It would be more useful to know what it did reach.
Van's Air Force
The definitive Van's Aircraft support community! Buying, building or flying an RV? Join our exclusive family of mentors and enthusiasts!
Red cube failure mode
- Thread starter Dorfie
- Start date
It would be more useful to know what it did reach.
I too am starting to get the dreaded Red Cube failure. Just over 400 hours. Symptom is that I get unexplained drops in FF, like shown below. Sometimes it only drops a few GPH, sometimes to close to zero. Recovers in somewhere between a few seconds, and up to 30 seconds. Far from a safety of flight issue, I'll try to find a replacement and watch it for a while. Red Cube is hard mounted (and probably grounded) to engine between mechanical fuel pump and fuel servo. I took extra care to make sure that the wiring was done right and carefully protected and supported, after reading about so many failures.
I am quite unhappy with this Red Cube product. Mine is suspended in the hoses between the engine driven fuel pump and the carburettor. Since only 50hrs from new, it has been intermittently failing. The failure mode in my case is the impeller sticking. If I remove the cube and squirt through some WD40 it seems to last another 50hrs or so before sticking again. In my case this presents itself as low fuel flow with occasional zero fuel flow indication, especially at low power on the ground.
The WD40 doesn't make much sense because the avgas will wash it way immediately. I think it was just the force of the liquid squirting through the cube that freed up the impeller.
With 300hrs on the cube and 2 years since purchase, I decided to buy a new one. The new one is working well currently but I dismantled the old one. The impeller is mounted on a shaft with pointed ends that sit in jewelled bearings - or at least some kind of white coloured material that has a conical indentation. The machining of these pointed ends is terrible, honestly really bad. This photo was taken on an iPhone and shows how poor it is.
After a time this seems to gall the bearing surface and so the thing sticks. I built a 00 gauge model train track in the office a few years ago, and the axles for the rolling stock use a similar bearing setup. The model train axles have quite finely machined points - vastly better than this aviation grade product.
EI said that they've never heard of this failure before, which I don't believe because we have two cubes in the hangar from two totally different aircraft/installations/engines which both have the impeller sticking issue. They offered a replacement at half price but they advertise a 10,000hr life...
When this new cube fails I'll switch to a Floscan 201B.
The WD40 doesn't make much sense because the avgas will wash it way immediately. I think it was just the force of the liquid squirting through the cube that freed up the impeller.
With 300hrs on the cube and 2 years since purchase, I decided to buy a new one. The new one is working well currently but I dismantled the old one. The impeller is mounted on a shaft with pointed ends that sit in jewelled bearings - or at least some kind of white coloured material that has a conical indentation. The machining of these pointed ends is terrible, honestly really bad. This photo was taken on an iPhone and shows how poor it is.
After a time this seems to gall the bearing surface and so the thing sticks. I built a 00 gauge model train track in the office a few years ago, and the axles for the rolling stock use a similar bearing setup. The model train axles have quite finely machined points - vastly better than this aviation grade product.
EI said that they've never heard of this failure before, which I don't believe because we have two cubes in the hangar from two totally different aircraft/installations/engines which both have the impeller sticking issue. They offered a replacement at half price but they advertise a 10,000hr life...
When this new cube fails I'll switch to a Floscan 201B.
This really doesn't mean anything unless you compare it with a new one. You need to know if it came this way, or did something in your fuel system cause this.
The new one doesn’t have a sticky impeller (yet). Holding the old and new cube side by side and gently blowing towards them, the impeller on the new one would spin but the old one would not.
That impeller shaft should have a finely machined point, I don’t see how it would end up looking like this from wear. You can see how rough the machining is from the photo.
Do we feel that the flowscan is more reliable? We need some smart guys like you @IO390 to apply the ultrasonic technology to create a better fuel flow meter in a reasonable package for aviation.
I shudder to think about where those bits of plastic are going - I only have a "last chance" filter in my fuel servo after this fuel flow sensor...not a failure mode that I considered.
Guess I have been lucky...
Had a Flowscan FF sensor on my previous engine, and that ran with no failure for about 2Kh, mounted as @IO390, suspended between the engine driven fuel pump and the carb.
Since upgrading my EMS from a VM1000 to a 3GX, I went for a red cube, and this has been working for the better part of 400h now, again, no failure and running strong. As we all know electronics don't like being shaken in a hot environment, and so I decided to mount this one directly on the engine mount, using some reworked Temu Aviation motorcycle headlights brackets. Will see how long that red cube lasts for...
Had a Flowscan FF sensor on my previous engine, and that ran with no failure for about 2Kh, mounted as @IO390, suspended between the engine driven fuel pump and the carb.
Since upgrading my EMS from a VM1000 to a 3GX, I went for a red cube, and this has been working for the better part of 400h now, again, no failure and running strong. As we all know electronics don't like being shaken in a hot environment, and so I decided to mount this one directly on the engine mount, using some reworked Temu Aviation motorcycle headlights brackets. Will see how long that red cube lasts for...
Radioflyer
Well Known Member
Is that impeller shaft plastic? If so, the white conical bearings are probably some plastic also like teflon or Delrin. A sharp tool should be able to leave a dent on the bearings, just to know. I propose that the wear you show is due to vibration. (Probably stating the obvious.) On such a light part, even mounting between pliable hoses are too stiff to offer perfect isolation. Every engine installation has different vibration exposure to the sensor, so my guess as to why people have varying results.
@Radioflyer - the shaft is steel, and the surface finish is definitely from poor machining. The bearing inserts are white in colour so I guess they could well be PTFE.
The second failed cube that I mentioned - also with a sticky impeller - has a much better surface finish though I don’t know how many hours are on this unit and whether the pointed end has worn to the rounded shape over time, or whether it was manufactured like this. Either way this shows considerable variation in production quality.
The second failed cube that I mentioned - also with a sticky impeller - has a much better surface finish though I don’t know how many hours are on this unit and whether the pointed end has worn to the rounded shape over time, or whether it was manufactured like this. Either way this shows considerable variation in production quality.
Attachments
I used a small amount of loctite 542 on mine, not sure about the other failed cube here.
No fuel lube/EZ Turn in my system. I only use it to stick washers and nuts to my finger.
I copied this mounting method after seeing someone doing a similar thing on VAF. No issues so far after > 150 hours
