The Eagle’s Heavy Wing Issue - Solved!!!

A big shout-out to Tom in Kentucky …  thanks for posting on the VAF forums about your observation that your RV-12’s wing skins aft of the rear spar were not flat. It seems that Tom, much like myself, had a heavy wing … although Tom’s was the right wing and the DOG Aviation RV-12 had a heavy left wing. As mentioned in an earlier post, during early flight testing, I discovered a heavy left wing and followed Van’s suggestion of flattening out the aft edge of the flaperon on the light wing (right wing in my case). After flatting the aft edge just a little bit, went for a test flight and still had a heavy left wing, but seemingly slightly better.


Before bending more flaperon metal, decided to have a look on the VAF forums to see what others have done. I knew the rod end bearings were set correctly, so was looking for other options. Fortunately, I ran across Tom’s thread and read where Tom discovered the upper wing skins aft of the rear spar on his RV-12 were not flat … after Tom flattened the wing skins in this area, his RV-12 flew hands off without rolling. As mentioned in the previous post, decided to have a look at mine and sure enough, discovered I too had places on both wings where the skins were either low or high and proceeded to level this area on both wings.


Today I made a very late afternoon test flight during very calm conditions at the airport … the winds were very light with an occasional gust to 7 knots. There was no turbulence, so the RV-12 flew like it was on rails … I’m happy to report Tom’s suggestion regarding leveling the wing skins aft of the rear spar really made a HUGE!!! difference … no more heavy left wing!! Yay!!! The DOG Aviation RV-12 now flies level hands off.


A tip for fellow RV-12 builders that discover they too have a heavy wing: I would suggest prior to bending flaperon metal or adjusting rod end bearings (especially if you were meticulous when installing them), the builder should first consider taking a very good look at the skins aft of the rear spar. Drop the flaps to gain some clearance, then adjust the skins flat using a straight edge and block of plywood as documented in the previous post.  Fly again and if there is still a heavy wing, then look elsewhere … possibly getting draconian with the aft edge of the light flaperon or adjusting rod end bearings.


I’ve been holding off on really delving into the test flight cards since I have 40 hours to fly off, there is really no rush … so figured it best to tweak the RV-12 to obtain straight level flight first and then proceed to working through the flight test cards once the RV-12 flies straight ... which I'm happy to report, now it does.

What To Do About The Heavy Wing?

After installing the trim tab and prior to making a test flight, a seeming tool was used to ever so slightly flatten the aft edge of the “light “ (in my case the right) flaperon in the hopes of reducing the heavy left wing. This is the Van's suggested method for correcting the issue.

Using a seeming tool with tape on the jaws to ever so slightly change the shape of the trailing edge of the right (light) flaperon.


After making a slight adjustment to the right flaperon, the RV-12 was taken for a few loops around the pattern to see how well the rudder trim tab worked and if there was any improvement with the heavy left wing issue. I would have preferred to have flown away from the airport for an hour or so but there was an approaching storm front, so I just remained in the pattern for a couple of loops. Since I did not get up to cruising speeds, not sure if any adjustments to the newly installed trim tab will be required … but initial indications are the trim tab has helped quite a bit with correcting the yaw component. Now onto the roll issue.


As for the heavy left wing, there was seemingly a very slight improvement, but the left wing is still heavy. So will need to delve into it a little more before bending more flaperon metal. Went online and did a little research on the VAF forums to see what others have done to resolve their RV-12 heavy wing issues. There was quite a mixed bag of solutions and combinations thereof posted by builders. Some involved adjusting the rod end bearings that support the flaperons to the wing, some involving adjusting the shape of the trailing edge of the flaperons and one in particular that caught my attention … adjusting the upper wing skin aft of the rear wing spar. I’m very confident my issue is not with a rod end bearing adjustment, because I was extremely fussy about making sure all the rod end bearings were screwed into the flaperons the exact same amount and went through great lengths to make sure the measurements Van’s gave in the plans were strictly adhered to, so I’m leaning towards ruling out making any rod end bearing adjustments at the moment.


