Step 13.7 Baffling

Given a choice, air would rather not cool your expensive airplane engine.  Due to its stubborn nature air must be confined and directed to flow past the cooling fins on the engine's cylinders.  This is not such an easy thing to do, but fortunately Vans has thoughtfully included a baffling kit within their 'Firewall Forward' kit. So what exactly is a baffle?  It is simply a box inside the engine compartment that has inlets in the front to let the cool air in, and outlets beside each cylinder to let the air out through the cooling fins.  The box must fit tightly around the top half of the engine so that all of the air passing through does its cooling work.  Much of the work in assembling the baffles is the trimming and test fitting process that tailors the baffle kit to a specific engine.  Let's get started:

In this photo I've just begun building the back corner.  The baffling kit is actually pretty good and the instructions are clear if not entirely complete and we shall see.

This is a hole I put in the left rear to connect a 4" hose to the oil cooler.

These two holes will be connected to become a spark plug wire pass through.

Here is a view of the right side mostly complete.

Time out to play.

A well know defect of the cylinder cooling design has fins that are too short or blocked near the base of the cylinders 3 and 4.  A solution shown below, it to pop out the box a bit to allow a little more air to flow by in this region.

One of the really annoying things about the ECI cylinder is that it has tapered fins that reduce in height toward the base of the cylinder.  This was probably done to reduce weight, but the baffle kit is not setup for these tapered fins.  Consequently, some additional pieces had to be fabricated to seal the box along the cylinder base.  As you can see it is a complex shape that takes a bit of time to discover by trial and error.  In this case, error and trial, seems more accurate.

Its just about impossible to get a good photo on these things installed.  The black item behind the baffle is the base of a cylinder.  Using some imagination, one can see how the complex shape forms a cap to fit the inside edge of the straight baffle to the bottom of the tapered cylinder.

It was about this time when I realized that the baffle instructions did not include the "snorkel."
The snorkel is the pipe that directs air from the front of the baffle box to the engine's air intake. Because the intake is below the engine this pipe runs up to the baffle it kind of resembles a "snorkel." Anyway, to fit the snorkel to the baffle, a big hole had to be cut out of the front left side of the baffle and then a flange was fabricated to attach the snorkel.  I really hated to take the snips to the nearly completed baffle, but I also really hate not finishing the plane...

I didn't take time to photograph the snorkel before I found out that it doesn't fit at all.  I had to make multiple adjustments to alleviate interference from the starter and from the alternator.  When I finished glassing in those changes I realized that it was just too long to mate up with the baffle box so I cut a half inch out of the middle and glassed it back together.  The photo below shows some of my handy work. The hole is a second stab at clearing an unused mounting tab that is inconveniently sticking out of the bottom of the starter motor.

After getting the snorkel to fit. I began work on a sliding door to act as an alternate air source.  The theory is that were the input to become clogged with ice or some other debris, it would be nice if the engine didn't shut off for lack of air.  The alternate air door can be opened in this unusual case to allow air in from inside the cowling.  Although it is unfiltered air, it's better than nothing.  The Vans supplied door has been found lacking -- the ability of close it once opened, for example,  So I thought I would try to design my own sliding door.  

And so here is the snorkel with the alternate air door completed.

A view of the snorkel from below after painting.

Air filter installed.

And finally the last step on the baffle project is to apply the fabric seal to the top of the baffle box. The seals press against the inside top of the cowling to prevent the air from escaping out of the top of the baffle box.

Step 13.6 Oil cooler

Air cooled engines, like the one in my airplane, are actually cooled by more than just air blowing past the cylinder's cooling fins.  Internally, some of the heat is carried away by the engine oil.  This cooling is improved by the addition of  a radiator for the oil.  In this posting, I will illustrate the installation of my oil cooler.

The engine in my plane is a little larger that the standard engine for this aircraft and so I elected to go with a larger oil cooling radiator.  The trouble is that the larger radiator will not fit in the standard location which is hanging off of the baffles behind the rear left cylinder.  To overcome this problem, I will be relocating the cooler to the left side fire wall.

Whenever you veer off of the plans to make some sort of  modification to the stock aircraft you are skating on ever thinner ice as you go.  But this mod doesn't have any structural ramifications so I think I'm pretty safe here.

First up:  make some brackets to mount the cooler to the firewall.

The cooler's air source will be the higher pressure air above the engine on the left side and will be connected to the cooler by a flexible 4" hose.  An intake plenum is required to adapt the hose to the cooler and that will be constructed of fiberglass.  A male mold is fashioned using modeling clay and a roll of tape that is just the right size for the hose (after I peeled off about 5 ft of tape).

The mold is covered with about 4 - 6 layers of  9oz glass fabric and West Systems epoxy.

The plenum is then readied for painting 

And the brackets are installed.

And then the painted plenum is mated to the cooler and bracket.

Finally, with the addition of the hose, the cooler is complete.

