Tuesday, January 2, 2018

Dynamic Propeller Balancing

Ever since I had my prop balanced in 2014 somewhere up in Phoenix I had the feeling that the guy who did it had not done a good job. He only had done it on direct drive Lycoming and Continental engines before and didn't care about inquiring about the details of the Rotax beforehand despite me offering to get him any information he might desire.
He claimed that the prop was already pretty well balanced when I got there (despite my toes experiencing quite some vibrations in flight) and he said he got it down to 0.02 IPS with one washer in one location on the spinner mounting plate. Pretty lucky, ey?
Well, I was suspicious but did not want to spend $4k to buy my own prop balancing equipment. Lucky for me, my friend Don deep down in Texas, had bought a PB-4 from SmartAvionics in the UK and was willing to lend me the tool to do my own balancing job.
This tool is a lot cheaper than traditional tools, i.e. Dynavibe, partly because they require WiFi connected device for the visualization of the data and for the user interface. A smartphone or a tablet or a small laptop would all work with the PB-4 as long as there is a web browser installed.
I used my iPad Air 2 as it seemed to be the best compromise between display size and ease of use.
Before I bore you with the set up of the sensors and prop indexer, let me summarize that the first measurement indicated 0.4 IPS @ 4000 engine RPM with the balancing weight installed and 0.35 IPS at the same RPM with the weight removed. That means whatever the guy was doing the first time around was making it worse instead of better. Of course, nothing had changed on my prop between 2014 and now. So my suspicions were confirmed.

Now to the set up. Don had never used the tool before and likely wouldn't have cared to use it on a Rotax anyway as he has a Viking engine on his RV-12. So I had to find a way of attaching the sensors.

Optical Prop Indexer

Close-up of tape installation

The prop indexer was a bit tough for me to get right as I misunderstood the purpose of the tape that goes on the back of the prop. I think it just needs a rough white or off-white tape to register the red LED light from the sensor. Instead of reading the manual I just tinkered around (waste of time, I know) until it worked for me which was a piece of white paper along the rotation axis of the prop (taped on with clear tape) and I added a piece of aluminum tape vertically along the prop blade in the middle of the white paper. That produced a stable RPM reading on the PB-4 side which was what I wanted to accomplish. You might get away with just some white tape on the back of the prop.

The actual accelerometer was mounted just outside of the view of this picture to the right and went on the back of the reduction drive. It has tapped holes there for M6 bolts which came with the PB-4.
Speaking of bolts... The angle that I built from scraps that holds the optical sensor, is mounted to the engine with M8 bolts that go into tapped holes opposite of the fuel pump location. That allows for a sturdy mounting point that gets the sensor close enough to the prop with enough clearance to allow for vibrations during start-up to not enter the propeller and cause havoc.

The cables were all hooked up and tied down with cable ties and lead staright under the canopy into the cockpit where they were attached to the PB-4 box.
That allows for an easy handling of hte on/off switch of the unit and a close proximity to the iPad in the cockpit.
The balancing procedure is pretty simple. Remove all previously added weights from the spinner, Run it in polar view and find a reasonable RPM (I chose 4000 engine RPM to start with) and see where the dot settles. Take some readings and this will be your starting point - 0.35 IPS in my case.

Then you add a bit of weight - the manual says anywhere - but I decided to put it opposite of where I saw the imbalance in my polar plot. That got me straight down to 0.1 IPS. For the new point, add where you added how much weight and it will tell you where you should put the weight in the next step to improve the imbalance. Rinse and repeat until you are satisfied.

Some advice on "being satisfied". I had my value down to 0.02 IPS at 4000 ROM and was very happy. 4000 is not a realistic value for flying the airplane though as we usually cruise above 5000. At least I do, 5400 usually. So I ran the engine up to 5000 (I stopped there because the whole frame started to wobble around and my prop is set to not exceed over 5200 WOT on the ground anyway). That was disappointing as the point of imbalance changed now and the IPS had increased to 0.12 IPS indicating it would get worse at 5400.

