Fuel Flow Jabiru Engine

[rainier]

Well, this is a very good thread and it shows that measuring flow of any liquid becomes an art if the flow is not even.

Fuel pumps with the exception of turbine or rotor based designs create nasty pressure pulses - the fuel does not flow evenly but in rapid shunts in tune with the pulse rate of the pump. This is difficult to measure with any degree of accuracy - in particular if your fuel lines are not made from metal. Any fuel line or other part in the fuel system that can expand with pressure will force the fuel in whatever direction it can go if pressure reduces.

Fuel filters tend to get used as chambers that can absorb these pressure pulses - but there is a problem with this - this only works as long as there is a sizable cavity filled with vapor in the filter - once the chamber is completely filled with liquid it does nothing much at all.

Rubber fuel primer bulbs installed between pump and flow sender are a much better way of catering for the pressure fluctuations. I have also seen metal chambers that are partly filled with air - isolated from the fuel by a flexible membrane - those tend to work well. Some of the mechanical crank or engine driven pumps have such a chamber built in. Older Rotax fuel pumps for example did have this - but this was removed when they changed to different makes and from then on measuring fuel flow on these engines became more tricky.

[JimJab]

Hi All,

It's been a while since the last post and thanks for Rainer's comments, once I have some base line frequency figures, I will try putting a fuel primer bulbs in the line to see what the signal outcome is like with an oscilloscope on the signal wire.

Sadly, I could not find a portable handheld Oscilloscope (/Multimeter/Wave Generator) to borrow and take flying.

So I did some google research and found a Hantek 2D72 hand held Oscilloscope/Multimeter/Wave Generator, $235.00 Aus. There is another brand called OWON which is basically a similar unit but cost a little more, each seem to have slightly different specs to each other, so depending on what you want either to do, both could be ok. Anyway the Hantek unit is only days away by the tracking app.

As to my Fuel Flow Testing, after my first flight with my box of bits as a test rig, I found changing over the power supply voltages was a bit hard in flight. So I modify the test rig and added switch so I could easily switch between the RDAC 5VDC supply and the 10VDC regulated power supplies to the fuel flow sensor.

Today I had a chance to go for a fly, so I did some further Fuel Flow Sensor monitoring and testing. I could not do much without the portable Oscilloscope, only to see if there are any changes in the EFIS indicated fuel flow rates as I changed between the 5VDC and the 10VDC power supplies.

What I found in my situation, the EFIS's LPH flow rate readings did not change much between the 10v and 5V power supply, I used the same value pull up resistor for both voltages.

But, this is only part of the story, as you really don't know what the quality of square wave signal is really like with each voltage until you plug in the oscilloscope to see what the signal to nose floor ratio is like for your aircraft setup and if there is any EMI entering the fuel flow sensor wiring whilst in flight.

I am looking forward in being able to get an oscilloscope into the air to do some further testing.

Notice the small switch

FuelFlowPowerTestRig2V2.jpg (88.75 KiB) Viewed 9569 times

Cheers
JimJab

[JimJab]

Hi All,

Well, its been a number of weeks since I have had time to do further testing on my EFIS and MGL fuel Flow Sensor.

A few days ago I got the chance to use the Hantek 2D72 hand held Oscilloscope/Multimeter/Wave Generator it seems to be a solid unit for it's money.

But there is a problem, the MGL EFIS could not detect the test pulse signal from the handheld unit.

So once back on the ground, I did some further testing of the Hantek unit with my 240v test gear, I found the Hantek could not generate a pulse voltage Peak to Peak over 2 volts, which is not high enough to be detected by my MGL EFIS's.

FuelSensor3unitsofTestUnitsV2.jpg (78.5 KiB) Viewed 9514 times

After some testing I found the test pulse signal needed to be over 2.7 volts before the EFIS could detect the pulse wave and calculate the fuel flow. So if I want to test the system in the air with a pulse generator, I would need a handheld test generator that can generate at least a 5 volt square wave peak to peak.

That's a stuff up on my part, but I found the Hantek 2D72 oscilloscope function to do the job in the air and can give you a readout of the pulse signal frequency once the Frequency counter is selected in the menu.

I have a few days in the next week if the weather is going to stay good, to go up and do some more oscilloscope and pulse frequency testing, per flow rates etc.

Cheers
JimJab

[JimJab]

Hi All,

"I have come back and edited this post and added another Data Sheet."

I have back tracked a little with this post.

I did this chart up, in the first column is the Pulse Frequency in Hz. and in the second column what the Mathematically calculated LPH for that pulse frequency would or should be.

The third column is the recorded EFIS's LPH reading when testing my Voyager EFIS's with a 5volt DC square wave pulse, using my aircraft's fuel flow senor's wiring and my Sine Wave Pulse Generator. My EFIS's was set to a Fuel Flow Sensor's K-Factor of 6665 which was most accurate when I bench tested my new MGL Fuel Flow sensor.

I did quite a bit of testing of the Voyager EFIS's LPH readings for any given test signal frequency and when judging it against the Data Sheet mathematically calculated LPH figure, it all seems to be pretty accurate.

During this testing, the aircraft was on the ground, engine not running and other avionics were turned on and off, including the electric fuel pump, we saw no changes to the EFIS's LPH reading as avionics were turned on and off, the electric fuel pump added no EMI to the sine wave generator pulse signal. But remember the fuel flow sensor was not connected to anything during this testing.

We then did this all again with the engine running and saw little change to the accuracy of the EFIS's LPH readings against the test frequency readings.

