PAP Section G6: First engine start

Before the first engine start, a procedure must be followed which purges air bubbles from nooks and crannies, and most notably the valve lifters, throughout the engine.  This is accomplished by removing the spark plugs to allow easy engine rotation, removing the oil return line at the oil tank and providing a clean container to collect any oil which makes it that far, and turning the prop vigorously until a 40 psi reading shows on the pressure readout in the cockpit.  This causes the oil pump to move oil from the tank throughout the engine and back to the now-disconnected tank return line (maybe).  The instructions say that this may take 40 - 60 revolutions of the prop.  As with all things these days, many Ewe-Tube (they're a bunch of sheep, but that's another story) videos exist showing this process.  The best I found is here.

This process can be sped up by capping the oil tank overflow line and pressurizing the oil tank to 10 psi with an air source before turning the prop.  It is claimed that this step is optional and simply speeds things up.  My friend and ace Light Sport mechanic Bill Snodgrass had done this procedure before and had fabricated a rig to facilitate this.  We first tried it without the air pressure and couldn't produce any reading on the oil pressure gage by turning the prop.  With the air pressure, however, we quickly saw an oil pressure of 55 psi and declared it done.  No oil made it to the catch container but Bill said this is normal in his experience.

After the purge, I did a normal "burp" of the system, which is done before every engine start with a Rotax.  This being a dry sump oiling system, oil which leaves the crank shaft, rods and rockers and accumulates in the crank case must be returned to the oil tank.  This is done in a novel way: rather than using a pump the way race cars do, blow-by from the piston rings pressurizes the oil, forcing it back to the oil tank.  After the engine is run and shut down, oil is left in the crank case, making it impossible to check the oil level in the oil tank.  With the engine off and the cap off the oil tank, the prop is rotated in the normal direction until the distinct sound of a flushing toilet is heard, indicating that the oil is now back in the tank and ready to be checked.

Now it's show time.  With my ex-fireman friend Chad Rennicke, complete with fireman's hat, manning the fire extinguisher, I inclined my head a few degrees and said a silent prayer that I had hooked everything up right -- all the wiring, gas line fittings, oil line fittings -- then turned the ignition key for the first time.  It cranked immediately, oil pressure came up, gages looked good, relief flooded over me, then it quit!  Instantly I knew I had forgotten to turn the fuel valve on.  This done, it fired back up and ran great.  No fire, no smoke, no funny sounds.

Incredibly, after working on this airplane since 2011, I feel for the first time that I'm within sight of the end of the build.  I'm ready to fly.

PAP Section G4: Measuring fuel flow from the electric pump

It was with fear and trepidation that I poured four gallons of fuel into the tank for the first time, exposing the entire system -- all the fittings from the tank to the engine and back to the tank -- to gasoline.  I had tested the tank itself when I first built it back in North Carolina (see earlier post detailing that particular Klöster Föken), but the rest of system had never seen fuel, much less pressurized fuel.  When I first added the fuel, I did so with the fuel valve in the cockpit closed, limiting the gasoline to about half the fittings with gravity. providing the only pressure (~0.5 psi).  All appeared well.  I then opened the cockpit valve.  Seemed OK. When I switched on the pump, however, I immediately had a leak which I eventually traced to the fitting going to the fuel flow meter.  Tightening this seems to have fixed it.

For the actual measurement of the flow rate, the manual says to remove the fitting at the gascolator outlet, slip a 5/16-inch fuel hose over the fitting, turn on the pump and measure the time required to pump one gallon into a gas can at waist level.  The time is not to exceed 180 seconds.  

The first problem with this scheme is that without completely removing the bottom cowl, which involves detaching the oil heat exchanger from the cowl (a major PITA), the fuel fitting must be accessed from above.  I did remove the piano hinge wires from the lower cowl, allowing it to swing down a few inches with the oil cooler still attached.  With the new RV-12s, the oil cooler is no longer attached to the cowl, eliminating this headache.

