Anomalous Fuel-flow readings??

[yankee-flyer]

I've adjusted the return fuel flow and K values as per the posts here and things seem correct. However, the last two reasonably long (45 min to 1 hour each way) flights have produced strange numbers-- or maybe I just don't know what I've been seeing??
On the outbound leg (east) fuel flow readouts at 5200 rpm, 5500 feet, OAT in low 60's showed 5.2-5.6 gph. After landing and spending some time on the ground (fly-in breakfasts). the return leg at 4500 feet, 5200 rpm, OAT about 70, reads 4.1- 4.2 gph, which is what I thought it should. Dividing fuel burned by hours flown gives me the same 4.1 (or thereabouts) gph, so I don't think it's running rich on the first leg of the day. Choke cables checked OK at 100-hour 20 hours ago.

Any thoughts, guy, or am I simply getting more info from the Dynon than I need (or understand)?

Thanks

Wayne 120241/143WM

 

[rvbuilder2002]

My first thought would be to ask, that in stead of just evaluating whether the reading looks correct, have you made a flight and compared the actual fuel used (how much it took to fill up) to how much the computer said you used?
The PAP and the Dynon documentation both describe this as the way to "calibrate" the fuel flow sensor. Using the calibration factors that others have posted will only give you a starting point.

 

[BigJohn]

Wayne,

Scott is right on with his advice. I have "calibrated" my fuel system over a series of cross-country flights so that normally my calculated fuel useage corresponds almost exactly with the number of gallons I add at fill-up after the flight.

Notice the word "normally." I still encounter a situation every so often where the fuel flow indictaion jumps up into the 9 gph range. I first thought this was due to the early model fuel pump beginning to fail. So I replaced it. I have recently seen a repeat of this behavior with the new pump. I am now beginning to think the problem may lie with the FT-60 sensor. I'm still trouble shooting, and I mention this behavior to you to emphasize that there are multiple factors that can cause anamolous fuel flow indications. BTW, when my fuel flow indicator jumps up, it happens very quickly, does not affect engine performance, and drops back to normal inducations when I pull the electric pump fuse.

John

 

[yankee-flyer]

Thanks guys

Scott, I've only had this happen twice and on relatively short (breakfast) cross countries. But I did manually compute the fuel burn (that's what I meant by dividing gallons used by hours flown) for those flights and the actual fuel used, as closely as I can see for these 1.5 hour flights, is about 4.1 gph.
I could not get close to that indication on the D-180 even with K set to 99,900 so I used John's method of setting the return value (tweaked until fuel flow was zero with electric pump running, but didn't have the engine running, and then adjusted K lower). Now I'm normally seeing indicated 4.1-4.2 at cruise.

John, I hadn't thought of pulling the fuse. I'll try that next time I get a high reading and let you know what happens.

Can't think of a physical reason, other than running WAY rich or dumping fuel overboard, for the reading to be that high so I'm hoping there's an electronic glitch somewhere.

THANKS

Wayne 120241/143WM

 

[Peterk]

Wayne,
My Floscan 200 gave up the ghost at about 330 hours. It didn't go suddenly but it eventually took a final gasp. I removed it see if there was anything restricting the little ferris wheel from turning but there was not. Both that and the Cube retail at $200 so I just went into my Dynon set-up and turned it off. I have always tracked my fuel flow manually after every flight so that is a non-issue. Yes you could have a hose pop off and start pumping over the side but my electronic fuel level on the Dynon is quite accurate and I back it up with the Moeller sight gauge. So...in my opinion, enjoy it while you can but its not worth $200 to replace. Think of the years we flew without. And of course if you depart with a full tank and fly by time....

Pete

 

[rvbuilder2002]

Scott, I've only had this happen twice and on relatively short (breakfast) cross countries. But I did manually compute the fuel burn (that's what I meant by dividing gallons used by hours flown) for those flights and the actual fuel used, as closely as I can see for these 1.5 hour flights, is about 4.1 gph.
I could not get close to that indication on the D-180 even with K set to 99,900 so I used John's method of setting the return value (tweaked until fuel flow was zero with electric pump running, but didn't have the engine running, and then adjusted K lower). Now I'm normally seeing indicated 4.1-4.2 at cruise.

