Takeoff Loss Of Power Experienced - After Fix Video

Earlier last week I was planning on making a trip to the furthest airport in my phase one fly off area. The air was cool and crisp, clear skies and very light winds …. a perfect day to begin working on seriously attacking the flight test cards.


After getting the oil temperature up and performing the preflight run-up, took to the active runway and decided on a 65 – 70 knot climb out. The engine was running good down the runway and developed over 5200 RPM as the climb out began. At about 250 feet off the deck I caught a whiff of fuel and a moment later there was a partial loss of power. I had lost approximately 1,200 RPM … I quickly throttled back some then advanced the throttle a little but the engine seemed “flat” so it was throttled to keep the engine around 4300 RPM where the engine was running OK and seemingly smooth , decided it best to abort the flight so called the tower for clearance to return to terra firma to conduct a “little FBI Double-O-Seven-type investigatin” to coin a lyric from a Jr. John song.


One of the really nice features of the Dynon SkyView is there is a built in flight data recorder that constantly records a plethora of parameters …  input from all of engine and fuel sensors, GPS, transponder, autopilot, airspeed, altitude, attitude, ect., ect. By default, the sampling rate is 16 times per second (this can be changed in the setup menus) which provides approximately 2 hours of very detailed data capture. If the sampling rate is lowered, then much more than 2 hours of storage can be obtained … as an example, a sample every 10 seconds will result in 150 hours of flight data storage.


Decided it best to make a data dump of the SkyView's log to a flash drive and try to analyze what happened ... this is done by saving the SkyView's data logs onto a flash drive plugged into the USB port. But before delving into that, I should mention the USB port under the instrument panel base connects to one of the USB ports on the back of the Dynon SkyView. The under the panel USB port is used for a plethora of tasks such as upgrading the SkyView’s firmware and allowing for the monthly updating of navigational data bases. In addition, third party chart software can also be utilized by the SkyView to display FAA sectionals, IFR approach plates and detailed airport diagrams called “Safe Taxi”.  Plus, the USB port allows flight plans to be loaded into the SkyView or saved from the Skyview along with allowing the pilot to make backups of all the SkyViews internal settings and the biggie for me at the moment, exporting of the SkyView’s user data logs. All of this can coexist on one flash drive ... it just requires plentiful storage space on the flash drive.


Some of the above features such as FAA sectionals, IFR charts and “Safe Taxi” airport diagrams require leaving a flash drive in the under the panel USB port so the SkyView can access the data as needed. This can present a problem, because a typical flash drive would extend down from the bottom of the instrument panel and could very easily be snapped off from contact with the knees or an arm. So one of the many niceties the DOG Aviation procurement department has recently purchased consists of two tiny PNY 32 Gig Elite-X USB flash drives. They are small  in stature (yet big on available storage space) … they are just long enough for the fingers to get on them to pull them out of the USB port. At 32 Gig, there is plenty of storage for the software revisions, monthly updates, third party charts, flight plans, saving internal settings and the biggie at the moment, saving the user data log recordings … with plenty of room left over. Two of the flash drives were purchased so one flash drive can be at the house to get updated with the latest maps, ect, then taken to the airport and swapped for the one in the SkyView.

As one can see in the above photo, compared to a rivet, the PNY 32 Gig Elite-X Fit flash drive is tiny and will not be subject to breakage from the knees because it barely extends beyond the USB port.


OK, back to the user data log dump … after making a safe landing and taxing back to the hangar, the flight data logs were saved onto one of the PNY flash drives to take home for analysis. Saving the user data logs to a flash drive plugged into the USB port is accomplished by pressing and holding buttons 7 & 8 on the SkyView to enter into the Setup Menu. The first item in the Setup Menu list is System Software … selecting this will bring the user to a sub-menu that has an entry of Export User Data Logs. Selecting Export User Data Logs will save the data logs onto the flash drive plugged into the USB port on the bottom of the RV-12’s instrument panel. The files are saved as a .csv file which is a computer file standard meaning … comma separated values. The Microsoft Excel spread sheet is capable of opening and displaying the contents of this type of file.


A tip for those builders using Excel to view the SkyView’s data log:  Do yourself a favor, after opening the data log file with Excel, click on the View tab on the top of the window and click on Freeze Panes … then select Freeze Top Row. What this does for you is freeze the top row which is where the name for each column is located … such as RPM, EGTL, EGTR, Fuel Pressure, Fuel Flow, ect. Freezing the top row allows the spreadsheet to be scrolled to where the event being analyzed takes place without losing the name for what the column represents. The user has to analyze what the numbers mean and form a picture in “your mind’s eye” as to how the numbers correlate with one another. So a lot of back and forth scrolling is needed … but there is a better way.


