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More info on fuel flow reading

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yankee-flyer

Well Known Member
Flew in very hot (100 F) weather last week with Young Eagles program but never got above 6000 Density Altitude. Fuel flow readings normal-- 5.3 or so in climb and 4.2 to 4,2 in cruise at 5200 RPM. Went to pancake breakfast this morning; climbed to 5500 MSL (6620 DA) and fuel flow readings stabilized at 5.9 GPH. After 15 minutes I descended to 4500 MSL (5500DA) and FF dropped to 4.1 to 4.2 GPH. After a few minutes I climbed back to 6600DA and fuel flow readings stayed 4.2! Return flight at 4500 MSL,5500DA. fuel flow at 4.2. Flew 1.6 hours and burned about 6.5 gallons: 4.1 gph.

I still think this is a density altitude problem with the D180. Can you guys going to OSH talk with Dynon people. John, did you ever get any feedback from the data you sent.

Wayne 120241
 
yankee-flyer said:
Flew in very hot (100 F) weather last week with Young Eagles program but never got above 6000 Density Altitude. Fuel flow readings normal-- 5.3 or so in climb and 4.2 to 4,2 in cruise at 5200 RPM. Went to pancake breakfast this morning; climbed to 5500 MSL (6620 DA) and fuel flow readings stabilized at 5.9 GPH. After 15 minutes I descended to 4500 MSL (5500DA) and FF dropped to 4.1 to 4.2 GPH. After a few minutes I climbed back to 6600DA and fuel flow readings stayed 4.2! Return flight at 4500 MSL,5500DA. fuel flow at 4.2. Flew 1.6 hours and burned about 6.5 gallons: 4.1 gph.

I still think this is a density altitude problem with the D180. Can you guys going to OSH talk with Dynon people. John, did you ever get any feedback from the data you sent.

Wayne 120241
Click to expand...

Wayne, thanks for the data. Next time could you include your power settings as well? MP and RPM would be good. Off to OSH this AM. One leg will be high, over Lake Michigan. Will note readings and watch for anomalies. Hope the alarms don't go off - I have a passenger! :eek:

Never got anything meaningful from Dynon.

John
 
One theory for the increased flow indicated but not accaully being used by the engine is that the excess fuel is beiong returned to the tank in the return line. Maybe this is caused by the reduced pressure in the fuel tank perhaps caused by too much restriction in the fuel cap vent. I too had this happen after installing the new and improved fuel pump. Since I reduced the restriction in the fuel cap vent, I haven't had it happen again. Just a theory maybe without merit.
 
All fuel flow readings

are at 5200 RPM, John. To be honest I don't pay much attention to MP since I can't do anything about it. Readings are 22-23 in but are continuously fluctuating up and down a few tenths.

I'll be interested to see what you see, If you have the chance, try climb/cruise, descend/cruise and climb/cruise again to see what happens when you climb back above 6500 DA.

Have a good (and safe) trip.

Wayne 120241/143WM
 
Some progress towards a resolution

On the OSH trip I flew several legs at 8500' to 9500', and the fuel flow indication jumped to over 10gph every time I went up high. I discussed this with the Dynon folks at their booth, and they understand it is an issue with several builders, not just me. I received assurances that they will look into the problem. I volunteered to allow extra sensors to be installed in my airplane if that is required to isolate the problem. I have the direct email address of the engineer I spoke with, and I wil stay in touch.

I also spoke with Mitch Lock and he experienced this behavior in New Blue before the Skyview upgrade, but not after, so it is apparently an issue with D-180 installations only.

I'll report on status when appropriate.
 
That's GREAT, John

I've not gotten much in the way of interest from Dynon, but it sounds like you got their attention. The fact that Mitch had before and after different results is especially good to know and I assume they're aware of that. The -12 is such a good high altitude bird (took me FOREVER to get to 7500 Ft in the AA-1) that I'll just keep flying high and ignore the fuel flow readings. Next time you see a high reading try pulling the power back for 30 seconds or so and then go back to cruise. Seemed to fix the readings for me Sunday.

Wayne 120241/143WM
 
In doing the initial testing, I noticed that the fuel psi went to 10.5 above 9000'. Leveling of at 10,000 it dropped back to 8psi and stabilized. On decent it returned to normal of around 5.... Could pressure altitude account for the varied readings?

Not psi. GPH and flying skyview
 
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Above 6500 Density Altitude

Most of us with this fuel flow anomaly reading are seeing it when density altitude is about 6500' or more. I've noticed that if I climb to DA above that, my fuel flow readings are 5.9 GPH or more/ Descending below that returns readings to 4.2 or so. More experimenting indicates that just pullling the power back for about a minute, the climbing back ti cruise altitude/airspeed will "fix" the reading. Seems to be a function of exceeding 6500DA in continuous power setting. Computed fuel burn (actual gal/actual hrs) is in the 4.3-4.5 range.

Wayne 120341
 
Happening with Skyview too....?

KALEWIS said:
In doing the initial testing, I noticed that the fuel psi went to 10.5 above 9000'. Leveling of at 10,000 it dropped back to 8psi and stabilized. On decent it returned to normal of around 5.... Could pressure altitude account for the varied readings?

Not psi. GPH and flying skyview
Click to expand...

Very interesting! First I've heard of it in the Skyview installation. Other Skyview folks - please report if you have seen this behavior. If it is happening with both D-180 and Skyview, that may be significant. I am waiting (and hoping) to hear back from the Dynon folks. We may need to get a dialog going between Dynon, Van's, and some of the builders who are seeing this in order to get a resolution. I will do my best to facilitate this discussion. Stay tuned........
 
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