Friday, December 9, 2016

Replacing Some Bing Carburetor Parts

Frequent readers of the DOG Aviation Blog will remember a couple of weeks ago a partial loss of power occurred during climb out from the airport moments after there was a faint smell of fuel. Of course, the flight for the day was aborted and the RV-12 was immediately landed so inspections could be made. After looking at the Dynon SkyView’s flight data log, it was determined the issue was caused by the left carburetor going rich … so the carburetor bowls were removed for inspection of the carburetor’s parts.

Nothing unusual was discovered with the left carburetor except for a very tiny piece of grit in the bowl (which may have caused the issue but it sure was small) … however, the same could not be said about the right carburetor which had a good sized flake of what appeared to be a flat black paint laying on the bottom of the bowl. It was noticed that the float bracket was entirely black as opposed to a shiny brass … looks as though it had been coated. The only shiny brass was where the float pins made contact and where the clip for the needle valve rides … which revealed a large shiny brass area which I suspect is where the flake came from. Having taken the Rotax maintenance classes, I knew this was not right. In the realm of aircraft, when you see something you know is not right, it needs to be addressed now … not later.
Here is a photo of the right carburetor after removing the bowl. One can see the entire float bracket is black except for the shiny brass area where the clip for the needle valve was riding … this is the area that I believe the black flake discovered on the bottom of the bowl during the first inspection came from.

I placed a call to Lockwood and ordered replacement parts and a few spare items such as gaskets floats, etc., just to have on hand for ongoing maintenance. While on the phone to Lockwood, asked to be transferred to tech support to find out if they had ever seen a black float bracket … so explained to tech support what I had discovered. I was told that they have never seen such a thing. The only conclusion we could come to was that Bing (the manufacturer of the carburetor) placed a float bracket in the carburetor that is used on another type of engine. I was told Rotax does not assemble the carburetors they are purchased from Bing intact … so it had to have come from Bing that way. This must be the case because if the black coating was caused by alcohol or some additive in the fuel, one would think the float bracket in the left carburetor would look the exact same way … nope, it is shiny brass.

A few days ago the DOG Aviation procurement department received the new parts from Lockwood (great service – two days) and surgery began on the carburetors. To remove the float bracket and associated needle valve, the pin the float bracket pivots on needs to be removed. Before attempting to drive the pin out, one needs to take a VERY close look at the pin … one end of the pin has a taper at the edge of the pin (as seen in the above photo) and the other end of the pin has a knurled edge which provides friction when driven into the carburetor. The pin needs to be removed by tapping it out from the tapered end so the knurled end is pounded out of the body of the carburetor at which point the pin slides out easily with only finger pressure. On my carburetors, the knurled end of the pins went into the carburetors on the side of the carburetor where the bowl vent tube resides. This is kind of a three handed job in that, one person needs to hold the carburetor while the other person wields a small hammer and taps out the pin by using either another pin or a small pin punch … I used a pin purchased as a spare. Bernie was able to lend assistance, so we had the pin moving after just a few light taps with the hammer. Once the knurled portion of the pins were clear of the carburetor body, the pins on both carburetors slid out easily. During reassembly, each pin was positioned so the knurled end seated into the existing groves in the carburetor.
Here is a close up of the 861-192 float bracket from the right carburetor alongside the new shiny replacement float bracket.
Same parts as in the previous photo ... but flipped upside down.

Because the floats in both carburetors were floating well and weighed the correct amount, they were left alone. However, decided to replace the needle valves and float brackets in both carburetors even though those parts looked OK in the right carburetor (the one that went rich). After replacing the float brackets and needle valves, the carburetors need to be turned upside down so the float brackets can be adjusted. The float bracket is adjusted so both arms that the pins on the floats contact are parallel with the body of the carburetor. This is accomplished by bending the tab on the float bracket that the needle valve rests against and slight tweaking of the arms on the float bracket for fine tuning to get them both parallel with the carburetor’s body. The parallel float arm can sort of be seen in the first photo above  …. although not directly a side view as one would use when adjusting the float bracket, the viewer can see the arm on the float bracket is parallel to the body of the carburetor (portion that the green gasket goes into).

Have not flown the RV-12 since the carburetor parts have been replaced as the weather here in northeast Ohio has not been good for weeks. It has either been raining, snowing or there have been very low clouds as can be seen in the following photo.
After replacing the carburetor parts, it would be nice to go for a test flight but the weather has just not cooperated … it has either been raining, snowing or the days have been dreary with low clouds as can be seen in this photo.

Yesterday, we began getting into real winter conditions with a significant drop in temperatures along with snow forecasted off and on for the next few days … so at this point not sure when the next clear day will be coming along so another test flight can be made. It is official … winter has come to northeast Ohio.

Tuesday, December 6, 2016

Compatibility Issue Discovered Between Dynon SkyView And Garmin GTR 200 Radio

Have discovered a compatibility issue between the Dynon SkyView Touch and the Garmin GTR 200 radio installed in the DOG Aviation RV-12. Below is a detailed description of the issue and a workaround what works.  I felt Dynon support should be made aware of the issue and have notified them about the problem. If there is a solution forthcoming, I’ll return from the future with the info and edit this post accordingly. I’m guessing the solution will ultimately require a SkyView software update.