Getting high tech … deciphering the SkyView data log can be taken to the next level by using a service provided by a company named Savvy Analysis. Savvy Analysis offers a service for pilots that allows the Dynon SkyView’s user data log to be uploaded and converted into a graph chart which is visually much more meaningful …. various parameters can be selected by the user to be charted simultaneously, very cool!! And best of all, the service is free … unless you want them to analyze the data log results for you. Below is a copy of the Savvy Analysis chart showing the “event”… once I had the chart on the computer screen, I converted it into a .jpg file to post here on the Blog.

Uploading the Dynon SkyView’s data log to Savvy Analysis for conversion into a chart will yield an easy to look at chart of the event… which greatly aids in analysis of the event. Here the sudden loss of RPM can be seen accompanied with a cooling of the left cylinder’s exhaust gas temperature (EGT) while the right EGT remain unchanged. Looks like the carburetor for the left side went rich, probably due to the carburetor’s float needle valve getting stuck on a piece of debris.


As can be seen in the above chart, the Rotax 912ULS is turning out a steady 5,200 RPM during the climb out then instantly drops to roughly 4,000 RPM the exhaust temperature on the left side of the engine also takes a drop suggesting there was a rich mixture coming from the left carburetor. Also of note, at the time of the “event” the fuel pressure dropped from roughly 5.5 PSI to around 5 PSI which, to my way of thinking, would correlate with a stuck needle valve in the left carb reducing the fuel pressure because of the momentary excess flow of fuel. It is not a fuel pump issue because the minimum pressure for the Rotax 912ULS engine is 2.2 PSI so that is not an issue.


There are only a few things that would contribute to a carburetor going rich … excess fuel pressure (not the case here) choke being applied (it was full off) which leaves … floats sinking in the bowl, debris preventing the needle valve from closing, bad needle valve or float level adjustment being off … all of which require removing the bowls from the carburetors. So the bowls on both carburetors were removed for inspection. All the floats appeared to be floating nicely. Just to be sure, each float was weighed at 3 grams and each pair weighed 6 grams … so they are spot on weight wise. The left carb bowl (suspected problem one) had just one little speck of debris in it. I decided to turn on the master switch and use the electric fuel pump to flush out the float needle valves while moving them up and down with the float bracket. Next a check was made to see if the needle valves would stop fuel from flowing when closed … all seemed well. Also checked the arms on the float bracket which should parallel the body of the carburetor when in the closed position … both float brackets appeared to be correct. Interestingly, the right carburetor had much more debris in the bowl than the left carb did and also had a very small flake of what appeared to be a flat black paint or coating that appeared to come from the float brackets. This got me off on a short tangent thinking perhaps the wiring for the EGT probes got switched or the probes were attached to the wrong port on the engine monitor… I used a heat gun on the right exhaust pipe near the EGT probe to verify the Dynon SkyView data log file recorded the heat on the correct sensor … fortunately, it did so the “event” was a left carburetor event for sure.


After the carburetor bowls were placed back onto the carburetors, decided to make a test flight with a shallower climb out of 80 knots. The test flight reveled no engine problems. Engine RPM remained constant around 5,250 on the climb out until I pulled back on the throttle … so for the next few flights, will plan on staying in the traffic pattern for a handful of takeoffs and landings so I can incrementally steepen the climb outs to make sure the issue has been resolved. Below is a couple of videos of the takeoff and landing after working on the carburetors. The videos are heavily edited to meet the under 100 Meg requirements of Blogger. Unfortunately, the camera switched files just as I landed so there is a little skip in the video at that point as I landed with a slight thump. Also will have to make improvements on mounting location for Mike’s camera to get it a little sturdier so the camera does not rattle.

A takeoff video made after working on the carburetors all seemed to go well … had a steady 5,250 RPM on climb out although it was a shallower climb out than when I had the “event”.

During the landing, I kept the RV-12 purposely high until on final then slipped a bit to lose the excess altitude which can be seen during the period of time when the horizon looks canted while on final to the runway.

I would have flown a few more loops around the pattern but needed to get on the ground to install a winter heating system that requires temperatures around 70 degrees to cure the epoxy properly … and there are only two warm days left before the winter plunge. More on the  heating system in the next post.

