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Red Cube Heat Shield

mountainride

mountainride

Well Known Member
After ~350 hours my red cube gave some erroneous fuel flows varying between 5 and 18 gph on the last flight. It seemed to work properly later in the flight but I assume its at the end of its life. I am trying to figure out how to better protect from heat in the standard RV-14 location on the intake tubes. TS Flightlines has a relocation kit to mount on the engine frame but I was hoping to just swap it out with my existing fuel hoses. I created a heat shield out of scape aluminum but am not really sure if this will help or possibly make it even worse. I was going to put some stick on refective heat shield on top. What is the correct thermo evaluation of my solution?

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Add some Shiny tape and I think DanH would approve of this. :)

You do have the two shields already installed on the #2 and #4 exhaust headers...right?
 
mountainride said:
After ~350 hours my red cube gave some erroneous fuel flows varying between 5 and 18 gph on the last flight. It seemed to work properly later in the flight but I assume its at the end of its life. I am trying to figure out how to better protect from heat in the standard RV-14 location on the intake tubes. TS Flightlines has a relocation kit to mount on the engine frame but I was hoping to just swap it out with my existing fuel hoses. I created a heat shield out of scape aluminum but am not really sure if this will help or possibly make it even worse. I was going to put some stick on refective heat shield on top. What is the correct thermo evaluation of my solution?

ZAp1vbe.jpeg


pq9iZ2x.jpeg
Click to expand...

Vic Syracuse's book "Maintenance Handbook for Van's RV Aircraft" has a write up on this. Vic recommends wrapping the Red Cube with heatshield/heat barrier (like those you can buy from Aircraft Spruce).
 
Aluminum is a good conductor though your airgap will save you. That said if you are shielding from radiant heat, only that material directly between the device and source are doing any protecting. Best to follow the advice above and move it to a better environment if possible.
 
I swapped out the red cube this morning. The failure was at the top joint. It looks like the factory heat shrink was slightly melted. It was a loose in the fitting and also appeared to have let some errant oil that ran down the wire in. I think that adding some high-temp RTV at this joint might solve the majority of the red cube failures. The new install has the aluminum heat shield and some self healing silicone tape to prevent any oil or contaminants running down the wire into the electronics.

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Mike S said:
Methinks it would work better if there was some fresh air flow in there.
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Even a 1/4" ID hose or tube can provide a cool envelope, if thermally insulated the only fluid cooling it is fuel. Also, the root cause could be mechanical vibration if hard mounted to the engine. Nice shield tho . . :)
 
As I have posted in the past, the Van’s location for the red cube is problematic. Here are the mounting requirements:

General Placement Recommendations for Fuel Flow Transducer
• Do not install the fuel flow transducer, hoses and fittings near exhaust system or
turbocharger. Excessive heat can damage fuel system components.
• Do not install 90 degree fittings (elbows) on the input or output of the fuel flow transducer.
Doing so will cause turbulence in the fuel flow which causes inaccurate fuel flow data.
• Install the fuel flow transducer with the three wires pointed UP.
• Install a fuel filter UPSTREAM of the fuel flow transducer to screen out debris.
• For best measuring performance, the fuel should travel uphill by one to two inches (25-50
mm) after leaving the fuel flow transducer.
• Placement of the fuel flow transducer is dependent upon other components in the fuel
system and is ultimately determined by the installer. It is common to place the transducer
downstream of the last fuel pump.
Due to vibration issues, never connect the fuel flow transducer directly to the
engine.

This mounting meets all the requirements.
Carl
 

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The latest revision (I) of the FT-60 Data Sheet requires that the cube be suspended by flexible hoses (and not bolted directly to anything) viz:
This transducer must be suspended between flexable (sic) hoses on the inlet and exiting ports. The hoses must be supported within 6 inches of the transducer.
Click to expand...

There is now no stated restriction by EI on the use of 90 degree fittings on the inlet or outlet.

The sum of the real and perceived constraints makes it almost impossible to install the cube in an RV without violating one or more of them!
 