Before going into the “issue”, for the reader’s benefit, the aircraft/avionics configuration is a Van’s RV-12 outfitted with a Dynon SkyView Touch running version 14 software and a Garmin GTR 200 radio with the latest 2.7 firmware. The wiring and configurations are such that a list of airport frequencies can be displayed on the SkyView, the desired frequency can be pushed to the GTR 200 radio’s standby by pushing a button on the SkyView. Also, GTR 200 active and standby frequencies are displayed on the upper line of the SkyView’s display. The Garmin GTR 200 radio is wired to the SkyView’s serial port #4 and the device name of GTR 200 was selected for the serial port … all a standard Van’s RV-12 configuration. Additionally, I have wires running from switches on the control stick to the GarminGTR 200 radio’s discrete inputs 1 & 2 … one stick switch flip-flops the GTR 200's active and standby frequencies and the other stick switch cycles through the GTR 200’s COM user frequency data base.

A few weeks ago I decided to take advantage of the programmable COM user frequency database built into the GTR 200 and began entering all the pertinent frequencies for my home field and the CTAF (common traffic advisory frequency) frequencies for some the county airports within my assigned phase one flight testing area. I did not enter airport ID’s … instead, I used the actual name of the field such as Knox, Carroll, Wayne, Holmes, Clever, Downing, ect.

The "issue" I ran into is two pairs of airports shared the same CTAF frequency ... Wayne & Clever share one frequency, while Holmes and Downing share another. What’s the big deal you ask? Well, the name of the airport displayed on the GTR 200 radio was dependent on the order in which the airport name was entered into the COM user frequency database.

Example: Holmes was entered into the COM user frequency database before Downing and when cycling through the database and stopping on Downing, the GTR 200 would display Downing briefly then the name displayed would change to Holmes. This also happened when selecting Clever … Clever would display on the GTR 200 for a few moments and then the display name would revert to Wayne which shares the same frequency but was entered into the COM user frequency database ahead of Clever.
Here the COM user frequency database was cycled through to select Downing as can be seen in this photo … a few moments later, the name changes (see next photo).
As can be seen in this photo, without touching any buttons the name displayed in the previous photo on the GTR 200 radio has mysteriously changed from Downing to Holmes.

For the last week or so, I have been working with Garmin support via Email exchanges and looking at settings, etc. … all of which seemed to be correct. After verifying the settings were correct, one test Garmin support wanted me to perform was to power down the SkyView but leave the GTR 200 powered on and see if the names displayed correctly when cycling through the COM user frequency database … THEY DID!!! When I powered the SkyView back on, the names began changing again. This indicated the issue was actually being caused by the Dynon SkyView.

After another Email exchange, Garmin support suggested that I try changing the device name associated for serial port #4 from GTR 200 to SL40. I did that and it appears to have worked! The GTR 200 now displays the correct name for the selected COM user frequency in the database and the SkyView no longer mysteriously changes the selected name displayed on the GTR 200. Also, by changing the device name associated with serial port #4 to SL40, there has NOT been any loss of functionality … in that, the SkyView can still push frequencies to the GTR 200 radio’s standby and the active and standby frequencies selected on the GTR 200 display on the top line of the SkyView’s screen.

However, the same cannot be said for the airport name that the SkyView displays on the top line. For example: If the GTR 200 displays Clever 122.800  for the active frequency and Knox 123.050 for the standby, the top line on the SkyView  will display the correct frequencies for both the active and standby but does NOT display the name assigned to the frequency in the GTR 200’s COM user frequency database correctly. Instead, the SkyView changes the name to an airport code based on the frequency … resulting in a name code that may not correct as can be seen in the photo below.
One can see the Garmin GTR 200 radio’s active frequency is Clever 122.800 and the standby is Knox 123.050. However, when looking at the SkyView’s top line the Skyview displays an airport code of 3G3 for 122.800 and 15G 123.050 … the airport codes are incorrect for both those airports. However, 3G3 and 15G are valid airport codes for closer airports to the airplane's current position that share those same frequencies.

It appears to me as though the SkyView is looking at the current GPS position and selecting an airport name code based on the closest airport name corresponding to the selected frequency. I can live with the SkyView changing the name on its own display (rarely look at it anyway), but not on the GTR 200 radio … now that SL40 is selected, that is no longer an issue. As mentioned I don’t really look at the SkyViews top line showing the selected radio frequencies, so it is not a big deal that the airport name may not be correct from time to time. I would turn it off altogether … but should the display on the radio ever go on the fritz, the display on the SkyView can be used to see the frequencies the GTR 200 radio is being tuned to ... so the SkyView makes a great backup display for the GTR 200 radio.

Don’t know why the SkyView would mysteriously change the selected COM user database display name on the GTR 200 when the serial port is configured for GTR 200 … but it does for me. Sure glad changing the device name to SL40 solved the problem without a loss of functionality. I’m guessing this may not be unique to the RV-12 and will likely apply to any aircraft outfitted with a Garmin GTR 200 radio connected to a Dynon SkyView optioned to display com & display com in top bar.