Fuel system options for fuel injection

[niceez]

Jim,

 

Now I like that idea. Only thing I would do different is put the electric pump in the sump and make it fairly easy to remove the whole sump for annual MX. (Change sock filter and thoroghly clean interior of sump).

 

Best part is we will get to see how well John system performs also:D

 

Dale PS Now to go fishing for an hour or so

[Jim Sower]

Submerged pumps are certainly to be preferred (if you have easy, LEAKPROOF access). It does make for a bigger sump tho. If I was going to have a sump, I would want as much (5 or 6) usable fuel as possible. That way, when the low-sump light comes on, I can actually USE that information and GET somewhere. A 5-6 gal sump will pretty well cube out the hell hole of a Cozy and not leave much room for A LOT of stuff that has to reside there.

 

If I have to give up on a sump with a useful fuel volume, I would have to have photocell low fuel transducers in the strakes so I would have a REAL reliable indication of 5 gal or so remaining. Not a big challenge, but something to pull my fat out of the fire when I forget to monitor my fuel, and an indication of assymetric transfer to the sump

Good luck fishin' ... Jim S.

[John Slade]

Jim,

I don't see how you're going to get 5 - 6 gallons in the hell hole of a Cozy IV. I'm not using it, but I did make a tank that fits exactly into the accecible part of the hell hole, right up to the back seat. It held 3 gallons. I even lowered the horizontal bulkhead an inch or two and moved the heat duct pipe. The tank doesnt dip down each side into the area where the lower engine mounts are because it would not have been removeable. If you made the entire area into a tank (not a good plan - I think), you might just get 5 gallons.

Regards,

John

[Jim Sower]

John,

You're right of course. There's just not room in a Cozy hell hole for a practical sump ("practical" being defined as an emergency tank, or one that holds enough fuel that you can actually travel somewhere on the sump fuel). Your three gallons or less is, as a practical matter more space than you can afford to dedicate to a sump in a Cozy. A small sump like that would be usable in that you'd have a place to dump return fuel without lots of plumbing but that's the extent of it and it would scarcely be worth the bother.

 

What I'm really talking about is something I'd like to see in a sump, but almost certainly won't. I can't make a compelling argument for a sump with significant fuel since the EZ and Cozy don't have anything like that and seem to work OK. But it does seem like a nice thing to have.

You're on the right track withoug it .... Jim S.

[Norm M]

I still like the design I came up with way back when. Pressure pump on each tank, plumbed into the fuel rail (perhaps at opposite ends).

 

Use a motorized valve for the return side, that has one lead from the motor connected to the left pump, the other to the right pump. When you power one of the pumps, the return moves to that tank. If you power both pumps, it stays put.

 

You can use the fuel guage contacts on the valve to give you an error signal if the valve should stick and begin returning fuel to the tank opposite where you are drawing it from.

 

I have tested these valves, if they stick in the middle they act like a tee. If they stick on one side, the switch would tell you it was in the wrong position.

 

You can control the pumps in a couple different ways with the switches. That is a whole discussion by itself, to determine how one pump is always powered, or sometimes two pumps.

 

Depending on how you trust the check valves in the pumps, you may want to have an extra check valve feeding the fuel rail for each pump to connect to.

 

So long as you never expect consensus, this is the perfect forum for developing alternatives!

[John Slade]

Makes sense, Norm. This is exactly what I'm planning to do.

So where do I get the valve you're describing?

Do you have a supplier or part Number?

 

>You can use the fuel guage contacts on the valve to give you an error signal if the valve should stick ...

I don't follow this comment.

John

[geograham]

Dear John,

 

I looked through years of NTSB accident reports before

making this decision. I learned that your friend is

correct in that the fuel selector has killed many.

 

I know that you have more flying in than I do, but you

must admit that things can get very busy in the pattern.

That is when your motor quits, there isn't time to relight,

and the runway is too far off.

 

My $.02, is to toss the selector, install a sump and live

with it. (Not the header idea, the sump, you already have

fuel in the cockpit inside the lines where they can trap

shards of fiberglass and plug up). I also know the only

person who had trouble with the Velocity system, it was

his fault (wrong caps), not the system design.

