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Red Cubes - Junk?

This is an interesting question. Static is one of my favorite topics as it happens to be perhaps one of the most neglected issues in many constructions.

In my opinion the chance of a static discharge damaging the senders opto electronics is not going to happen - the metal body of the sender, grounded, will shunt any change to ground easily. Should the housing however not be grounded it would form a ready interface for any charge to cause a discharge internally into any of the three wires connected to the sender or to any part of the internal electronics. Just depends on the path of least resistance. In a case like this (as unlikely as it may be) you could very well end up with damaged electronics.
Of course the charge has to be high enough to overcome any insulation - gut feeling tells me this is not going to happen.

Rainier
CEO MGL Avionics

This raises an interesting question. Do we believe that in the case of the red cube, does the ground going to the transducer circuit also ground the frame of the red cube.

Larry
 
This raises an interesting question. Do we believe that in the case of the red cube, does the ground going to the transducer circuit also ground the frame of the red cube.

Larry

Cannot find a reference to this in the FT-60 docs. My guess is that the housing is not connected to ground (in my opinion that would be the correct way of doing this).

Reason: Nothing should be grounded to your airframe that could induce any form of electrical current, DC in particular. If your FT-60 is mounted onto your airframe in a conductive way (which I guess would be the norm) and it is also internally grounded you have a recipe for a number of problems.

Having seen what galvanic corrosion caused by DC currents can do to a metal aircraft it is now one of the first things I check when I get to look at an aircraft. It is often easy for a builder to ground electrical equipment to the frame rather than pulling in additional wires but this is not a good idea.

Apart from the potential galvanic corrosion cause by DC current flow, you can very easily couple small amounts of EMI (RF interference from digital sources mostly) directly into your airframe converting this into a giant antenna to radiate it ! If can make small EMI problems all but impossible to solve.

In addition it can cause equipment damage due to ground faults - should some of your equipment loose its regular ground it may find a secondary ground via other ground connections through attached other equipment - potentially damaging that equipment by high ground currents it was not designed to handle.

An example of such a current path might be landing lights via airframe to COM antenna ground and antenna cable shield to ground connection of your radio - something like this is not uncommon.

Experienced builders know this of course and will avoid creating random ground connections like the plague. Best is a single ground connection from your battery negative to the airframe. If there is only one ground point no DC current can flow through the frame. Accidental grounds on COM/XPNDR antennas etc can be avoided by connecting these grounds via a small ceramic capacitor (10nF does the job nicely). Some radios have their antenna ports DC isolated - in this case you don't have to worry about this.

Getting back to the FT-60 - I don't have one here, can somebody check it out ? Is the housing connected to ground ?

Rainier
CEO MGL Avionics
 
What voltage might the cube tolerate?

Of course the charge has to be high enough to overcome any insulation - gut feeling tells me this is not going to happen.

Rainier
CEO MGL Avionics

Fast flowing fuel can easily generate 30,000 volts (material dependent). A spark jumps through the hose to a ground making pin holes, so it is pretty high and can develop in a few inches.

What might be the insulation break down point?
 
Fast flowing fuel can easily generate 30,000 volts (material dependent). A spark jumps through the hose to a ground making pin holes, so it is pretty high and can develop in a few inches.

What might be the insulation break down point?

Certainly a lot less than that :)

If it's going to go through the insulation it will be at the light source (LED) or light sensor (usually a photo transistor) and the insulation would be relatively thin here.

However in order to get that kind of voltage you would need a significant amount of fetch over a large conductive but otherwise isolated surface. Difficult to see how that could happen in a small aircraft.
You could help it along of course - let's assume you have a fairly long piece of metal fuel pipe which happens to be completely isolated. It so happens it is nicely aligned with copious amounts of dry air flowing over it via some duct (quite conceivable, nice flying day in low humidity conditions).
We have nice, uncontaminated avgas flowing through the pipe which changes into a nonconductive pipe (say rubber or similar) and then that happens to go to the Redcube and the body is not grounded but of course the internal electronics is via the power supply.