So I went back and redid the balancing procedure to get it down to 0..04 at 5000 engine RPM with a slightly higher value at 4000, I believe it was 0.08.

Now how does it feel in flight. I have to admit I am not completely impressed with the in-flight improvements yet. I can still feel quite some action going on in the rudder pedals that I believe to be vibrations from prop imbalance. Don't get me wrong, it did improve a lot over the previous condition but it feels much worse than when on the ground at 5000 RPM. I suspect that the nose wheel being on the ground impacts how the forces can resonate which likely skews the readings. The perfect setup would be one where you can record the measurements in flight.
Another way of getting close to the in-flight measurement might be to raise the nose of the ground during the balancing job. Maybe by adding a pulling force on the tail tie-down point.

BTW, I ended up with about 3 grams of washer in two places each to make a big improvement over the naked spinner setting.

Blue is my 0.35 starting point

Point 1 was with the wrong weight in place, the blue dot marks the real beginning with the wrong weight removed. The yellow spot indicates where I decided it to be good enough and close to noise measurements. I wish the PB-4 would allow to record the vibration spectrum in flight without the prop indexer in place. Unfortunately, without a proper index signal (0 RPM reading) it wouldn't show any data at all. All I would like to know is what mixture of vibrations I am seeing in flight. It would be easy to determine which spike the one is that is caused by the prop as it would engine RPM divided by gear ratio in the spectrum. Maybe what my toes are feeling are not prop related vibrations and couldn't be fixed by tuning it down more. Would be nice to know and I just don't see a good way yet how to install the optical indexer in a way that's safe for flight. 

Oh, and at last - after all the on/off/on for the engine which really is tough on the battery - I finally pulled my original Odyssey battery and replaced it with a new one. After 4 years it was getting a bit weak on cold days and as a matter of fact, the first start that morning of the balancing job, the blade moved to the compression spot and briefly stopped before pushing through and starting. That showed me that the battery's life span had reached its end. 

Saturday, November 25, 2017

4th Annual Inspection

The RV has 227.0 hours on it and a few things started to indicate that some work had to be done. The engine had started to run a bit rougher than I remembered it from the first year. The vibrations were noticeable at all RPMs and even at idle.
The carburetors are supposed to get overhauled at 200 hours which felt overdone to me but I decided to do it as I could not explain the roughness other than by being carb-induced (the balance was fine last year).
Also, my oil temperature indication was going haywire since a few hours ago. In the middle of a cross country the indicator would erratically drop below 120degF which would make B*tching Betty call out "Engine Speed!" 3 times in a row for every drop below 120degF. As it would frequently go back to a more believable reading and then drop again one can imagine how annoying and distracting this can be. Thank Van's for the "Isolate" switch on the intercom which shuts off dear Betty and lets you focus on flying the aircraft.
I also wanted to use the occasion to finally stop the oil drain bolt from leaking by installing a quick drain valve using Loctite 243 to seal it.

And so another Annual begins!

The spark plugs (these were the Iridium version of the NGK plugs) had reached a hundred hours and they definitely didn't feel that great anymore during the ignition check, so I decided to replace them. As I still have a stack of standard NGKs I decided to put the regular type in to reduce my inventory.
The plugs that came out showed the usual rich pattern with the exception of the top aft plugs on both sides that showed a healthy light brown color. It escapes me how this could be possible but that's what I found.

I ordered more of the Iridium plugs as they really make a difference in the Rotax when they are new but I'll first use up the old stock that I have accumulated. 

The visual inspection of the engine looked good. A very slow leak on the bottom of the oil canister as I have grown used to but creating enough of an annoyance to make it onto the to-fix list. 

The temperatures all looked within tolerances with the voltage regulator still being a bit on the high side. Something I am planning to address next time around by adding a fiberglass laminated scoop in the tunnel to increase the air flow for cooling. 

