Building An Airplane From Plans
11/4/12 – Dan got in the garage and match drilled some of the spar assembly. To locate the spar spar attach block, Dan made a pin to fit in the 3/16 hole in the attach block. He also made a #40 hole in one end this pin. With a #40 drill bit in this end we can locate the attack block to the correct hole in the spar web.
(Been a while since I have been at the workshop since learning and replacing a retaining wall in the spring/summer 2012 – Tim)
Having matched drilled and clecoed most of the RH (Right Hand) spar we began work on the LH spar.
First order of business is laying out the correct order of all the spar layers. The plans are a little tricky with the right & left sides so Sonex provides some 3D CAD exploded views (RH & LH) . These still take a little head scratching since one does not want to mess up the expensive spar caps.
Dan came up with a good way to set the spar cap distance. He placed two carpenter squares, face to face, on one ruler so we could set the outside spar cap distance.
Sonex sells (or we could make) precision spacers that fit between the spar caps, but we would be depending on the precision of the spar cap “T” leg dimension. Another side note is that the match drill holes are in the spar web, so they need to be on top. This makes the spar caps’ “T” leg on the bottom underneath the spar web .
Our method measures the outside distance which is the dimension shown in the plans. We double-check setting the gap between the squares with a precision ruler and with a 8″ digital mircrometer that I borrowed from work. Since we are measuring an outside distance there is some feel to it. There is some friction, or tightness, of our outside gauge against the spar caps. We tried to be consistent with the same amount of drag feel of the gauge. You can easily have the gauge not perpendicular to the caps. To help this we would put pen marks on the caps with a square so we could line the gage up with them.
We would clamp the spar caps on the spar web and check the distance with the gage. The next step is to make sure the spar web is centered with respect to both caps. This took some iterations, but it got easier with two people.
Once the we felt the caps were clamped in the right place we drilled and clecoed one end , then the the end, then the middle. We kept splitting the distance to be in the middle of the gap. After about six times of this we just match drilled the rest.
To get a good perpendicular drilled hole we place a block of aluminum on the spar web next to the drill bit. By using the two edges of the corner it helps us see if the bit is off in either angle.
Summer Months, June – July (More Info & Pictures Coming)
Dan got the all layers together for right hand spar and match drilled them. Quite a bit of work and a little imtimidating to drill that first hole with the $$ spar caps and all the time put into the spar webs. Great job.
We have the assembly cleco-ed together. A couple of the angle parts still need to be added.
(These pictures were taken recently)
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.
I was able to create the flat pattern for the aileron and flap ribs. After a test one, we printed them out glued them the sheet metal and bent them up.
Dan fabricated the Aileron and Flap drive plates (W04-4 & W06-6) during the week.
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.
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:
Here are some pictures of finishing the rear spar bends. As usual the first time you try something new, like these really long bends, it takes a while and you learn the little subtleties. For example we noticed that the ends of the bend would form much more than the center, slightly bowed, perhaps the center of the brake is bending a little. Since we have to go past 90 degrees we have to bend it a second time since the brake can only rotate 90 degrees before it binds. We have to bolt another flange (or a peice of wood) onto the brake. Well if we don’t push at the ends for this second bend it all seems to average out.
Here we can see that we got the first flange angle but it looks pretty wavy along the length
When you bend the flange on the other side it all straightens out:
That looks awesome!!
Here are the two completed rear spars. These are the long lengths (108 7/8″) so we don’t need the splice plate (snx w12-04).
During this process you can see we were using lots of C-Clamps. Here’s what happens when Dan wants something tight:
Since we finished “Big Bend” (the David Clay bending brake design) we were eager to try out the beast. This is the method we have developed for accurate bends.
Here is the rear spar cut to shape and edges deburred and smooth. One can calculate the width from the standard bending formula tables. We mark the centerline of the spar blank
We clamp the flange side in the bending brake so we can push up against the larger center portion. From the bend formulas you can calculate the tangent points of the bend. Since the part will be formed around the radiused nose of the brake, we need to locate the part’s tangent line right on the tangent line of the nose of the brake. How can you do this if the part’s tangent line is covered up? What we need is called the “Sight Line”. Looking straight down on the un-bent part this theoritical line should be located right at the nose of the profiled brake angle. It happens to be the radius of the bend from the tangent line. I will post a summary of this with lots of pictures. It is tricky to get this line in the right position visually, so we use a caliper and measure from the center line out to the nose of the brake. (In the picture below we are using the top fingers of the caliper. The paint on brake nose was sanded off so it is a bit shiny.)
Tighten up the clamp bolts on the brake
** Important ** When we clamp on the narrow flange section we have less than .5″ of the sheetmetal clamped so the top angle will tilt back since it is 3″ long. This reduces the clamping force and the little flange can slip during the bend. We insert shims of the same thickness of the bend piece in the backside of the clamp to keep it level.
Here is the first bend, we can only get about a 90 degrees (with the spring back) since we can only rotate the brake up a little more than 90 degrees.
We put in a piece of wood to continue the bend.
During the week Dan aligned the second hinge to the other angle and match drilled them. While this sounds easy is involves having all five hinge sections joined with their hinge pins in supporting the angle in the right position wile match drilling.
This Brake design uses one of the angle pieces at the bending nose for the sheet metal. That is why we bought 1/4″ thick angle, so we could get a 1/8″ radius bends. Now standard angle does not have a full radius at the end of the legs. We broke out the vixen files and filed until we got a nice bull nose. Here is a little 1/8″ radius template from a piece of scrap.
Once we liked the bend radius we located this angle and drilled holes for the clamping bolts
Here is the completed Big Bend brake:
