Step 10.4, Test fitting the wings

The wings attach by bolting the wing's main spar into a slot in the fuselage's main spar carry through structure.  The main spar and the spar carry through were pre-drilled at the Van's factory and are delivered as a matched set to insure perfect alignment for the close tolerance bolts that will join the two pieces.

There a few important parameters regarding the wing attachment which are set when attaching the wings. First is the dihedral angle.  This is the amount that the wing tips are higher than the wing root.  Dihedral helps keep the top side of the airplane pointed up.  On the RV7, the dihedral angle is set by the predrilled holes in the spar attachment so nothing needs to be done on that.

The next parameter is the sweep angle which is a measure of how far back the wing tips trail the wing root in the horizontal plane. On the RV7 the sweep is 0 degrees, so the leading edge of the wing forms a 90 degree angle with the centerline of the fuselage.  The sweep is fixed by the rear spar attachment which is not yet drilled.

And the last parameter is the wing incidence.  Incidence is a measure of the angle of the wing (chord line) relative to the fuselage.  Incidence of the wing is set by the designer such that at cruise speed the fuselage will be in a level attitude.  Like the sweep adjustment, the incidence angle is also set by the location of the rear spar attachment.

The basic idea is that the sweep and incidence are both adjusted and then the rear spar attachment is drilled and bolted to lock in those parameters.

This will be a test fitting of the wings because they will have to come off again for paint.  Before moving on to the wings I took time out to install the control column which had been previously assembled.  Because I had made the tops of the four inside ribs removable, the control column could drop straight in with out any struggle whatsoever.  The photo below shows the ribs with the top sections removed.

I did have to disassemble the column pivot and move the bolt head to the opposite side for clearance.

After the control columns were in place, I painted some of the interior that would not be covered with fabric.

Then I began the process of fitting the wings.  First, checking the level across the longerons and then along the longerons.

 At this point I realized the it wasn't necessary or desirable to level the plane before fitting the wings.  Oh well, at least now I'm familiar with the procedure.

Guess what?  I have no pictures of the wings going on because everyone involved had their hands full.  On the right wing I had the help of Carol and her nephew, Cody.  A few days later, Rob and Tony from work came over to lend a hand on the left wing.  In both cases, the fit was very tight, but an application of Boelube to the mating faces helped some.  I used hardware store 7/16" bolts with the threaded end ground down to complete the temporary connection.

Once the right wing was one done I set out once again to level the airplane.  The reason we want to level the airplane is that the wings must be attached perpendicular to the fuselage.  To accurately measure this angle a right triangle formed by the leading edge of the wing and the centerline of the fuselage is transferred to the floor, which as it happens, is a mostly flat surface good for measuring.

The first thing is to find the centerline of the fuselage and then transfer that line down to the floor.

The self leveling laser comes in handy here.  I didn't completely trust the laser though, so I checked its accuracy with a plumb bob.  It was spot on according to gravity, which I reluctantly accept as an authoritative source.

The next step was to measure string a line across the floor directly beneath the leading edge of the wing. Once again the plumb bobs find the line.  This line will not intersect the center line at exactly 90 degrees if there is any sweep in the wing (not perpendicular).

Then I measure where the extended leading edge line crosses the centerline and take a measurement of that line and of the length of the centerline from the leading edge back to the tail.  Now having two sides of the right triangle, I find the length of the hypotenuse via Pathagoras and draw a line on the floor at that length.

Now here is the tricky part.  I have to move the wing so that tail to wing tip matches the length of the hypotenuse just calculated and then reset the leading edge line.  With the line reset, I remeasure the lengths of the leading edge and centerline and find that they remain unchanged -- at least to the accuracy of my ability to measure. Considering the lengths of the sides and the precision of the tape measure, the calculated angle should be within a few 1/100s of one degree.  Ok, Close enough, moving on.

Now the sweep is set, but the incidence must also be set at the same time.  

Van's has this high tech method for setting the incidence.  A premeasured block of wood setting on the rear spar forms the incidence angle relative to the main spar.  Remember that the fuselage is leveled before starting this process, so the procedure is actually true measurement of incidence.  I don't have a lot of confidence in the precision of a bubble level, but after turning the level end for end a few times I was convinced that the level was good enough.  The actual incidence is a not nearly as important as getting both wings set the same.  Since I used the same block and the same level and most importantly, the same two eyes, I feel that the two wings will be pretty close to the same angle.

Now that the sweep and incidence are correct, a series of increasingly larger holes are drilled through the rear spar attachment ending with this 5/16" reamer.

And there it is.  Let's hope that both wings get set the same.

Now do the other side.

With a little help from a jack.

Finally, check the fit of the fuel lines and add the vent lines.  

And here is is.  Wings on for the first time.