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Alternatives to the "Red Cube"?

DRBuilder

DRBuilder

Well Known Member
So frustrating. I have replaced the fuel flow transducer twice, and now the 3rd cube has failed. The 1st cube lasted nearly 150 hours before the readings began to be erratic. I replaced it with a new one and the second one lasted about 20 hours before experiencing the same issues. I read on the forum about heat being an issue so on the 3rd cube I wrapped the entire fuel line and cube in a fire sleeve. It didn't last 10 hours. Are there any alternatives to the red cube? Maybe another brand? I have dual Dynon Skyview HDX PFD's. This is the only issue I am having. All other components have been working flawlessly.
 
How is it mounted? I ask to try and correlate your experience with others that have mounted theirs in the same fashion.
 
I think the avg life of a red cube is many 100's of hours, though have no real data. If you have experienced 3 failures in under 100 hours, either you have really bad luck in the quality lottery or there is something unique in your installation that is causing the early failures. IMO, your situation is relatively far from the norm and I would be investigating whether or not there was something in my setup causing those failures.

I don't think heat is the issue, as many/most folks mount it under the cowl. Suspect most do not insulate it, nor do I think that would help, as insulation only works for a while until the thing heat soaks. OTOH, if you placed it somewhere close to an exhaust pipe, I could see that level of heat killing it.
 
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lr172 said:
I think the avg life of a red cube is many 100's of hours, though have no real data. If you have experienced 3 failures in under 100 hours, either you have really bad luck in the quality lottery or there is something unique in your installation that is causing the early failures. IMO, your situation is relatively far from the norm and I would be investigating whether or not there was something in my setup causing those failures.
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I have a floscan sitting in a parts box at home. It came with an EMS system that I bought. Never tested it but was told it worked when removed. Would sell it cheap if you wanted to try it.
 
Auburntsts said:
How is it mounted? I ask to try and correlate your experience with others that have mounted theirs in the same fashion.
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It's mounted between the 2 flex fuel lines down in the "recommended" location below the cylinders. It is "floating", not mounted to the block to reduce vibration. It is also completely wrapped in a fire sleeve.
 
lr172 said:
I think the avg life of a red cube is many 100's of hours, though have no real data. If you have experienced 3 failures in under 100 hours, either you have really bad luck in the quality lottery or there is something unique in your installation that is causing the early failures. IMO, your situation is relatively far from the norm and I would be investigating whether or not there was something in my setup causing those failures.
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^^ This ^^

This is exactly the reason I harp on finding the root cause -- without understanding why something failed, and remediating the causes, you're just throwing good money & time after bad. Not a fruitful exercise.
 
DRBuilder said:
It's mounted between the 2 flex fuel lines down in the "recommended" location below the cylinders. It is "floating", not mounted to the block to reduce vibration. It is also completely wrapped in a fire sleeve.
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Hmmm. As a data point, I've got mine mounted the exact same way to include the fire sleeve and got 560ish hours out of it before I started getting erractic readings and finally replaced it after insuring I didn't have any wiring issues or debris.
 
lr172 said:
I think the avg life of a red cube is many 100's of hours, though have no real data. If you have experienced 3 failures in under 100 hours, either you have really bad luck in the quality lottery or there is something unique in your installation that is causing the early failures. IMO, your situation is relatively far from the norm and I would be investigating whether or not there was something in my setup causing those failures.

I don't think heat is the issue, as many/most folks mount it under the cowl. Suspect most do not insulate it, nor do I think that would help, as insulation only works for a while until the thing heat soaks. OTOH, if you placed it somewhere close to an exhaust pipe, I could see that level of heat killing it.
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What steps would you recommend to begin trouble shooting? Wiring is correct. Hard to misconnect 3 different colored wires. Especially since it worked perfectly for the 1st 150 hours. Possibly debris in the fuel lines? How would I check for that? Would debris be visible in the fuel coming out of the cube while draining on the bench? I think the only other solution would be to locate the cube up against the firewall, away from the engine block and exhaust tubes.
 
DRBuilder said:
What steps would you recommend to begin trouble shooting? Wiring is correct. Hard to misconnect 3 different colored wires. Especially since it worked perfectly for the 1st 150 hours. Possibly debris in the fuel lines? How would I check for that? Would debris be visible in the fuel coming out of the cube while draining on the bench? I think the only other solution would be to locate the cube up against the firewall, away from the engine block and exhaust tubes.
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Post some pictures of your particular installation...
 