 

As an added bonus, you really won't need a aileron trim,

as mine never needs adjustment.

 

Best wishes,

 

George Graham

[John Slade]

Hi George,

Good to hear from you. When are you coming back over to check out my engine installation?

 

I don't think the presence of a fuel selector has killed anyone. It's not using the fuel selector when needed that kills people

 

Anyway, I'm not installing a fuel selector. Selection will be done by powering one pump or the other. The valve we're talking about is for switching returns.

 

If I remember correctly, you have normally a aspirated carburetor installation. Adding turbo (faster fuel draw) and fuel injection (requires returns) complicates things a little.

 

My current dilema, in case anyone has a comment, is whether or not to fit a gascolator on each fuel line. I have fuel drain points at the front of the strakes, and a course gauze filter in each strake, per plans. There will also be filters between the pumps and the rail. Do I need the additional water trap and filter provided by a gascolator before the pump on each side? Who was it that just bought my gascolator? Wanna sell it back?

 

John Slade

[geograham]

Well John, My sump is my gascolater, and a big one!

 

In that i have a drain in the floor, the fuel is

sucked out two inches above the bottom, any return

line I add will be near the top of the sump.

(someday, when I add the EFI to get rid of carb heat).

 

BTW, after five years of sitting outside in the rain

and snow, I have still not had any water in the tanks

or sump, just bragging !

 

I use two electric pumps in series for the carb, but

can imagine the parallel setup that Tracy Crook uses.

The return comes off the pressure regulater, so you

only need one into the sump.

 

I would love to fly over for another visit! I really

enjoy your company.

[Jim Sower]

Norm,

I have some questions ...

<... Use a motorized valve for the return side ...>

What happens to the motor when when the valve sticks mid-travel? If the motor stops when the valve stops (as one would intuit), that would stop back(counter) EMF and increase the current through the motor very significantly (like maybe double or so?). Does it just sit there and smoke, or blow a C/B or fuse, or what?

 

<... that has one lead from the motor connected to the left pump, the other to the right pump. When you power one of the pumps, the return moves to that tank ...>

I am assuming that when the motorized valve arrives at a selected position, the valve somehow turns the motor off (so it doesn't sit there and cook like above) but I guess that would all be internal circuity in the valve (lots of failure modes?). In any event, I'm having trouble visualizing how the pumps would be wired to such a valve. Perhaps by "connected" you're implying "through some relays and diodes and etc"? I'm having trouble visualizing the circuit. Also, unless wired through relays (each one a failure mode) the pumps could be expected to draw an order of magnitude more current than the valve circuit required. Which level of current do you protect (fuse)?

 

<... If you power both pumps, it stays put. ... >

I'm REALLY confused by this one. Guess I'll have to see a circuit diagram or somethng.

 

Either way, how do you go about getting that last couple of gallons out of one tank so that late in the flight ALL of your fuel is where you want it?

 

John,

George makes a compelling case for a sump. You've made a compelling case that there's no room in a Cozy hell hole for a usable sump. It looks like a stand-off (which typically leads to a major compromise or an awkward work-around). That sort of brings me back to Tracy's design. One could maybe move a step or so toward having it both ways. He uses his right wing tank for a sump, returns all excess fuel from the rail to to the "sump". But instead of gravity feeding the sump from the left tank, he uses a facet pump to transfer left to right. Pressure pumps are not dedicated to either wing tank. You alternate them any way you please. But that's all been said.

 

As for gascolators, my EZ has one on the bottom of the firewall (marginally) accessable from the NACA duct. Any water from the blisters through the selector and associated plumbing would presumably gather there. I found a cc or two water in the strakes on a pretty regular basis but never in the gascolator. I get a lot in the Velocity too. Both live in a hangar. Don't know how George avoided water in the strakes unless he used mogas in an area with lots of alcohol added. Anyway, I theorized that the plane would have to stand upright for extended periods for water to get there, and that was impossible without LOTS of ballast. I gave up on the crawling around it took to look there unless it had stood upright and ballasted for a long period of maintenance or it had been a LONG time between flights. For your application, look at the volume of the fuel system (plumbing and a filter or two) from the blister to the rail make a guess as to how much ground operation would be required to consume that much fuel. Sounds like it would run through the engine long before you could taxi to the runway. Just be sure and mount your fuel filters vertical (if they're horizontal, a good bit of water could accumuate in them that even a gascolator couldn't detect).

