge of the ailerons skins.


Dan compared the markings on the two ailerons to make sure the measurments matched

Here is the aileron counter weight arm hole

The plans show to cut out the slot all the way to the flange edge.  We are going to try to keep that connecting piece in and see if we can assemble the aileron.

Using the electric shears

Cutting outside the line and file it.

Trying to test fit the end rib.  The plan’s drawingg of this rib is really tricky.  Dan made a test run of this rib and that is what you see in the pictures.  It does not fit too well

Notice the corner sticking out.

The inside looks really nice.

Here’s that end rib again

We are going to check our pattern for the end rib and make another test end rib.

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Bending Flap and Aileron Skins

April 7, 2012

We recently bent the rear spars with “Big Bend” brake so we wanted to bend the aileron and flap skins.  We decided to build the aerobatic ailerons, they are a little wider and hence the flaps are a little shorter.  This makes the aileron and the flap close to the same length which is easier to make with the brake.

Using a CAD program at work I was able to generate the flat pattern of the aileron and flap.  We were able to dimension the tangent lines and the sight lines of the bends.  We made some test bends with narrow strips to check the dimensions.  The first ones may have slipped in the brake but the second try turned out great.

Since these parts have a 160~170 degree bend at the trailing edge, the sheet metal runs into the vertical leg of the top steel angle when using the brake as it is built.  See the picture below

We wanted a really good bend on the trailing edge, and from the rudder experience we would need to bend a full 180 degree with the sheet metal spring back.  We bought a 1/4″ thick plate of steel and grinded/filed a bull nose in it so we have our 1/8″ radius on the front.

We bought the steel from a local metal supplier and found it in their “drop” section.  These are pieces left over from other cuts and the price was really go.  I think the part is 1/4″ thick x 5 1/2″ wide x 55″? long.  When we replace the top angle on the bending brake with this flat part we can get a full 180 degree bend.  We had to match drill it to locate it to the existing brake assembly.

Using the sight lines we located the skin in the brake.

It is tricky to accurately locate the sight line looking straight down at the tangent point on the bull nose of the angle.

We use a steel rule against the tangent point to locate the sight line on the sheet metal.  (Notice the shim on the left side of the bolt, the shim is the same thickness as the sheet metal.)

To get as much stiffness on the top angle of the brake (to prevent bending) we jammed a 2×4 between the angle and the ceiling.

For the trailing edge we would make the first bend to ~90 degrees with the standard brake design.  We clamped an angle to the brake to bend it until the skin hit the vertical leg of the top angle.

Now we switched the brake’s top angle for the flat plate with the bull nose.  We nested the partial bend into the bull nose, clamped it, and pushed it to the ~180 degree point.  With the spring back it came out really well.

Here is a picture of a rib sitting the formed skin

We are really happy with the results.

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Cutting Out Flap and Aileron Skins

April 1, 2012

Having completed the rear spar bends we could now use the big brake for the aileron and flap skins.  Using a CAD program at work I was able to generate the flat pattern for both of the skins so we have the outside dimensions.  We marked the sheets being mindfull of how to best use the material given the parts we have left.

Dan used the electric hand shear to cut them out pretty close to the marks.

Even though we used two factory edges of the original aluminum sheets Dan wanted to make sure  they were perpendicular to each other.  If they are not then dimension errors will creep in and with skins one can get twist at final assembly.

Dan pulled out his trusty framing square that is pretty true.  We used the long “bottom” factory edge as the primary datum.  We marked the other factory edge with the sqaure and you can see on one side there is barely any pen:

But the other side has a thicker ine of pen as the perpendicular line.  To me this shows that you cannot rely on the sheet edges being perfectly square.

Dan saved us a lot of headaches by this check.  We trimmed and filed off the pen mark.

Now we have two perpendicular datum edges.  In theory the “top” long edge should be parallel with the “bottom” long edge since it was measured from it.  Here are the finished skins:

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