Monday, November 21, 2016

Broken Wire, Or Is It?

What an interesting annual inspection I am having this year! After last years slip into the new year (I usually started inspection at Thanksgiving), I decided to make some changes this year.
One of those changes was to start earlier and instead of planing on a long downtime and doing it all at once, I was going to split the annual up into smaller packages that could be completed in a weekend and allow the plane to usable on the following weekend.
So I did the wheel bearing service with replacing the brake linings about a month ago, utilizing my newly acquired HF Racing Jack.

Worked like a charm! No more assistance needed to get the plane on sawhorses for this task.

I also completed the engine inspection 2 weeks ago and hopefully repaired an intermittent right CHT connection by recrimping the wire. Unfortunately, the problem only shows in flight. The sensor always reads fine on the ground but goes haywire right after take-off.

Other than that, no findings firewall forward.

Now the plane is down for a longer period as I opened the tailcone bulkhead and working on the flight controls. First item was to fix a problem that occured the first time after a SkyView software update (I think it was the update to V7.0) when it finally supported the standby network wires we had put in during the build. Mine was showing as defective and later versions even allowed the problem to get pinpointed to the standby network of the roll servo (behind the bulkhead).
Having access to it now, allowed me to finally see what was causing the problem. After a lot of measuring I was surprised to find that it is a problem with the wiring harness. Somewhere between the Y-crimp at the pitch servo which extends the orange wire (standby network 2B) from the roll servo through the tunnel to the aft of the bulkhead where it connects to the roll servo, this wire is broken.
If you have built an RV-12 or seen the tunnel of a completed one, you know that replacing a wire in this over-stuffed tunnel wire bundle is a very difficult task to say the least.
As I already had worked around this issue before when adding a wire harness for the ADS-B receiver (which I put behind the bulkhead) which runs from behind the panel under the longerons on the left side all the way aft of the bulkhead. I did make this wire conduit larger than necessary for such a case as this one where I see the need to add more to it.
I will utilize this wire path to connect the 2B network wire to the roll servo. Ideally these network wires should run in pairs and get twisted to reduce the noise they might pick up on the way. I am still contemplating if I just accomodate that by running a twisted pair back to it and just not use the one wire of the original harness that does work ok.

It turned out not be a broken wire at all.

After I ran the replacement wire for the failed connection to the 2B terminal of the servo and crimped it onto a showrt stub of the orange wire that connected to the servo, I still did not have a successful continuity from the panel to the servo. This could only mean one thing!
I disconnected the spade connectors for that wire on the servo side and measured again. No connection! A closer look into the connector revealed that I must have pushed the stripped wire passed the crimp part and had crimped the connector onto the insulation of the wire.  Duh!
Measuring between panel and the stripped part of the wire confirmed that it had a good connection.
I fixed this crimping issue and hooked up the servo and the Skyview display confirmed that everything was working now:

I also confirmed that the SB that most worries me (forogt the number , but it is the one about the little bridge taking the flaperon forces where the pushrods connect to the torque tubes) is still not an issue at 178 hours.

Left side

Right side

The rest of the inspection went without any hitch and a maintenance flight confirmed that the roll servo is no longer creating warning messages about the backup network within Skyview..

We also did not have any signs of overheating the voltage regulator:

Although I wish it was running a bit cooler. Maybe I do prepare to work on a scoop for the next oil change time when I have access to the radiator side of the lower cowl.

The ignition modules were doing fine too:

She's back in service since the Day after Thanksgiving.

Quick update from about a month later:
- the recrimp of the right CHT probe connector did its job for now. The CHT indication is solid but I expect that the repeated heating and cooling of the crimp as well as the engine vibrations might require repeated attention to these connectors in the future.
- It's really nice to fly without a constantly flashing warning indicator on the Skyview!

Monday, May 23, 2016

The End of The Blue Plague

I was out at the hangar on Saturday morning to fly out for breakfast but the wind had not developed as forecast. It had looked like I might have a small window to get to fly before 10am but it turned out that the wind had developed way before that. At 6:30am it was already at 11kts, gusting to 16, and 40 degrees cross to the runway with the crosswind runways closed for maintenance. The wind would turn further cross during the morning and also increase to 20+ knots, so I decided to just take a quick hop around the pattern as I has not flown for a few weeks due to a vacation.
The good thing about this blown out morning is that I finally got to remove the last trace of the Blue Plague from the bottom of the left wing.