 

Every answer seems to raise more questions ... Jim

[John Slade]

Jim,

Lots of useful and thought provoking input. Thanks.

Rather than use a three-way valve with all the potential failute points you mention, I was thinking of using continuous duty, normally open solenoids to switch the returns. Wiring would be fairly simple since they would be switched on the opposite pump switch. Wiring would be for total load, i.e. a pump and a valve. Worst case, a solenoid fails and you're returning to both.

 

I didnt say there's no room for a useable sump in the Cozy. You were asking for 5 gallons because of you're obsession with having that extra couple of pints of fuel when you've burned the rest. Most people with sumps are doing fine with three gallons or less. The Cozy IV hell-hole will accomodate a three gallon tank. I know - I made one.

 

I like the way you describe Tracy's system - one tank is a sump for the other. This makes it sound much better. However, recognizing that fuel starvation is the number 2 cause of accidents after VFR into IRF, I've decided that I want a redundant system. In Tracy's system crud or contamination of the main tank makes the reserve tank inaccessible. You second pump wont help you.

 

Interesting data point on the galcolator, and I like the fuel usage during taxi comment, but I'll measure this (rather than guess)

I suppose water could build up in the blister gradually and bite you eventually. Maybe this is another good reason for redundancy. I'm considering putting a drain in each blister anyway.

 

I didnt know about mounting the filter vertically. Thanks.

 

As always... learn a little each day.

 

Regards, and thanks for all the valuable input.

John Slade

[niceez]

Wow!

I have been flying my LEZ some 16 years now and have only twice had water enter the system. (Caps are Shaw Aero mil-spec type) And then I would be willing to bet it because I was flying through rain and it entered through the vent. A side note; I usually only have 10 gallons or less in the tanks as they sit in the hanger.

I find this very curious however very understandable for the midwest and east coast locations.

Maybe consideration should also be given to fuel filters that allow fuel to pass and dis-allow water to pass through?

 

I have also thought that if are traveling at the cruise speeds that we do, that the pressure from the vent inflow should account for some forced flow thus fuel pressure.

 

-Dale

[Jim Sower]

John,

<.. continuous duty, normally open solenoids to switch the returns ..>

Goes to simplicity. Continuous duty might be more apt to fail, but the failure mode seems fairly benign. What about a pump failure? If your pumps are wired to the valve terminals could a valve failure precipitate a pump failure? What are all those failure modes? The solenoid valves "fail open" by design. Actually, they are "Y" type L-R valves with one outlet plugged (so you might only need one). We don't have any idea as to failure modes that might be *outside* of the design.

 

<... I didnt say there's no room for a useable sump ...>

My definition of "usable" implied a half hour or so of usable fuel. Looking back, that was tied to avoiding some of the consequences of my own ongoing problem of not knowing whether a tank was transferring modestly or not at all. Guess I was trying to "lower the height of the limb I was crawling out on". In any event, it is a bogus condition. Your 3 gal or so should be adequate. Particularly if you can put it somewhere that is relatively impractical for anything else.

 

One thing I would NOT want in a sump is a flat bottom. Make the bottom slope a little toward the center and put a drain point there. Mine is flat, and if the plane is not sitting exactly dead level (which is rarely the case) the drain point is not at the low point and I will almost always have some water in the tank. Also, my fuel line to the pump is 2" off the bottom of the sump which I think is entirely too far. 1/2" to 3/4" should be enough. The inlet(s) go an inch into the tank so there's that much of a "bubble" in the sump. Flush with the top would be nice.

 

<... fuel starvation is the number 2 cause of accidents ...>

And I've suggested that fuel *management* is the number 2 cause of fuel starvation. How would you manage your fuel with a solenoid valve failure? Keep switching pumps all the time (and, of course, never get to that last 2 or 3 gal that I'm so anal about)?