VR abit higher than I'd like

No indication on either ignition module

The oil change didn't reveal anything abnormal. And after 4 years of flying I also removed the magnetic plug for the first time only to find a very small amount of shavings on it. Just as you'd expect from a Rotax.
I installed the oil quick drain valve with Loctite 243 as planned and safety wired it to ensure it could not open in flight.

So far no leaks, so I hope the inside of the cowling will stay clean from now on. 

Off came the carbs for he first time/. The air filters looked really good by the way. No cracks, no chafing, no dirt. I think these green ones will be staying with this engine. 

A little bit of build up on the intake side

I had not taken these off in the first years as nothing had pointed at any type of issue and I am a strong believer in leaving a system alone if it isn't broken but I was very curious what I would find inside this time.

Opening the bowl revealed that on theleft side I had a small piece of debris in the carb and I have no idea how it could have gotten through the system that far.

Nothing else was found that didn't belong there. The floats were removed and put on a scale and - WOW - what surprise! As I said, nothing had indicated an issue but when I put the floats on the scale it showed that one had drowned.

Drowned float

still good

I assume the carb never showed a problem because one floating float is enough to keep the bowl from overflowing. I never had an issue with fuel smell or fuel residue in drip pans below the carbs.

old parts coming out

Needle shows signs of wear

Viton valve and arm were replaced for good measure although the valve did not show signs of wear yet. The needle though did and so I replaced needle and jet hoping that this was the reason for my rough running engine.

The interior was cleaned, seals lubricated and put back together.

The way I did the overhaul was one side ata time so I would have an untouched carb to look at if I was in doubt how something would go back together. So the next day I installed the overhauled one and took off the remaining carb of the engine and did it again.
The right side carb also had one slightly sunk float!

Too heavy

Still within tolerance

No other findings on the right side carb, and doing the overhaul for the second time was a lot faster than the first time around. 

The engine test run revelaed that the roughness was gone. The engine was running very smooth, almost purring, with no indication of imbalance. The only thing that did change was the idle setting. You have to know that the way I removed the carbs from the engine was by removing all throttle and choke linkages from the carb so the balance settings would not get affected. So I was quite surprised to see the engine idling at 2200 RPM now, given that the throttle cable was in the very same position. Apparently the engine was running leaner now at idle which increased the RPMs. 
I opened the idle cable stops and readjusted the setting after the engine had heated up and set the idle to 1400 RPM which feels like the engine is just about to quit on its own. On final with forward movement the prop will turn easier and the engine will be ok with that low idle but it will allow me to slow down as much as possible.

The Skyview battery test next and it passed ok but it looked like it was just at the edge of failing. So I'll be prepared next year to swap it out with Dynon again. Probably do the test early on so I don't have to wait for shipping when I'm done with the mechanical part of the annual inspection.

Pretty low voltage close to end

The oil temp sensor was an interesting chapter. I tried to find a replacement from VDO to have one on hand in case it turns out that the temperature fluctuations I saw were caused by the sensor itself and not just by a bad connection. Don't get me wrong, the behavior strongly suggested a connection issue but I want to be ready in the case it did turn out to be the sensor anyway.
As I have documented on the forum, the cost of a Rotax temperature sensor for oil or CHT (p/n 965-531) is somewhere between $195 to $275 (as of 2017) which is completely ridiculous. VDO builds these for them and they usually run around $18-$25 when bought in an auto parts store. So to protect their business Rotax decided to use a thread on the sensor that was not commonly sold by VDO and so finding the correct type was a bit of a hassle. What you would be looking for from VDO is not one of their regular part numbers but a more complex internal ID system:: 323-801-010-001D, a.k.a. 801/10/1,  which should translate to 300 degF (150degC) NTC with a M10 x 1.5 threading and a flathead connector that allows a female spade connector to slide over it.  The regular VDO sensor in M10 (VDO #323-423) comes with a 1.0 pitch thread and will not fit on the Rotax.

