Red Cube fuel flow incorrect reading

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Red Cube fuel flow incorrect reading

Postby Corby202 » Fri Aug 12, 2016 3:26 am

Have any of you guy's got a red cube f/f transducer connected to a Ultra Horizon unit??. I have just installed one but can not get an accurate reading. I put the correct K factor into it but according to the panel my Jab is using 35litres/hr.
Thanks
Phil Bird
Sonex 759 JAB 2.2 Tailwheel
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Re: Red Cube fuel flow incorrect reading

Postby peter anson » Fri Aug 12, 2016 6:14 am

Hi Phil,
I have the fuel flow sender supplied by the Australian agent for MGL but the procedure should be the same. I ran fuel through the sender into a measuring container over say, 5 minutes to get the fuel flow rate, then converted it to litres per hour. While the fuel was running I read the flow rate indicated by the Ultra Horizon and then got a ratio of indicated flow/real flow. According to the manual the K factor is the number of pulses per litre, so you would multiply the existing K factor by the ratio you have calculated.
For example, if your indicated fuel flow is 30 litres per hour but your measured flow is 20 litres per hour, the ratio is 1.5
Multiply the K factor by 1.5, so 1.5 x 7000 = 10500
Change the K factor to 10500 and retest. It should be correct or at least much closer to the correct value, and you can repeat the procedure.
Now bearing in mind that I did all this about 4 1/2 years ago and I have lost many brain cells since then, I may be wrong, but I do recall measuring flow rates at least. It's one of those jobs where it would be good to have two people, oh, and a fire extinguisher.

Peter
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Re: Red Cube fuel flow incorrect reading

Postby Corby202 » Fri Aug 12, 2016 7:25 pm

Thanks Peter, I will try that first. When I first hooked it up I had the fuel pipe going into a container, switched the pump on ( this sensor I have after the electric pump but before the mechanical pump) the reading was 70 litres /hr which matched the pre flight checks I had recorded, it also had a reading of 2 litres / hr with the pump off. The K factor on mine is 18000, the panel only lets you put a figure in up to 30,000 which I put it up to whilst flying but didn't drop the reading by much.
You see this is what happens when the weather is no good for flying, I sit at the computer buying things I don't really need LOL.
Phil
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Re: Red Cube fuel flow incorrect reading

Postby peter anson » Fri Aug 12, 2016 10:54 pm

I assume you have the pull-up resistor fitted or you wouldn't get any flow indication?
I find the fuel flow reading really useful - effectively set my cruise by flow rate. Did a flight to Queensland last week with the longest leg 280 NM from Griffith to Walgett - monitored fuel almost constantly.

Peter
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Re: Red Cube fuel flow incorrect reading

Postby Brett » Sat Aug 13, 2016 1:33 am

When I run my fuel pump the red cube reading is almost double in my aircraft. Basically I only use the boost pump for initial startup with the Rotec throttle body then turn it off. When I switch the pump off it reads fine. Having only done 15 hours or so I have found it to be quite accurate. Very closely matches what I need to add to the tank when refuelling.

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Re: Red Cube fuel flow incorrect reading

Postby Corby202 » Sat Aug 13, 2016 3:15 am

I have just come back from the airfield, rechecked the flow into a container, using the electric pump only it seems very close, panel showing 71 litres/hr, timed rate =75 litres/hr.
I know you have a bing carb and mechanical pump Peter, where in the fuel line is your sender??
Thanks Brett.

Phil
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Re: Red Cube fuel flow incorrect reading

Postby peter anson » Sat Aug 13, 2016 5:41 am

Hi Phil, the fuel circuit is:

Fuel tap>> Electric fuel pump>> gascolator>> fuel flow meter>> mechanical pump>> Bing carbie

The electric fuel pump is a SU diaphragm pump (the type that old English cars used to have that make a tick tick tick sound when running) which I normally leave on all the time. It has a pressure controlled output so only pumps on demand. I haven't noticed any difference in fuel flow indicated if I turn it off, which I occasionally remember to do.

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Re: Red Cube fuel flow incorrect reading

Postby mike.smith » Sat Aug 13, 2016 11:52 am

I have a Gold Cube on my AeroVee because the company told me the Gold Cube was the most appropriate for the gravity feed fuel system. But I have been flying for a few months now with the Gold Cube and my MGL Xtreme. I don't get any consistent readings at all. I will be in cruise burning (from calculations based on time and quantity of gas on fill-up) an average of 4.5 gph, yet the reading in the cockpit may say 4.8 gal, then 5 minutes later (having not touched the throttle or mixture at all) it shows 9.6 gallons. 10 minutes later it might show 7.4 gallons. And it keeps fluctuating, even when I don't touch the controls. I've emailed the company to see if they have any input for me.

If anyone on this thread is running a Gold or Red cube on your AeroVee I'd be curious to hear your experiences, but so far for me it's completely useless.
Mike Smith
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Re: Red Cube fuel flow incorrect reading

Postby sonex1374 » Sun Aug 14, 2016 9:38 am

Mike,

Where is your Gold Cube located in your system? I use the Red Cube and place it inside the cockpit right after the shutoff valve. It reads very accurately. I think this is due to the straight run from the tank outlet to the firewall, and no fuel pump pulses to confuse it. It might simply be the Gold Cube is not the right sensor for your system (despite what the Rep told you). Perhaps selling the Gold Cube and substituting the Red Cube is all it will take to get a better reading.

Regardless of the sensor used, I think getting a smooth flow into and out of the sensor is key, so you may need to consider your mounting location as well.

Jeff
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Re: Red Cube fuel flow incorrect reading

Postby fastj22 » Sun Aug 14, 2016 9:54 am

My red cube generally gives very accurate numbers. But recently I've been getting erratic flows, usually too high. Its one of the gremlins I'm chasing with the MGL. I have it mounted right after the gascolator before the carb. My first Red Cube died after 100 hours. I'm on 150 hours with this one. I think the readings may be caused by a dying voltage regulator noise causing some extra blips in the signal.

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