 

Tracy's system has only two failure modes that result in reduced access to fuel: blocked inlet and Facet failure. Yours has blocked inlet and solenoid valve failure. Oversize gravity feed lines (bet you never dreamed you'd hear that from ME ;o) to the sump and plumb all return fuel to the sump (no moving parts) has only one: blocked inlet. Of course, we have to assign a weight to each item in order to arrive at a really rational decision. That's hard. I'd need some help from Al Wick to do that properly. Of course Al would measure the pressure drop between the tank and pump inlet and have the "Monitor Girl" warn him "... you're sucking fuel through some trash, big boy ... You might want to check your inlet screens ..."

 

Bottom line: what do you really know about these solenoid valves and how do you react to surprises around them? Your "generic tapped plate" access to the strake tanks would be a really good start. Gives you lots of flexibility for relatively little effort.

 

<... mounting the filter vertically ...>

If it's not much extra trouble, I would feed the injectors off the bottom of the rail instead of the top. This way, you run EVERY drop of water straight away into the engine before he can muster enough friends to give you a problem

 

Lots of interesting questions. Glad it's you doing the installation and me doing the abstract guesswork instead of the other way around;)

 

Jim S.

[Norm M]

<<<Norm,

I have some questions ...>>>

 

I understand why you have questions. Until I got one on the bench to do some testing, I wasn't really sure how they were plumbed and wired up. I have been through the factory where these valves are built, and talked to the people that designed them, but that was 10 years ago.

 

If you want a system with redundancy, three tanks, multi control modes, etc, you are going to end up with some level of complexity. I have a design with a reserve tank that can be switched in for last ditch, but everytime I mention it I get flamed with the complexity argument.

 

Here is the skinny-

 

If you fly a plane that doesn't return fuel, you can argue for days about common sump, valve type, and placement, and never come to consensus about the ultimate system.

 

If you choose to fly an engine that returns a significant amount of fuel, you must have a fuel managment scheme that allows for deaereation of the returned fuel, temperature dissipation, valving for return fuel, valving or some other tank selection criteria, plus all of the issues associated with the trivial non-return design in the previous paragraph. Propose any solution, and it will be attacked with arguments of complexity and non-reliability.

 

These forums are interesting and entertaining, but seem to be of minimal value for advancing the art of the design. Ultimately, the designer of the system needs to make their decisions, design, test, evaluate, and live with it. Looking for intelligent feedback from a forum group is like asking my flight physical doctor for feedback on my charging system design for the airplane.

 

The information that is of value comes from those people who have made an intelligent decision, have built it, and have pushed the state of the art forward. I apreciate how Tracy has put his system together, and how it has worked out. It is of 100 times greater information value than what the rest of us might sketch on napkins. Of course, 100 opinions are much easier to get than one flying example.

 

I suppose I could go find that valve selector and carve it open and do some motor stall tests. But I don't intend to fly with one, so I don't think I will go any further with that concept. I have offered to send the valve down to John for his enjoyment.

 

My fuel system is pretty much by the book, right up to the boost pump. I am running the Airflow Performance package which uses a scheme that is also debateable ad nauseaum. I just had the oil cooler lines and two fuel lines crimped up Saturday. $78 total. Dang that aircraft stuff is expensive. (Watch for the 666 lines and fittings on eBay soon!)

 

Regards-

Norm

[Jim Sower]

Norm,

<... everytime I mention it I get flamed with the complexity argument ... an engine that returns a significant fuel ... must allow for deaereation ... temperature dissipation ... valving ... tank selection criteria... Propose any solution, and it will be attacked with arguments of complexity and non-reliability ..>

 

Yup. I agree entirely so far ...

 

<... interesting and entertaining, but seem to be of minimal value for advancing the art of the design ... intelligent feedback from a forum group is like asking ...>

 

Afraid we part company here.

To the extent that John is pretty much plowing new ground, I feel he needs to consider all the angles. He thinks of as many as he can. The rest of us come up with our ideas. Nobody can quantify squat. The most informed decision John can make is to dig up every factor he can (with a little help from his friends) and evaluate them as best he can (lots of gut feeling here, not so much hard, reliable data). When he gets flying with whatever system he decides on, he reports results. The next guy, who does things a little differently, reports his results. Pretty soon we all have a much better idea as to what does and does not work. That, IMO, is how you "advance the art".

