Fuel flow transducer location

[petep]

Consider a red cube or gold cube fuel flow transducer. They both say the from the transducer's output the fuel line must slope upward for vapor lock protection I assume. Using the recommended continuous downhill slope on the fuel line from tank to AeroInjector how is that possible? Anyone installed one in this fuel line configuration? If so how was it installed?
Thanks,
Pete
OneX 0128

[mike.smith]

Consider a red cube or gold cube fuel flow transducer. They both say the from the transducer's output the fuel line must slope upward for vapor lock protection I assume. Using the recommended continuous downhill slope on the fuel line from tank to AeroInjector how is that possible? Anyone installed one in this fuel line configuration? If so how was it installed?

I have mine directly on the thru-firewall fitting, on the engine side. Then I have an inline fuel filter, as short section of braided hose, and finally the AeroInjector. Everything is insulated, and the filter and fuel line also have fire sleeve around them. I have no gas collator.

I originally put the fuel filter first, then the Cube, but the flow readings were WAY, WAY OFF! I mean REALLY off!

[Gordon]

Fuel Flow Transducer Question.........?

According to the information from Electronics International you should only use the Gold Cube for a gravity fed system. The Red Cube is only for a pressure system (fuel pump). I installed the Red Cube on my RV-7 but on my Onex I have went with their advice and installed the Gold Cube. Some people have used the Red Cube with success in their Sonex installation.....but why try to prove the company that makes the transducer wrong? Go with the Gold Cube. Jabiru owners would use the Red Cube.

The preferred installation is a straight line of at least 2" IN..... and a straight line of at least 2" OUT of the Cube. It is also best to avoid too much heat (heat soak). I mounted mine on the AFT side of the firewall. The fuel line comes out of the tank....into the Gold Cube.....then into the remote fuel shut off valve....then through the firewall into the gascolator..........then a firesleeved braided line to the Zenith carburetor.

If you email me I can send you a few photos of the installation. gdbaxter78@gmail.com

Gordon........Onex.....Hummel 2400

[mike.smith]

I think most people use the Red Cube based on the company's published fuel flow numbers. But I got the Gold Cube because the company said that was most appropriate. It's about 85% accurate. It was 0% accurate when I had it mounted after my fuel filter.

[sonex1374]

Red or Gold, the key thing is to mount the sender such that flow into and out of the cube is smooth and stable. As Mike mentioned, mounting anything immediately upstream will cause erratic readings. I've seen bunches of problems caused by fuel filters, 90 deg elbows, or other stuff being too close to the cube. The instructions state to route the fuel line such that vapor can't be trapped within the cube. This can be accomplished with either a slope up or down of the line, but you don't want it dead flat, and definitely not at the top of a curve.

Also worth noting is that the "K-Factor" is different for each cube due to their different internal construction. I use the Red Cube with my Dynon Skyview and the pre-programmed Red Cube K-Factor has been dead on. I'm not sure what the factor is, but apparently Dynon knows their stuff! I didn't intend to buy a Red Cube, but that's what came with my Skyview, so that's what I used.

Looking at the specs of both cubes (link below to specs), the Gold Cube has less resistance to turning (e.g. less pressure drop), so therefor is more suitable to high-flow systems (up to 125 gph flow rate). However, this low-resistance would magnify the effects of turbulence into the unit and show itself as fluctuating flow readings, which is what Mike experienced. The Red Cube has more internal resistance and a higher pressure drop, but the readings are likely more stable. The pressure drop could be a problem for fuel systems that deliver marginal flow to begin with, so take that into account before going this route. My fuel system tests at 15+ gph through the system as installed (including Red Cube), so it can be made to work.

https://www.emapa.aero/Electronics-Inte ... sducer.htm

Jeff

[petep]

Thanks for the discussion on red verses gold cube. After talking with EI it is clear that either will work but the gold does have a slightly less pressure drop. The whole bit of not using a red cube on a gravity fed systems seems to have evolved out of instructions to meet certification for certified airplanes. I will probably go gold cube but my real question and concern is that EI wants an upward sloping line on the cube's output. With a constant down hill slope from tank to Aeroinjector that is impossible. As I said before I am pretty sure that the upward slope is to insure no vapor problems in the cube. How many people have a constant downhill slope fuel system and still use a cube?

[sonex1374]

I posted a short video of performing a fuel flow test last week in my hangar.
https://youtu.be/0_Y-4l0aoUo

Periodically I clean and inspect my fuel system, and during this servicing I decided to perform a flow rate test to ensure I was receiving sufficient fuel flow to the carb. The standard is 150% of WOT (full power) fuel flow, or in the case of the Jabiru 3300 (approx 10 gph at WOT), the target is 15 gph.

Results:
Starting with 14.6 gal in the tank, initial flow rate was 20 gph, falling to 18 gph at the half-full tank level, and ultimately ending up at 15 gph with less than 1 gal remaining in the tank.

The Dynon Skyview and Red Cube combination performed superbly (as it always does), recording exactly (to the tenth) the amount drained out as was reported in the tank to begin with. Impressive!

Details of my fuel system can be found at the link below:
http://sonex604.com/misc/Sonex_1374_Fue ... _Feb17.pdf

Jeff