The second problem is that a 5/16-inch fuel line doesn't come close to fitting.  The male threads on the fitting measure about 0.55 inch, so a 1/2-inch line fits well.  I used a short segment of 1/2-inch, a right-angle fitting, then the rest 5/16-inch.  The right-angle fitting made it possible to hook it up from above.

The time required to pump one gallon was 170 seconds.  Next up is doing the purge process to get the air out of the oil lines and lifters, burp it, and start the engine!

I recently returned from my 36th pilgrimage to Oshkosh.  The big news at the show was the final publication of MOSAIC, the long-awaited update to the rules governing Light Sport aircraft and Sport Pilots.  It's simple now: any aircraft with a clean stall speed, Vs1, of 59 knots or less can be flown by a person holding a Sport Pilot certificate.  All of Van's airplanes with the exception of the RV-10 qualify.  No medical.  Retractable gear with a variable-pitch prop: check.  Wanna fly a 182 or a Stearman?  You're good.

SB-00102 Control Stick Pushrod Inspection

The purpose of this post is twofold: to document that I have performed this Service Bulletin and to prove to my friends following this blog that I'm still alive and still working on the airplane.  The Service Bulletin was brought about by a fatal accident involving an RV-12 which resulted from improper installation of the rod ends on the aileron push tubes.  Over 600 RV-12s are flying so I guess over 599 builders did it right, but Van's says that "out of an abundance of caution" (seems like I heard that phrase a few thousand times back in 2020) the SB was necessary.

The diagram on the left shows the proper installation and the pic at right shows the improper installation on the accident airplane.  What I don't understand is this:  In the accident airplane, the stick on the right was functioning.  It's not much of a reach to put your hand on it from the pilot's seat.

To verify that did it correctly I snaked my borescope in through the cutout for the right stick and took a pic.

The alternative to this is to remove the floor pan, an odious task which involves removing hundreds of Phillips-head machine screws, half of which have the heads boogered up (that's the official machine-shop term) from five or six previous removals.

Back in 1948, Edward Murphy said "If a thing can be done two ways, one of which results in disaster, someone will eventually do it that way." 

Off Topic:

I'm getting ready to move my antique car from North Carolina to Colorado, causing me to look longingly at some pics of it.  What you see is an example of what can happen when your engineering students have too much access to your car.  It can grow teeth.

Page 42-F: Installing the ACK Emergency Locator Transmitter

Installation of the ELT seemed straight forward, not even requiring a blog post.  The only semi-difficult task involved stripping and soldering four small wires onto an electrical connector.  The hook up was done by following the instructions in the KAI and looking at the diagrams in the booklet which came with the ELT from AKC.  All the wires and the unit itself along with the enunciator box and a mysterious RJ-11 connector, were then neatly zip tied onto the ELT tray previously installed.  Easy peasy, I thought. One of the previously installed wires, an RJ-11 phone wire, goes from the display/switch unit on the instrument panel back to the ELT behind the passenger seat.  When everything was hooked up, the enunciator box starting emitting a ticking sound and a red light on the display unit on the instrument panel started to flash.  A call to ACK revealed that the RJ-11 wires and connectors are either straight through (polarity preserved) or crossed (polarity reversed).  According to ACK, they should all be straight through, but on all Van's aircraft the long wire from the instrument panel display unit back to the ELT is always crossed.  Something needs to un-cross the wire.  It turns out that the previously mentioned mysterious RJ-11 connector was supposed to be crossed, thereby fixing the problem.  Mine was not.  Amazon's aviation department to the rescue.  Problem solved.  I waited until the big hand on the clock was straight up, activated the ELT, tuned my hand-held radio to 121.5, and was rewarded with the irritating peyow, peyow, peyow sound that an ELT makes.

Build delayed by more broken bones: A while back in North Carolina I fell on my bicycle, breaking my left femur and having a titanium rod installed from the ball joint to just above my knee.  This joined titanium already in that leg from the knee to the ankle.  The Spousal Unit and I always go roller skating each Monday night at a local rink.  Confirming the expectations of my friends, I'm now recovering from surgery to install a titanium plate in my left wrist, fixing one of the most common roller skating injuries (broken wrist).  It's hard to work on the airplane one-handed.