Now back to my case of fluctuation. I removed the spade connector and found a very slight movement when tucking on the wire. So I decided to solder the wire in the crimp and add silicone on the connection between wire sleeve and crimp to help dampen the movement caused by vibrations.
The readings were a lot more solid on the ground where I had previously seen a ibt of a nervous 5 degree fluctuation up and down. Now it just sits there rock solid, so I have good hopes that this did indeed fix the problem and I won't be needing to replace the sensor.

This concluded the burning issue list items. A while back I had decided to finally add the carpet interior to my 12 as the interior noise on long flights was somewhat tiring and I hoped that the carpet could help with that - next to looking really nice of course.

Needed some custom trimming as I still have a sight gauge and my Moeller is not in the official spot as I added before Van's adapted this to their kit

It will be nice for the passenger to have something to rest their feet on

I did not install the carpet over the forward tunnel as this part gets very hot in the summer on take-off and I am worried that carpet would increase the interior heat to a damaging point.
The other part I did not install yet is the upper triangular piece that covers the area around the vents. I have a headset hook installed there that I 3D printed and I need to see how I can keep that with the carpet.
Next time at the hangar I will perform a dynamic propeller balance and hopefully notice that the interior is really quiet now.

I'll post a separate article about the prop balancing as I have a feeling this will be a longer story.

Also, after the balancing I am going to install a new battery as preventative maintenance. The 4 year old one got a bit tired in the winter before and I was getting worried about not being able to start the engine. Voltage dropped to 9V when cranking longer than usual and any small engine hiccup that would have delayed engine start could have left me with a dead battery on the ramp. IThis winter is really mild and so far no issue but I thought after stressing the old battery with a succession of engine starts for the balancing, I might just retire it before I get stranded somewhere on a cold morning.

I also forgot to take a full cockpit picture once all the carpet and seats were back in which I shall add after the next weekend.

On to another 11 months of fun flying!

Update on the Fuel Pump

After about 25 hours on the replacement pump all the pressure readings are back to normal. The first 5 hours or so I was watching a break-in period though. The pressure would oscillate at about half a Hertz. Rise about half a pound, fall about half a pound and so on. It all worked itself out over the first few hours and the overall pressure also came back up to known levels.
So if you ever have to do this and the new pump appears to be behaving differently, give it some time and stay in gliding range of a landing opportunity during evaluation.

I finally got around to open the old pump and I was a bit disappointed.

This is the inside of the head

I actuated the diaphragm but regardless how close I looked I could not find any tear in the diaphragm material. Still, I know the pressure dropped to zero when I turned the electric fuel pump off, so there has to be a leak I just can't see it.

Monday, July 31, 2017

Fuel Pump Failure

End of June I wanted to depart on a breakfast flight to Benson with my wife, when ~3 minutes after take-off the cockpit quickly filled with a strong stench of gasoline. It wouldn't pass for a minute or two and I knew what that meant.
I turned around and climbed to 10,000 feet. Once over the field I turned off the electric fuel pump and watched the fuel pressure drop quickly to 0.2 PSI when the engine started running rough. I turned the electric pump back on and landed the plane, canceling our breakfast plans. Apparently the diaphragm on the engine-driven fuel pump had ruptured and leaked gas out the weep drain and overboard. At just 207 hours, that's rather frustrating.

out comes the old one....

It didn't take too much time replacing the pump, besides the inaccessibility of course. With crow's feet it's pretty impossible to put any controlled torque on the bolts and that includes the fuel distributor block.

... and in with the new one.
I did an extensive engine ground run at full throttle with only the engine-driven pump running to see if it was working alright. Then I headed for a test flight, steep take-off staying over the field and climbing to 10,000 ft.. Stayed there for 20 minutes before moving away, always staying in gliding range.
Without the electric pump running, the fuel pressure was oscillating between 2.6 and 3.4 PSI. I never saw that with my previous pump. It was a very repetitive oscillation pattern, almost rhythm-like.
Even on a cross country flight a week later I could still see this oscillation pattern but it never dropped below 2.6 PSI.
After coming back from Oshkosh (flying commercial) I had another flight where the mechanical pump produced rock solid 3.9 PSI. No oscillation and no jumps. Apparently, a new fuel pump does need some break-in period.