The one post by Tom, a RV-12 builder in Kentucky, that really caught my eye mentioned he noticed a small difference in the upper wing skins between his left and right wings in the area aft of the rear spar. Tom said reshaping the upper wing skins in this area solved his heavy wing issue. For those not familiar with the way the RV-12’s wing is designed, there is a rear spar that runs along the span of the wing and the upper wing skins overlap this spar by a couple of inches. This is done to present a smoother airflow to the upper surface of the flaperons rather than having a large gap between the rear spar and the flaperons which would create a significant amount of turbulence over the surface of the flaperons. Anyway, I used a straight edge to check this area and sure enough, there were differences between the two wings and even on the same wing. In some places the aft edge of the upper wing skins were high and some places they were low. So using the straight edge and a piece of plywood, the wing skins were massaged until the wing skins aft of the rear spar were fairly straight.


The process begins with raising the flap handle to full flaps to open up the gap between the flaperons and the wing skins to make room for a block of wood. One can see in the following photos that at some locations the aft edge of the upper wing skins were low and other locations were high. Also of note, the amount of deviation was actually a lot more initially, but I began hand massaging the skins before thinking of taking any photos and using a piece of wood to really dial it in as close as possible.

Here one can see the upper wing skin that extends aft of the rear spar is bent down at this location and needs to be raised.

Using a piece of wood to flex the aft portion of the wing skin up to raise it a bit at this location.

In this area, the upper wing skin aft of the rear spar it too high, as can be seen in this photo.

With a lot of patience I was able to get both wings tweaked so the upper wing skins aft of the rear spar are now fairly consistent between the two wings and for the most part, flat aft of the spar. Will need to test fly the RV-12 and see if there is any improvement … I have a good feeling there will be a change, hopefully the one I’m looking for.

Landing Light Lenses – Instillation Woes

Prior to performing the weight and balance calculations that need to be completed for the airworthiness inspection, every piece of the airplane needs to be installed so accurate measurements can be obtained. One seemingly small task that needed completing was installing the landing light lenses. That small task turned out to take quite a bit of time to get accomplished.


The issue revolved around the W-1223E lens backing strips. Van’s plans call for using double sided tape to stick the backing strips onto the lens then insert the lens into the wing. In order to insert the lens into the opening in the wing the lens needs to be flexed a bit and wedged in behind the leading edge of the wing but in front of the landing light ribs. With all the flexing the backing strips kept popping off. I think the big issue was that I was using the thin double sided tape that looks like Scotch tape … guessing I would have been better served with the thicker foam type double sided tape.


It took quite a while trying different methods to keep the backing strips in place with no real success. Was just about to close up shop to head out and get some of the foam type double sticky tape when an idea came to me that ultimately worked great ... and I can whole heartily recommend it to fellow builders who don’t want to fuss with double sticky tape. I ended up using two lengths of waxed cord (the thin type used for jewelry crafting) looped through the center two holes of the W-1223E backing strips but instead of tying a knot, the waxed cord was twisted a few times so it would hold the strips in position while inserting the lens into the leading edge of the wing.

Because the double sided tape was not working out to hold the backing strips onto the lens, to get the task done waxed cord was looped through the two center holes then twisted a few times. Ultimately this worked out quite well to hold the backing strips in place while the lens was inserted into the cutout in the leading edge of the wing.


After the lens was in an approximate position, the outer two screws were threaded into the nutplates. Once the outer two screws were started, the twists were removed from the wax cords and they were pulled out so the remaining two holes could be secured with screws. The wax cord used was the thinner style found at arts and crafts shops for making jewelry.

With screws in the outer edges of the upper backing strips, the waxed cord was unwrapped and is now ready to pull out. The bottom backing strip is now in position and ready to receive screws in the outer two holes.


After the outer screws are in place and the waxed cord removed, the center two holes on each backing strip received screws to complete the instillation of the lens.

Completed instillation of the landing light lens in the wing … one down one to go.

Gee, this was so much fun … think I will do it again for the additional landing light in the other wing.

