My Fokker DVII Project - Page 119

Jeff Brooks · 3 September 2008, 03:40 AM

Here is the original system ... note how the valve to the fuel pressure gauge does nothing but turn the gauge off.

There is also a pressure relief valve somewhere in there. I am not sure where though.

Bookmaker · 3 September 2008, 04:08 AM

Jeff, In reference to a "return" line to the fuel tank as John suggests for "bleeding" air.

I submit this. I assume the carburetor is float type, therefore any air in the lines to start with will pass through the float bowl without closing the needle until fuel fills the bowl. At that point however, any air in the system will be stuck there until it can reach the bowl. It will escape then, however, if there is enough air it could cause a fuel starvation.

Not good.

Do you know how the modern carbureted aircraft fuel systems are designed to prevent this? It might be a good idea to get a fuel diagram for a carbureted Cessna or Piper set up to follow for the basic setup.

Just a thought.

ALso, my suggestion for the pilot operation of the system is the KISS method. A boo boo moving several fuel valves around could add your plane as a statistic.

Dale

Jeff Brooks · 3 September 2008, 04:24 AM

The carb is an Ellison Fluid System Throttle Body Injector Model EFS-4-5. A really neat system that will run in any position. There is no float. You can read more about it here: Ellison Fluid Systems: Home Page

Bookmaker · 3 September 2008, 04:48 AM

That would seem a better setup. I would still look over a current fuel system to see what "tricks" are used to elimate potential problems.

Your project is coming along nicely.

Dale

Jeff Brooks · 3 September 2008, 05:27 AM

I have reviewed several helicopter fuel systems... Huey, Apache, Blackhawk & Cobra. They make my system look simple. But they also have other issues to contend with. Nitrogen charging units to prevent fire, closed circuit refueling, and transferring fuel for weight & balance.

US95Damiani · 3 September 2008, 07:10 AM

Jeff,
I help out on a Ranger powered great lakes with a Bendix PS-5 pressure carb.

In that installation The excess fuel is ported back to the tank.

In a carbureted installation there is no need to have a return since the fuel pressure is so low usually 4-6 psi the bowl of teh Carb is vented to atmosphere so there is also no need for a vapor return. just a fuel line to the carb and maybe a pressure line off of a "T" to the gage.

Jeff Brooks · 3 September 2008, 07:16 AM

If you can get any diagrams of layout, I would love to see it!

Bookmaker · 3 September 2008, 07:19 AM

I would assume that the throttle body injection setup would run on higher pressure than a carb system as well. Possibly requiring a return line to the fuel tank.

That brings up a question as to if there is a metering system in the return to keep the pressure up rather than just sending all the fuel back to the tank. If so, how is it set up?

Jeff, I hope I am not being a pain, but I know one of the major causes of experimental aircraft accidents is fuel flow/ management related.

Just hoping to add to the think tank.

Dale

US95Damiani · 3 September 2008, 08:15 AM

I'll See what I can do.

US95Damiani · 3 September 2008, 08:22 AM

Quote:

Originally Posted by Bookmaker

I would assume that the throttle body injection setup would run on higher pressure than a carb system as well. Possibly requiring a return line to the fuel tank.

That brings up a question as to if there is a metering system in the return to keep the pressure up rather than just sending all the fuel back to the tank. If so, how is it set up?

Jeff, I hope I am not being a pain, but I know one of the major causes of experimental aircraft accidents is fuel flow/ management related.

Just hoping to add to the think tank.

Dale

Dale,

You are correct most fuel injection systems require from 12 up to 45 PSI depending on the injection systems. so the excess fuel has to be re-routed somewhere... Usually back to the fuel tank.

In the case of a Bendix pressure carb or RSA type Fuel injection system,
the Pressure carb or Servo unit meters the fuel to the engine as well as porting the excess back to the tank.

In the case of the Museum's Ranger with a PS-5 it requires 16 PSI to operate correctly. This particular pressure carb is set up to flow the same as a 200 HP Lycoming IO-360. Airflow Performance performed the work for us. It is Ideal. the engine runs flawlessly smooth with this setup.