Year 4 Retrospective

Well another year passes and I find that it's helpful to consider the progress made.  My lack of blog posts recently is indicative of this final stage of construction -- the 90% complete with 90% to go phase.  It seems that many of the tasks at this point are interdependent such that completing one requires completing all of them and I have been reluctant to post on half completed tasks.

It is tempting to feel that not much progress is being made and so to remind myself and the gentle reader, last year's progress is reviewed to dispel any doubt that I have visited the shop this year. Once or twice...

January:  The interior components are test fit and the wiring is wrapping up.

By February I was on to fitting the rear window.

In March I was cutting the slots for the canopy hinges in the top forward skin.  This is the last skin to be riveted on and it marks a major milestone -- fuselage structure complete.   Later that month I decided to add electrically activated cowl flaps. The cowl flaps allow more cooling air to be cycled through the engine compartment.  This is important to while climbing to keep engine temperatures down.  At the same time, closing the flaps allows for a modest speed increase in cruise because the cooling drag is reduced.

 

Around April I thinking seriously about hanging the engine.  The first step was to transition to the engine stand where I could more easily add the accessory components 

In May we were working on the canopy.  We added a targa strip over the top and two side lips to help center the canopy and stiffen the structure.

And by June we were painting.

The painting continued right through the summer and fall.  Somewhere along the line I applied the N number.

...And hung the engine.

By December I was connecting control cables to the throttle quadrant.

An oil cooler (right) was added and the engine baffling (left) was begun.

By the end of December the cowling was being prepared for paint.

Trina slept though most of it.

And on the last day of this year's work, I mopped the shop floor.  This was the first time the plane has been rolled outside.

Step 13.5, Hanging the engine

I've been trying to run a just-in-time airplane factory.  Just-in-time is, as expected, the concept that the purchased materials for a product to be built are not warehoused at the factory, but instead are brought to the factory at the last possible second before assembly.  Thus increasing efficiency and lowering costs.  It seems like I may have jumped the gun on purchasing my engine as it has been sitting in my factory for well over a year.  Thus decreasing efficiency and increasing my costs. That's how I roll.

And so, the time has finally come to mount my IOX370.  Previously, I had the engine on an engine stand where I attached the vibration isolators to the tubular steel dynafocal engine mount.  The dynafocal mount is designed in such a way as to transmit less vibration from the engine through to the fuselage.

To mount the engine, I needed to drill the holes from the engine mount to the firewall.  I had previously drilled through the firewall to mount the fuselage to the rotisserie, but I used a smaller diameter bolt for that so that when the time came to mount the engine, the larger engine bolt holes would (hopefully) be drilled through the same holes.  But if there were some misalignment with the engine mount, the larger mount holes will overlap the smaller holes previously drilled.  Using the dynafocal mount itself as a drill guide, the six holes are enlarged to 3/8 inches. 

The mounting order that I used is different from the Van's aircraft recommendation.  They have you fix the engine mount to the fuselage first, then hang the engine.  I suspected that hanging the engine on the mount to be the more difficult challenge so elected to do that first.  

Slip the front landing gear into place.

The front landing gear is held in place with a single bolt.

With the front landing gear secured, I moved on to torquing down the engine mount bolts.  Each of the six are secured with a castle nut and cotter pin.

Move the engine hoist out of the way and Ta Da!  My airplane is on its gear with an engine.

I'm very happy to have finally reached this milestone.  It is a curious fact that it was much easier to hang the engine than it was to install the landing gear.  Go figure.

Step 13.4, Main gear

With the majority of the painting done I can finally get on to some more interesting stuff eventually leading to the hanging of the engine.  My first task with my newly painted fuselage is to get it off of the rotisserie.  Here's a picture from way back showing the rotisserie:

Removing the fuselage is much simpler to to say than it was to accomplish.  My first thought was to move it on to some saw horses, but that would require two moves -- the second being from the saw horses on to the main landing gear.  Being naturally thrifty when it comes to expending physical effort, I think one move sounds better since two moves will take longer. And let's not kid ourselves, my very presence in the same room as my just painted fuselage puts it at significant risk for some kind of damage.

First up, installing the left gear.  Using the rotisserie, I roll the fuselage over allowing easy access to the left landing gear mount.  The left gear slides right in with firm pressure and a little grease in the socket. Then I let that side down until the wheel is resting on the floor.  This is where the trouble starts.

I have a great deal of difficulty wiggling the rotisserie off of the fuselage. The contributing factors were: The shop was hot and I was in a hurry because we were about to go out to lunch. However, the proximal cause I identified as binding on the forward rotisserie bearing. The binding was caused by the off axis angle that the fuselage makes relative to the rotisserie when the fuselage is made to slip past the tail end of the rotisserie for assembly or disassembly.  This was a shortcoming of my rotisserie design that I discovered when I first put the fuselage on the infernal contraption.  If there ever is a version 2.0 of the rotisserie, it will have a removable bearing top at the front and back that would allow the fuselage to be lowered straight down, thus preventing many bad thoughts.