Instillation Of Navigation/Strobe Lighting Completed

It has taken a little longer to get the navigation and strobe lighting instillation completed  than expected (mostly due to not being at the hangar) but Thursday it finally all came together … although there was a small bump in the road I’ll mention later. During the last couple of short work sessions the wires were stripped back and male .062 Molex connector pins were crimped onto the wires then placed into the Molex connector body. Because the DOG Aviation RV-12 is using shielded cable for the nav/strobe power leads (which is a modification), the cable for each wing tip light was stripped back and the shields were connected to the ground wires that attach onto the outer wing tip skin ... this was accomplished by using heat shrink solder sleeves and removing a band of insulation from the ground wire so the solder sleeve could make contact when heat was applied to shrink and melt the sleeve.

Wires attached onto the Molex connector for the left wing’s navigation/strobe lights.

After the wires from inside the wing were connected to the Molex connector for each wing, the W-1222 wingtip extensions were prepared for final assembly. The assembly instructions call for using a thin coating of fuel tank sealant on the flange of the wingtip extensions that will sit on the W-1204D wingtip closeout skin … this requires masking off the area so when the tank sealant oozes out while riveting, it won’t make a huge mess. A really thin strip of tape also needs to be cut and placed on the edge of the W-1222 extensions between the rivet holes and outer edge of the part. My circuit board etching tape would have been very handy for this, but it was 75 miles away at the southern Outpost ... so I resorted to cutting thin strips of electrical tape with scissors.

Electrical tape was placed on the wing’s skin leaving about a 1/32” gap between the tape and the W-1222 wingtip extension. One can also see thin strips of tape were placed between the rivet line and the outer edge of the extension.


At this point the W-1222 wingtip extensions were slathered with a thin layer of fuel tank sealant and riveted in place.

The W-1222 wingtip extension riveted in place onto the left wing. The fuel tank sealant can be seen as the dark area under the flange the rivets are set into.


Unfortunately, when installing the nav/strobe lights, I discovered that the oval slots on the extensions cutout for the Molex connectors were too small for the body of the Molex connector attached to the wires coming from the nav/strobe lights to pass through. The Molex connectors from the wings passed through the slots just fine, but the Molex connector housings on the ends of the wires from the nav/strobe lights are larger … so they would not fit through the opening in the extensions until the slot was made a little larger. It was a little disheartening to discover this after riveting the extensions onto the wings, but the issue was easy to resolve spending 10 minutes on each wingtip extension with a couple of jeweler’s files. Note to fellow builders: Check that the body of the Molex connector that is wired to the lights passes through the slot in the F-1222 extensions prior to riveting the extensions in place.


The physical instillation of the navigation/strobe lights onto the wingtips is a snap (once the Molex connector body can pass through the slot on the W-1222 extension). After the Molex connector body is passed through the slot in the F-1222 wing tip extension and the housing for the light sits directly over the bracket, it is then pushed aft to lock it in in place on the bracket. To secure the light housing onto the wing tip, there is a small set screw that screws into a hole on the aft edge of the light’s housing which tightens up against the bracket preventing the light from moving forward and unhooking itself from the bracket.

Photo of the completed instillation of the navigation/strobe on the left wingtip. My finger is pointing to the hole for the Allan set screw that secures the body of the light onto the bracket.


One item I forgot to take a photo of was the use of a wire tie to secure the Molex connectors together. The Molex connector used is for five wires but only four positions are used for the nav/strobe lighting. I used the ScotchBrite wheel to shave about 1/64 inch from the edge of a small wire tie so it could be passed through the unused hole in the connector and tightened. This will prevent the Molex connector from separating on its own. I also pulled  out the spare slack of the pull string that runs through the electrical grommets in the wing and tied the pull string onto the Molex connector so it would not get lost in the wing.

F-1222 Wingtip Extensions Prepared For Final Instillation

After letting the flox mixture cure overnight, the remaining two #30 holes were drilled into the F-1222 extensions, through the cured flox and into the W-1204E wing tip ribs. Upon drilling the two holes in each extension, they were removed and the clay plug was removed and that area cleaned up … although not necessary, some of the excess blobs of flox were cut away with a Dremel tool.