Might be worth a call to EI and see what their thoughts are. They also might be willing to bench test yours to see if they can determine a cause.
 
DRBuilder said:
What steps would you recommend to begin trouble shooting? Wiring is correct. Hard to misconnect 3 different colored wires. Especially since it worked perfectly for the 1st 150 hours. Possibly debris in the fuel lines? How would I check for that? Would debris be visible in the fuel coming out of the cube while draining on the bench? I think the only other solution would be to locate the cube up against the firewall, away from the engine block and exhaust tubes.
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debris is certainly possible. I would pull the finger strainer in the servo and see if there is anything that has been caught there. if debris killed 3 of them, there is amost certainly some of it getting past the cube and that should be captured in that filter. I would also post a pic of the cube installation to let the group examine it and see if we catch some issue that may not have been obvious to you.
 
DRBuilder said:
So frustrating. I have replaced the fuel flow transducer twice, and now the 3rd cube has failed. The 1st cube lasted nearly 150 hours before the readings began to be erratic. I replaced it with a new one and the second one lasted about 20 hours before experiencing the same issues. I read on the forum about heat being an issue so on the 3rd cube I wrapped the entire fuel line and cube in a fire sleeve. It didn't last 10 hours. Are there any alternatives to the red cube? Maybe another brand? I have dual Dynon Skyview HDX PFD's. This is the only issue I am having. All other components have been working flawlessly.
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I’ve had one on my RV-14A for 5 yrs and 500 hrs and have never once had an issue with it. It’s well supported and away from any heat sources.
 

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Had the Floscan 201b in my RV-8A, the airplane has 1500+ hours on it now with no flowmeter issues. However, it was mounted in the cabin. My general impression is the FT60 (aka red cube) seems to have a higher failure rate than the Floscan but agree with others that the OP likely has something exacerbating the problem. There are other threads discussing this for the RV-14, including mods to mount the flowmeter to the engine mount (less heat/vib) with associated fuel line rerouting. That's probably what I will do if I end up with a Lycoming installation.
 
lr172 said:
debris is certainly possible. I would pull the finger strainer in the servo and see if there is anything that has been caught there. if debris killed 3 of them, there is amost certainly some of it getting past the cube and that should be captured in that filter. I would also post a pic of the cube installation to let the group examine it and see if we catch some issue that may not have been obvious to you.
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also have to wonder about air bubbles from a leak source. possible that the cubes are not failing, but instead giving inaccurate readings due to air/gas bubbles.
 
lr172 said:
also have to wonder about air bubbles from a leak source. possible that the cubes are not failing, but instead giving inaccurate readings due to air/gas bubbles.
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If this helps, the readings fluctuate between 2 gals per hour and 25 gals per hour in straight and level flight without even touching the mixture. It varies between a slow fluctuation and sometimes a rapid fluctuation between readings. I have been leaning using solely EGT's instead of the fuel flow since I can't get a steady reading out of the cube. This also causes the fuel remaining reading to be incorrect. I'm glad my fuel gauges are pretty accurate!
 
Many years ago, we were having a problem with our FloScan in our GRT system. Greg (the owner) at GRT showed us to clean it by flowing fuel thru it backwards, ie apply fuel to the out side. We were shocked to see debris come out of the transducer.

Jim Butcher
 
DRBuilder said:
...Are there any alternatives to the red cube? Maybe another brand?...
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There are many fuel flow sensors in the market place, the "Digiten G 3/8", being the cheapest. We are "Experimental" so we can research, build, test. Engineered testing is imperitive...for example I vaguely recall something similar to the referenced alternative causing a fatal accident in a canard aircraft when the nipple snapped off and poured fuel on a hot engine. I would have encased that unit in a leak proof enclosure fitted with metal AN in/out nipples.
 