 

Tracy does have a working system. I submit that his is not the only system that works, even if it is the only one that works NOW. We can improve on Tracy's system only to the extent that we dapart from it (but depart advisedly, since it is, after all, the one that works).

 

<... and carve it open and do some motor stall tests ...>

I think it would be really interesting and valuable to take the tour of the plant you took 10 yrs ago and get the answers to the questions I asked (and probably a bunch more). I have no doubt the engineers could quantify a LOT of stuff and either put my fears to rest, or tell me what I could expect along those lines. That would provide a lot of the "hard data" that is so tough to come by when you're "advancing the art".

 

John has to evaluate all of the many (and occasionally not too well thought out) ideas and considerations. I think it is important that he be exposed to as close as he can get to ALL of them, and I don't think anyone knows for sure what ALL looks like. When he thinks he has what he needs, I recon he'll quietly retire from the thread and go to work...

 

Just a theory .... Jim S.

[John Slade]

>I recon he'll quietly retire from the thread and go to work...

On the contrary, I'll be reading comments on this one until I fly and afterwards too. This thread has over 1000 views for a good reason. People want to find the "right" way to do this job.

 

I got my fuel pumps and fittings back from Ed Heishman yesterday. He made AN flare fittings to fit both ends of the pump I got from Tracy, so now I'm ready to finalize the fuel installation. (he also beefed up my mount, made and welded AN fittings for the rad, cutoff and welded my water pump and made AN fittings to fit my oil coolers).

 

I've abandoned the idea of solenoid valves. (too much added complexity and too many associated failure modes)

 

Based on all the input from here and elsewhere, my latest plan is Tracy's system with a couple of modifications...

 

My left tank will be the "sump". Return will always be to this tank.

I will run a pump and filter from each tank to the rail. That's it. No fuel drains in the blisters. No gascolators. No valves. No Facet pump. I'll measure the time on idle to drain the blister and make that the minimum pre-takoff running time to check for possible fuel contamination. No need for a transfer pump since running on right tank only will return to left tank and thereby transfer fuel. I have capacitance gauges installed, but I'll also be able to see the sight gauge on the right tank to monitor it. With this system I'll still have my redundancy, but I'll also have simplicity. I wonder what happens when you're running both pumps in a system like this, and one pump runs dry. I'll test that one on the ground. The other thing I'd like to test on the ground is running both pumps, engine idle, with both tanks full to the brim. Will the left tank vent fuel?

 

I've already plumbed the returns to the firewall, so I think I'll T them and install a manual on/off valve to the right side. This way I'll be able to experiment with a "return to both" system at some point down the road.

 

Thoughts anyone...

[niceez]

John,

 

Your original thoughts were:

>>Current situation.

Cozy IV with plans fuel system, weatherhead valve in the seatback and 3/8 lines. No returns plumbed and no fuel level sensors fitted.

 

Problem

I'm installing a fuel injected Mazda 13B rotary which requires 40 + PSI fuel pressure and returns. I'd like two independant fuel supplies to the rail with a filter and pump on each. So, how do I handle switching the returns<<

 

It appears you have come close....

 

Everyone has a different Idea and all that really matters is that you are aware what needs to be done in case of an emergency and that is for you to decide. The hardest thing to remember is that most of these airplanes will remain one owner - one pilot airplanes, and it really doesn't matter where you put your valves, pumps, return lines, or anything else. There will always be a "better way" according to someone else. Some of us have systems design background and others do just as good experimenting. It is obvious Burt is not a systems guy. None the less, the airplane (EZ design) built stock will do just fine. An older professor once told me, if your going to err.... do it on the side of simplicity. Airplanes built this way always have been a good formula due to the necessity of reduced weight (mass) in order to defy gravity.

 

My idea, which I never posted is to use a central sump (only 4 gals and have two lines exiting the sump leading to independent filters then separate electric fuel pumps which in turn lead to the rail. (I would only have one pump if the engine comes with an engine operated pump). I fall short here having never worked on a Rotary engined vehicle.

 

This method takes into account that YOU and ONLY YOU must refuel your airplane. (Eliminating the wrong fuel) In your case where you are porbably going to use Mogas this does not work as easily.