John, I hadn't thought of pulling the fuse. I'll try that next time I get a high reading and let you know what happens.

Can't think of a physical reason, other than running WAY rich or dumping fuel overboard, for the reading to be that high so I'm hoping there's an electronic glitch somewhere.

THANKS

Wayne 120241/143WM

Wayne,
From your original post it wasn't obvious (to me anyway, I am slow sometimes) that it had worked trouble free for quite a while and just now acted up.
I have seen flow readings drift some on occasion but have never nailed down a reason, other than when a fuel pump was beginning to fail. This is the first thing I would check if I encountered an unexplained high fuel flow.

 

[BigJohn]

........I have seen flow readings drift some on occasion but have never nailed down a reason, other than when a fuel pump was beginning to fail. This is the first thing I would check if I encountered an unexplained high fuel flow.

Scott, I've had the same experience as you mention. I replaced the original pump and never expected to have this problem again. Then it came back. Very strange. If you come to OSH this year maybe we can discuss. John

 

[MartySantic]

Scott, I've had the same experience as you mention. I replaced the original pump and never expected to have this problem again. Then it came back. Very strange. If you come to OSH this year maybe we can discuss. John

Have seen the same thing. Fuel flow will drift up to 5.8-5.9 gpm and then drift back down when at a constant power setting. I have replaced the engine driven fuel pump with the new model. Saw the same with the old fuel pump. Have not tried to pull the electric fuel pump fuse as John has.

I still have the original Flowscan unit installed.

This has to be a Dynon anomoly. Noise induced?

 

[BigJohn]

Have seen the same thing. Fuel flow will drift up to 5.8-5.9 gpm and then drift back down when at a constant power setting. I have replaced the engine driven fuel pump with the new model. Saw the same with the old fuel pump. Have not tried to pull the electric fuel pump fuse as John has.

I still have the original Flowscan unit installed.

This has to be a Dynon anomoly. Noise induced?

Hi Marty,

I would be happy with 5.8 - 5.9. When it happens, mine goes up to 9GPM, occasionally goes over 10 and sets off the high fuel alarm. Pull the fuse and it goes right back down. A real head scratcher. I don't kmow if it's possible that that much fuel could actually be flowing back to the tank. Doesn't seem likely, so I think the problem is in the FT-60 sensor or the Dynon.

John

 

[rvbuilder2002]

When it happens, mine goes up to 9GPM, occasionally goes over 10 and sets off the high fuel alarm. Pull the fuse and it goes right back down.

John,
This is a classic symtom of a failing engine driven fuel pump... Remove the input pressure (pull the aux. pump fuse), and pressure returns to mormal.

If I owned your airplane, before I flew it again I would be looking closely at the engine driven pump for signs of fuel leakage.

 

[BigJohn]

John,
This is a classic symtom of a failing engine driven fuel pump... Remove the input pressure (pull the aux. pump fuse), and pressure returns to mormal.

If I owned your airplane, before I flew it again I would be looking closely at the engine driven pump for signs of fuel leakage.

Hi Scott,

I'm not sure how to tell if the new style pump is leaking, since leakage is piped overboard. My new-style pump only has less than 50 hours on it.....

More info - I dumped the D-180 memory and plotted fuel flow, fuel pressure, and RPM. When the fuel flow jumped from around 6 to 9 gph, the pressure remained constant at about 4. When I pulled the fuse, flow immediately returned to about 6, while pressure dropped only slightly to about 3.7. Replaced fuse and pressure returned to about 4, while flow again jumped to nearly 10. Fuse out again, same effect. Later in the flight I plugged the electric pump back in, and everything was normal!

Go figure......

John

 

[rvbuilder2002]

Hi Scott,

I'm not sure how to tell if the new style pump is leaking, since leakage is piped overboard. My new-style pump only has less than 50 hours on it.....