In my 7A, the red cube has worked great for 14 years. I can't believe you'd have THREE failures when most last a long time. I would almost be leaning towards a wiring or compatably with equipment problem. One thing I have learned is before I start changing out any parts that are wired in is to ALWAYS check every electrical connection. With the way you describe the fluctuating readings, it really sounds like a bad connection. Once I was having an issue with something electrical but can't remember what it was. I had eyeballed all connections and thought they were good. I finally ended up completely redoing a few and it solved the problem. If I was building today... I would put a drop of solder on each as I was building. Any repairs I've done over the years are done this way. Also to eliminate any vibration breaking strands of wire over time, make sure the wire is supported before and after any connections.
 
Here's an option - no idea of the cost, but I guess very high.

FlowSonic® LF - Sentronics

Ultrasonic low flow fuel meter designed for the flow conditions in road car engines. Ideal for emissions testing to RDE and WLTP standards.
sentronics.com sentronics.com

1778683593595.png
 
h&jeuropa said:
Many years ago, we were having a problem with our FloScan in our GRT system. Greg (the owner) at GRT showed us to clean it by flowing fuel thru it backwards, ie apply fuel to the out side. We were shocked to see debris come out of the transducer.

Jim Butcher
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As a vendor that makes install packages for the FT60 on a variety of experimentals, let me say that I have only heard of 1 'failure" of a FT60 due to the mechanical failure of the shutter wheel/photocell. Actually it wasnt the failure of either, it was a blocked inlet port that cut off the fuel flow. All of the others, that I know about, were electrical. Either the termination of the wires, or lack of strain relief, pulling the wiring loose at the cube body. The wires are hair thin, and can break with alot of movement. Now, what is somewhat strange, is that for some models of the same aircraft, the cubes mounted in the same location, some have anomalous readings, some intermittently. I know of 1 aircraft where multiple locations were tried, and after a period of time (usually 20 hours) the same anomalies would occur. Except it was at a particular altitutude. Higher or lower and the readings were on the money. Again, differetnt locations were tried ( yes with all new hoses), different wiring, and 3 different transducers. Yep--gremlins for sure. There were no engine misses, strange EGT or CHT data, nothing to indicate an issue other that the fuel flow would go wacko. Told him not to fly at 4000 feet, and he didnt report any more issues. Kinda like you go to the DR and say my elbow hurts when i do this, Dr says, dont do that and it wont hurt.
Not making light of Dennis' situation, but a fool proof, systematic troubleshooting procedure needs to be deverloped and adhered to .
 
czechsix said:
Had the Floscan 201b in my RV-8A, the airplane has 1500+ hours on it now with no flowmeter issues. However, it was mounted in the cabin. My general impression is the FT60 (aka red cube) seems to have a higher failure rate than the Floscan but agree with others that the OP likely has something exacerbating the problem. There are other threads discussing this for the RV-14, including mods to mount the flowmeter to the engine mount (less heat/vib) with associated fuel line rerouting. That's probably what I will do if I end up with a Lycoming installation.
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I have also had a Floscan 201b installed for 16 years and hundreds of hours and it is still running fine. Mine is mounted in a long section of fuel line in the fuselage downstream of the fuel selector valve.

Every couple of years it does start to read low or stop, and I just remove the fuel lines from both sides and flush it out with fuel or carb cleaner and it works fine again.

Steve
 
DRBuilder said:
If this helps, the readings fluctuate between 2 gals per hour and 25 gals per hour in straight and level flight without even touching the mixture. It varies between a slow fluctuation and sometimes a rapid fluctuation between readings. I have been leaning using solely EGT's instead of the fuel flow since I can't get a steady reading out of the cube. This also causes the fuel remaining reading to be incorrect. I'm glad my fuel gauges are pretty accurate!
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Same symptoms for each of the three? that just kind of feels electrical to me; an educated guess, nothing more. especially true if the symptoms are intermittent. not hard to connect three wires, however, thatr doesn't account for bad crimps somewhere else or a bad grd or a strand of shielding wire touching a dsub pin, dirty power source, etc. I would consider some troubleshooting on the electrical side, especially if the symptoms were consistent across all three.
 
Longez said:
I have also had a Floscan 201b installed for 16 years and hundreds of hours and it is still running fine. Mine is mounted in a long section of fuel line in the fuselage downstream of the fuel selector valve.

Every couple of years it does start to read low or stop, and I just remove the fuel lines from both sides and flush it out with fuel or carb cleaner and it works fine again.