Not a very good photo but I hope you can see the lack of any blue plastic sheeting on the bottom skin.
I guess that completed the build :-).

Next I will really have to take care of the unpainted plastic and fiberglass surfaces as the sun is starting to take its toll on the surfaces.

Thursday, March 17, 2016

Cracked Gas Can Caps

This is not really an issue with the airplane itself which is what this blog is focused on, but as the fueling system I use is one that many others are using as well, I thought it might be of use to some anyway.
After 3 years of use 2 of my 3 caps for the 7.5 gallon Flo-Fast jugs showed cracks like the one in the following picture.

I contacted Flo-Fast and they said that they had a batch around those 3 years ago that had some size deviations that led to cracks like these. They were sending replacements free of charge. They haven't arrived yet but I had already ordered replacement caps from a vendor (I am pretty impatient when it comes to exchanging emails. If a company doesn't answer within 24 hours I assume they don't care about emails) before we got some successful email exchange going. The caps I received are clearly made from a different material (I would guess it's fiberglass and not polyethylene or styrene like the old ones), so maybe it was not so much a size issue but a problem with the material used.
My jugs got exposed to a lot of temperature difference while closed and that might have added to these stress cracks.
Anyway, now you know that it might be a good idea to take a closer look at these caps when you notice a pronounced gas smell around them.

Update: The 3 replacement caps from Flo-Fast arrived over the weekend and they look exactly like the ones previously ordered from a car supply shop. The material looks like it is fiber-reinforced and seems to be a lot sturdier than the original caps that came with the jugs. We'll see how they hold up.

Monday, January 11, 2016

Yet Another Annual

The plane is down for inspection since December. I am by no means ready to formally document everything yet but there was one issue I should inform readers about before they run into the same problem.
The nice blue air filters I had installed during the last annual (and which appeared just fine in March when I installed the Ducati regulator) both showed cracked bodies just behind the attachment flange. They were both cracked almost to 50% of the circumference and clearly did not provide much filtration at that point. When I removed them, I found that the rubber appeared to have worked its way into the serrations of the hose clamp that was holding it on, on both. One was so deeply connected that it ripped the rubber of when I removed the hose clamp. It almost looked like the rubber or plastic was not able to take the heat under the cowling as it looked partially melted into the hose clamp.
I was about to order replacement filters from the same place and am happy now that they ran out of stock. That gave me a moment to reconsider that they might just not be the best solution as an aftermarket product anyway.
I found a smaller sized K&N but decided to give Green Filter a chance. They have one model that just fits the Bing flange and I like that it is a fully paper/rubber model with no metal parts.

It has a pretty nice clearance and a very good fit to the rubber flange of the Bings. Actually, I had taper the inside of the filter flange a bit to be able to get them to slide on. The type number is 7069 and it appears to be only one that would fit the Bing inlet. Let's hope this one holds up to the vibrations better than the blue filters.

It was also time to replace the spark plugs. I did not do it at the 50 hour mark as they looked prestine. I just cleaned them and put them back in. They still did not look like they needed replacement but I did notice a deeper drop during the 4000 RPM ignition test in the last months, so I went ahead and threw them out.


Of course I had to try something new for the replacement, so I installed the Iridium version of the same DCPR8E plugs which have an EIX suffix. They are a bit pricey but then again they go into an airplane so we are used to overpaying, right?
The result by the way was amazing. The ignition test dropped the RPM only by 50 instead of 70-90 with the 8E plugs. We will see how they hold up and if this deteriorates over time but for now I think they might be worth it.

I might have to improve the air scoop for the voltage regulator as the temp indicator hit the lower mark so far and I don't believe she flew a lot during Arizona's hot summers....

One of my concerns last year was the plastic buffer in the tail cone that should keep the lower cable for the elevator from sawing through a bulk head. It was worn down very close to the metal and I had greased it with silicone grease to reduce friction.

I pushed the cable out of the way to get a better shot of the actual friction area and it looks like it did not deepen any further since last year. If it was touching the metal the primer would have rubbed off and there is no evidence that this is happening yet. I just re-greased it and will check again next year. The tension of the cables held up pretty well too and I did not tighten them.

