Fuel system question

[Charles Davis]

My question has to do with how to route the fuel lines aft of the firewall.  I can't follow the Rutan plans exactly because of how we've mounted the oil cooler, carb intake, and I have an electronic ignition coil pack to accomodate.

Here is what I have:
I've mounted the electric fuel pump close to the gascolator (since they blow well but do not suck well).

From the point the fuel line leaves the gascolator, it goes to the electric fuel pump, then through a flow-Ez fuel filter, and then to a fuel manifold that distributes to the solenoid primer valve, the mechanical fuel pump (via a flow meter), and has a fitting for the fuel pressure gauge.  Nothing in this system is above the lower engine mount line (except the primer hoses).

My question is this:
From the point the hose leaves the gascolator, is it important that the hose always moves "up hill".  That is, that the hose never dips at all.

I've heard that dips can cause bubbles to get trapped in the "high" parts of the system and cause problems.  Is this a myth, or a rule that I should adhere strictly to?

Thanks for any insight you can provide.


FYI Status of N138CM:
Engine/engine hardware is mounted.  Most electrical/electronic hardware is mounted.  I have everything to complete the plane (ie: no more big checks to write!).  Once the fuel system is in, I start pulling wires.  We still hope for a first flight in Dec this year.

[Delta Mike]

Firewall Fuel Routing:

Put the inline filter in the hell-hole using standard automotive fuel filter, cheap and easy to replace – the 3/8 ID low pressure rubber fuel hoses make for easy connection to 3/8 aluminum fuel lines. This filters any particles before they get to the electric pump.

Through the firewall using straight pipe which connects to rubber fuel line on downstream side of fuel filter. Turn it on the firewall side with a 90 fitting, preferably one that will connect directly to the electric fuel pump.

The electric fuel (boost) pump is the first in line. The CPs have some discussion on the right boost pump to use.

Use a back to back short-as-possible female coupling to go directly from the boost pump to the gascolator. The fellows at Peterson Aviation (http://webworksltd.com/autofuelstc/pa/PetersenAviation.html) specialize in approved STC autofuel conversion for certified airplanes. Their words of wisdom is that it is better to have the gascolator downstream of the boost pump since most vapor lock happens in the gascolator. The gascolator is pressurized (only) when the boost pump is on, typically during take off and landing - when vapor lock is least appreciated.

The gascolator is next in line, but needs some modification before installation. First, take of that silly drain cock that has to be reached up into the NACA scoop for access (not to mention it is sticking down in the cooling and intake air flow). Put on a quarter inch fitting and route a short line to a flush mounted drain somewhere on the outer skin. Next mod to the gascolator before installation: Thread the electric solenoid valve directly into the top of the gascolator using a simple pipe to pipe fitting (assuming the gascolator has a prime port on the top). Rotate it so that alignment is good for firewall installation of the gascolator (make sure to use fuel lube on pipe threads). The gascolator-electric primer is now like one unit. The prime line can now be routed directly to the primer manifold and ports.

From the gascolator outlet use a flexible steel braided fuel line to go directly to the engine driven fuel pump inlet. This line isolates the engine vibration from the firewall components. Make sure the line has plenty of clearance from the engine mount or anywhere else, else holes will be rubbed.

Use a rigid or flexible line to go directly from the mechanical pump outlet to the carb inlet. The fuel pressure sensor should be teed in at the carb inlet. Fuel pressure should be sensed at the inlet to the carb so that mechanical pump pressure can be sensed when the boost pump is off. It also provides the best true carb fuel inlet pressure at this point. Try to keep the sensor as close into the carb as possible so that it is not sticking out and disrupting the cylinder cooling air flow.

If an Ellison TBI is to be installed, the plug at the opposite end of the fuel inlet may be tapped with a quarter pipe thread. Screw the fuel pressure sender directly into the tapped plug and the tee arrangement is not needed at the inlet side. Figure out how to put a fine mesh screen in this mod since access on the plug side is unfiltered.

Try to do a system check before installation, make sure all components are fuel tight under pressure. Check for even flow from all the primer lines.

If all else fails call Bob the Plumber.

[go ez]

Dont mount the fuel sender on the carb  whatever you do - - put it on the firewall away from vibration, the pressure difference will be negligible /immeasurable.

Be warned, Dick Rutan nearly lost his Ez when a fuel sender mounted on the carb just as you suggest sheared off. and bathed his engine compartment in avgas. He dead sticked it in but nearly threw up when he saw the blue avgas stains all over his engine compartment & cowling.

One reason why I'd never ever fly with autogas - it is more volatile, evaporates quicker and lights up at lower temperatures!!!!

The Rutan mandatory grnd instruction on this  is in one of the CP notes. Can advise Number if required.

Regards
Steve

[Delta Mike]

Thanks for the heads up. Delta Mike still has alot of canard pusher reading to do.

[Charles Davis]

Just what I needed: practical advice and a new perspective on things.


Here is the current plan:
1. Rigid aluminum line from the selector valve to the in-line fuel filter.  Adel clamp the body of the filter to the fuselage or firewall forward of the firewall.  
2. From the removable cap of the fuel filter to the fuel pump, run flex line.  Mount the fuel pump also foreward of the firewall.
3. The gascolator I have mounts right to the firewall, with the inlet facing the firewall.  It has 3 output ports: 2 are 3/8, 1 is 1/4.  