So in this case we have the perfect storm - charge gets supplied by the airflow, the fuel transfers it to the Redcube - the housing is in contact with the fuel so it collects the charge (bring your finger near it and you will get zapped). So now it is just a matter of enough voltage to overcome the isolation barrier and we will get a nice spark discharge and most likely a damaged Redcube.

It is certainly a possibility but the builder will have made a few mistakes to get to this point. If he simply ensures that no metal part, whatever it is, is electrically isolated - this cannot happen.

Typically, discharges in the engine bay happen in my experience around oil and coolant radiators - often these are mounted using lord mounts or similar arrangements - that's why you often see a copper strap around one of them. Leave that off and interesting things can happen.

I have never witnessed a case where a fuel line or fuel system part was involved - but it is not impossible, you are quite right.

Rainier
CEO MGL Avionics
 
I'm going to keep this thread alive since I've done more testing, still have not solved the problem and have seen more Red Cube failure posts. I've increased the bias voltage, as suggested by a viewer, changed from FF1 to FF2 on the RDAC and remounted the Red Cube using all straight fittings and wrapped in fire sleeve. Added rubber to the Adel clamps. Still it reads and fails as it pleases, ALL other sensors/inputs work fine on both RDAC's.

I contacted EI, talked to product support and I'm shipping this third Red Cube to EI to be tested. They said they will test with vibration and heat to see if it will fail. If it passes then I can move my troubleshooting to other areas.

I will post the results of the test when I get it.
 
On my Jodel I installed one ahead of the firewall in 2011. It has been flawless and very accurate. It is wrapped with a very wide piece of firesleeve to protect it from heat and closed with high temp rtv. The voltage supply and ground are obviously critical as mentioned. I would suspect those first. I did not use those silly clamps that came with it. I think I soldered it and put on lots of heat shrink to support the joints.

There was this guy on Youtube who flies a cirrus. He videos every flight and posts it. On one flight he had his fuel flow and rpm and a couple of other things go all wonky on him in cruise. So he figured that the airplane was about to burst into flames and explode and declared a mayday. The engine was running fine, he had control, 20 miles visibility, light winds. It was no emergency. At best it was a pan, but not even. Clearly the common thread to his issues was a bad ground for the various senders, which should usually be a wire directly to the block, not to the ground bus bar. Half a turn with a wrench, or at worst some cleaning or a new terminal and job done.

Everyone in the comment section high fived him for declaring an emergency and being "safe". Well, except me. :p

Moral of the story is that usually bad sensor data is ground or contact related. But not always.
 
Well, dammit...after 7+ years and 750 hours, it looks like mine is starting to fail. Drops down to 0.0, stays there a while, then goes back to normal for a while, then quits again. If I had to guess, I'd say the impeller is seizing up.

Time to get ahold of the company for a replacement and to find out their warranty.

Got my attention the first time, but since the engine was still running, I knew right away it was a sensor or indication problem, nothing more.

Grrrrr....
 
Knock on my head, mine has been bullet proof for 6 years 700 hours.

Mounted in front of the oil pan as recommended on a piece of spring steel with the intake slightly lower than the outake and straight not elbow connectors.
 
Cable failure

I had an FT-60 fail last year on my way back from OSH. The failure was intermittent at first, but after a few weeks became permanent. When I swapped it out I found that the cable had been damaged at the point where it entered the cube. The cable wasn't secured as well as it should have been and apparently vibrated just enough to break one of the conductors.
 
Is the red cube an item that should be replaced at any certain interval or is it a use it until it fails then replace it? I have one and it's worked flawlessly for the 500+ hours/8 years it's been in use. Last night I was flying and noticed it was fluctuating .2-.3 tenths of a gallon on fuel flow. I've don't recall noticing this in the past. Wondering if this is an early failure symptom.
 
Is the red cube an item that should be replaced at any certain interval or is it a use it until it fails then replace it? I have one and it's worked flawlessly for the 500+ hours/8 years it's been in use. Last night I was flying and noticed it was fluctuating .2-.3 tenths of a gallon on fuel flow. I've don't recall noticing this in the past. Wondering if this is an early failure symptom.