One of the improvements this year was to finally add the APRS radio beacon. I am a licensed Amateur Radio operator, so it was just natural to put that license to additional use with the RV-12. I took quite some time to choose the right antenna for this project. I had an antenna from DeltaPop Aviation but was afraid that it was too heavy and catching too much wind load for the super thin skin on the bottom of the tail cone. I looked into mobile Amateur Radio antennas and considered different antenna bases and so on. After long deliberation with myself I decided to go back to the initial thought of using the whip antenna from DeltaPop Aviation. It is exactly tuned to the APRS frequency, has a matching network that eliminates static build-up and it is proven to survive the 120 knots TAS of an RV-12. The mobile antennas won't get used much above 80 mph and their radiator could separate from the base and fall off the plane if the set screw ever gets loose. All I needed to do was to properly reinforce the skin on the bottom of the tail cone to avoid vibration cracks over time.


The little fin is the PCAS antenna that I had installed last year. I finally hooked this one up to the Zaon MRX unit this year too. The base of the APRS antenna is 4 feet away from the base of the VHF Com antenna and I only had to slightly increase the automatic squelch of the SL-40 to not open up when the beacon sends a position (from 56 to 75).


So you can see that I took the reinforcement very serious. The large sheet is 40/1000" thick and a foot long, I put the transponder reinforcement plate on top that came with the RV-12 antenna and which we never used and I also installed some left over angle on the perimeter of the base sheet to stiffen it up while keeping it very light weight.

On the interior I did not get very fancy for now but it might turn out to be a good spot anyway. The Byonics radio was attached with cable ties to the tank fill spout (some foam in between to dampen vibrations). And the GPS antenna for the radio was riveted to the center bracket of the rear window to give it a good view of the satellites.

The only required switch on the dashboard is a breaker of 3 Amps that is labelled "Beacon" which I felt was quite accurate.

It worked right away when I switched Main and Avionics on. If you would like some advice on where to wire this into the existing 12V bus without causing a fire, just email me.
As you can see the Zaon MRX was finally installed too and it is connected through the 1 Amp breaker to the Avionics bus. So far I have not seen a case where it would have detected traffic when ADS-B did not see it but I haven't been flying in rough mountainous terrain yet, so the jury is out if this PCAS install was a waste of time.
The APRS beacon works great and you can now follow the travels of N128TL by following this link.

Besides adding stuff I was also able to determine the cause of my problems with the EGT sensors. The sensors work just fine but the wire of the right sensor (on the sensor side) had vibrated off. The stiff wire of the sensor harness is not just hard to reliably crimp a connector too but is not itself not very happy about vibrations. I did a brute force approach with a tube of red solicone to address that after soldering (yes, yes, I know, we will see if it breaks again) an extension to the broken harness wire.

I just smothered the EGT temp wires in a layer of red silicone in the hopes of softly reducing the vibrations enough to avoid future breaks.

This should have been the last item on my list but then Dynon announced the release of the GPS-2020 that would be the last piece in my Avionics system to be fully 2020 compliant. I couldn't pass that chance up to replace my current GPS while the plane was all opened up now, could I?
Dynon was very quick in delivering the GPS and I figured from the RV electrical schematics that this was a drop-in replacement. As I did want to reroute the 4 wires through the firewall, I just cut off the wires of the old GPS and soldered the new wire harness to the existing wires.

Getting the old GPS out was a hassle. The metal lock screws are almost impossible to hold well enough to turn the bolts. I ended up dremeling the case of the GPS back to I could get a wrench on them. The GPS still works but sure doesn't look so good now. Oh well.
Please note that you do need to upgrade your SkyView software to V14.0 or beyond to be able to use the GPS-2020. And you will have to go into the setup and manually make all the changes to make it understand that the previous GPS has been replaced.

I also checked that worrisome Service Bulletin item about the flaperon torque base in the tunnel. Sorry I can't remember the exact phrasing or the number right now. It's the one where an aluminum bracket starts developing a crack from a rivet hole after around 200 hours of operation. I took photos and they show no issues yet at 113 hours.

And the final installation was a piece of plastic that I designed and printed out on a side project I completed in December last year. It's a Kossel 3D printer and it allows me create neat stuff that would be hard to find otherwise. In this case it is a headset hook that allows me to finally have a good place for my Bose headset while I am away from the RV.

This is a prototype and I am trying 3M double sided tape on the back (the red type) but I a mnot sure if it will stay there when the plane heats up in the summer on the tarmac. So I will design another one that takes rivets for installation - just in case. Anyway, for now I am very happy that the headset is nicely stored under the avionics bay and out of the sun.