Fuel Flow Jabiru Engine

[JimJab]

Hi All,

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.

For all those who have been following this post by the hit numbers, sadly I have not been able to get back to my plane for other than the odd quick flight due to my business work loads.

Sometime in May or June, I should be able to get some further testing and setting of the K-factor calibration inline with my actual fuel usage.

Cheer
JimJab.

[JimJab]

Well May and June has come and gone.

I do have something to post for the Jabiru owners that might find interesting and something I had over looked about our fuel system.

A few weeks back, I looked at those Fuel Cap Vents tubes and wonder if they worked as they should. I had read or was told they put positive pressure into the fuel tanks during flight and also have a small one way valve in them.

I never gave these one way values much thought until the other day when I was dipping my tanks.

So with the fuel cap out, I blew through the vent tube, then sucked air back through the vent. I thought that's not right, so I checked my other Fuel Cap Vent and could also blow and suck air freely in and out. The small one way valves in both vents weren't working.

So I gave the top of the vent tube a few gentle taps with a flat bit of wood whilst holding the fuel cap, then blew through the vent and this time as I sucked the valve blocked off. I did the same with the other fuel cap and the vent valve blocked off as well when sucking.

When I first got my plane, I did noticed on a number of occasions after re-filling the tanks to full and doing a short 10-15-20 min flight home, my fuel usage seemed to be to high and did not add up when I dipped my tanks during my next pre-flight.

At the time I thought I had a fuel leak, I found nothing, I even thought about fuel venting out past the fuel cap o-rings, but never thought about having fuel venting straight out the top of the fuel cap vent tube when the tanks were near full, add some unbalance flight with these little valves stuck open and it could have been venting fuel.

This may well answer why my fuel dipping and Virtual Tank calculations are not adding up, if fuel was being vented.

Cheers
JimJab

[JimJab]

Hi All,

This may well be getting off the MGL path a fair bit, but if it helps some else to get their Jabiru/MGL EFIS fuel flow reading sorted, then I think its worth sharing. With my last post, I gave my fuel vent breather some taps to get the ball valves loose so they work as they should.

Fuel Cap One way Vent Valve.jpg (21.86 KiB) Viewed 8942 times

After a few weeks of sitting, I check the fuel breather valves again and found they were stuck again. So it was time to replace them and once again thank you to the Australian Jabiru team, I really do find they have great service. I had the 2 ball valves and the breather caps in my hot little hand in just a few days from ordering them.

To give you the heads up, if you don't have the authority to do this type of work on your plane, then find someone who does.

With that sorted, if you find you can replace your fuel cap breather valves, then read the Jabiru 430 construction manual and look at the pic of the parts. The valve breather caps are Loctite to the tube using Loctite 620 and this stuff does get a good grip on the world. So to get these caps off the tube, you'll need to heat the Loctite's grip between the tube and cap, a hot air gun may not do the job. But one of those small pencil flame gas burner did it easier and yes the valve balls are plastic and you'll melt them in this process into the breather valve cap. So make sure you get 2 new balls with the 2new breather caps.

Oh yes, and don't do this with the fuel caps on the plane, they are easy to take off, just take the Allen key bolts right out of the fuel cap and the top of the fuel cap will come off with the breather tube and the base plate with the earth strap will stay attached to the plane.

So now with new fuel cap breather valves in place and fixed. Hopefully this will stop any fuel venting out in flight when my tanks are full to the brim.

At time of adding the pic, sadly, I have not been able to get back to any in flight fuel flow testing and changing my MGL K-Factor calibration.


Cheers
JimJab

[VacaMoo]

This thread has helped me a lot in learning more about the fuel flow sender installation, thank you. I have a Floscan 201 on a Lycoming IO-540 with an MGL Extreme EMS. The RADAC-MAP manual I have doesn't mention any resistor but the Lycoming does, however the programming instructions aren't what I see on my EMS. Frustrating because I don't know if I have the latest instructions.

I just received a troubleshooting checklist from Floscan and will be doing that this week since I've pretty much already done everything else mentioned here.

I updated my post to include more info because I just read yesterday's post by Rainier where the spam attacks are holding up comments. Just wanted to make sure I'm not deleted, I'm real, and I still have more questions about the MGL Extreme EMS on this new-to-me plane.