Attachments

Carl Froehlich said:
As I have posted in the past, the Van’s location for the red cube is problematic. Here are the mounting requirements:

General Placement Recommendations for Fuel Flow Transducer
• Do not install the fuel flow transducer, hoses and fittings near exhaust system or
turbocharger. Excessive heat can damage fuel system components.
• Do not install 90 degree fittings (elbows) on the input or output of the fuel flow transducer.
Doing so will cause turbulence in the fuel flow which causes inaccurate fuel flow data.
• Install the fuel flow transducer with the three wires pointed UP.
• Install a fuel filter UPSTREAM of the fuel flow transducer to screen out debris.
• For best measuring performance, the fuel should travel uphill by one to two inches (25-50
mm) after leaving the fuel flow transducer.
• Placement of the fuel flow transducer is dependent upon other components in the fuel
system and is ultimately determined by the installer. It is common to place the transducer
downstream of the last fuel pump.
Due to vibration issues, never connect the fuel flow transducer directly to the
engine.

This mounting meets all the requirements.
Carl
Click to expand...
Except the 90 degree fitting on the input :)
 
Carl Froehlich said:
Nope - the cube is on the aircraft side of the engine isolation mounts.
Click to expand...
True it is not on the engine, however it should not be hard mounted on anything else either (firewall, engine frame etc.) It must be suspended in mid-air by flexible hoses, per the manufacturer. Just sayin!

I hope your curved 90 degree inlet fitting is steel and not aluminum?

(FWIW I too (!) chose to attach the cube to the frame with Adels and if there is a problem then I will add a rubber isolator between the cube and the bracket.)

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Carl Froehlich said:
Nope - this is a curved tube.
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I guess now we have a new definition for the 90 degree fitting. Here is one of the guidelines.
"The fuel flow transducer(s) should be installed in a straight section of your fuel line. (6 straight inches on each side is desirable)."
 
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PaulvS said:
And also attaching it directly to the engine mount instead of suspending it by hoses ;)
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If anything, you would want it to be mounted someplace solidly instead of being suspended. The engine mount should provide a fine and relatively vibration free location so in that regard, it is a good place to be mounted.
 
bjdecker said:
Aces!

Now replace those AN816-6D and AN823-6D fittings with the Steel equivalent.
Click to expand...
Have there been issues with the aluminum fittings? I had a red cube failure last month and took the opportunity to move it to the engine mount as Carl did but I used the standard aluminum fittings. There’s very little stress on the hoses where they connect to the cube as far as I could tell. Is there really a danger of failure or just an abundance of caution? I agree this would be a really terrible place for a failure though so, as I think about it, maybe that’s reason enough.
 
Bavafa said:
If anything, you would want it to be mounted someplace solidly instead of being suspended. The engine mount should provide a fine and relatively vibration free location so in that regard, it is a good place to be mounted.
Click to expand...
Personally I agree with that however it is contra to the EI installation instructions which state that the cube should be suspended in mid air via the flexible tubing that is then clamped to a support within 6 inches either side of the cube. I couldn't find a workable way to do that and instead attached the cube to the mount like Carl did. The engine mount and firewall will vibrate less than the engine itself, but there will likely still be some vibration.
 
Carl Froehlich said:
As I have posted in the past, the Van’s location for the red cube is problematic. Here are the mounting requirements:

General Placement Recommendations for Fuel Flow Transducer
• Do not install the fuel flow transducer, hoses and fittings near exhaust system or
turbocharger. Excessive heat can damage fuel system components.
• Do not install 90 degree fittings (elbows) on the input or output of the fuel flow transducer.
Doing so will cause turbulence in the fuel flow which causes inaccurate fuel flow data.
• Install the fuel flow transducer with the three wires pointed UP.
• Install a fuel filter UPSTREAM of the fuel flow transducer to screen out debris.
• For best measuring performance, the fuel should travel uphill by one to two inches (25-50
mm) after leaving the fuel flow transducer.
• Placement of the fuel flow transducer is dependent upon other components in the fuel
system and is ultimately determined by the installer. It is common to place the transducer
downstream of the last fuel pump.
Due to vibration issues, never connect the fuel flow transducer directly to the
engine.

This mounting meets all the requirements.
Carl
Click to expand...
Hi Carl, Thanks for the good advice. I noticed on the photo that you use a 90 degree fitting on the input. Is that OK to do?
 
Hi Carl, Different subject, Im currently building an RV-8 and do not like the location of the inline fuel screen under the fuel selector valve. It sems difficult to get to for inspection and cleaning. Any good ideas on an alternate approach? I used an Aerolab sump on my last project. Its working good but out of stock everywhere.
 
