Fuel Flow Jabiru Engine

[Steevo]

Hi All,

I thought I would post this here as reference for anyone that is interested.

I have been working with MGL kit since about 2013 and have used and installed a fair few systems for myself, friends in our group and some other people that asked for help. The people I deal with mostly have Jabirus or Jabiru engine aircrafts. For the most part the installs work great and there have been very few problems. Most were people that didn't really know how to use the units.

One of the things I always struggled with on a Jabiru engine (and there were a fair few posts from other people on the old forum) was getting fuel flow to read anywhere near accurate on a Jabiru. I am sure some people got a good, reliable figure but I have never managed it. Until now!

I have lost count of how many fuel flow senders I have installed in a jabiru aircraft from the MGL one, FloScan and RedCude. In virtually every instance I have never been able to get an accurate reading. I always thought it was the fuel system or types of fuel pipe used. I tried everything from dampers to re-positioning the sender in various places. Different pull-up resistors etc. In virtually all instances, the only way I could get a reading that was anything like it should be was to change the k-factor to 2 or even 3 times what it should be and even then it was only accurate at certain power settings. It got to the point where I gave up using the senders.

Then a while ago, someone gave me a FlightData Systems FC-10 as part of a clear out. I didn't bother with it for a while and then I decided to try it in my aircraft expecting much of the same. To my surprise, when I installed it, I got fairly accurate readings straight out of the box. This was using the same wiring and the sensor in the same position as it was before and no physical changes to the fuel system.

This got me wondering, what was so different about how the FC-10 did things and how the MGL did things. After all, fuel flow is only a matter of counting pulses. I didn't do anything else for a while and then curiosity got the better of me.

So I dug out my oscilloscope and wired it in to my aircraft so that I could watch the pulses while I was flying. First I did it on the MGL for a while and then I did it using the FC-10. To my surprise, there was a vast difference in the pulses being received. The MGL was very jagged with spikes and troughs whereas the FC-10 was a nice, consistent square wave. I just couldn't understand how this could be the case as both units just purely receive a pulse from the sensor. From this, I could see why I had to play with the k-factor on the MGL and it was so variable. The only time it was reasonable smooth was when the engine was off with the electric pump on or sometimes I got a reasonable figure with the engine idling.

After further testing, I discovered the difference. On a standard installation using MGL, the most likely installation was to power the sender from the aircraft bus and then put a 5K6 resistor on the RDAC to pull the sensor up to 5v for the pulse wire. The FC-10 does this differently. The FC-10 powers the sender directly. All 3 wires from the sender (PWR, GND and Sensor Wire) go directly to the FC-10 d-sub connector. You do not power the sender from the aircraft bus. What I discovered was that the FC-10 provides a constant, regulated 10v supply to the sender with the signal line pulled up to 10v via a 10k resistor.

So I decided to this a try on the MGL. I made a little 10v regulated power supply using standard electronic components. So the regulator was powered from the aircraft bus but provided a constant 10v supply to the sender and a 10v, 10k pulled up voltage on the signal wire. The signal wire went directly in to the FuelFlow input on the RDAC with no resistors on the RDAC.

I wasn't really expecting much but to my surprise, the MGL then started to display very accurate FuelFlow figures with the k-factor as it should be.

The Jabiru electrical system is not great. The charging runs from a stator that is all over the place and very noisy. The voltage varies between battery power and about 13.5v and it very erratic and noisy. This variable and noisy power I can only assume affects the sender causing the pulses to be erratic as well.

Just to prove this was not a fluke, I made the power supply for a couple of other Jabs at the airfield that also had inconsistent fuel flow readings. Once installed, both started showing very accurate figures.

Anyway, I thought I would share this as it has been quite a victory for me.

[Tasmag]

Stereo,

I suspect you are into something here!

It has always bugged me that an identical setup on a jabiru using Dynon is spot on while MGL is not.

I have always wondered if the ground was the problem with the jabiru charging system but it appears you have solved the problem.

Is they any chance of a quick and dirty writing diagram for what you have installed and I will make one as well.

