Skyview Fuel Computer

I need to fine tune my fuel computer. As many have posted, the fuel flow shows much more fuel than is actually being used, mainly due to the fuel return line that we have on our RV-12s. I get the fuel mismatch warning on almost every start, and it is always off by at least 30%, even with my "K" factor set at 85000. I have found some mention of changing the return parameters, but I can't find that field in the hardware setup menu. I have no problem getting to the "K" factor, but I would really like to get the return parameters right first. I found no help in "search", or at Dynon's site. Can anyone guide me through getting to the return field in the Skyview system.

Thanks in advance............Tom

"Return"? Some people put a red cube in the supply line and another in the return line. The net result can be configured to be calculated as fuel consumption. The RV12 has only the one in the supply line so the K factor is a correction factor based on your usage. The Installation manual covers the details. there are some other threads about setting the K factor.

I had a hi flow alarm once. In the troubleshooting I put a bore scope in the filler tube to observe the return flow. It barely bubbles over the end of the tube. I don't think it contributes much to flow error because it is small and the variations are smaller so it is a pretty consistent error that can be accounted for in the K factor. My discrepancy between totalizer and fuel truck fill up readings is typically a few tenths of a gallon on a 3 hour flight.

Do Toni T & Big John Have Return Fuel Sensors??

Bill, you may be right, but I had found several posts from Toni T, and Big John, back in 2011, about setting the return flow value, as if it were a set value, not a measured value. I guess I was hoping to hear from one of those guys as a verification. They either added the extra sensor, or found an illusive return flow file somewhere.

Tom

Bill, here is a copy of a post from Toni T, with comments back from Dynon. So, what are your thoughts??
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I received a response from Dynon on the question about the return flow function. I'll post the question and the answer for anyone interested. You can also read the Dynon forum here:

My question in the Dynon thread:
I would like to resurrect this thread to ask if the RETRN FLOW parameter is only applicable if there is a second flow sensor in the system to measure return flow?

The response:
Re: Return Flow function
Reply #4 - Today at 4:40pm Quote No, it's to there to simulate a second fuel flow sensor being there on a EMS-D10/D120/D180 that always outputs the same theoretical fuel flow rate (not really what happens in the real world in many conditions, but it can be passable in some configurations). With those products, it is possible to measure the difference between the main fuel flow sensor and a 2nd actual fuel flow sensor for return flow via a Matronics box. SkyView can do it natively.

This indicates that the RETRN FLOW function is there to "simulate" a second fuel flow sensor in the return line.

As to any question of whether the fuel return line is actually used in the RV-12, you will see when you install the fuel lines in the system that the only restriction to flow in the return line is a small orifice in the fitting that attaches to the return plumbing.

My only reason, really, for going through all of this is that my FT-60 K-factor adjustment had to be so high that I may have to adjust it higher than what it can be set at. Using the return flow function would solve that problem.

Tony
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Tony
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RETRN FLOW parameter

Tom,
I don't like to post in the SV threads because I don't have it, have not read the manuals, and would only add to the confusion with nothing useful to say. But you have sorta dragged me into it now.

To answer about the RETRN FLOW parameter: It exists in the D-180 SETUP menu, submenu SENSORS, submenu FUEL FLOW. It appears there if the GLOBAL/ENGINE TYPE setting is set to ROTAX. John and I do not have a return flow sensor, just the Red Cube. Because of the return flow we found that we would have to set the K-VALUE to a number greater than possible on the D-180 menus. But, as noted above in your post, you can simulate a return flow sensor by using the RETRN FLOW parameter. John, being a clever guy, found that with the fuel pump running he could get the fuel flow to read zero by adjusting the RETRN FLOW parameter, thus compensating for a constant return of fuel to the tank. We don't know if it is constant but it must be close to constant. With that done, it becomes possible to put in a K-FACTOR value that is within the range of what is allowed in the K-FACTOR menu.

This is for the D-180 not the SV. SV may have something similar in it's menu's. I don't know, have not read the manuals.

Thanks Tony T

Thanks Tony, sorry for dragging you into this, but with your post, and a little investigation, I have figured out the fix, which I will share with the rest of our world. I never did find a return fuel flow file, however, with the Skyview, we have and addition digit, allowing for a much higher "K" factor than 99,999, which I thought was the highest number that we could enter. The extra digit will make it very easy to set a very accurate "K" factor. Just for grins, I set it at 100,000 this morning, but I will post my final number when I finish tweaking. Anyway, thanks again for piping in. The confusion was all on my part.

Another mystery solved by a terrific users group.

Tom

Tom, my Kfactor is 102260 which works well.

Setup - Hardware - EMS - Fuel Flow
Bill

Thanks Bill. I will try you "K" factor

Tom

Nobody seems to have mentioned here that the Dynon SkyView 10.0 setup has two lines for Fuel Flow Calibration (i.e two parameters to be adjusted).

I have the SkyView D1000 Screen in a standard ELSA RV-12.
This has only one "Red Cube", i.e no fuel flow sensor in the fuel return line.
When I go to SETUP MENU> HARDWARE CALIBRATION> EMS CALIBRATION > FUEL FLOW CALIBRATION
I see two lines:
PUL/GAL (PIN C37 P14) 68000
PUL/GAL (PIN C37 P19) 68000
There appears to be no mention of "K Factors" either on screen or in the SkyView Version 10 documentation.
The question here, perhaps for a Dynon expert to answer, is what is a typical value for each of these two lines in a standard ELSA RV-12 setup?

PS: First flights - everything went nicely, no immediate trimming or changes needed
Rich D

1980 Evans VP1 completed, sold
1995 Avid Speedwing completed sold
RV-12 120259 First flight July 2014.

Just a guess: Since 68000 is the recommended starting point if you don't know the K-factor for your cube, I would guess the 68000 pul/gal is the K-factor on SV. I have the D-180 which uses the Kfactor terminology.