Red Cube Fuel Flow K Value

[Vantastic12]

Greetings Fellow RV-12'ers.

Just completing Phase 1 testing on N850VH. 14.5 hrs. flying, apx. 20 on the Hobbs. My SkyView touch fuel flow is indicating about 7.5 GPH in cruise, but it's actually only burning less than 5 GPH. Obviously with only one Red Cube, it is only measuring fuel supplied to the engine, not the unused fuel returned to the fuel tank. The Dynon manual says the default K Value is set at 68,000 and to increase it if the GPH is reading too high. Van's says to adjust it up by 10,000.

Question: what is the K Value set at in your RV-12?

Thanks for any responses.

[Top Cat]

I've been fiddling with k-factor on my SLSA.
It came with the upper fuel flow number at 98000 and the lower 68000. I believe one setting is 19 and one 14.

Comparing fuel loaded against fuel burned as well as monitoring the EMS and Moeller gauge I figure my burn is 4.8 gph at 5300 rpm and 4.4gph at 5000
I had the top number set at 87750 and left the lower one at 68000. This brought my fuel flow to read what I was physically burning and showed about 6.2gph for after take off climb and about 2.9 at idle with around 3.8 doing run up at 4000 rpm.

Then of course today at 7500 ft and 5000 rpm on a hot day the cruise burn at 5000 rpm was reading high. I tweaked it up and got it closer to where it had been.

Just my fumble fingered response to your question and ready to learn more about the error of my wYs!

[tomkk]

I've been using 90000 for both. Seems to be quite accurate block-block but not necessarily correct at all power settings throughout the flight.

[Top Cat]

I wonder if the mechanism sending the pulses to the fuel flow needs a little time to settle down for a period after say a high power climb to 7500' where I then reduce to a cruise setting of 5000 rpm.

After tweaking a little today I did get a fuel flow indication where I thought it should be as well as shut down fuel very close to where it should be.

[DHeal]

The single red cube in the RV-12 measures total fuel flow (engine consumption plus returned fuel). While there are two fuel flow adjustment settings possible in the Skyview, only one of them is used for the RV-12 since there is no "return flow" sensor input source. On my RV-12 I believe I have my one K-factor set at 107,000 and I am happy with that accuracy (@ 0.1 gallons difference over a one-hour flight). My other K-factor is set at the default setting of 68,000 although I believe that is not utilized and is of no consequence. I have seen fairly weird fuel flow readings occur during the course of a typical flight but at the end of the flight the overall consumption values are very close. In other words, the instantaneous fuel flow indications can be a bit erratic inflight, but overall the average consumption indication is very accurate.

[Top Cat]

Originally Posted by DHeal

The single red cube in the RV-12 measures total fuel flow (engine consumption plus returned fuel). While there are two fuel flow adjustment settings possible in the Skyview, only one of them is used for the RV-12 since there is no "return flow" sensor input source. On my RV-12 I believe I have my one K-factor set at 107,000 and I am happy with that accuracy (@ 0.1 gallons difference over a one-hour flight). My other K-factor is set at the default setting of 68,000 although I believe that is not utilized and is of no consequence. I have seen fairly weird fuel flow readings occur during the course of a typical flight but at the end of the flight the overall consumption values are very close. In other words, the instantaneous fuel flow indications can be a bit erratic inflight, but overall the average consumption indication is very accurate.

Thanks David I would agree about the somewhat irratic readings in the air and that at the end of the flight things seem to sort themselves out.

I'll try your 'magic number 107000' next time I fly! Thanks!

[Driftdown]

Originally Posted by DHeal

. . . "I have my one K-factor set at 107,000 and I am happy with that accuracy (@ 0.1 gallons difference over a one-hour flight). My other K-factor is set at the default setting of 68,000 although I believe that is not utilized and is of no consequence. I have seen fairly weird fuel flow readings occur during the course of a typical flight but at the end of the flight the overall consumption values are very close. In other words, the instantaneous fuel flow indications can be a bit erratic inflight, but overall the average consumption indication is very accurate."

Concur with that.
My k-factor settings are very close to yours. My 2nd setting is also at 68000. Dynon says it doesn't matter what the 2nd one is set to, because it is ignored by Skyview, since a return counter is not installed.
After a 4-hour flight, my actual consumption is as predicted.

Especially after a nice long cross country flight, just refine the setting as per Dynon Skyview Installation Manual. There is a ratio formula, just follow it and you will be really close. After each long cross country, I re-evaluate and adjust the k-factor as necessary. Only had to change it once in over the last 3 years.

[Vantastic12]

Thank you all for your responses.

Much appreciated and very helpful. I must be doing something wrong, I only see an opportunity to input one K Value number, defaulted at 68,000.

I'll do some more Dynon research.

[NinerBikes]

New to me with someone else's Van's RV-12 being purchased, and I am trying to sort this out.

My 2012 with Skyview Classic, when I refuel, shows fuel usage much greater than how many gallons it actually needs to fill up the tank. It might say after I have filled up, that I HAD 8 gallons of fuel left, when I obviously had 12 or 13 gallons left, and do I want to match the numbers?

Does an adjustment to the Red Cube number to 107,000 help correct that on fill ups, or does it just correct the indicated GPH consumption rate shown in real time on the GPH gauge?

Or is all my student pilot time spent hardly using any fuel, learning how to taxi straight goofing up the averages? Also been flying somewhat slow in circles, practicing stall work, slow speed work, rectangles, etc, so I am not really keeping the throttle very close to normal cruise values, and fuel flows.

[rvbuilder2002]

The Dynon Skyview manual shows how to factor displayed fuel used against actual fuel used to calculate a new K factor. That is the only way to get it adjusted accurately. Using someone else?s # is just shooting in the dark.

A lot of low powered operation will skew the accuracy because with an approximately 1.5 you return flow there is only absolute accuracy at what ever power setting it is calibrated for. When calibrated for cruise power it is quite accurate at cruise power but not idle or low power.