Mike

[Steevo]

Pretty simply. I purchased an LM2596 voltage regulator module from Amazon.

You just wire the IN+ to the aircraft bus and the IN- to aircraft ground. Obviously make sure there is relevant circuit protection. I 3D printed a case for it with JST connectors at each end so I could insert it in the middle of my existing wiring.

The OUT+ goes to the sender positive wire (orange/white) and the OUT- goes to the sender ground wire (blue/white). The white sender wire goes straight to the RDAC. Then put a 10k resistor going from the OUT+ to the white wire.

The LM2596 has variable voltage output so you need to initially set the output voltage to 10v. Just connect a multimeter to the OUT+ and OUT- and adjust the screw until you get 10v.

I did use shielded wire in my install. Make sure you remove the 5K6 resistor from the RDAC (if you had it installed that way).

The above is based on a RedCube FT-60 but should work with them all. Just different wire colours.

EDIT: Sorry, ignore the wire colours above. They are my shielded wire colours not the sender.

[Tasmag]

Stereo

Thanks for that, I'll give it a go. Might take me a bit as I am away from the aircraft for a while now unfortunately.

It sounds like the difference is the removal of the red cube from the aircraft bus and using the converter as a filter for the power and signal. I wonder if putting a converter in and using the standard wiring would also work. (If you haven't already tried it)


Mike

[Steevo]

You can just insert the regulator in to the existing wiring. Just cut the positive and ground wires going to the sender and insert the regulator as described above.

That's all I did on the 3 Jabs I have tried it on. I didn't change any wiring at all. The module is fairly small. My sender is inside the centre console with a fuel filter before and after it to act as a fuel damper. I literally cut the power wires and put JST connectors on both ends but any connectors will do or even soldered on to the module.

Make sure you remove the 5K6 resistor on the RDAC before doing anything, else you will pump 10v in to the 5V output on the RDAC which I am not sure it would like.

I can kick myself for not doing this before but I was convinced it was a fuel pulsation problem causing the sender to send out too many pulses. A Jab at the airfield has Dynon and their Fuel Flow reads fine. But that is also powered from the Dynon harness just like the FC-10 so it definitely seems the noisy Jab electrical system caused this issue all these years and since on the MGL there is no power provided for sensors, they just use whatever is on the bus.

[JimJab]

To the Experimental Jabiru Owners,

Hi Stevo,

Thank you so much for posting how you got your MGL / fuel flow meter set up to read more actually, when I get the chance I am going to do this in my Jabiru.

Here is something of interest for all the Jabbers amongst us, when I did my first Jabiru fuel tank/gauge calibration and trying to sort out why my MGL fuel gauges always reading full (I found the wing tank gauges were not earthed to the engine/RADC earth point, but to the instrument panel earth bus, this prove to causing many of my EFIS engine gauges to be very flakey and misread).

So after fixing this earth issue, I found one of my wing tank gauge/sender units was reading 1/4 full when the tank was actually empty, when the gauge was reading 3/4 full the tank was actually 1/2 full, not a good thing to have happening.

The Jabiru wing tank gauge/sender units are connected to the float on the inside of the fuel tank via magnetic coupling. In my case the magnetic coupling needed to be re-calibrated and to do this required the wing to be removed as I was told.

So I needed another solution and the following allowed me to fix the gauge/sender unit magnetic coupling calibration and allowed me to actually match the fuel level and sender unit reading for use with my MGL EFIS, by having a slip collar around the gauge/sender and being able to adjust the sender unit ohms.

Fuel Gauge Base Plate.jpg (221.05 KiB) Viewed 13461 times

Fuel Gauge Slip Collar.jpg (241.21 KiB) Viewed 13461 times

Fuel Gauge Slip Ring.jpg (202.11 KiB) Viewed 13461 times

[JimJab]

Hi All,

I have finally got around to making up Steevo's idea of a 10v DC regulated power supply for my Fuel Flow Sensor in my Jabiru.
The module I am using is a Jaycar XC-4514 DC-DC Step-Down Module.

