Yep. The red cube again!

[Veetail88]

I know this has been beaten to death, but I have a couple of questions for the VAF brain trust.

#1 I am planning on firesleeving the aluminum loop, but even with the sleeving, is tha aluminum tube adequate.

#2 The assembly is very ridgid, but do I need to support the loop?

#3 I needed the 90 that is on the bulkhead fitting on the other side of the firewall, which is why I'm coming through with a straight outlet, which is why I need the loop and the 90 just before the transducer. Has anyone used a 90 just prior to the transducer and does it still read accurately?

Here's the pic.

Thanks in advance for your responses.

[bkthomps]

i've got no suggestions to offer but i would say simply i would not do that, the tube is not supported and is just a weak link waiting to happen

also i thought you had to have it mounted with 6" of no bends no turns no fittings straight flow to it

[penguin]

My answers are:

1. The Al tube is adequate, we can debate all year whether firesleeve is required, but there is no down side from using it.

2. No

3. The installation instructions specifically recommend against an angle fitting on the inlet (or outlet), so you are potentially heading for a problem. I would have bent the tube 90* as soon as possible coming out of the firewall, gone vertical, the 270* right to bring the tail back on to the inlet with a few ins of straight run.

Hope this helps. Pete

[Brantel]

The post from the manufacturer's employee on this board seem to suggest a different opinion.....

Originally Posted by Mathew Sharp

As far as I know Dynon distributes both the FloScan 201B as well as EI's FT-60.

The FloScan unit is much more sensitive to the angles/fittings entering and exiting the unit. EI's unit does not care. You can run 90 degree fittings in and out of ours without problems.

JPI does not sell EI's FT-60

Maybe you can get Dynon to trade you for a FT-60?

Good luck!

Matt

Originally Posted by Mathew Sharp

You do NOT want to rigid mount the transducer to the motor (any part) using just a fitting. It is a huge safety issue. The fitting could theoretically fatigue and break. You absolutely need to have flexible line on both sides of the Floscan 201B or the EI FT-60 (that Dynon now utilizes).

After manufacturing/supporting flow instruments for a good number of years we have seen that flow transducers accuracy is typically better when mounted after both fuel pumps. They simply seem to prefer to have fuel pushed through them, not pulled through. The truth of it though is that many installation drawings still read as though we were still using the older Floscan 201 transducers. I have seen installs that mount the transducer between the pumps with claimed success. The Floscan units were much more sensitive in regards to mounting location, angles of fittings in and out, and attitude. Our new design will tolerate a lot more. Frankly we don't care if the thing flows straight up, or if you put 90-degree fittings in and out (FT-60 only) of the transducer. Just don't mount it upside down or flowing sharply downhill.



Hope this helps,

Matt Sharp

Originally Posted by Mathew Sharp

Hello All!

Your friendly neighborhood EI Tech support rep here!

There are really two issues in regards to EI’s specifications on flow transducer placement.

1. Accuracy of the output of the flow transducer.
2. Safety.

Issue one is pretty basic. After manufacturing flow instruments for a good number of years we have seen that flow transducers accuracy is typically better when mounted after the mechanical fuel pumps. They simply seem to prefer to have fuel pushed through them, not pulled through. The truth of it though is that many installation drawings still read as though we were still using the older Floscan 201 and 231 transducers. I have seen installs that mount the transducer between the pumps with claimed success. The Floscan units were much more sensitive in regards to mounting location, angles of fittings in and out, and attitude. Our new design will tolerate a lot more.

The other more serious issue is in regards to safety. We want to make absolutely sure that the fittings on the transducers never are subjected to conflicting vibration planes. The engine will flex in the motor mounts creating conflicting vibration planes between the engine and the airframe. This is why the “flexible line in” and “flexible line out” is called out so often. This is also why we don’t want the transducer rigid mounted, via a fitting, to a carburetor or fuel pump. A contradicting vibration plane will focus the energy directly to the fitting. It is our sincere concern that with the two conflicting vibration planes here could cause the fitting to fatigue and crack. This would be bad…and we have seen it happen….

On the bright side, we don’t care if the thing flows straight up, or if you put 90-degree fittings in and out of the transducer. Just don’t mount it upside down, flowing sharply downhill, or before the pumps.

Please let me know if you have any questions or if we may be of any assistance.

Matt Sharp

Based on the info from the above, I installed a 45 deg fitting on the input and a 90 deg on the output. Over 175hrs ago and typically my fuel totalizer is within .2 gallons at fillup.

