Fuel flow transducer

[Nev]

How are people installing fuel flow transducers in their Bearhawks ? (I’ve got a Gold Cube FT90 fuel flow transducer to install). My initial plan was to bolt it to a frame between bulkhead B and the firewall. This gives great maintenance access, tons of room, a solid mounting point and the required uphill flow after the transducer.

However the instructions state that it should be installed after the last fuel pump, and should be supported by flexible fuel lines - presumably to dampen vibration, but the unit does have enough weight to it that I would have been inclined to bolt it to something solid. A search around the web shows quite some variation on installation method and location. There’s also some that were supported between solid fuel lines that subsequently detached. Would appreciate advice if anyone has firsthand experience. Thanks.

[zkelley2]

My gold cube is behind the firewall before the fuel pumps. Works fine. Doesnt get heat from the engine.

[spinningwrench]

Gold Cube.jpg
I welded in a mount to support the Gold Cube,. Based on recommendations from mechanics I used a flexible fuel line to the firewall as the firewall will have vibration that can cause fatigue failures in solid fuel line fittings. If you weld a solid tab to the frame at the firewall then a solid line would be OK as they do in a Citabria's fuel line feed.

[robcaldwell]

My fuel injection system is Airflow Performance. Don Rivera (the owner and designer) has me using the Red Cube and wants it mounted on top of the engine case.

IMG_2350.JPG

[AKKen07]

Hey Rob, do you have any pictures of your final installation of the red cube? I’d like to see how you routed all the hoses etc if it’s not too much trouble.

[robcaldwell]

Unfortunately I did not get a pic of the final hose connections. But lines follow the same routing you see here. Next time I pull off the plenum I will try to remember to get a pic.

[AKKen07]

Ok, thanks Rob! I think I get the idea. Continental routed my fuel line up to the spider one cylinder aft of where yours comes in (which I didn’t notice in your picture till now) so I might have to change that if I’m going to fit the cube up there. After the pumps I don’t see any other good options.

[alaskabearhawk]

FWIW, the installation instructions say to mount it on the firewall and that's where I'm putting mine (gold cube):

Mounting Procedure:
1. Find a convenient location on the firewall (away from any hot exhaust pipes) and mount a bracket
for the Fuel Flow Transducer. Check both sides of the firewall for clearance before drilling any
holes.
2. Mount the Fuel Flow Transducer onto the Bracket. You must use the FT-90 (Gold Cube) Fuel
Flow Transducer on a gravity feed system or for any engine over 350 H.P. If the Transducer
is mounted within 6" of an exhaust pipe, the Flow Transducer must be wrapped with
Fire Sleeving.
3. Remove the fuel hose which goes from the Fuel Pump (or the Fuel Filter on a gravity feed system) to
the Carburetor (or Fuel Servo).
4. Purchase two new hoses, one to be used from the fuel pump (or the Fuel Filter) to the Fuel Flow
Transducer (making provisions for the fuel pressure transducer as necessary) and the other to be used
from the Fuel Flow Transducer to the carburetor (or Fuel Servo). There must be flexible hose in
and out of the Transducer. The hoses must meet TSO-C53a Type C or D FAA specifications.
The new hoses must be the same size as the current hoses in the aircraft.

[Battson]

Flexible hose is only necessary on the forward side of the firewall.

[Battson]

Gold Cube.jpg
I welded in a mount to support the Gold Cube,. Based on recommendations from mechanics I used a flexible fuel line to the firewall as the firewall will have vibration that can cause fatigue failures in solid fuel line fittings. If you weld a solid tab to the frame at the firewall then a solid line would be OK as they do in a Citabria's fuel line feed.

This is very similar to where I put my red cube and it works great.

Annoyingly, they come with install instructions which I cannot find on the website... I will dig them out when I get home.

It's worth having a straight and slightly uphill run of fuel line across the transducer, to improve the stability of the reading and avoid bubbles getting trapped. Wires have to go on top.

Not being an expert, I have no idea why they are so commonly mounted to the engine or firewall (heat + vibration disaster area). It seems the worst possible place to install sensitive electronic equipment which is prone to heating up and trapping vapour bubbles. It must reduce the service life, no doubt about it.

They also say it "must" go after the fuel pump. I ignored that advice - same with our sister ship Bearhawk 4-place ZK-FHR. Both work great.

P.S. I put my solid fuel line through the firewall right next to the engine mount bolt, between that solid point and the cowling flange - zero vibration.

[zkelley2]

Those transducers fail all the time when mounted under the cowl. They are notorious for it.

[Nev]

Thanks for all the feedback, exactly what I was after to see what others had done.

I’m still not sure whether the manufacturer intends for the unit to be suspended from the flexible fuel lines or if I’m interpreting it in a way they never intended. There look to be two AN4 bolt holes right through the transducer (as in Robs picture) begging it to bolted to a solid fitting. I can now see the logic for using flexible fuel lines around the engine - presumably between any two parts separated by the engine mount isolators.