[rainier]

No Spam attacks since you registered so no problem.

Regarding fuel flow senders - basically all of them have what it termed "open collector" outputs. What this means it is effectively a simple switch with one end connected to ground and the other is your signal line. The switch opens and closes. The faster it does this the higher your flow. The number of open/close events per liter or gallon is called your k-factor. Our own senders do about 7000 of these events per liter. U.S. sourced flow senders tend to give the k-factor in gallons.
Our instruments work fuel flow k-factor in liters. So just divide the gallons based k-factor by 3.79 to get liters.

Our instruments are looking for a voltage pulse - in order to use the switch to create such a voltage pulse we need a "pull-up" resistor. Normally we use a resistor in the 2000 - 8000 ohms range - standard values tend to be 2200, 3300, 4700, 5600, 6800. The actual value is not really critical.
The resistor is wired from your sender output to a supply voltage. Our instruments like to see a voltage swing of 5V or more. More is better. So if your aircraft has a 12V power system, simply wire the resistor between the signal output of your sender and the 12V. If the switch is open you should now get 12V (through the resistor) and if the switch it closed you get zero volts.

Our own sender has a suitable resistor already built in so this is not needed.

To test use a voltmeter at your sender output and with power applied and resistor fitted measure the voltage. Blow through the sender very mildly just to get whatever moves in there to move and you should see the voltage flipping between zero and your supply voltage - the harder you blow the faster it should flip.

[VacaMoo]

I haven't been able to check anything but will be doing that this week. Thanks.

[JimJab]

Hi All,

I have re-edited this post after some further research.

It's been sometime since I posted to this thread. So to recap, we spent a fair bit of time checking out our aircraft's electrical systems, using oscilloscopes, electronic signal generators to emulate our fuel flow signals both on the ground and in the air.

So with some confidence, I was feeling pretty good that our aircraft's electrical system was not causing any type of EMI that could add extra pulses or could smother our fuel flow signal to the RDAC at any point.

So we moved onto the job of fine tuning our EFIS's LPH and Virtual Tank readings, by adjusting our K-Factor.

I had found in the "MGL RADAC-X Technical Instruction Manual" a section, how to re-calculate your K-Factor.

So without questioning this equation, we re-calibrated our K-Factor a couple of times and with each K-Factor change, we seemed to spend even more time flying around and burning more Avgas in trying to work out why our Virtual LPH were not getting any closer to the actual Avgas litres we were burning.

Finally, I could see a pattern with each new K-Factor we used, the Virtual Tank litres/ LPH readings were getting even less with each re-calibration of the K-Factor.

Finally I believed, "This MGL Equation is Totally Wrong as in the Manual and pictured below"


Cheers
JimJab

KFactorCalcV2.jpg (103.49 KiB) Viewed 592 times

[JimJab]

Hi All,

I have edited this post to be straight to the point.

After thinking the MGL K-Factor Equation was wrong, I started surfing the internet about K-Factors and reading through a few different MGL & RDAC Manuals to see if I could find another K-Factor Equation.

In the "Stratomaster EFIS - User Manual " I found the following about the K-Factor, " If you find your Flow Sender reading low, decrease the K-Factor, if you find your sender reading high, increase the K-Factor. " .

This description was what I thought should have be happening with the MGL new K-Factor. But this MGL Equation was doing the exact opposite, my Flow Sender reading was low and yet, it was increasing the K-Factor number.

I then asked for some further advice from our MGL N.Z. Dealer, who I have found to give very good service. Stuart emailed me the following K-Factor Equation.

" New K-Factor= ( Virtual Litres Used / Actual Litres Fuel Used) * K-Factor "

I also found a similar K-Factor equation on the Vans Aircraft Forum.

So I have now gone back through all my K-Factor calculations, replacing the MGL Equation with this new K-Factor Equation from Stuart.

Oh boy, this K-Factor equation is giving me new K-Factors between 6508 and 6780 which is all around my sender's bench test K-Factor of 6635.

I am now quietly confident we are now much closer in having an EFIS fuel Flow reading that will have some accuracy about it.

Cheers
JimJab