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.

The Eagle Receives A Rudder Trim Tab

During the second test flight where the RV-12 was flown for over an hour and away from the home field’s traffic pattern, it was noticed there is a yaw component that needs addressed. To keep the airplane flying without yaw, it required a constant pressure on the right rudder. This is not unusual for a RV-12 without rudder trim … in fact, I would say it is the norm. As mentioned in a previous post, this was expected because I can’t remember seeing any RV-12’s at Oshkosh that didn’t have a trim tab or a wedge on the left side of the rudder. Van’s now has a trim tab available for the RV-12, but unfortunately it came out after the DOG Aviation RV-12’s rudder was completed.


A few weeks ago I ordered a bunch of goodies for the RV-12 such as a canopy cover, sun shade and a trim tab which will be installing now before the temperatures plummet … I wanted to use AKZO primer which is temperature sensitive, so instead of flying more at this time, we are spraying paint. The part number for Van’s trim tab for the RV-12 is R-01220 … the trim tab comes predrilled and pre-bent for the amount of trim that is typically needed at cruising speeds to achieve flight without yaw.

The pre-bent R-01220 trim tab and associated AD-41-ABS rivets used for instillation.

Installing the R-01220 trim tab on a completed rudder requires the removal of one rivet … the lower aft rivet on the left side on the rudder. Prior to removing the rivet and begin drilling, decided to prime the mating area first because the temperatures were forecasted to get much colder than would be suitable for the Akzo epoxy primer to cure properly. The trim tab was held in position and a line was traced around the trim tab so the area could be masked off and sprayed with primer along with the mating surface on the trim tab.

After placing the trim tab in position, a line was traced around it to denote the area that would require masking and scuffing with a ScotchBrite pad.


A one ounce batch of primer was mixed up and the RV-12 was rolled outside and the primer was airbrushed onto the rudder and trim tab along with a couple of other small parts that I want to install in the future.

Akzo primer was airbrushed onto the surface of the rudder where the trim tab will be installed.

As mentioned above, the lower aft most rivet on the left side of the rudder requires removal so the mandrel requires being pounded out so the rivet can be drilled and removed. Those following the DOG Aviation Blog know flush rivets were used during construction, so the rivet being removed is a flush rivet … this will require dimpling the corresponding hole in the trim tab. All the remaining holes that will be drilled will NOT be dimpled because the rudder is now built and there is no access. Also, the rivets are so close to the trailing edge that there is not room for the dimple dies … so the trim tab will only receive one dimple where the flush rivet is being removed and the remainder of the rivets will not be flush.

My finger is pointing towards the only rivet that requires being removed. This rivet hole is used to orientate the trim tap in the correct position while match drilling the remaining holes into the rudder. Because a dimple already exists here, the trim tab will be dimpled only at this location.


Not wanting to just pound on the rudder with a hammer while the rudder was on its stop, decided it best to ask for assistance … so asked Bernie if he could come by the hanger for a few minutes to give me a hand. Bernie held a rag covered block of wood on the right side of the rudder on the rib opposite of the rivet being removed. I used a hammer to pound out the mandrel in the center of the rivet using a mandrel from another rivet that was tapered on the end a little on a Scotch-Brite wheel. Once the mandrel was removed, the head of the rivet was drilled until it popped off so the remaining portion of the rivet could be pushed in clear of the rivet hole. After the rivet was successfully removed, the F-01220 trim tab was secured onto the rudder with a Cleco so the bend line on the trim tab could be aligned with the aft edge of the rudder. Once in position, the trim tab was taped in place so it would not move while drilling.

Match drilling the rudder trim tab to the aft left side of the rudder. Notice the drill has a drill collar. It was adjusted to only allow the drill to penetrate just a little deeper than the skins so the drill bit would not hit the opposite side of the rudder.


After drilling, the rivet holes in the trim tab and the rudder’s skin were deburred. To install the R-01220 trim tab, the lone dimpled hole received a flush rivet and the remaining nine rivet holes received the AD-41-ABS rivets supplied with the trim tab.

Using the hand rivet puller to rivet the F-01220 trim tab onto the RV-12’s rudder. The lower left hand rivet is a flush rivet because the rudder was already dimpled at this location … the remaining nine rivets are AD-41-ABS rivets.

Completed instillation of the F-01220 rudder trim tab on the DOG Aviation RV-12.

