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.

Step 10.3, Brake lines

I gave myself a stern lecture about keeping the work area tidy.  In time, it became apparent that I just wasn't taking myself seriously and that the warning was unlikely to have any effect, so I fired myself.

Moments later in an act of diabolical shrewdness, cunning, and business acumen that would make captains of industry blush and Wall street tycoons salivate, I hired myself back at half my former salary.

It's true that I would be receiving half of nothing, but I was happy to be building an airplane once again.

I decided to install a parking brake system.  And by system, of course, I mean a simple valve that can be closed when the brakes are depressed to maintain pressure on the brake calipers.  Sounds easy enough,  I need two valves, actually, because the airplane uses differential braking to steer on the ground. The left and right brakes are completely independent.  But I also want the two valves to open and close and the same time, so what I would really like is a dual valve with a single stem. Fortunately such a valve is produced, albeit at an astronomically high price.

I looked around the internet and found that only about half of the RV7s built are equipped with parking brakes.  I decided to ally myself with the camp that is willing to add 8 oz. to the airplane to prevent it from rolling away before the chocks can be employed.

I found a location for the valve that does not require any linkage to actuate the brake and that location is also generally along the path of the brake lines so very little additional brake line is required.  The location of the valve is behind and just to the left of the auxiliary fuel pump.  The valve lever extends through a slot cut in the fuel tank selector valve cover.

Here is the location on the outside of the cover as I measure for the lever slot.

The valve is supported between the fuel valve cover and a support that is riveted to the floor.

The valve temporarily installed so that the brake lines can be plumbed.

The lines take a few turns, but it's really just a matter of understanding the radius of the tubing bender to make everything come out right.

Here's the first line connected.  It's the left side output.  Note that the aux fuel pump and fuel valve are temporarily removed.

It's tight quarters trying to get flared ends on the tube after it is bent and routed.  There's probably a better way to do this.

From the it goes without saying department: It's much easier to flare the ends when the brake line is still on the bench.  Perhaps we should change that to it goes without reading department.

And now the aux fuel pump and fuel tank valve are re-installed.  The parking valve fits nicely to the left of the fuel selector valve and behind the aux fuel pump.

On the fire wall, the hard lines terminate at these bulkhead fittings.  Flexible lines continue up from here to the rudder pedals where the brake cylinders are mounted.

The rudder pedal assembly is dropped in and the brake reservoir is added to the firewall.

The reminder of the brake lines are flexible nylon.  Here is the routing from the brake reservoir down to the passenger side.

The brake lines then continue from the high pressure side of the passenger brake cylinders to the low pressure side of the pilot cylinders.

The final segment of the fuselage's brake system are the hoses from the high pressure side of the pilot brake cylinders to the firewall mounted bulkhead fittings.  Apparently, they come in the finish kit which has not yet arrived so I'll just call this step complete for now.  Notice the precision impacting instrument in the lower left of the photo above.  It's remarkable how frequently this device is required.  

Step 10.2, Aux Fuel pump

So here comes a box with a fuel pump and filter some check valves and some Aluminum tubing to connect them.  This particular kit comes to me from Air Flow Performance via Van's Web Store.  The basic idea here is to filter the fuel coming in from the tanks and provide a backup means to pump fuel to the engine.  The back up in this case is an electric fuel pump that augments the mechanical fuel pump which is attached to, and driven by, the engine.  The electric fuel pump is designed to be switched only during critical phases of flight.  What is a critical phase?  Well, that would be a flight regime where fuel starvation of the engine could present a life threatening condition.  Just after take off, for example, when the aircraft is not yet high enough to glide to a safe landing.  Think of the auxiliary fuel pump as a $700 insurance policy against the mechanical fuel pump failing and wrecking your day.

The fuel pump kit from Van's also includes a base plate to mount the pump and a fuel filter.  In addition there are anodized fittings to connect the pump to the check valve and sufficient aluminum tubing and fittings to complete their interconnections.  At first glance, the plumbing looks to be quite complicated, but after thoroughly studying the supplied instructions and drawings I would say the it is only 'very' complicated. 

Out of the box and on to the base plate.

I really enjoy the bending of the aluminum tubing.  I don't know why.  The first step is to cut the tubing to length and square the cut end.  I like to run the end past the Scotch-Brite wheel to smooth the edges before go on to the flaring of the ends.

  

It's really important to remember to put the B-Nut and sleeve on before  flaring the end.  I really can't stress this enough.  Also one needs to pay attention to the direction of the nut and sleeve before the flare goes on.
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Here's the first bend complete.

And here we are about half way through with the plumbing.  Note the addition of the TEE which will connect to the Andair fuel selector valve.

This is the fuel selector valve without the handle connected.  It doesn't really look like much, but it has two very important jobs:  To relieve excess wallet pressure which it does with breath taking efficiency, and to select from which tank the fuel will come.

And mounted on the pump assembly.

Here it is in the plane with the left and right fuel lines run.

Is that a rats nest or what?  It's a bit too modernist for most of the rats I know.  Perhaps some German rats would like it -- I don't know.

Here is some more showing the routing of the fuel lines coming in from the tanks.

And then the line exits the fuselage in the wing root.  The left side is long because it still needs to go through the forward wing attach bracket at left and then turn toward the wing near the leading edge.

The fun is not yet over as I still have the fuel tank vents to route.  These are 1/4" soft aluminum tubing and are quite easily bent.  One can manage most of the bends without the tubing bender.  The vent comes into the fuselage at fuel tank level and travels up to the main longeron and then back down to the floor.  The rise in elevation, I suppose, is to prevent the vent from draining the fuel tank.  Not a bad design feature for the cost of 4 feet of tubing.  Here is the vent entering at the wing root.

Going up, turn, and back down again.

At the floor, the vents terminate at fittings which protrude into the air stream.  These AN-4 fittings have been cut at 45 degrees and the threads sanded off.  Then a small piece of screen is glued to the face with Pro-Seal.  After the Pro-Seal cures, the edges and screen will be cleaned up and the fittings will be installed on the ends of the vent tubing facing forward -- into the airstream.  

By orienting the vent this way, the tank is slightly pressurized by high speed air entering the vent. This may help to feed fuel, but more importantly, a vacuum is not created at the vent opening which could suck fuel overboard.

Installed vent facing forward illustrating the 45 degree cut.

That's about it for the auxiliary fuel pump and fuel line routing.