I am yet to install this in my Jab 430 and will report when I do so.

But I am really thankful to Steevo who found this solution that worked for his Fuel Flow Sensor in his Jabiru and then sharing it with us and I am hoping it works for me as well.

In my prototype power supply, I have run the Fuel Sensor signal wire through the box, as I am hoping this will not pick-up to much electrical noise as I want to be able to easily jump the Pull-Up-resistor from the signal wire terminal to the positive wire terminal inside this box.

Steevo or anyone else, if you can see any problems with my prototype set-up, please don't hesitate to comment and share your thoughts.

I am pretty excited to see if this 10v DC power regulator unit will make my Fuel Flow Sensor read accurately through out my entire RPM range.

Cheers
JimJab

FuelFlowSensorPowerV2.jpg (230.22 KiB) Viewed 11055 times

[rainier]

Firstly, well done.

In our experience not all Jabiru electrical systems are created equal. A variety of regulator/rectifiers were used and I assume this may also be different in different countries of assembly. It appears original regulators come pretty much directly from agricultural equipment and are indeed very rough.

The RDAC provides a regulated 5V supply intended for sensor supply - it was originally intended for use with our fuel flow sender.

We have had quite a few installations that opted to use our isolated DC/DC converter to supply critical equipment and apparently it fixes radio noise problems on some installations. If the supply is so noisy that it actually affects a fuel flow sender (it really must be pretty bad to have an effect) then it will affect a radio as well.

[JimJab]

Hi All,

I hope Stevo is still active on the forum to see your comments Rainer.

Two Questions,

I would like to ask Stevo how or what circuit in the Jabiru he used to installed and powered up this DC-DC module?

Also, would it be OK to power this DC-DC module from my instrument panel 12v + and 12v- buses bars and then connect the fuel flow signal wire to the RDAC without causing any type of Earthing Differential in my EFIS system?



Some may think, what is this "Earthing Differential", when I purchased my plane, all of my engine management gauges were reading very flaky or at times very erratically. All this was being caused by this "Earthing Differential" at the RDAC and this issue was so bad it made me even consider replacing my whole EFIS system for a new system after it made me have an emergency landing after giving me this very sudden and erratic swings in the oil pressure and temperature for serval minutes in the air and then stopped before we could land.

But like a dog with a bone, I finally found the caused of all my engine gauge problems. The wing tank fuel gauge/sensor had been earthed back to the instrument panel earth bus as per the Jabiru wiring schematic at the time, but these wires needed to be wired back to the RDAC earth bus. Once I re-earthed these two wires my EFIS engine gauges suddenly became rock solid and my fuel tank gauges started reading fuel levels as well.

Also once I understood what this "Earthing Differential" was all about I was able to simulate my very sudden and erratic swings in oil pressure and oil temperature during ground testing of the earthing system for the RDAC and EFIS system.

So it's now time to look at my Fuel Flow Senor set up with the RDAC signal to see if I can get this Jabiru/MGL fuel flow system to be rock solid throughout the RPM range with the correct K-Factor number for my type of Fuel Flow Sensor.


Cheers
JImJab

[JimJab]

Hi All,

Firstly Steevo, if you still are reading your thread, I have sent you a PM', as I am hoping to touch base with you personally, if that is OK.

I am still working out the details where I am installing the DC-DC power supply for the Fuel Flow Sensor.

But so I have a base line of what the current flow signal is currently, I put a scope on the signal wire at the RDAC.

I think I have a pretty good 5V DC wave signal coming from the Flow Sensor at the RDAC with the fuel flower sensor back behind the sound wall near the header tank and electric fuel pump. I was thinking there may have been a voltage drop over that distance, but it seems ok.

But what I have noticed is that the pulse frequency is fluctuating pretty bad, like from 18Hz to 25Hz or 4Hz to 7Hz for their given engine RPM setting.

Cheers for now.

JimJab

Signal Base 5v from RDAC

CheckingFuelPulse0622V1.jpg (61.7 KiB) Viewed 10931 times