Flight Testing The DOG Aviation RV-12

It has been a few weeks since the first flight but at this point there has now been a few hours of phase one flight time logged on the RV-12. For those non-aviation readers of the DOG Aviation Blog not familiar with the rules for initial flight testing, here is a quick rundown. The FAA imposes a flight testing period called “phase one” testing. The required phase one “fly off” time period will vary depending on the certification type of aircraft. Because the DOG Aviation RV-12 was built and certificated as E-AB (experimental- amateur built), the FAA’s rules dictate the required phase one fly off time be 40 hours. The FAA will assign a flight testing area (this area can be negotiated within reason) for the phase one flight testing. During the phase one flight testing of the aircraft, the pilot must conduct all test flights within the boundaries of the assigned phase one testing area solo … no passengers allowed. After the phase one testing is completed, the shackles are lifted and the airplane is free to fly wherever the pilot desires … also, at this point, passengers can be given rides in the aircraft.


Being a “test pilot” is something not to be cavalier about … it needs be taken quite seriously and methodically as confidence in the aircraft is gained all the while slowly expanding the flight parameters. My hope was to have more time on the RV-12 by now, but the weather has not cooperated as much as I had hoped. There have been rainy days, days with very low clouds and days that although sunny, had way much more wind than I felt comfortable with for the first few hours of flight testing. Admittedly, thus far, I’ve been overly conservative on my weather requirements but there is no shame in that … in fact, it is prudent.


The RV-12 flies really nice and I'm very pleased with it thus far. But it can be made to fly even better ... in that, there are a couple of minor issues that need to be addressed. Now that I’ve got more hours on the RV-12 and have been up to fast cruse speeds there are two small issues that need addressed. First there is a slightly heavy left wing. It only requires fingertip pressure on the stick to keep the airplane level, but it will not fly level if the finger is removed. Letting go of the stick allows the left wing to slowly drop off from level and the aircraft begins to roll to the left. Having a heavy wing is quite common and for the most part fairly easy to resolve. The solution Van’s suggests trying first is reshaping the aft edge of the flaperon on the LIGHT wing (the right wing in my case). I made a small adjustment a couple of days ago and flew the RV-12 again yesterday and although slightly better it was not enough correction. After landing, I carefully used a pair of seeming pliers to tighten the bend (ever so slightly) on the aft edge of the right flaperon so will see if that was enough. Van’s says it does not take much to get the desired results so I did not get very aggressive. This type of tweaking requires lots of patience … make a small adjustment and go fly … repeat … until satisfied with the results.


The other small issue that I knew would be present at cruse speeds is yaw. The right foot needs to constantly apply steady pressure on the right rudder pedal to keep the aircraft flying straight without any yaw. Of course, that gets tiring after a while, so a rudder trim tab will be necessary. Read more about that instillation in the next post.


The other issues that were discovered after the first flight appear to be resolved. The oil line that had a smear of oil on the fitting was tightened and is not showing any signs of leakage now. Also the oil that was found dripping from the bottom of cylinder #1’s rocker arm cover was traced back to the exhaust stud during inspection and cleaned off. Now after the after the second flight of well over an hour, is almost cleared up now. After removing the cowl for inspection a slight amount of dark oil was found under the exhaust flange stud for the #1 cylinder as can be seen in the photo below.

Using an inspection mirror to view the small dark oil mark coming from cylinder #1’s exhaust pipe flange stud.

As can be seen in the above photo, the amount of dark oil is now just a small streak after over an hour of flying. The first flight only lasted fifteen minutes and there was oil all the way under the rocker arm cover and a drip onto the lower cowling. Now after an hour, there is just a small streak of dirty looking oil, so I’m convinced this is either oil left over from the machining process or an anti-seize lube of sorts … my money is on lubricant left over from the machining process working its way out of the thread gallery for the stud.


The other unexpected issue discovered a week ago was a small fuel leak coming from the fuel valve on the bottom of the gascolator. At first I thought it was a leak from the valve not sealing correctly ... but upon closer inspection, it was determined the fuel was actually leaking from the threads on the fitting. The fitting was tightened … twice in fact, and although the leak diminished somewhat, it did not stop.

The CAV-110 fuel valve can be seen here screwed into the bottom of the gascolator.

Close-up photo of a CAV-110 fuel drain valve.

I ended up deciding on just replacing the CAV-110 fuel valve and also used a different type of thread sealant (TiteSeal) on the threads … seemingly no issues now.