fuel flow sensor

[NDrv8r]

Hi all. I'm new to the forum, and a new RV7a builder although I have 41 years in aviation. Most of my time has been in Avionics and turbine aircraft.

I have a IO-360-A1B6 and have a question how to route the fuel return line from the distribution spider. Does it take a special valve to route the return fuel back to the tank it came from?

Next, the fuel flow sensor(s). I am planning the Dynon EMS with fuel flow. I am aware of the Matronics adapter that uses a sensor in the main and return fuel flow lines and outputs the single signal to the receiving fuel flow computer.

Now, being cheap and somewhat inventive, I designed my own adapter. It is simply a microprocessor that takes the main sensor and subtracts one pulse for every return fuel pulse it receives and outputs a open collector signal for the receiving electronics.

I have the engine and have completed the empenage and am waiting for the wings. I move pretty fast with the construction, but I doubt that I will be running the engine on the airframe in the next 12 months. I have tested this unit electronically, but would like to see if anyone out there would be interested in receiving a free unit to help test this. This is available for experimental aircraft only.

I am looking for someone who is already flying. I have 3 units available. When I figure out how to post a picture I will.

[nucleus]

What return line? Perhaps you are thinking of automotive injection?

[chaskuss]

Originally Posted by NDrv8r

snipped
I have a IO-360-A1B6 and have a question how to route the fuel return line from the distribution spider. Does it take a special valve to route the return fuel back to the tank it came from? snipped

Larry,
Unlike Continental fuel injection, Lycomings do not use a fuel return line. Even the [experimental market] Airflow Performance fuel injection system does not require a return fuel flow sensor. The purge valve on the Airflow Performance unit only returns fuel during the "pre start" phase. This is done to clear the hot fuel from the lines, servo and spider. The purge return line does not go all the way back to the fuel selector, so a duplex selector is not needed.
Only the [experimental market] ECI fuel injection system would require a return line. The ECI fuel injection is similar to the Continental system. The Continental and ECI systems are the only ones which need the items below:

Duplex fuel selector valve
Fuel tank return lines
Return fuel flow sensor

Assuming your engine has the stock Bendix RS5A fuel injection, you do not need the parts listed above.

Charlie Kuss

[cfiidon]

The previous post threw me off as the format was truncating the text. For clarification:

Whether or not you use a fuel return line is a function of your fuel injection system. As I understand it, a Bendix system does not. The fuel injection system with my ECi Titan IO-360 DOES require a fuel return line through a duplex valve (Andair) and back to the tank.

[Bevan]

Although it's not necessarily required, running the return fuel from the purge valve through an Andair duplex valve will take this little bit of fuel back to the tank that fuel is being drawn from. If you use the ECI fuel injection system now or in the future or any other future fuel system that may require a return(possibly when 100LL goes byebye) you'll be ready.

Bevan

[Rick S.]

Well there is a return system on mine and anyone else using the AFP fuel pump and manifold system for injected engines. The fuel returns to the system at the selector valve from the fuel mainfold attached to the pump. No need to worry about the fuel flow sensor, it only reads fuel sent to the engine after the pump. I do have a purge valve that as said before is used for hot starts and normal shut down, you will need to run a return for that, if you have one that is.

[NDrv8r]

Thanks for all the good replies.

After some additional research, it does indeed appear that the Bendix RSA system does not utilize the return line. This is apparently the source of many of the hard hot start stories.

This engine came off of a acro sport, and as received it had a #4 line line from the throttle body to the distribution block, and a #3 line coming out of it. The #3 line looked like it was long enough to go back to the firewall. There was also a line coming off of the throttle body from the fuel pressure port.

I have seen the purge valve, and this does not have one. Any thoughts on what this line would have been used for?
Larry

[rocketbob]

Yes. Combination mechanical manifold pressure/fuel flow gauge. Fuel flow is derived from metered fuel pressure at the divider. If you look closely it will be connected to the port on the divider stamped "GAUGE".

[Noah]

Originally Posted by NDrv8r

Thanks for all the good replies.

After some additional research, it does indeed appear that the Bendix RSA system does not utilize the return line. This is apparently the source of many of the hard hot start stories.

This engine came off of a acro sport, and as received it had a #4 line line from the throttle body to the distribution block, and a #3 line coming out of it. The #3 line looked like it was long enough to go back to the firewall. There was also a line coming off of the throttle body from the fuel pressure port.

I have seen the purge valve, and this does not have one. Any thoughts on what this line would have been used for?
Larry

The #3 line coming off the distribution spider to the firewall is for a fuel flow sensor. Fuel pressure at the spider is directly proportional to fuel flow, so some certificated fuel flow sensors using this injection system are really just pressure gauges which are calibrated to read in gal/hr or Lb/hr, rather than in psi. If you ever have a rough-running engine and your fuel flow gauge goes up significantly with one of these fuel flow sensors, it is most likely due to a plugged injector.

Most experimental installations these days ditch this pressure-derived fuel flow indicator, and instead use an in-line fuel flow sensor which is very accurate and not subject to this potential plugged injector issue. On the A1B6, they are typically installed between the fuel servo and the distribution block. Here's a pic I found on the net of one of these in the typical location just under the distribution block:
http://i42.tinypic.com/azbdvm.jpg

[Mike S]

Originally Posted by NDrv8r

Hi all. I'm new to the forum, and a new RV7a builder

Larry, welcome to VAF, good to have you aboard.