Here are the mounting instructions that came with the transducer. They are slightly different to the online version for some reason.

BD30380F-A680-4B89-8EB7-40FCEED5F963.jpeg

[whee]

I took the instructions at face value and suspended my red cube between two sections of flexible hose. I had to put it after my engine driven fuel pump because that is where the return fuel tees off. I didn’t want it in the engine compartment but had little option. No problems so far. If I didn’t have return fuel I would have put mine between the firewall and the electric fuel pump below the floorboard.

[JimParker256]

When in doubt, why not call the manufacturer (EI) and talk to their support engineers? They are the experts, and provide EXCELLENT tech support before and after the sale. Great folks!

My opinion (worth exactly what you're paying for it) is that the installation guide gives clear instructions and provides the rationale for those instructions. Personally, I do anything I can to avoid vapor lock, and when EI tells me "install it after the last fuel pump to avoid vapor lock" that's what I'm gonna do. Ditto for their instructions to install "wire side up" and to install with flexible lines sloping up through the sensor (again to avoid vapor lock and erratic readings). I've done four of them now – all according to the instructions – and have had zero issues with either vapor lock or with erratic readings.

At one point, on the Citabria with the O-200, I thought I was having erratic readings, because the fuel flow would fluctuate at low power settings, but was rock solid at higher power settings. Turns out it was actually sensing the fuel flow stopping momentarily when the carb float rose high enough to shut off the flow, then resuming when the float dropped and flow resumed. The EI guys talked me through changing the FP-5L configuration to resolve the fluctuation. I needed to change the "filter" setting (in the power-on setup) from F1 (for fuel injected engines) to F2 (carbureted engines). I had purchased this particular gauge from a friend who had used it with a fuel-injected IO-540. He had purchased a CGR-30P, and the FP-5L was redundant, so he sold it to me (cheap!). Of course, he had set it up using the F1 fuel injected) filter and neither I nor my A&P noticed it during the installation / setup. Easy fix, and rock-steady (and dead-on accurate) readings after that!

[zkelley2]

I do wish they didn't use 1/4 NPT ports, between this and all the fuel selector valves they are the choke point in the fuel system. I makes me think going to 1/2" lines wouldn't do anything. Really it's the fuel selector valve. That tiny slit in the 1/4 NPT ID isn't much area for fuel to flow.

[Tim213]

I mounted my gold cube on the firewall per the instructions, and used flexible fuel lines as well. On my RV7 I have the red cube installed and suspended in air, and haven’t had any problems for 6 years.

[JimParker256]

Tim, could just be the perspective of the photo, but it looks like you've got the lines routed to the gold cube such that the cube itself is the high point in the installation. That is contrary to the instructions, that state to install it so that the fuel continues to flow uphill after passing through the gold cube. Their stated reason is to prevent any gas bubbles that form in the line from remaining within the cube itself. If that were to happen, you'd definitely get "erratic" fuel flow readings.

[Bcone1381]

Another data point......Rob Cladwell's post had me a bit curious....I wasn't going to say anything, as he referred to Don Rivera at AFP....I talked with Kyle at AFP in July. Kyle recommended I mount the transducer between the fuel servo and the fuel distribution (spider) ...like post #8 ....suspended on flexible hoses as it rises from the servo to the spider.

[svyolo]

I am surprised that the installation instructions have the wires coming out the top, and they didn't at last specify a drip loop.

[Nev]

After 150 hours on my Bearhawk the fuel flow transducer was giving erratic readings. Essentially it would read accurately when the electric fuel pump was running, but when turned off the fuel flow would usually indicate 20LPH higher. Obviously this meant that the Calculated fuel remaining on the EFIS was not accurate either,

Mine was mounted behind the firewall and between the electric pump and the engine driven pump. I had been keen to keep the transducer aft of the firewall for all the reasons mentioned above. However if it didn't read accurately there was no point having one.

At the last 50 hour check I decided to relocate the transducer forward of the firewall onto the the engine mount. This was actually quite straight forward. I made up one piece of hard fuel line to fit where the transducer had been. I then mounted the transducer on the engine mount and used flexible lines to the engine driven pump and fuel servo. I purchased the flexible Teflon line and end fittings from the local car racing supplier. So now it sits downstream of both fuel pumps. I noted that the majority of installations done by TC Flightline were between the servo and the fuel distributor, probably to situate it downstream of any fuel return line, which my system doesn't have.

The initial flights after relocating it showed it to be reading very accurately, and now when I activate the fuel pump there is no change in the indicated fuel flow. I'm interested to see how it performs over the next few hours, and I'll update here with the results.

[AKKen07]

Great info Nev, thanks for sharing