Red Cube Heat Shield

[mountainride]

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?

 

[bjdecker]

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?

 

[llaux]

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?

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).

 

[Mike S]

Methinks it would work better if there was some fresh air flow in there.

 

[Carl Froehlich]

Or, move the cube outside the heat areas and end the problem.

Mounting after the mechanical fuel pump on the engine mount works well (no heat shields and such).

Carl

 

[Freemasm]

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.

 

[mountainride]

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.

 

[BillL]

Methinks it would work better if there was some fresh air flow in there.

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 . .

 

[bjdecker]

Aces!

Now replace those AN816-6D and AN823-6D fittings with the Steel equivalent.

 

[Carl Froehlich]

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

 

[PaulvS]

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.

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!

 

[Bavafa]

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

Except the 90 degree fitting on the input

 

[PaulvS]

Except the 90 degree fitting on the input

And also attaching it directly to the engine mount instead of suspending it by hoses

 

[Carl Froehlich]

Except the 90 degree fitting on the input

Nope - this is a curved tube.

 

[Carl Froehlich]

And also attaching it directly to the engine mount instead of suspending it by hoses

Nope - the cube is on the aircraft side of the engine isolation mounts.

 

[PaulvS]

Nope - the cube is on the aircraft side of the engine isolation mounts.

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.)

 

[Bavafa]

Nope - this is a curved tube.

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)."

 

[Bavafa]

And also attaching it directly to the engine mount instead of suspending it by hoses

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.

 

[Navy76]

Aces!

Now replace those AN816-6D and AN823-6D fittings with the Steel equivalent.

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.

 

[PaulvS]

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.

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.