Steve
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My Floscan 201b has been bulletproof for 18 years. I even installed it firewall forward. I have it wrapped in heat shield material. It’s dead nuts on always.
 
Is the are where the wires enter the cube well sealed? Some builders have added a bit of RTV around the location. Any mist of oil accumulation on the wire eventually builds up and can run down the wire to the cube itself.
 
Jumpbat74 said:
Is the are where the wires enter the cube well sealed? Some builders have added a bit of RTV around the location. Any mist of oil accumulation on the wire eventually builds up and can run down the wire to the cube itself.
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I had my red cube fail after a couple hundred hours. Mine is mounted on top of the engine on a bracket opposite of the injection spider. After the failure I surmised that the wire going into the red cube has relatively no strain relief and that possibly the wire broke due to vibration. I put RTV around the wire where it exits the replacement red cube and have now got 400 plus hours with no problems. I don’t know if that was the problem but so far it has worked.

Best regards,

Bill Wuorinen
Osprey 2 amphibian N137W
RV-7A N237W
 
Bo1000 said:
If our EFIS's had an "oscilloscope" mode, we'd know in a flash if the EFIS's flowmeter input was horribly noisy.

In the meantime, you could record the input waveform with a cheap recording multimeter.
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This is exactly why I wanted @scrollF4 Sid's dead red cube -- Hook it up to the bench supply & oscope and blow a little air through it...

Of course, it would/might appear differently on the bench instead of in-situ with all the other electrical sins...
 
Here is a picture of Sid's Paddle wheel out of his Red Cube. Note the wear of one side of the shaft pivot point. That is the side under the cover plate with the five screws. On the cover plate, the socket is worn also. The optics were foggy and when I wiped them off, they became clear and shinny. The shaft socket in the main body is clean and sharp but the optics were also foggy and when I wiped the off, it was clean and shinny. Strange they don't use hard points in the case for pivots sockets , like a watch. Didn't do any electrical tests.
 

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I wonder if your 'floating' installation introduces more vibration/fatigue than mounting it to the intake runners as in the plans?
 
It's mounted between the 2 flex fuel lines down in the "recommended" location below the cylinders. It is "floating", not mounted to the block to reduce vibration. It is also completely wrapped in a fire sleeve.
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It is a troublesome spot and folks keep installing there.
Ever thought about installing it on the cool side of the firewall?
I expect mine to go to engine TBO or longer and so far, 800 plus hours, I see no issues or reasons why it wouldn't.
 
Full Throttle said:
Here is a picture of Sid's Paddle wheel out of his Red Cube. Note the wear of one side of the shaft pivot point. That is the side under the cover plate with the five screws. On the cover plate, the socket is worn also. The optics were foggy and when I wiped them off, they became clear and shinny. The shaft socket in the main body is clean and sharp but the optics were also foggy and when I wiped the off, it was clean and shinny. Strange they don't use hard points in the case for pivots sockets , like a watch. Didn't do any electrical tests.
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So might the suggestion be that the unit be best mounted such that the paddle wheel is always vertical ?:)
 
1924.1 Tach hours since first flight in 2015. Only ever burned 100LL. Fuel filter is part of the electric fuel pump in the cockpit floor, RV stock, but also filters the fuel supply to the engine-driven pump (I think). Inspected/replaced every year by Monk.

Does this help?
 
I have had Floscan 201 FF sensors in three different airplanes with zero issues or maintenance (around 1200 hrs or so between the three). I am building an Long EZ now and bought an Electronics International EMS for it. They supply the EMS kit with a Red Cube FF sender. I asked EI if a Flowscan will work with their system and they said absolutely. I am planning to use a Flowscan in place of the Red Cube for the Long EZ based on a 25 year history of good troublefree performance. I have a new Red Cube that was delivered with the EI EMS system that I would sell to someone seeking a replacement/deal.
 
It does bother me to see folks having problems with the Red Cube. My travails are mentioned in this thread, but that's after over 10 years of flight ops averaging 200 Hobbs hours yearly. My one-off experience is that it has served me well...I certainly got my money's worth. To each, I bid you good fortune, whether it's an EI cube, Flowscan, or whatever.

Now let's see how long this new Cube lasts.
 
My floscan came to me used with unknown hours, and I have put another 750 on it without a hiccup. Mounted aft of the firewall, FWIW.