DataSheetFuelFlowCalcsReadingV2.jpg (121.04 KiB) Viewed 9490 times

I have edited this post to add another Data Sheet to show the mathematically calculations for a FT-60 Red Cube using a K-Factor of 18,000 and what the calculated LPH would be for the given Frequency. Hope this will help some one with Scope checking their fuel flow and pulse frequency.


Cheers
JimJab

RedCubeFrequencyCalcsV2.jpg (175.6 KiB) Viewed 9316 times

[JimJab]

Hi All,

I took to the air yesterday after inserting my test box into the Fuel Flow wiring, so I could switch between the RDAC 5 volt DC power supply and the 10v DC regulated power supply with a flick of a switch.

I connect the handheld oscilloscope to the signal wire at the RDAC to see the pulse signal at the RDAC.

The 10v DC regulated power will not fix every issue you could be having with your fuel flow system. Like I found, having a stuffed Fuel Flow Sensor that needed replacing.

The handheld oscilloscope worked Ok, the 10 volt DC pulse signal had a good solid square pulse and frequency. The RDAC 5 volt DC pulse had a rising edge signal that was rounded and the pulse frequency seemed less even.

The RDAC 5 volt DC pulse signal still worked ok as I saw little change in the EFIS's LPH reading when switching from the 5v DC to the 10v DC pulse signal.

But, I do think the 5v DC power supply does not have the voltage head room (an audio expression) needed to overcome a margin of electrical inference we may get with the Jabiru and this can lead to signal degeneration and inaccuracies with the EFIS's LPH readings.

I also think when comparing 5v to 10v, I also feel Steevo is right with his 10v DC regulated power supply to power the fuel Flow sensor in our Jabiru's and worth the effort to get a 10v DC power supply to have a better voltage margin with any possible electronic interference and to help maintain a more reliably LPH reading throughout the rpm range.

I did some further flying where we recorded the RPM settings, along with the EFIS's LPH readings and what the frequency reading was on the oscilloscope with these readings. This all takes time, so I want to get back in the air and do another round of RPM, LPH and Frequency reading, before I report any further.

But, I can say my EFIS's LPH readings are more even now having a new Fuel Flow sensor installed.

Cheers
JimJab

[Matt007]

Hi JimJab, I have just joined the Forum today and this will be my first post.

I am looking at installing a MGL FF-4 fuel computer into my J160 and have been very interested in the use of 10V vs 5v supply to the Transducer.

The FF-4 has a 5V power supply (Brown wire) and wondered if anyone has tested this for noise spikes ?

Would a shielded cable for the brown wire to the transducer be sufficient to protect it from Noise/ spikes ?

Just asking, as I'm looking for the simplest and cheapest solution and to see if I can get away with using the 5V supply.

Thanks

Matt

[JimJab]

Hi Matt,

I am no expert with different MGL products, out side my own experience with my MGL EFIS and what my aircraft throws at me with my particular EMI and RF issues.

But, I would start trying to run the 5v DC from the unit, that will be the simplest solution and if LPH are good around the K-Factory spec for your flow sensor, it may be right for you.

I have gone through all my testing as I want my flow sensor to be as actuate as I can get it through my whole rpm range.

But, if you want to take the time and make up a 10v DC supply and your MGL head can handle a 10vpp square wave signal, I believe as Steevo has said, it will be a more robust fuel flow signal for our Jabiru's.

As to the cost in buying a 10v DC regulator board and a box for it, I think that's pretty cheap compared to the effort it may take to wire the unit up to have a 10v DC power supply.

As to shielding, it always helps when its done correctly, but more importantly it's a lot easier to shield when you are wiring up a unit for the first time, so I would do it.

Cheers
JimJab

[Tasmag]

Hi all

I eventually got around to fitting and testing my attempt to fix this issue.

1. Moved the Red Cube to the rear, after the fuel filter
2. Connected a buck converter outputting 10v
3. Connected signal line to clean 10v and back to Rdac with shielded wire.
4. Made an anti hammer device using a fuel filter.

It is definitely more stable, still needs to be set at 27k pulses, instead of 18k where it should be. But seems pretty accurate.

Pic below

IMG_20221125_144422_copy_750x1063.jpg (130.83 KiB) Viewed 9522 times

Mike

[JimJab]

Hi All,

This is most likely a question for Rainer, but I am wondering if there is a EFIS diagnostic page that shows you the number of pulses in Hz, the EFIS is receiving from the fuel flow sensors.

This would be handy to see, if you don't have an oscilloscope to capture the fuel flow pulse rate in flight.

Cheers
JimJab

[JimJab]

Hi Tasmag,

I think the vertical positioning of the filter would give a much better air trap and dampening effect than the way I have my dampening filter which is nearly horizontal.

Work is still getting in the way and I am still yet to complete my testing of my EFIS LPH against the calculated Frequency/LPH. I have done some testing with my portable scope in flight.

But now that I have flown a few hours since changing and adding the dampening filter, the amount of air trapped should have normalised, so testing further should be OK.

I am going to make up an inline adaptor so I can easily plug the scope into the fuel sensor plug at the sensor. That way I don't need to run the scope cable from the RDAC and around outside the cowl and back into cabin. Through the firewall gland is not an option, as it's already full and tight with wires.

Also I can leave the test cable rolled up on the shelf behind the Jab 430 seat and just pull the cable out when I want to do some further testing.

Tasmag, thanks for the post and sharing the pic of your damping filter setup.

Cheers
JimJab