[n82rb]

my 2 cents. aluminum and flammable liquids are never acceptable on the hot side of the fire wall. Period.

bob burns
N82RB

[Walt]

I would use 5052-O tubing or SS preferably, and yes it should be firesleeved.

[Lars]

Originally Posted by n82rb

my 2 cents. aluminum and flammable liquids are never acceptable on the hot side of the fire wall. Period.

bob burns
N82RB

Carburetors, fuel servos, flow dividers, mechanical fuel pumps are all made of aluminum. Just sayin'...

My red cube is mounted on a bracket at the back of the engine, between fuel servo and flow divider, pointed straight up. 90 degree fitting on the end of the hose on the outlet side. I only have about 30 hours on mine, but so far it seems to be accurate to about 0.1 gallons in 30, and doesn't care if the electric pump is on or not.

That said, a piece of 3/8" aluminum tube installed like that in a high vibration area looks like a tuning fork. In fact it is similar to a tuning fork. The question is whether one of its natural frequencies will get excited by the forcing function created by engine vibrations. If it does, it may not be long of this world. I'll second Walt's recommendation of st. steel, and yeah, add firesleeve.

[Snowflake]

Originally Posted by Lars

Carburetors, fuel servos, flow dividers, mechanical fuel pumps are all made of aluminum.

Not to mention the engine case, cylinders, baffles, vacuum pumps... Need we go on? :P

[mtnflyer]

So here,s the story,,,,about three weeks ago I'm ferrying an Almost new RV7A from east Texas to Denver with a stop in Clinton OK for fuel and breakfast. While descending out of 10 5 the bells and whistles go off on the Dynon with the fuel flow going from about 7 gal to over 25 gallons an hour. That, my friends will pucker up all sort of things real tight. I was able to get the bird down and shut off. LUCKY LUCKY me. So to make a long story short, It turns out the builder had mounted the red cube on a bracket bolted to the left forward corner of the crankcase with a straight 2&1\2 inch piece of alum tube going to the fuel servo. The tube had broken right at the flare on the servo end so at least there was fuel getting to that servo and the engine was still getting enough fuel to run. So here's my recommendation, never mount any aluminum tubing on the engine, to my way of thinking,aeroquicp 303 with firesleve is the only way to go forward of the firewall.
On my own RV7A, I mounted my fuel flow transducer in the low channel just forward of the electric fuel pump and is super accurate....PS the guys in the shop and that pretty gal in the FBO were great help getting me back in the air and home in time for dinner so if you in the area and need cheap fuel, stop in at Clinton Regional KCLK

[Veetail88]

Thanks folks for responding. Much appreciated.

Looks like the only definitive info, to me, is in regard to the 90 before the cube. Thanks Brian. This part is good because given the routing parameters, this seemed to make the most sense. I didn't want to go up and down creating a high spot for vapor lock. Seeing the post from the manufacturer, I guess I've seen that before, which must have been in the back of my mind when I was fabricating the assembly. Information goes into my head, and sticks, but concious recall of it isn't always obvious! In addition, I had a really hard time coming to a decision on where to mount the cube. Apparently it is best to locate the cube between the fuel servo and the distribution block, but unfortunately, I could not come up with any type of mount or routing that was acceptable to me. Struggled with that for months actually. So, as others have reported excellent accuracy with the cube between the electric and mechanical pumps, the fire wall it is for me.

In my mind, installing stainless lines and aluminum fittings doesn't make much sense, unless the melting point of the tube is substantially lower than the fittings, which it might be, I haven't researched it.

Other than transporting fuel from point a to point b, there seems to be two very important things here. 1. Keep the fuel inside the pipe. 2. Keep outside influences from causing a failure of point #1. (mechanical failure and heat)

For the mechanical side, I guess I'll be adding a support for the loop. Easily done with a couple of Adel clamps fastened to the motor mount tube.

As far as protecting from heat goes, the assembly is kept cool when the motor is running from the fuel flowing through it. If the engine compartment is on fire, I'm shutting off the fuel supply, and if the tube melts, oh well.

I will be adding the fire sleeve however, as I think I want to slow down the heat soak when the engine is shut down. It's all about that vapor lock thing again.

So, thanks again for all the help. It is indeed much appreciated!

Oh, I probably will refab the loop if I can kick up a piece of SS tubing conveniently. Hard to argue that stronger wouldn't be better here.