Could just as well be an indicator of another failure - like your carb floats or a misadjusted fuel injection servo.
 
I had one fail at around 500 hours and 4 years. I now carry a spare

That's okay, but I don't think necessary. I wouldn't want to change one out in the field. You don't actually *need* fuel flow meter to fly. Just lean the old-fashioned way (by EGT or roughness). If it dies during a flight, it's not an emergency...the engine will keep running :)

Mine started giving up the ghost a couple of months ago, at which point I ordered a new one and swapped it out at the next oil change, in the comfort of my hangar, without time pressure to "get it done ASAP" to get home, etc.
 
That's okay, but I don't think necessary. I wouldn't want to change one out in the field. You don't actually *need* fuel flow meter to fly. Just lean the old-fashioned way (by EGT or roughness). If it dies during a flight, it's not an emergency...the engine will keep running :)

Mine started giving up the ghost a couple of months ago, at which point I ordered a new one and swapped it out at the next oil change, in the comfort of my hangar, without time pressure to "get it done ASAP" to get home, etc.

I agree and would also rather do the swap at my home base hanger. That being said, the RV-10 has tons of room to carry spare parts and tools and if you have known small parts that fail often, why not.
 
Fuel will keep flowing

When my red cube failed on a trip to Canada, I had a conversation with the manufacturer and they confirmed that the unit was designed to continue to allow the passage of full fuel flow even if the impeller inside was completely frozen/ unable to spin. Just further confirmation that in the event of a ?catastrophic? failure, you can continue to fly home for the repair/replacement.
 
Failure Indications

When they do fail, are people seeing zero indications? or fluctuations, or? What is a normal failure indication? Mine was flawless through 480 hours.... seems to be about the mean failure time?

On takeoff, I got indications of very high fuel flow (54 gph on an IO-540) that in retrospect seems almost exactly double what was expected. When I pulled the power back to come back and land, fuel flow indications returned to normal.

I suspect the cube, but wonder if it is an electrical connection issue...

By the way...no big holes for fuel to come out of... checked that ;)

Thanks!
 
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HI Jeff,
When mine failed a few months back, it started intermittently showing FF or zero then would function fine. It finally went out and just showed zero. Mine had about 400 hours on it but that was over 15 years.
 
My red cube failed in about three years, the wire broke at the machined aluminum chassis. That joint is not very sturdy and the cable they used is pretty stiff with the outer jacket. The one I red RTVed the **** out that joint adding some support to the wire exiting the chassis.

Pay special attention when performing MX and not to stress that area.
 
Follow-up

Did you ever get to the bottom of this?

I'm going to keep this thread alive since I've done more testing, still have not solved the problem and have seen more Red Cube failure posts. I've increased the bias voltage, as suggested by a viewer, changed from FF1 to FF2 on the RDAC and remounted the Red Cube using all straight fittings and wrapped in fire sleeve. Added rubber to the Adel clamps. Still it reads and fails as it pleases, ALL other sensors/inputs work fine on both RDAC's.

I contacted EI, talked to product support and I'm shipping this third Red Cube to EI to be tested. They said they will test with vibration and heat to see if it will fail. If it passes then I can move my troubleshooting to other areas.

I will post the results of the test when I get it.
 
Early Failure Indication?

Is the red cube an item that should be replaced at any certain interval or is it a use it until it fails then replace it? I have one and it's worked flawlessly for the 500+ hours/8 years it's been in use. Last night I was flying and noticed it was fluctuating .2-.3 tenths of a gallon on fuel flow. I've don't recall noticing this in the past. Wondering if this is an early failure symptom.

I was about to start a thread to ask this question, but found this one in a search. My A/C (RV-10, IO-540 D4A5, GRT EFIS and engine monitor) is approaching 500 hours, which I note is a similar amount of time in several other posts. Perhaps a coincidence as others seem to be soldiering on much longer.