Plumb the outlets as follows:
a. rigid mount the fuel flow meter to a 3/8 steel fitting, and then flex line to the mechanical fuel pump.
b. mount the fuel pressure sensor to the other 3/8 fittting, using a steel adapter.
c. rigid mount the solenoid primer valve to the 1/4" fitting with a steel fitting, and from there direct to the primer harness.

A comment I've gotten about this setup is that I have more fittings in the crew compartment than absolutely necessary.   I'd use only the best quality fittings and hoses, and inspect this area regularly.

Another issue would be changing the fuel filter element.  I'll need to think about how to catch or drain out any fuel that would be remaining in the line and filter when I unscrewed the filter cap.

[Charles Davis]

Yikes, I really wanted to put the fuel filter and pump in the hell hole, but it is a hard place to work, to get the flow right (pump below gascolator, no arched loops).  It may also crowd out the oil heat system we wanted to stick back there.

I'm now thinking about putting the filter and pump under the pilot seat, and change out the rigid aluminum fuel line from the pump to the firewall with flexible line from the fuel switch, to the filter, to the fuel pump, to the gascolator.

This puts the pump very low so it will gravity prime.  It would be a lot easier to inspect, service the filter or replace the pump if needed.  I would also not have to guess if the fuel pump is on!

I don't like the idea of more fuel connections under my legs, but all my components are very good quality, the mounts are solid, and I'll inspect often.  Any fuel leak would be bad, but at least I'd know about this one and be able to shut off the fuel, whereas a leak aft of the firewall may be harder to detect.

It is very challending and frustrating sometimes working on these planes.  Everything is such a tight fit.  But I know I'm in the home stretch and that the effort will be worth it.  I'm still hoping for a December 2006 first flight.

BTW: Mounting the solenoid valve right to the gascolator works awesome.  I'll probably open up the mount holes in the gascolator to the next larger size (there is plenty of aluminum there to spare) since I'm attaching the fuel flow and solenoid valve direct to the gascolator body.

[GlennBob]

When you get close to your Dec.  '06  flight  ( first flight )  !  !  !    In all your excitement, . . be sure to follow Burt's advice and give your keys to a trusted friend  mechanic, . .and have him have a final " look over "  before letting you press on to the final adventure ! !    Could save your life ! !    Glennbob

[Charles Davis]

Great advice.  

Actually, I'm putting away my ego and desire and will have my brother fly the first 40 hours as he has about 600 hrs in Canards, including a first flight in a Cozy he built.  

We'll spend days working together to go over it nose to tail, not assuming any bolt is properly torqued.  First 20+ hours will be within gliding distance of the runway.  

We have a 5000' runway in Springfield, TN for the first flights.  Flat, open spaces, great place to test fly.

I hope to transition and take possession of the plane by early summer 2007.  Then slowly expand my radius of travel over the following year or so as I gain skill and confidence in the plane.

Still mulling over the placement of the fuel filter and pump.  Hell hole might still work if we can fab a suitable mount for everything so nothing interferes with the rudder cable conduit.  Opinions?

[Charles Davis]

I had a friend comment that I should not put the fuel filter and pump forward of the firewall.  He's a bit of a Rutan purist, and believes a rigid line between the fuel valve and firewall is lighter, and less prone to chaff than a flexible line.

He also thinks pressurizing the line fwd of the firewall, and adding the associated couplings to put the filter and pump ahead, is asking for trouble.

I want to maximize safety.  I also see real advantages of placing the pump and filter fwd of the firewall.

I know this is my decision and responsibility, ultimately, but would appreciate your opinion:

Stick to the plans, or move it forward?

[Delta Mike]

The fuel filter will probably get significant particles in the first 100 hours from all the washed off glass construction residue. After that the fuel system maintenance needing to replace filter and pump will be very rarely needed, if at all. It is probably worth having them located in the hell hole so you can have lightweight aluminum line as much as possible.

Make a schematic and post some pictures.

[Charles Davis]

Thanks for everyone's comments.  I was at Rough River Sunday... really awesome, and a huge motivator to push to the finish line.  

My wife came with me, and she LOVED the ez's, which along with everything else does make her THE PERFECT woman!

The only question remaining before I nail this down is whether the electric fuel pump should be placed ahead of, or after, the gascolator.

Some say don't pressurize the gascolator, and that you should have only gravity pressure fwd of the firewall.

It would be much easier to make everything fit if I could move the pump and filter off the firewall.

I'll make a final decision soon and then get on with finishing everything.

[Delta Mike]

A little more research shows there are some gascolators rated for pressurization. Aircraft Spruce sells the Andair Mini Gascolator for $130 wich is pressure rated, and it looks like a nice unit.

The people at Petersen Avation have a STC for the PA28 (Piper Cherokee) which specifically pressurizes the gascolator to mitigate vapor lock.

Looks like Delta Mike needs to get a pressure rated gascolator.

[Charles Davis]

OK, I've come to the decision to put the electric fuel pump on the firewall.

It would be SO much easier to mount it under the pilot seat.

But my concern is that even a pin hole leak in the fuel line inside the cockpit with the electric boost pump running would dump a lot of fuel in the cockpit before I could shut it off.

This is not only a fire hazard, but 100LL is very noxious even in tiny quantities in the enclosed cockpit space.

So, it will be a struggle, and I REALLY didn't want to do it, but I think it's best to keep everything front of the firewall gravity feed.  Once I figure out this puzzle, I'll be glad to furnish pics to anyone who is interested.

Thanks for all the input.  I'm glad I considered all options before coming to this conclusion.