Off topic: more Colorado wildlife

When I moved to Colorado from North Carolina, I often said that I wanted to see a Mountain lion in the wild.  Since arriving I'd seen bears, bobcats, moose, thousands of elk but no mountain lion.

 A couple of months ago the Spousal Unit awakened me at the butt crack of dawn, telling me to come see a mountain lion eating an elk behind the house.  Pretty exciting but a couple hundred yards away.

Then a trail cam on my back patio got a picture of one much closer to the house.

Then this.  Probably the same guy trying to cover a deer less than 100 yards from my front door.

No more pages in the build manual!

 As I approached the end of the build manual I was expecting the last part to contain instructions for loading the software into the Skyview HDX, adding the fluids, and doing the first engine start.  None of this was there.  There were no directions for finding additional documents that would walk me through this stuff.  Turns the documentation is there and I had to find out about it by reading other blogs and digging around on the RV-12 forums on vansairforce.net.  The first thing I should have gone to is called the Production Acceptance Procedure (always referred to as the PAP) which only exists because the RV-12 can also be had as a factory-built S-LSA airplane.  Other experimentals, E-LSA or EAB, don't have this document.  Early in the PAP another document is referenced, a read-me file on the downloads page at vansaircraft.com.  

This read-me file contains all of the steps required to download the Skyview software, settings files, databases, sensor definitions and current TFRs. It explains how to tell the software what equipment is installed and how to calibrate this equipment, including how to calibrate the stabilator position for takeoff, how to calibrate the fuel system, ADAHRS, AOA, autopilot servos and other stuff.  In other words, this is an absolutely vital document.  I went as far as I could in this, then came to some stuff that required the engine to be running.  Somewhere in here I discovered the PAP and everything started to become clear.

The reward for completing the steps in the read-me file was that I got to see the Skyview HDX all lit up in all its glory.  This was pretty exciting for me and I spent quite a bit of time staring at it.  On the right in the picture is my iPad running Foreflight propped up on the map box door.  I'm planning to mount it approximately in this position but standing off the instrument panel a bit and tilted toward me in the left seat.

At this point, with some fear and trepidation, I tried the landing light, navigation lights and strobe lights.  They all worked!  After patting myself on the back for doing such a great wiring job (prematurely, it soon became evident) I proceeded to test the Garmin GTR-200b radio.  This involved plugging a headset into the jacks on the pilot and co-pilot sides, which resulted in a loud squeal in both and an even louder string of swear words from me.  A wiring problem!

I'm convinced that 95% of all wiring problems involve a faulty ground, but where?  Since managing electrons is not something I'm good at, I enlisted the help of my EAA Technical Councilor, Dan Berry, to help track it down.  Like me, Dan is a mechanical engineer, but unlike me, Dan is a wizard with electrical things.  After studying some electrical diagrams that he pulled up on his phone from somewhere on the internet, he decided that the fault must lie somewhere in the wiring at the left wing root.  To get to it, I had to pull the wing.😡  This task is not as onerous as it might first seem since the RV-12 is designed for easy wing removal, very similar to that of a glider.

 I see a lot of talk on the forums about systems that allow one person to remove a wing unassisted.  Mine is simple: a 4x8 sheet of plywood with legs on casters.  The top of the table is just below the inboard end of the wing.  Moving blankets get stuffed between the table top and the bottom of the wing, accounting for dihedral.  When the spar pins are pulled, the table and wing can be easily pulled away from the airplane.

After removing the mountain of crap that had grown up atop my wing table, I pulled the left wing just enough to allow the wiring to be accessed. The tube seen going from the wing root into the side of the fuselage takes a pressure signal from the AOA port on the wing leading edge to the ADAHRS box mounted in the tail cone.

After Dan made some measurements to confirm his original diagnosis, I discovered that two of the seven wires going into the Molex plug shown had pins which were not properly inserted.  I still find this hard to believe since my standard procedure with Molex or d-sub pins is as follows: crimp the pin, tug the pin on the wire, insert the pin into the female plug, tug the wire to ensure proper insertion.