Drilling the second of the two #30 holes that needed to be drilled into the W-1222 extension, through the flox and into the W-1204E wingtip rib.

The W-1222L wing tip extension after removing the clay plug and trimming away some of the excess flox. Now knowing what the end game is supposed to look like, far less flox could have been applied to the part.


Looking at the above photos, one can see there is no flox on the outer edges of the extensions. When the extensions are Clecoed in place, I noticed there was a small area where there was somewhat of a gap between the extension and W-1204E wing tip rib right at the forward edge of the extension. Not wanting to stress the fiberglass when it is riveted, after all the countersinking coming up next was completed, a small amount of flox was added to that area on both extensions and they were Clecoed back in position to let the flox cure overnight.


There are three mounting holes that need to be drilled into the W-1222 extensions for the mounting bracket for the nav/strobe lights. There are tiny dimples molded into the W-1222 extensions to help position the mounting brackets for drilling. The mounting bracket is centered as best as possible over the dimples and clamped in position for drilling using a #27 drill bit. After each hole was drilled, a screw was placed in the hole to help hold position. Once the three mounting holes are drilled to #27, the W-1222 extensions require machine countersinking.

The mounting bracket for the left nav/strobe light is clamped in position on the W-1222L wing tip extension and ready for match drilling using a #27 drill bit.


With the mounting holes for the brackets now drilled, per Van’s instillation instructions, the W-1222 wing tip extensions require some machine countersinking for all the holes common to the outer surface of the W-1204E wing tip ribs using a #30-120 degree bit for the flush rivets that will be used in this area. Because the DOG Aviation RV-12 is using flush rivets on all the outer surfaces, in addition to machine countersinking the required rivet holes mentioned above, all the remaining rivet holes in the W-1222 wingtip extensions were also machine countersunk for flush rivets.

Machine countersinking the line of rivet holes in the W-1222L wingtip extension common to the W-1204E wingtip rib using a #30-120 degree countersink bit.

Completed instillation of the mounting bracket for the nav/strobe lights on the W-1222R wing tip extension.


At this point, I drove home to get a small hand held vacuum that could be slipped in through the access hole in the wing tip so all the metal chips from the drilling could be removed from inside the wing. By the time I got back to the hangar and finished with cleaning up the debris from inside the wing, it was getting a little late to continue on … so mixed up a small batch of resin and flox and applied it to the previously mentioned area where there was the small gap, Clecoed the extensions in position and left them to cure overnight.

W-1222 Wingtip Extensions Floxed

In order to finish off the repair of the leaky fittings on the brake master cylinders, it was necessary to bleed the brake lines once again. This time, Bernie and Mike K. were able to lend assistance yesterday morning with the brake line bleeding chore. The left and right brake lines were filled with fluid from the calipers up using the same pump oiler and method used before.  However, this time around it appeared the brakes were still a little spongy, so with most of the air out of the lines we switched tactics. I got inside the cockpit to pump on the brake pedals as Mike continually added fluid to a tube connected to the brake fluid reservoir while Bernie worked the bleeder valve at the caliper and monitored for air bubbles coming out of the line. The whole process took us a while, but the brakes appear to be quite solid now and so far, the fittings on the master cylinders are remaining dry.


With the brakes functional again, it was time to get back to working on the W-1222 wingtip extensions for the navigation & strobe lights. The next step for installing the W-1222 wingtip extensions involved flipping the wings upside down which Mike helped me do. With the wings upside down, a batch of resin mixed with flox is applied to the inside edge of the W-1222 extensions to fill the void between them and the W-1204E wingtip ribs. Prior to applying the resin/flox mixture, the areas around the wing that could come in contact with the flox are to be covered with wax … as is typical at DOG Aviation, this was taken one step further, in that the contact areas were covered with clear packaging tape and then Vaseline was smeared onto the tape as the release agent. There is also an area on the W-1222 extensions that needs to be protected from the flox so a nut can be installed later in the assembly process … Van’s suggests using a plug of modeling clay to protect the area from the flox, which was done.