More info - I dumped the D-180 memory and plotted fuel flow, fuel pressure, and RPM. When the fuel flow jumped from around 6 to 9 gph, the pressure remained constant at about 4. When I pulled the fuse, flow immediately returned to about 6, while pressure dropped only slightly to about 3.7. Replaced fuse and pressure returned to about 4, while flow again jumped to nearly 10. Fuse out again, same effect. Later in the flight I plugged the electric pump back in, and everything was normal!

Go figure......

John

I should have prefaced my post with "If you have the old style pump... ".
In your case, it could be anything from an air bubble temporarily caught in the transducer to, the xducer actually beginning to fail.

 

[Finley Atherton]

Have seen the same thing. Fuel flow will drift up to 5.8-5.9 gpm and then drift back down when at a constant power setting.

None of this may apply as I have a 9A with an Lycoming 0-320 (carb) and have no experience with the RV 12 and the Rotax Bing carbs. However I do have fluctuating FF readings which I understand is to be expected with a carb (float type) Lycoming.

Most FF instruments allow for sensitivity (responsiveness) adjustments. I need to have mine set on the least sensitive otherwise my FF readings are all over the place.
I have observed that changes in my FF indications are caused by changes in G force. My FF indications are steady in smooth air at constant power setting. Air turbulence or pulling/pushing on the stick will cause changes to the FF depending on the responsiveness setting. Positive G and the indicated FF increases. Negative G and it drops. I am fairly sure these are phantom fluctuations and that the actual FF through the main jet into the intake does not change.

Fin 9A

 

[MartySantic]

Hi Marty,

I would be happy with 5.8 - 5.9. When it happens, mine goes up to 9GPM, occasionally goes over 10 and sets off the high fuel alarm. Pull the fuse and it goes right back down. A real head scratcher. I don't kmow if it's possible that that much fuel could actually be flowing back to the tank. Doesn't seem likely, so I think the problem is in the FT-60 sensor or the Dynon.

John

John,

We will figure it out. Keep in mind I have the Flowscan and my return flow parameter is set to zero in the D-180. A bit different than your setup. But that still does not explain the discrepancy. I have not dumped the Dynon data when it has occurred. Will do so. Will also pull the fuse when I see it again.

Remote, yes. Could we be sucking air somehow?

 

[BigJohn]

Remote, yes. Could we be sucking air somehow?

Been thinking about that after Scott's comment about air. But where in the world would air be coming from? Fuel vapor? But why would fuel be vaporizing in a flowing pipe from a relatively cool tank? The only thing I can think of is the FT-60 sensor is reacting differently depending on the pressure in the line. When the electric fuel pump is running the input to the FT-60 is under pressure - when the electric pump is off the fuel is under lower pressure since it is being sucked through by the engine driven pump. But then, why would it not always act the same way?

I guess I could just bite the bullet and order a replacement FT-60 to eliminate that as a cause. But that would be just a shot in the dark at this point, and I hate making changes when I don't understand the root cause of something - it's the engineer in me

I'll scan the plot I made (RPM/Pressure/Flow) and email it to you.

 

[Peterk]

if all these possibilities were happening, wouldn't they be evident in a manually figured fuel flow determined after flying? The Floscan and Ht-60 have an awful lot of complicated moving parts: flywheels, lasers etc. that can get goofy. I used to have a JPI certified on a Comanche and it did the same thing (talk about a waste of money!).

Pete

 

[yankee-flyer]

Can't be electric pump on/off John

Neither Marty nor I have a switch to turn it off and apparently your readings only dropped after you pulled the fuse. I know the cooling fans are on that fuse and am thinking that something changes when you pull the fuse that affects the D-180. The only constant in the two times I've observed this anomally is that I've been at a density altitude greater than 6000 feet. Flying at 4500 MSL and then climbing to 5500 for a short time didn't cause flow rates to go up but I didn't stay there for more than a couple of minutes.

The pump would have to be spraying a steady stream of fuel to change the flow rate by 20%-- I have no fuel smell nor any indication of fuel on the belly. Also the manually computed rates match the "normal reading, not the high ones.

I still have the original pump but apparently both you and Marty observed this behavior with old AND new pumps. It's got to be in the red cube, the wiring from the cube to the D-180, or in the D-180.

At this point I don't THINK this is serious but it certainly is interesting.

Wayne 143WM