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.

Match Drilling The WD-1214 Flaperon Torque Tubes

Van’s RV-12 assembly plans instructs the builder to droop BOTH the left and right flaperons 1/8" prior to match drilling the flaperon torque tubes … so the metal shim pieces that were made for the occasion were used to create the droop. Using the sandwich method mentioned in the previous post worked out quite well and ended up being quite stable.

After the two 1/8" shims were in place and the flaperon drooped 1/8", pieces of flat bar stock were placed above and below the shims then clamped in position, sandwiching the shims in place.

A 1/8" thick piece of aluminum was used to verify that the correct amount of droop was achieved at the trailing edge. Looking good!

The right flaperon drooped 1/8".

After the flaperons were in a drooped position, a spacer 1/16" thick is placed between the WD-1215 flaperon torque arm and WD-1214 flaperon torque tube and the assembly is clamped for drilling. Prior to drilling, the WD-1214 torque tubes are to be positioned so the end of the tube is flush with the inboard edge of the WD-1215 torque arm. It was verified the torque tube was sitting flush on the spacer at both ends of the torque arm. At this point, the flaperon droop was verified once again and then flaperon torque tube was match drilled .

With the 1/16" spacer inserted between the WD-1214 flaperon torque tube and WD-1215 flaperon torque arm and verifying the torque tube is flush with the inboard edge of the WD-1215 torque arm the assembly is clamped for drilling.

Completed match drilling of right WD-1214 flaperon torque tube.

The above process was repeated to droop the left wing’s flaperon and match drill the flaperon torque tube. Now the wings will need to be removed so the bottom holes in the torque arm can be matched drilled into the flaperon torque tubes and all the holes enlarged to #12 so AN3 bolts can be inserted.

About to verify the left flaperon droop using a piece of 1/8" aluminum prior to match drilling the left flaperon torque tube.

This will be the last night the wings are left on until the RV-12 gets closer to completion. It will be much easier to move around the hangar without them getting in the way.

The Eagle Grows A Set --- Of Wings!!!

Yesterday was another joyous and momentous occasion in the evolution of the DOG Aviation RV-12 … in that the wings were successfully mated to the fuselage for the first time. It was another all hands on deck moment and with the assistance of Bernie, and team Mike (Mike T. & Mike K.) we were able to perform the initial trial fitting of the wings to the fuselage. Thanks for the assistance guys ... could not have done this without all your help.

Prior to installing the wings, a final inspection of the center channel area and correct positioning of the F-1204M rollers were verified. The rollers can be installed backwards so wanted to verify the SMALL step on the roller is in line with the slot the spar will be slid into.

Verifying the small step on the F-1204M roller is in line with the slot for the spar … this is good. The wing spar will roll on this roller as the wing is being inserted into the fuselage.

Left wing an inch or so shy of being fully seated. Helpers from right to left - Mike T., Bernie and Mike K.

There was a small issue with a little interference between the left wing spar and the lower edge of the F-1204H bulkhead cap. Was not surprised by this because other builders have reported this as well. The left wing was temporarily removed and placed back into the cradle so the bottom edge of the left F-1204H bulkhead cap could be trimmed a little. The spar just barely scraped the bottom edge of the bulkhead cap just prior to the wing being fully seated. After trimming some material away and reinserting the left wing, the right wing was inserted and it too began scraping the bottom of the right F-1204 bulkhead cap by about the same amount as on the left side. Guessing both F-1204 bulkhead caps only needed a 1/32" or so filed off, rather than holding everyone up while slowly filing the bottom of the bulkhead caps, decided to use the nibbling tool to quickly make a full cut all the way across the bottom edges of both F-1204H bulkhead caps … which on my tool removed a 1/16" of material.

Using a nibbling tool to remove a 1/16" of material from the bottom of the right F-1204H bulkhead cap.

