What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RED CUBE symptoms diagnosis.

NYTOM

Well Known Member
Replaced a 10 year old defective Red Cube with a brand spanking new one from ACS. For the first 10 hours or so the GPH reading was steady as a rock with any slow change in the mixture reflected in a slow steady rock solid change. On yesterdays flight it suddenly started fluctuating wildly. Changes in mixture changed the reading in a appropriate way but still jumped all over the place with a set mixture still showing a jumping value that wouldn’t settle down. Any suggestions would be greatly appreciated on what to try first other than the usual connections check?
 
How is it mounted? Hard mounted? Floating on the hoses? I believe the ideal mounting is firmly with the wires up, and horizontal with a slight tilt up towards the outlet to promote bubbles to move out of the unit. Post some pictures.
 
Bubbles

How is it mounted? Hard mounted? Floating on the hoses? I believe the ideal mounting is firmly with the wires up, and horizontal with a slight tilt up towards the outlet to promote bubbles to move out of the unit. Post some pictures.[/QUOTE

It’s hard mounted on a bracket on the firewall below the engine driven fuel pump. The line then goes up to the carb. It has ceramic insulation over it with heat shields. I don’t think heat is a problem but bubbles does sound like a cause. Was flying for about a hour and stopped for a fill up before flying back to my home field. Because of maintenance personnel on the runway I was held up idling in the run up area for a time. Seems like the 20 minute flight back to my home field would have had time to flush any bubbles past the cube into the carb.
 
The electric fuel pump can cause erratic readings. Was that shut off?
Remember, the red cube measures fuel flow to the carb, not the fuel flow that the engine is consuming. If you have a sticking needle valve it will see low to no flow and then high fly as the carb bowl refills.
 
WE really have no dog in this hunt, other than we have ALOT of our clients using our hoses in varying locations of mounted FT60s. Maybe it just me, but it sure seems that the newer cubes have some fluxuating readings as compared to ones are are being replaced, IN THE SAME LOCATION, that operated great for 10 years.
We've been monitoring this for quite sometime, as our posts have shown. We have no ties to EI, or any of the avionics companies. But we do alot of the plumbing for the cubes, in various locations, in various types of aircraft and manufacturers. I just seems that there are some "strange" occurences with newer cubes. WE now have 2, verified anomalous cube readings, 1 of which was installed in the same location as the replaced one, and it acts the same as one other that has been posted on VAF. Different numbers, but a similar scenario. Just so happens, these 2 aircraft have the same avionics.

Tom
 
While the cubes can die earlier than we like, they have a pretty good history of reliable operation before that time. I would suspect a wiring flaw where the new cube's wires were tied into the chassis wires.

Larry
 
Larry, they certainly do have a great track record. NO doubt about it. Just some 'strange' occurences on some replacement installs.
Tom
 
Larry, they certainly do have a great track record. NO doubt about it. Just some 'strange' occurences on some replacement installs.
Tom

Definitely not implying that this couldn't be one of those, but I would rule out a wiring mishap first.
 
Troubleshooting

Definitely going to check wiring first. Boost pump was on when problem was first noted but continued with it on or off. New cube is mounted exactly as the old reliable cube was. I can’t believe it would fail in such a short time. Has anyone sent a cube back to be tested by the manufacturer. I would think they would be interested if this has become a reoccurring problem. Just wondering if the jeweled movement of the turbine is sticking and releasing to cause the fluctuations.
 
Tom---In the 1 case that i'm VERY familiar with, yes the cube was sent back to EI for testing. According to the owner, he reported that EI passed the cube with 'couldnt find anything wrong with it'. He reinstalled it; same situation. We moved it---again---same situation. He purchased a new unit, went back over all the wiring to quadruple check things, same situation.
With all the other options having been eliminated, we came up with the only other common piece to this whole thing. I spoke with another build at OSH and he stated he had a similar anomaly, different numbers, but similar. There was 1 common thing between both aircraft.

So I'll put this out to all that have a FT60, inhopes that we can finally put this to bed. Has anyone had an anomaly where in cruise flight, with all engine paramenters (RPM, EGT, CHT, MAP, FP) being VERY steady, have you experienced the fuel flow to take a drop from, say 6.5 gal/hr, to say 4.7 gal/hr, and stay that way for a period of time, and either return to a more 'normal' reading, or after engine shutdown and rebooting, the readings return to normalfor a period of time, then repeat?

IF SO---I'd love to hear about it along with pertnant information, like engine, injection system, avionics, transducer location, and whether any other strange occurances happen. WE think we have a common thread, but would like some more data.

Tom
 
I took my FT-60 back to EI and discussed my unusual performance. They tested the unit and gave it a clean bill of health. As the OP noted, I had a once reliable transducer only to start noticing some odd reading, mostly during LOP operations but also during taxi. I've worked with Tom on several permutations including alternate mounting locations. I've re-wired the system from the GEA 24 to the FT-60 and replaced the fuel lines using several angles of fittings. None of these changed the behavior. I purchased a new FT-60 thinking the EI guys were snowing me..... didn't change. Wires up, down, forward doesn't seem to matter. It's become quite the conundrum. I know Tom S has spent many hours trying to help figure this out. It's going to take someone much smarter than I to finally get the issue ironed out but, when that happens, I'll buy that individual a very nice bottle of wine!
 
resurection of this thread---

FYI----on Don Eisele's RV14, they were having erratic flow readings. After some extensive troubleshooting with some of his friends, they determined that there was a wire interruption at the body of the cube, under the heat shrink. Not at the electrical connections.
They could make the flow go from normal to zero by moving the wiring at the cube body.

Just some valid information from 1 RV14 owner----

Tom
 
Back
Top