The blue connector shown automatically connects the wires from the fuselage to the nav and strobe lights and the stall warning vane when the wing is installed.  A corresponding one on the right side also has the wire for the landing light.  With the headset plugs hanging out in the air as shown and the blue plug not connected, the radio worked great.  Problem solved!  Turns out, one problem was solved and one was yet to be revealed.

Happily, I re-installed the wiring in the fuselage, re-installed the wing and plugged in the headset: loud squeal.  As Tom Cruise's sidekick said in the movie Risky Business, sometimes you just have to say WTF (abbreviated here due to the family nature of this blog).

Somehow, when the two halves of the blue plug came together, the squeal starts.  The nav and strobe lights work fine, which leaves the stall vane.  Turns out that by moving the stall vane around, I could make the squeal start and stop.  In its relaxed state, this normally-open switch was closed.  This new "squeal" I was hearing was the stall warning horn!  The switch/vane assembly can be reached (barely) by removing an inspection plate.  Sticking my phone in the wing, I got a picture of the assembly (shown).

The assembly consists of the microswitch and vane sandwiched between two plates.  When I built this thing I remember fearing that if I over-torqued the bolts I might crack the plastic housing of the switch.  The result was an assembly which was no where near rigid enough.  I could grab the outer plate and move it relative to the inner one.  Another self-inflicted wound.  Nothing to do but remove, re-torque and re-install.  Turned out to be one of the more challenging and frustrating things I've had to do on the build. 

The really maddening thing is that most people with AOA disconnect the stall vane after certification, which no doubt I'll do, making all this a waste of time.  But, being an E-LSA it must be built exactly like the ASTM prototype.  Right?

Off topic: more Colorado wildlife in my back yard recently.  Look at the rack on that one guy to the right.

Page 49: Cooling system

The Rotax 912 is an odd duck in that it has water-cooled heads and air-cooled (finned) cylinder barrels.  The water is actually a 50:50 mixture of antifreeze and distilled water.  From an engineering standpoint this is superior to the more typical air-cooled-only (Lycoming, Continental) arrangement.  Of course all the rejected heat ultimately goes to the air.  It just takes a different path with the Rotax.  

The components of the system which must be installed are the fiberglass duct which directs the ram air from just aft of the prop to the heat exchangers (shown again from the previous post), the oil cooler (air-oil heat exchanger), the "radiator" (a poor name since there's negligible radiation heat transfer) which is an air-water heat exchanger, a cabin-controlled door which can divert the hot air downstream of the radiator into the cockpit for heating (definitely needed here on the Front Range), and various hoses which transport the oil and water to various places.

The oil cooler is first bonded with high-temp RTV to an aluminum frame to which nut-plates have been riveted, allowing it to be attached to the bottom cowl.  The aft (left) end of the duct interfaces via a rubber seal (shown on the pic) with the radiator.

For the bonding process, the instructions call for a 20 lb weight to be used to ensure proper contact while the RTV cures.  I searched around the hangar weighing various things to use for this.

It turns out that a jug from a R-985 Pratt & Whitney radial from a twin Beech weighs almost exactly 20 lb.  I put the corresponding piston in the picture to show the beating it took when the engine swallowed a valve.  The jug (with cracked head) is sitting on a wooden plate atop the heat exchanger

The radiator (which doubles as a heater core) is also bonded to an aluminum frame which provides a flat surface against which the aft edge of the cooling duct interfaces.  The instructions specify that a 1/8th-inch gap should exit all the way around between the duct face and the aluminum frame.

A separate fiberglass piece bonded with epoxy (and RTV as a backup) to the duct itself makes this do-able.  The gap, which can be seen in the pic at right, was achieved by temporarily gluing inch-long segments of paint stir sticks from Lowe's (not Home Depot, too thick) around the aluminum and clamping everything together while it cured.  The rubber gap seal is bonded to the duct face later.  The seal can be seen in the first pic.