 

Off track here a little;

I will say that everyone should try a little test. Add 1 ounce of water to each fuel tank and then give it two minutes roll to the lowest point and see if you can recover the entire ounce of water. If you can't, find the lowest point in your system and install a drain. I did this during the construction stage of building my fuel strakes and it works very well every time.

 

Every system has a compromise. I think the system you decided on will be safe enough since your the designor and the operator all in one. Besides, we need someone to prove your system works:D

 

Keep goin' John

[John Slade]

NiceEz said:

My idea, which I never posted is to use a central sump (only 4 gals and have two lines exiting the sump leading to independent filters then separate electric fuel pumps which in turn lead to the rail.

 

That's a well proven alternative. I'm avoiding the central sump for a few reasons:

1. The gravity feed to a single sump can cause problems. Jim Sower has had some bad (read new underware) experience with this. Tell us all about it, Jim

 

2. I'd like to save the weight and space for the air conditioning system which I hope to fit in the hell hole one day.

 

There is no easy way to fit a mechanical pump to a Mazda 13B that I know of, and this probably wouldnt work for fuel injection anyway.

 

Was said:

<This method takes into account that YOU and ONLY YOU must refuel your airplane. (Eliminating the wrong fuel) In your case where you are porbably going to use Mogas this does not work as easily.>

I plan to supervise fueling, but just in case I slip up one time, I'm having special circular labels printed advising that the fuel type and the requirement for 2 stroke oil additive. (this is needed for lubrication if you remove the metering pump as most 13B flyers do).

 

>Besides, we need someone to prove your system works

Yea, right! I hate being everyone's elses test pilot. This is the biggest reason of all for sticking to something someone else has done if at all possible, but then of course, we'd all be lying down in a one-place pusher biplane....

[Jim Sower]

John,

Couple of questions on the latest iteration of your design:

< left tank will be the "sump". Return will always be to this tank >

I would use the right tank as the sump. It is the easiest to check visually (using Vance's sight gauges). It will usually have more fuel in it (tending to balance you laterally when flying alone.

 

< I will run a pump and filter from each tank to the rail >

This one scares me a little.

Suppose you've run off the left tank (pump) for a while and drawn the left fuel down to about half full. Now you switch to the right tank (pump) and start drawing it down, returning to the left tank. At cruise, we might assume for the sake of argument that you're returning about half the fuel pumped. You fly along filling up the left tank. About the time the right tank gets close to empty, the left one is close to full. You switch back to the left pump and the engine quits. The pump has failed. All you can do is switch back to the right pump, but it's dedicated to an empty tank. You only have just a few gallons left, and half of that is being pumped into an inaccessable tank. You're screwed. If you were at 8000' right OVER a suitable airfield, you'd still run out of gas before you could get down since at idle you're still pumping 30gph, and it's nearly ALL going to the dead tank.

 

If you parallel the pumps from the right tank and return to the right tank, one or the other will be drawing from that tank. You periodically Facet fuel from the left tank to keep the right tank topped off. If the Facet fails, you have a nearly full tank and two pumps to draw from it. The only common failure mode is the Facet transfer pump. You'd be left without whatever was left in the left (backup/donor) tank. Pump failure would be pretty much a non-event.

 

The only "unmanageable" failure mode is trash in the outlet line from the right (supply/return) tank. If you have screened off the entire blister, you'd need about half a bushel of trash to stop up the screen to where the engine wouldn't run. I don't think you've left that much stuff behind in your strakes. Anything that could get through the screen will happily flow through the plumbing to the filter (have one pump downstream from its filter, the other upstream if you want to to cover all the bases here ~ I prefer filters upstream to protect the pump as well as the injectors).

 

Please think long and hard about pumping out of both tanks and returning to one.

 

Best,

Jim

[John Slade]

Jim.

Damn. I thought I had it all figured out. You're right. Fuel pump failure on the return tank would be a bad situation. Of course I could add the facet transfer option to solve this problem, but then I'd need a check valve to stop fuel being sucked backwards through the facet pump. Maybe two pumps on the return tank is an easier way to go.