Sully73 said:
Hi Carl, Different subject, Im currently building an RV-8 and do not like the location of the inline fuel screen under the fuel selector valve. It sems difficult to get to for inspection and cleaning. Any good ideas on an alternate approach? I used an Aerolab sump on my last project. Its working good but out of stock everywhere.
Click to expand...
I wish I had a secret to offer so you can avoid this pain, but I don’t. As per plans I have the AFP pump mount between the left tower and the firewall, the AFP filter mounted aft of the tower in the per plans holder location. For Condition Inspection I remove the Andair fuel valve handle and top plate, then remove the left cover over all the plumbing and such. Once done getting the filter out is easy. The real PITA stuff on this is the initial tube bending to connect all this stuff and the gas tank runs. You will need to get creative. Plan on 4 or 5 “prototypes” of 3/8” tubing. Tubing is cheap so don’t try to make something fit that you don’t want to live with for a couple of decades.

Carl
 
Maybe a stupid question - if heat is the red cube's enemy, could I just put it aft of the firewall next to the fuel pump and filter in the cabin? The install docs just say it has to be downstream of the pump/filter/etc. Why not avoid heat entirely and have it near the pump rather than on the engine?

I'm currently gearing up to work on my RV-8's fuel system, and this idea popped into my mind when reading through the thread here and all the issues caused by not using heat shield.
 
inktomi said:
Maybe a stupid question - if heat is the red cube's enemy, could I just put it aft of the firewall next to the fuel pump and filter in the cabin? The install docs just say it has to be downstream of the pump/filter/etc. Why not avoid heat entirely and have it near the pump rather than on the engine?

I'm currently gearing up to work on my RV-8's fuel system, and this idea popped into my mind when reading through the thread here and all the issues caused by not using heat shield.
Click to expand...
Yep - this was how the RV-10 plans said to do it (cube between the fuel filter and the firewall). It works, but with the cube between the boost pump and the engine pump turning on the boost pump messes up the flow readings. This is not much and only when the boost pump is running but enough for me never to do that again (new RV-10 project almost done). That is why the instructions say “downstream of the last fuel pump”.

I suspect vibration is more of an issue (like my RV-14 experience), but tucking the cube against the engine by the exhaust pipes per the RV-14 plans is not something I would do.

Keep it off the engine between the and no need for heat shields.

Carl
 
inktomi said:
Maybe a stupid question - if heat is the red cube's enemy, could I just put it aft of the firewall next to the fuel pump and filter in the cabin? The install docs just say it has to be downstream of the pump/filter/etc. Why not avoid heat entirely and have it near the pump rather than on the engine?

I'm currently gearing up to work on my RV-8's fuel system, and this idea popped into my mind when reading through the thread here and all the issues caused by not using heat shield.
Click to expand...
You can certainly do as I had it that way in my RV7 without any issues but the instruction and common practice is to put it upstream of the fuel pump. It is believed to have a more accurate reading. In regards to the wrapping it for head, one issue is with the wrap/Insulation may also keeps the heat after shut down and not let it cool as quickly.
 
Oh of course 🤦‍♂️- I'm forgetting about the engine driven fuel pump because my mind is all on the boost pump right now. Hah, thanks! I knew there was a reason!
 
If you read the Garmin and Red Cube instructions. They like to avoid disruptions (turns) within 6 inches of the cube. They go on to specify they like the output end or wire end higher than the input end or some combination of the two.

I have seen cubes with 90’s on each side of the cube, and the cube mounted on top of a fuel injected engine with a hard 90 going right into the fuel injection spider.

Best practices is to use straight connectors and keep the turns very gentle within 6 inches of the cube. If you are going t mount it on the engine side of the firewall there is a fire sleeve you can protect it with.

www.aircraftspruce.com

Fuel Transducer Cover Firesleeve Black 1-1/2 Id | Aircraft Spruce ®

Fuel Transducer Cover Firesleeve Black 1-1/2 Id Black Firesleeve for Fuel Transducer Cover
www.aircraftspruce.com www.aircraftspruce.com
 
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inktomi said:
Maybe a stupid question - if heat is the red cube's enemy, could I just put it aft of the firewall next to the fuel pump and filter in the cabin? The install docs just say it has to be downstream of the pump/filter/etc. Why not avoid heat entirely and have it near the pump rather than on the engine?

I'm currently gearing up to work on my RV-8's fuel system, and this idea popped into my mind when reading through the thread here and all the issues caused by not using heat shield.
Click to expand...
I've got my red cube bolted directly to the engine. Less than 400 hours, so perhaps I shouldn't talk until I hit 2000 or so. I was careful about the routing of the wires - no stress or strain on them.

The first company that gets the ultrasonic flow sensors working in our aircraft will make a mint.
 
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