Let's see how long this one will last. Fingers crossed!

I'll disassemble the old pump to verify the failure mode of a ruptured diaphragm and I will update this post when I have the pictures.

Monday, January 9, 2017

Operating Limitations Overly Limiting

One of the things that most builders forget quickly after the exhilarating experience of turning a heap of metal into an airplane - also known as "receiving an Airworthiness Certificate - is that the whole world of experimental flying our kit planes is built upon something called Operating Limitations.
Without the OpLims, there is no experimental flying.

You will receive your Operating Limitations on the day you get your Special Airworthiness Certificate, better known as Pink Slip, and it explains in detail what you can do with the airplane in the initial trial phase, aka Phase I and what you can do once Phase I has been completed - which is referred to as Phase II.

You airplane will likely spent most of its flying life in Phase II, so those limitations are the most important ones for any owner of an experimental airplane.
When I received mine, I studied them and I found one odd set of limitations regarding Phase II and doing anything but flying in VFR conditions during the day.
I have to admit that because of the excitement of accomplishing a successful airworthiness inspection as well as the fact that I was going to fly the plane as a Sport Pilot this tiny weirdness did not bother me too much.
What it was you ask?

Well, here are the two limitations quoted from the OpLims:

10) This aircraft is to be operated under VFR day only

11) After completion of phase I flight testing, unless appropriately equipped for night and/or instrument flight in accordance with 14 CFR part 91.205, this aircraft is to be operated VFR day only.

The way the limitations were applied to Phase I and II respectively was by adding the numbers of the limitations that applied to a paragraph titled Phase I and II respectively.

Mine looked like this:

Phase I Limitations: 1, 2, 3, 4, ..... , 10, 12, ......

Phase II Limitations: 1, 2, 3, 4, ..... , 10, 11, 12, ......


Of course, you wouldn't want to fly your plane during the trial phase in adverse meteorological conditions like IMC or at night. So having 10) in phase I is perfectly fine. As 11) wouldn't apply, it is not listed under Phase I.
However, Phase II has apparently 2 limitations that deal with flying at night.
10) prohibits it altogether, and 11) would allow it if the plane was properly equipped (mine is).
10) is clearly more restrictive and I would think the FAA would use the more restrictive one as we are dealing with LIMITATIONS which are restrictive by nature.

Why do I even care? Didn't I say I was flying as a Sport Pilot anyway and Sport Pilots are prohibited from anything other than flying VFR day.

Yes, that was the case. However, I have started to work on my Private Pilot License and I wanted to use my RV-12 for all the required lessons I have to take with a CFI. That would include 3 hours of flying VFR Night and my OpLims clearly prohibit that.

I searched VAF and found that at least one other builder in Arizona was hit with the same mistaken limitation and that his DAR had told him that the FAA would not issue new OpLims but that this is clearly a mistake and only 11) would apply.
Hm, sounds like one would have to trust the federal government. That's quite a stretch, isn't it. And on top of that your CFI would have to be satisfied with this "explanation" too. Pretty unlikely as their job depends on it.

I contacted my DAR who had made my RV-12 an airplane about 3 years ago and explained the situation. He agreed that this set of limitations made no sense and contacted his person at the FAA who also agreed(!). What were the chances? Honestly!
My DAR was given authorization to issue amended  OpLims in accordance with the latest updated regulations and I should have them in my hands before the weekend. The new limitations are fully spelled out, much more narrative than the old ones and more importantly the issue of no night flying in Phase II has been eliminated.

What is the morale of this little story? Check your OpLims when you get them and get them straightened out if you find anything that strikes you as odd. It's likely easier when they just got issued and the copies haven't made it to the FAA yet.

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.