Hooking up the oil lines turned into an unexpected problem.  One line goes from the sump on the bottom of the engine to the oil tank (shown) at the top.  The ends of this particular hose are "clocked" by the supplier and the angle can't be changed.  The instructions warn not the twist the hose.  Looking at the pic at left, you can see that the female end can't possibly fit on the nipple on the tank without  significant twist.  I ordered a replacement ($288!) which fit perfectly.  The Mothership did give me a refund when I sent the bad one back.

Installing the oil lines, water hoses, gas lines and a couple of vent hoses in the tight quarters of the engine compartment was, in a couple of cases, a challenge.  Van's commonly requires the use of double Adel clamps, where one clamp attaches to a structural member, the other to a hose and the two are attached to each  other with a bolt, creating a sort of standoff.  I hate single Adel clamps, but two together requires the invention of new, stronger swear words.  In one case I didn't have a 3/8th-inch socket small enough to fit into the available space, requiring me to fabricate the wrench shown at right.  I've had to use it several times now.

In July I made my 33rd trip to Mecca (Oshkosh).  There I encountered this RV-12 with the best quality paint job I've seen on a -12.  If only I had a spare $20k!  As I've said before, I'm going to fly for a while with no paint, then wrap it in vinyl.  With wrap I can do it a bit at a time and if I screw something up I can easily remove the wrap and redo it.

Page 38: Finishing the cowling (good riddance!)

Cowling Par Deux

At the end of the previous post I described how I'd managed to somehow over trim the fiberglass, in spite of countless trial fitting iterations, along the seam where the top and bottom cowls join.  For a while I thought I'd come up with a solution.  Before drilling the rivet holes for the piano hinges which hold the

two halves together, I used clear packing tape to hold the cowl halves in alignment while drilling the upper cowling and piano hinge.  The pin had been inserted into the two hinge halves, holding everything in place.

It seemed to work well, drilling and clecoing front to back

With the drilling done and all the countersinking done in the fiberglass, I squeezed all the solid rivets and proceeded to install, for the first time, both cowlings with all pins inserted.

Since everything was riveted in place now, with no room for adjustments, the two curved pins along the aft edge of the top cowl were, to put it mildly, a (suppressing the urge to swear) problem.  They had been difficult before but now seemed impossible.  Dry Boelube helped, but not enough.  I ended up inserting some spare pin material into the hinges, chucking it up in my drill, and spinning it a bit.  This opened up the holes in the hinges enough to allow insertion of the curved pins.  The gaps between cowl halves looked good as did the gap between the prop spinner and the front face of the cowl.

What a clever builder I am!  I got to enjoy this fantasy until doing the next step: Fiberglass in the cooling duct.

The cooling duct as supplied is of necessity too large, requiring another iterative session of fit-mark-trim-fit-repeat.

The duct takes in the ram air just behind the prop and directs some of it to the oil cooler, which attaches to the duct, and the rest to the coolant heat exchanger which doubles as a heater core for cabin heat.

The fit between the duct and the lower cowl doesn't have to be perfect since the duct is epoxied to the cowl along with fiberglass cloth, making it easy to fill any gap.

The hard part is getting the duct to interface correctly with the face of the coolant heat exchanger which is attached to the airframe. A deformable rubber seal helps a little.

When the duct is satisfactorily fiberglassed to the lower cowl, before the epoxy sets up, the upper and lower cowls are attached to the airplane with all piano hinge pins and screws inserted.  This is supposed to ensure that the final fit is good.  The problem is that the duct is a large, rigid piece which inevitably distorts the lower cowl a bit, screwing up the perfect fit which I bragged about earlier.  Now the seems are no longer perfect.  C'est la vie.

At this point I fabricated and riveted in the oil cooler door, using the RV-12iS plans which include a nice holder for the oil cap riveted to the inside of the door.

The NACA duct used to cool the voltage regulator was fitted and glassed in.  I'm siffck of fiberglass.

Off Topic: more Colorado wild life.

My home in North Carolina was waterfront on beautiful Badin Lake, a 5500 acre reservoir 25 miles east of Charlotte.  There were quite a few nesting pairs of Bald Eagles there, so seeing them fly by was common, but never got old.  I never had one land on my house, however, until I moved to Colorado.