The Dynon Installation manual for the D180 says to adjust the K-factor for the fuel sensor to make the fuel computer accurate and gives a way to calculate an adjusted K-factor. This seems to work. However, with the Rotax engine the the fuel flow section of the on-screen menus includes a 'RETRN FLOW' parameter. This is set to '0' by default, as there are Rotax engine installations that do not have a fuel return line. The RV-12 does have a return and I am interested in using the RETRN FLOW parameter to get an optimum setting for the K-factor.
I searched this forum and found several threads regarding fuel flow and fuel return but nothing specific regarding the RETRN FLOW parameter. The Dynon manual only states that this function is generally used only by Original Equipment Manufacturers. Hmmm.
I then searched the Dynon Avionics forum and found one post by Dynon Support that states as follows:
"You set the RETRN FLOW in "K" and it subtract this "K" from your flow sender.
If your K factor is 30,000, that means 30,000 pulses per gallon.
If you expect a constant return to the tank of 1.5 GPH, then you would set this to 45,000 (30,000 X 1.5)
This will only work well if you have a fixed return orifice size and a relatively stable fuel pressure."
OK, this explains the RETRN FLOW parameter, and I think it is applicable to the RV-12. The only question is , How much fuel is bypassed back to the tank? I am guessing it is about 2 GPH. The Dynon suggested K-factor for the red cube sensor is 68,000, and with the RETRN FLOW at default '0', I have had to set my K-factor to about 96,000 and still not happy with the result. You can only go to 99,999 with the K.
A better solution may be to set the RETRN FLOW parameter to 136,000 (68,000 X 2) and then further adjustments to the K-factor would follow.
I could be over thinking this. There are over 90 12's happily flying around and no one has brought this up. I guess all those fuel computers are working just fine.
Tony
I searched this forum and found several threads regarding fuel flow and fuel return but nothing specific regarding the RETRN FLOW parameter. The Dynon manual only states that this function is generally used only by Original Equipment Manufacturers. Hmmm.
I then searched the Dynon Avionics forum and found one post by Dynon Support that states as follows:
"You set the RETRN FLOW in "K" and it subtract this "K" from your flow sender.
If your K factor is 30,000, that means 30,000 pulses per gallon.
If you expect a constant return to the tank of 1.5 GPH, then you would set this to 45,000 (30,000 X 1.5)
This will only work well if you have a fixed return orifice size and a relatively stable fuel pressure."
OK, this explains the RETRN FLOW parameter, and I think it is applicable to the RV-12. The only question is , How much fuel is bypassed back to the tank? I am guessing it is about 2 GPH. The Dynon suggested K-factor for the red cube sensor is 68,000, and with the RETRN FLOW at default '0', I have had to set my K-factor to about 96,000 and still not happy with the result. You can only go to 99,999 with the K.
A better solution may be to set the RETRN FLOW parameter to 136,000 (68,000 X 2) and then further adjustments to the K-factor would follow.
I could be over thinking this. There are over 90 12's happily flying around and no one has brought this up. I guess all those fuel computers are working just fine.
Tony
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