I've recently noticed an intermittent fluctuation of roughly +/- 0.3 gph at cruise (10 gph or so at 10K' and just under 60% power). MP, CHTs and EGTs are rock steady, and I would think I would see some change across a 0.6 gph fuel flow delta if it were real. I have not seen variations significantly outside this range as some others seem to have experienced. I haven't quantitated periodicity, but it's relatively slow--perhaps a minute or two from mean to peak delta.

Additionally, I compare each fuel purchase with the "expected" amount based on the totalizer. Absent significant differences in ramp slope, it has been amazingly accurate--typically less than a 0.5 g delta, always saying that that I used slightly more less than the totalizer indicated (thus the fuel remaining indication is on the conservative side). Recently, the delta seems to have risen to a bit over a gallon. On a 4 hour trip week before last, it was 1.3g, again with actual use lower (3%) than expected.

The red cube is in the tunnel, downstream from the aux pump. My tunnel is "warm", but (knock wood) I don't seem to have the hot tunnel issue discussed in other threads.

Like the poster quoted, I'm wondering if this is an early indication of impending failure...analogous to voltage fluctuations sometimes seen with a failing alternator. Thoughts?
 
Our experiences with RV10s and tunnel mounted transducers really havnet proved that to be a bad location. Seems to have been just fine for many years and flight hours on many RV10s. Similar reliable reading for many years on other install versions as well. Seems to me, that most of the anomalies we hear about are on more recently made transducers. 2-3 years and newer, and I have no idea why. I do know that EI tested one for one of our clients, passed it with no failure notice, it was reinstalled and flew several hours before the same exact anomaly occured. A new cube solved the issue, as far as I'm aware.

So I dont know if there is something about it that it doesnt play well with newer aircraft, but I suer woul dlike to find the answer.

Tom
 
Recently, the delta seems to have risen to a bit over a gallon. On a 4 hour trip week before last, it was 1.3g, again with actual use lower (3%) than expected.

The red cube is in the tunnel, downstream from the aux pump.

Like the poster quoted, I'm wondering if this is an early indication of impending failure... Thoughts?

More likely, the engine-driven pump's inlet valve doesn't seal quite like it did earlier in its life.
 
Our experiences with RV10s and tunnel mounted transducers really havnet proved that to be a bad location. Seems to have been just fine for many years and flight hours on many RV10s.

Tom, I've flown two configurations long term, cube prior to the engine driven pump, and cube between the FM200 and the flow divider.

In the former case, the overall totalizer accuracy was acceptable. However, it was never truly stable in cruise (0.1~0.2 random jitter), nor was it accurate at low flows (idle, taxi, etc), and the indication jumped up one GPH or more when the electric pump was running.

Relocating the cube to the divider line was like night and day. The jitter is gone, idle flow appears accurate, and there is no indication change with the boost pump on or off.

EI recommends installation downstream of the engine pump. I think (opinion warning!) many of them are being installed a bit too close to exhaust pipe radiant heating, but beyond that objection, my experience says the recommendation is spot on.

There are other factors. A cube's flow passage is less than half that of a -6 hose. When installed prior to the engine pump, the likely result is some pressure drop in the line between the cube and the pump. That line is subject to heating, and as you know, heating and pressure drop are a bad combination. We do hear reports of -10's requiring boost pump to maintain fuel pressure when hot.
 

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Red Cube

I have installed at least 7 of the Red Cubes without any issues. If you are not installing the unit with a slight UP angle at the "OUT " hose you can( and usually will) get erratic fuel flow indications. This is an important part of the install.
 
I have installed at least 7 of the Red Cubes without any issues. If you are not installing the unit with a slight UP angle at the "OUT " hose you can( and usually will) get erratic fuel flow indications. This is an important part of the install.

Th cube on my 6 is horizontal, with wire facing up, with no noticeable tip up at the out end. It has given very stable readings and variance at fill up is consistently around.2 - .3 gph. Been this way for 650 hours. It is mounted between servo and spider.

Larry
 
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