Once the interference issue with the bulkhead caps was resolved, both wings were successfully installed. There was a little hassle getting the spar pins to go all the way through the spars … it is a tight fit and requires a little grease along with some finessing … not to mention some gentle persuasion from a soft faced mallet. A few light taps got the spar pins moving as the wings were being giggled.

Left wing installed and the spar pin (painted red) on the right side is keeping the left spar held in position and ready for the right wing to be installed.

Instillation of the right wing went quite smooth after trimming the bottom of the right F-1204H bulkhead cap.

Successful test fitting of both wings on the DOG Aviation RV-12. It was smiles all around as it is beginning to look a lot like an airplane. Unfortunately, both wings need to come off to install the flaperons.

After both wings were successfully installed, a fair amount of time was spent “taking it all in” before removing the wings so the flaperons could be permanently installed onto the wings.

Removing the left flaperon from the wing cradle.

Mike K., myself and Bernie aligning the left flaperon to the left wing so it could be bolted in place.

Bernie, Mike K. and myself taking in the moment … both wings reinstalled, this time with flaperons attached and now ready for the procedure to match drill the flaperon torque tubes.

All that is missing is the engine … and that should be arriving within the next week or two.

Both wings complete with flaperons attached to the fuselage, nothing damaged, nobody hurt ... a proud moment.

 Ready for flaperon drooping and drilling of flaperon torque tubes.

RV-12’s Right Flaperon Completed

This first day of the new month marked a milestone for the RV-12’s construction … the completion of the right flaperon which also signifies completion of the RV-12’s wing kit.

After the A-1202A&B aft skins were riveted onto the A-1205 ribs using the same method as on the left flaperon, a small assembly procedural change was made for the way the nose skins were riveted. After the counterbalance tube was installed on the left flaperon, theA-1201C outboard nose skin was riveted in place first, then the inboard and center skins were riveted in place. This time, since the nose skins were already match drilled, after the counterbalance tube was riveted in place on the right flaperon, the A-1201A, B &C nose skins were secured in place onto the right flaperon’s skeleton with Clecos, then riveted with flush rivets.

Securing the A-1202A skin onto the right flaperon’s skeleton with Clecos.

Using the pneumatic rivet puller to rivet the right flaperon’s aft skins in place with flush rivets.

                             As with the left flaperon, the hand rivet puller was used to set the aft most row of bottom

                              rivets which sit high at first because they touch the set rivet on the opposite side.

Right flaperon’s aft skins riveted onto the A-1205 ribs with flush rivets.

Riveting the counterbalance tube onto the right skeleton’s outboard nose ribs with a LP4-3 pop rivets.

Placing Clecos into the A-1201C nose skin to secure it onto the right flaperon’s skeleton.

All three nose skins attached to the right flaperon skeleton with Clecos and ready for riveting.

Using the pneumatic rivet puller to rivet the nose skins in place with flush rivets ... almost finished.

Setting the last flush rivet in the right flaperon with the pneumatic rivet puller.

 

After completing the riveting of the skins, the last thing the instructions call for is to install two pivot bearings on each flaperon using Loctite 243 on the first third of the threads. The plans instruct the builder to screw the pivot bearings into the pivot brackets until the center of the bearing hole is 11/32" above the flaperon skin. Because the bearing wants to flop around, measuring can be tough … one tip on the forums was to place a long AN3 bolt (which is 3/16” diameter) through the bearing and then measure ¼" from the bottom of the bolt to the flaperon skin … which would be the 11/32" minus 3/32" (half the thickness of the bolt) or ¼".

 

That procedure was utilized and improved upon by cutting two small pieces of ¼" OD tubing to use as a visual reference. The pivot bearing was screwed in until the bolt touched both pieces of tubing evenly. Then a square was used to true up the bearing.

                                         Using two pieces of ¼" OD tubing and a long AN3 bolt to achieve a

                                         clearance of 11/32" from center of the pivot bearing to the flaperon skin.

Completed left and right RV-12 flaperons riveted with flush rivets.