Hi Mike,

Have you removed and measured how much fuel was actually in the tanks?  What did your fuel gages say at the time?  What is your tank capacity?  Each wing on my plane holds 33 gal, so getting down to 5 gal with very little dihedral in the wings, means I am pretty low on fuel.  1/8 tank in fact.  The way I calibrated my gage was to drain the tank dry, add one gallon, calibrated this to be Zero, then added 4 gal and calibrated this to be 1/8, and then each 4 gal was another eighth, etc.  I think it would be very easy to unport my tanks with only 5 gal in them.  With the plane sitting level on the ground, it will drain the tanks dry.  When the engine quits from fuel starvation, you can not get a drop of fuel out of the sumps.  There are two of them on each wing and they are both dry when the engine quits sitting on level ground.

I think in flight would be a different matter tho’.  I think there should be some “unusable” in flight but I don’t have any plans at present to try and find out.  When I get to ¼ tank, I plan to “get er down”.

Assuming any kind of reserve, how much flying time did you feel you had when you were down to 5 gal in each tank?  Reading this last question, it sounds like I am being critical but it couldn’t be further from the intent.  :>)

If you had 5 gal in the tank, what angle of bank would it take to unport the fuel on the ground?  You could jack up one wing to try it.  If it is a low angle, very little turbulence would be required  even if you were coordinated.  I think my dihedral is 3 degrees, so 4 degrees would run everything to the outboard side.  Hardly any movement of the plane and you can hear fuel sloshing around in there.

Bill B

I'm pretty sure the turn was coordinated. Knowing that both tanks were approaching (if not below) 5 gallons, it was the first thing I thought of and I looked at the ball. It was centered. And I'm sure there is going to turn out to be about 5 gallons left in the tank so its hard to understand how this could have been an issue with the pickup uncovering. I just don’t have a better explanation. If the pump failed I would expect it to stay failed, not work fine on the ground.

I didn’t copy it, but my system I believe is the same that Ian Beadle used. I have 1 pump for each tank. The outputs are T'eed together - check valves built into the pumps prevents crossfeed. Both tanks have return lines. The return line from the fuel rail goes through an industrial grade electric valve.

I chose this design for a couple of reasons:

1) Operational simplicity. I reasoned that most fuel related problems in flight are due to stupid pilot tricks so wanted a system that was as simple to operate as possible. In its original configuration all that was required to switch tanks was to flip a single toggle switch on the panel which would energize the appropriate pump and configure the return valve to return fuel to the tank it came from. This has since been modified slightly to have individual switches for each pump so both can be on at the same time if needed.

2) I had previous experience (bad) with EFI in some project cars before I built the airplane. I had a couple of fuel pump failures and in researching found strong recommendations against putting the fuel pump too far from the fuel tank. These pumps are designed to push fuel, not draw fuel. A design where both pumps have access to both tanks requires the pumps to be downstream of the fuel selector with several feet of fuel line ahead of the pump. I wanted to avoid this type of design although it apparently is working fine for Ed. My pumps are just inboard of the wing roots literally a couple of inches from the pickups in the tanks.

Tracy's system is mechanically simple but has the potential for pilot error resulting in pumping fuel overboard if the transfer pump is forgotten and left on. Yes, I know there are ways to address that. And clearly it works for him.

I think (thought?) I pretty well understand the pros and cons in my setup. All things being equal I think before yesterday's incident I would do it this way again. If it turns out that the issue was due to uncovering the pickup (not real sure how to prove that) I'd consider changing to include a header tank with a deep sump to prevent re-occurance. But I don’t think I'd rely on suction to fill the header, think I'd use a low pressure pump like the typical Facet pump.

One thing is for certain. Unlike a carbureted engine which has a little cushion due to fuel in a float bowl, the instant fuel pressure drops this engine quits. It's an attention getter. Particularly when you are at the opposite corner of your test box from your home base. I ended up flying back about 70 miles hopscotching from field to field.

Mike 

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.rotaryaviation.com/Rotorhead%20Truth.htm

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bktrub@aol.com
Sent: Friday, March 12, 2010 11:43 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: fuel supply problem?

I just copied Tracy's setup- all fuel is pumped from the right tank, and fuel is transferred from the left into the right by a Facet pump. I didn't want to get into having a six port fuel valve in order to get the fuel injection to return to the tank I was using at the time.  

It's really simple, and hopefully that means reliable. We'll have to see, as this plane is looking for it's airworthiness inspection in the next few months.

Brian Trubee