A plug of yellow modeling clay is used to protect a location that will be used for a nut to secure the mounting bracket for the  nav/strobe lights. Looking closely at the area my finger is pointing to, one can see the line of the packaging tape which was rolled over the outer edge of the wing tip. Another strip of tape was used on the other side of the wing adjacent to the outer edge. Prior to applying the flox, the packaging tape was slathered with Vaseline so the extensions can be removed to work on the electrical connector and the mounting bracket attachment after the flox mixture cures.


After applying the flox mixture to the inside edge of the W-1222 extensions that will contact the W-1204E wingtip ribs, the extensions are secured onto the wingtips using Clecos. It appears the main reason flox is used here is to fill a void between the W-1222 fiberglass extensions and the W-1204E wing tip ribs … because after the flox mixture cures, it is necessary to drill two more rivet holes through the extensions and into the W-1204E wingtip ribs … that area can be seen between my fingers in the photo below.

After the resin/flox mixture is applied to the inside edge of the W-1222 wingtip extensions, the extensions are secured onto the wing using Clecos to hold position as the resin/flox mixture cures. After the flox has cured, the area between my fingers will receive two #30 holes for rivets.


Prior to leaving the hangar for the day, I wanted to get a little more done so the ELT antenna and bracket was installed. This has remained off for access, but now that the fuel tank and rear window are now installed, figured it was time to mount the ELT antenna. Nothing out of the ordinary here so no photos were taken since this was covered earlier this year ...  it was just a matter of installing three screws and attaching the antenna wire to  the connector on the base of the antenna.


Now that the flox has had time to cure overnight, the first order of business today will be  drilling the two#30  rivet holes, then remove the extensions to continue with the mounting of the bracket for the navigation & strobe lights and the electrical connections.

Brake Fitting Replaced & Instillation Of W-1222 Wingtip Extensions Begins

Despite getting a late start at the hangar yesterday, was able to get a couple of things done. The new brake 90 degree brake fittings arrived so the first task of the work session was to install the fitting onto the co-pilot’s master cylinder. I’m pretty sure I could have used the old fitting but because I was really torqueing on it to attempt to get the last 180 degrees necessary decided it best to just try another fitting. Along with the new fitting decided to use a medium bodied thread sealant that has been recommended as being a good product for this task called TiteSeal. It is available in both a light weight and medium weight formulation … for this task the medium weight formulation was chosen.

TiteSeal medium weight sealant compound. Far as I know, this 1 lb can is the smallest quantity that can be purchased … enough for the entire RV-12 fleet many times over.


Between replacing the fitting and using the TiteSeal, hopefully the leaking at the master cylinder will be cured … time will tell. Moving on, went to work on fitting the W-1222 wingtip extensions onto the RV-12’s wings. The fitting process for the W-1222 extensions begins with drilling four #30 holes through the fiberglass and into the W-1204E wingtip ribs. The W-1222 wingtip extensions were placed on the outboard edges of the wings and the two forward and two aft holes for the extensions are #30 drilled into the F-1204E wingtip ribs. The hole locations are marked on the fiberglass as tiny dimples to set the drill bit on. After the four holes are drilled, the extension is removed for deburring and then Clecoed back in place so the lower flange on the W-1222 extension can be drilled into the W-1204D closeout skin.

After positioning the F-1222-R wingtip extension on the right wing and securing it with tape, the two leasing and two aft hole locations marked on the F-1222 extensions are #30 drilled into the W-1204E wingtip ribs.

Completed drilling of the F-1222R wingtip extension.

Looking at the above photo where the flat mounting surface is one can see there a large span with no rivet holes drilled at this time … this is because there is a void behind the fiberglass that will require filling with a resin/flox mixture. After the flox hardens the remaining two rivet holes will be drilled but the process requires flipping the wings over so will need some ground crew assistance for that.