Chris
 
I' ve had 3 Floscan 201b transducers installed in 3 LongEZ's I built; they began use in 1983, 1986 and 1989 and as of May 2026 all 3 original 201b's are in constant use with over 5,100 aggregate hours flown with zero problems. The V35B I bought 4 years ago came with a red cube that failed in flight after 340 hours time in service; it was replaced with a Floscan 201b coupled to a JPI 930... and after 250 hours is still working fine. No more red cubes for me!
 
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My RV7 never had an issue with the red cume that was mounted on the firewall with a piece of angle that intersects a stiffener. As far as I know it is still going strong.

There are a couple of installation requirements in the manual that I followed exactly when installing mine.

I did have a bad electrical connection once due to a poor crimp.
 
The signal is especially sensitive to vibration in the connection... make sure that the wires overlap inside the barrel of a high vibration coupler and that the set screw is tight.
 
scrollF4 said:
It does bother me to see folks having problems with the Red Cube. My travails are mentioned in this thread, but that's after over 10 years of flight ops averaging 200 Hobbs hours yearly. My one-off experience is that it has served me well...I certainly got my money's worth. To each, I bid you good fortune, whether it's an EI cube, Flowscan, or whatever.

Now let's see how long this new Cube lasts.
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As far as I can tell from scrubbing VAF and other forums, most if not all of the issues with the Red Cube come down to improper wiring/terminations.

@scrollF4 Sid's issue seems to be caused by years of running on "Hyde-gas" from 52F ;)
 
I finally found the issue with my red cube! I have replaced it 3 times and after only a couple of hours, the readings became erratic. Turns out, there was a TINY scuff in the yellow data wire coming out of the EMS module mounted behind the panel. The wiring harness faces upwards towards the canopy hinge. While the canopy is open, it seems miles away from anything. I was in the process of preparing to rewire the cube and noticed a tiny scuff the size of a pin prick, in the yellow wire. I couldn't figure out how it got there then suddenly I noticed a tiny little black spot on the bottom of the canopy hinge. I pulled the canopy down and figured out that the yellow wire (Located towards the TOP of the wiring harness) BARELY touched the canopy hinge in the closed position. I taped the wire, installed a nylon conduit over the harness for protection and zip tied the wiring harness away from the canopy hinge. NO MORE ERRATIC READINGS! Prior to my discovery, I had relocated the cube away from the exhaust pipes and behind the rear baffles to minimize heat. I also left it suspended, not mounted to the engine block. I definitely recommend suspending the cube vs. mounting on the block, although I don't believe that was an issue. Mine worked perfectly, suspended between the cylinders and exhaust pipes for 150 hours. Turns out, that's how long it took for the wiring harness to chafe through up against the canopy hinge. Just glad to have found the problem after 3 expensive replacements.
 
DRBuilder said:
I finally found the issue with my red cube! I have replaced it 3 times and after only a couple of hours, the readings became erratic. Turns out, there was a TINY scuff in the yellow data wire coming out of the EMS module mounted behind the panel. The wiring harness faces upwards towards the canopy hinge. While the canopy is open, it seems miles away from anything. I was in the process of preparing to rewire the cube and noticed a tiny scuff the size of a pin prick, in the yellow wire. I couldn't figure out how it got there then suddenly I noticed a tiny little black spot on the bottom of the canopy hinge. I pulled the canopy down and figured out that the yellow wire (Located towards the TOP of the wiring harness) BARELY touched the canopy hinge in the closed position. I taped the wire, installed a nylon conduit over the harness for protection and zip tied the wiring harness away from the canopy hinge. NO MORE ERRATIC READINGS! Prior to my discovery, I had relocated the cube away from the exhaust pipes and behind the rear baffles to minimize heat. I also left it suspended, not mounted to the engine block. I definitely recommend suspending the cube vs. mounting on the block, although I don't believe that was an issue. Mine worked perfectly, suspended between the cylinders and exhaust pipes for 150 hours. Turns out, that's how long it took for the wiring harness to chafe through up against the canopy hinge. Just glad to have found the problem after 3 expensive replacements.
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Thanks for closing the loop on this, Dennis! Another excellent reminder to us all to ensure our wiring is "chafe-free."
 
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