Getting in a big ass hurry is a time honored tradition for me and a recipe for disaster. Although I was vaguely aware of this at the time, I still had an acute case of get it done-itis, which of course trumps rational thinking.  No need to prolong the suspense any further... Nothing bad happened.  The rotisserie was unbelievably stubborn, but I was eventually able to get it out from under the plane, but not before getting grease all over me, the rotisserie, and the landing gear.  I kept touching the rotisserie bearing which is greasy while looking for a hand hold to pull. Why I couldn't remember not to do that I don't know, but I had to stop and wash my hands about 5 times during the process which only elevated my level of aggravation.

With the rotisserie out, I could lift the fuselage up onto a jack that I placed under the right side main spar.  I was thinking the whole time that the jack was not exactly stable and that if it slipped, it would punch a 4" hole right through the passenger side floor.  It was not unreasonable to be thinking that this was a real possibility because I could see it slipping a little as I was vigorously wiggling the right landing gear back and forth while trying to force it upwards into its socket.  Back and forth, up and down, I was applying a great deal of pressure to no avail.

I find my patience with others greatly compromised when I'm preoccupied by a mechanical contrivance with a flair for noncooperation.  I'm sure the gentle reader will agree that when a thing that must fit, doesn't, it's extremely maddening. At this point I'm out of breath from trying to force the gear and I've only made about 1/2" of progress into the gear socket.

So Carol has had about enough of my ever increasing state of agitation, and heads back up to the house.  I am still in a hurry, but I decide to take time out to just sit down and study the geometry of the gear leg. Why is it so much more difficult than the left gear?  I make some small adjustments to the jack allowing me to get a better angle on the gear. I find nothing at all to give me any confidence whatsoever that my next assault on the summit would be any more fruitful.  Never-the-less, I decide that I would make one more big push and then go to lunch. Three or four more minutes of really hard effort and it finally capitulated to my will.  Ahh-ha, ha, ha. (crazed maniacal laughter).  It was a fustercluck to be sure, but I had my airplane sitting on its main gear for the first time.  

And the reason for all of the mechanical intransigence?  Paint.  When the gear was fully seated, it was apparent from looking at the open end of the gear socket (inside the cockpit), that it had peeled a very thin layer of paint from the inside of the socket tube as it was pushed through.  I thought I had the tubes blocked off for painting, but some paint must have gotten in there anyway. 

So here it is on the gear for the first time.  Note to self:  That black rotisserie spindle is very greasy.

Step 13.3, Painting the Fuselage

In early 2010, long before I even began the RV-7A project, I was planing to paint it.  The design of my paint booth depended on the size of my airplane's fuselage.  And the size of my shop depended in part on the size of the paint booth.  It is a really good feeling to finally be at this point now and I am pleasantly surprised to find that the fuselage which is the largest single piece that I will have to paint on this project, just fits.

There were minor dings that were hammered flat and some that needed filling and when that was complete the fuselage was rolled into the booth for primer.

After priming the fuselage was rolled back out for sanding and another round of minor body work.

And then the real fun begins.  Laying out the stripes.  

To lay out the stripes I wanted to first make a paper template so that I could be sure that the stripes would be identical of both sides of the aircraft.  To make the template, I taped some paper down along the length of the fuselage and then went to work adapting my paint scheme drawing to the full sized aircraft.  I went to a lot trouble calculating angles from my drawing, finding tangents at selected points along the curve and then transferring those points to the template in an effort to replicate the drawing exactly at full size.

The big problem with this approach is that it doesn't take into account that the transformation from drawing to fuselage is a transform from 2D to 3D.  Although when viewed exactly straight on from the side the resulting stripes did look like the drawing, there were certain angles that were aesthetically challenged.

In the end, I did a lot of adjustment by eye, as it were, to get the flowing shape I was initially going for.  Once the template was complete the fine-line tape is applied to the fuselage along the edge of the paper, recreating the shape of the stripe.  Flipping the paper over gets the same stripe on the other side of the plane.

Here a stick is employed to hold the rudder cables out away from the fuselage during the painting process.

The first stripe pained is the silver stripe.  The photo below is after the stripe has been painted and the re-taping process is underway.

The stripe is taped off and cover with masking allowing the blue stripe to be completed.  Once both stripes are done the white can be laid down.  Here Carol is preparing the masking for the blue stripe.

Finally, the white goes on and the fuselage is done:

Now, I start the whole process over on the vertical stabilizer and rudder:

There is still a lot of work to do on the paint; the cowling, the wheel pants, and the landing gear fairings, for example.  But the vast majority of the hard work on the painting is done.  The remaining pieces are manageable in size and should not be a major time sink like the fuselage and wings were.

Before I take the fuselage off of the rotisserie, I'll attach the four antennas that go beneath the plane (2 COMM, 1 Transponder, and 1 ADS-B IN).  That leaves 3 antennas to attach on the top side, but I'll save that for later.