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  #1  
Old 08-09-2018, 12:02 PM
JackinMichigan's Avatar
JackinMichigan JackinMichigan is offline
 
Join Date: Nov 2012
Location: Canton, MI
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Default Multiple fuel flow transducer failures.

I have the EI FT60 'Red Cube' flow transducer mounted in the center tunnel up near the firewall, just forward of the electric boost pump. It's the most inaccessible component on that entire airplane, and I neglected to install an access panel when I had the chance.

It failed after only 20 hours. I spent nearly 3 weeks taking everything apart to get at it and replace it, and the new one functioned just fine after several tests. That is, until I got the entire airplane put back together and had it out on the tarmac for engine startup. That's when the new transducer failed, with essentially zero hours on it. I had to walk away before I took a crowbar to that **** airplane.

This transducer is not in a high heat area (125 degrees F has been the max tunnel temp so far) and vibrations aren't excessive. Does anyone know what would cause these things to fail so quickly? I consider the flow sensor as a mission critical piece of equipment - the plane won't fly if it's not working.

P.S. - Do yourself a huge favor and install an access panel in the tunnel everywhere you have a critical piece of equipment. You will thank yourself later.
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RV-10 N1861G
Build #41389, started Oct 2012
Current status: 1st Flight 11/10/17
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  #2  
Old 08-09-2018, 12:36 PM
TS Flightlines TS Flightlines is offline
 
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Reading off scale low, or high, or leaking? Do you have fuel flow?
The internal orifice is kinda small---see Dan Horton's autopsy of one. VAF thread on the subject. Generally electrical if it doesnt read.
Tom
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Old 08-09-2018, 01:09 PM
Bevan Bevan is offline
 
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Wouldn’t it be better and safer to put the fuel flow sender FWF downstream of the fuel pumps? On injected motors, many are putting the fuel flow sender downstream of the servo and prior to the spider. I moved mine to this position (RV7A) and solved three problems and now it works good.

Bevan
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Last edited by Bevan : 08-09-2018 at 01:14 PM.
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  #4  
Old 08-09-2018, 01:32 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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What was the failure mode of the first one? e.g., impeller stuck/won’t spin? Internal electrical connection?
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  #5  
Old 08-09-2018, 01:46 PM
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JackinMichigan JackinMichigan is offline
 
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Quote:
Originally Posted by BobTurner View Post
What was the failure mode of the first one? e.g., impeller stuck/won’t spin? Internal electrical connection?
It wasn't wiring, and the impeller wasn't stuck. It just quit working.
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RV-10 N1861G
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  #6  
Old 08-09-2018, 01:53 PM
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JackinMichigan JackinMichigan is offline
 
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Quote:
Originally Posted by TS Flightlines View Post
Reading off scale low, or high, or leaking? Do you have fuel flow?
The internal orifice is kinda small---see Dan Horton's autopsy of one. VAF thread on the subject. Generally electrical if it doesnt read.
Tom
Reading zero. Not leaking. I have it hooked up to a Garmin G3X for readout.

I had a local A&P share with me a trick to determine if wiring is the issue. Take a piece of wire and, with the transducer fully hooked up, splice it into the signal wire. Tap the other end of that wire to ground. This will simulate a signal coming from the transducer, and if everything else works you should get a reading. That's what I did and was able to get a reading, indicating that it was the transducer itself that failed. After I got it off I notice that the impeller wasn't stuck or clogged, it just quit working.
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RV-10 N1861G
Build #41389, started Oct 2012
Current status: 1st Flight 11/10/17
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Old 08-09-2018, 02:53 PM
TS Flightlines TS Flightlines is offline
 
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I'll defer to EI, or Dan Horton, but sounds like an internal wire failure.
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Teflon Hose Assemblies for Experimentals
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  #8  
Old 08-09-2018, 07:04 PM
BobTurner BobTurner is offline
 
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I'd try to get a second or third set of eyes on this. You may be just the victim of incredibly bad luck, or there may be something obvious that you as the builder are overlooking from habit.
Wires oriented up? input attached to "IN"? What sort of thread sealant did you use? Did you blow compressed air thru it to make sure it worked (don't!)? Exceed the recommended torque on the connections? Possible intermittent electrical connections (the worst to trouble shoot)? Any foreign objects in the fuel line?etc....
Call the manufacturer and ask for help. If they've had two in a row fail like this they should be interested.
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Old 08-09-2018, 07:48 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
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Default Fuel flow transducer

My guess is the transducers are not the problem, but an intermittent wiring connection is. What is the probability that you could see that many failures when the rest of us almost never see failures where the wheel is not stuck? Memory is the wheel spins in front of a light and a photo cell sees flashes as the wheel obstructs the light when it turns. The photo cell is a modulated output dependent on how fast the wheel turns, this measures flow. The wheel can get stuck, the light can burn out or the photo cell can fail. Or? any of the 3 wires can have an intermittant connection.
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  #10  
Old 08-09-2018, 09:34 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by BobTurner View Post
I'd try to get a second or third set of eyes on this. You may be just the victim of incredibly bad luck, or there may be something obvious that you as the builder are overlooking from habit.
Wires oriented up? input attached to "IN"? What sort of thread sealant did you use? Did you blow compressed air thru it to make sure it worked (don't!)? Exceed the recommended torque on the connections? Possible intermittent electrical connections (the worst to trouble shoot)? Any foreign objects in the fuel line?etc....
Call the manufacturer and ask for help. If they've had two in a row fail like this they should be interested.
+1

With the second unit failing just as quickly, I would be looking beyond mfg defect.

One thing to look at is voltage. The red cube runs off 5 volts, not 12. Most EIS systems provide a FF power pin, but some expect you to tie into the instrument's general 5 volt bus.

Larry
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Last edited by lr172 : 08-09-2018 at 09:36 PM.
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