 

On the issue of which tank to return to, my thinking was that that I need to keep an eye on the tank that doesnt receive the return fuel. As you say, the return tank will tend to have more fuel in it, and this tends to balance the pilot when solo, but I'd rather trim the plane and be able to watch the one with the least fuel.

 

John

Still "blowing in the wind" looking for THE answer.

[niceez]

John & Jim,

 

This ability to suck air is what scares me with part of the plan. It is to complicated. Why not then just a 1 or 2 gallon sump. Just make a place that you can transfer fuel with dual pumps pumping fuel to the engine (Rail). The sump is merely a big place in the fuel line. Wish I was there to spend a day using some string and a milk jug to demonstrate failure modes.

 

I know Vance put his sump under the rear seat and it seems to work fine in his Lycoming powered Cozy. Some people will argue about "oh that would mean fuel in the passenger area...." Not a valid point since the strakes are bonded to the fuselage and on my LEZ its the exterior wall in the baggage area.

 

Dual return lines on your installation could make sense too (Tee'd so they will take the path of least resistance. One thing I don't know is if you could return fuel to the sump. Would really make things very simple and easy too. After the fuel pumps if you ran the lines to a "Tee" so only one line was going to the rail you would only require one fuel valve (On / Off) if you think you want one. I think they are needed on airplanes but that is my own opinion. There is also nothing wrong with puting filters in between a tank and a small sump with just gravity feed. The failure mode of a single sump fed by two tanks with two separate pumps to the rail is as simple as I can get with very little failure modes. Takeoff and Landing would require both pumps running in case of a pump failure.

My own take on a sump is not a place to store extra fuel, rather just a place to transfer it, so it doesn't need to be very big. A fuel valve in between the tank and sump would also be a way of purging contaminated fuel and the smaller the sump the better.

 

This is the most simple and safest system I can think of and my .02 cents worth.. I have traced yours out and it seems a little scarey for me and I don't scare easily. To make a place where the fuel pump will never suck air is the most important to me. And of course there is more then one way to do it.

 

Single on / off valves could be installed between the tanks and the sump for maintenance but I would leave them on most of the time.

 

Don't know how this will square with your idea's but I hope it helps. Trace it out and let us know what you think

A good idea will come to you since you seem like a pretty smart guy.

[geograham]

I agree with Dale!

 

I also like the idea of bench testing the return flow

as to how big a sump needs to be.

 

I happen to have a spare fuel rail with injectors,

if John has a pump, we could hook'em up. and watch

it bubble into a old 2liter pop bottle etc.

 

You must have a gallon of mogas around (or maybe

your neighbor does).

 

George (loves the sump) Graham

[John Slade]

Dale

>This ability to suck air is what scares me ...

I don't want to get into the game of defending what I have (or plan) but I don't see where sucking air comes into it. Am I missing something?

 

In a nutshell, here's the current design...

The feed comes from the right strake tank, through a gascolator, splits to two pumps and filters then goes to the rail. Return is to the right strake only. A facet pump draws from the bottom of the left strake and feeds to the top of the right strake to permit fuel transfer.

 

For ease of discussion, lets call the left strake the "reserve" tank and the right strake the "main" tank. OK, if you drain the reserve tank dry by transferring all fuel, then the facet will suck air. No big deal. Other than this both pumps always have fuel as long as there's fuel in the plane.

 

With this (Tracy's Crooks) method the "main" tank can be considered the "sump" with all the benefits you list for a sump. You just have two tanks instead of three, thereby eliminating the "complexity" of installing a third tank without loosing any of the benefits.

 

>A good idea will come to you since you seem like a pretty smart guy.

Well thanks, but this is the part of the trouble. There are a lot of pretty smart guys in this world of experimentals, and they all have good ideas. The tricky part seems to be bringing all the good ideas together and designing a system with all pros and no cons.

 

So, what are the remaining cons in the above system? Jim & I have discussed the issue of blocked vents by phone, and we feel this is a non issue unless both vents get blocked at once (unlikely). Pilot workload is the only "con" I can see, and having become disciplined to tank switching in a Piper, I really dont see this as a problem. Rather an advantage. I guess this is a personal issue, but I prefer a system which requires periodic pilot intervention (and allows a back-up fuel supply) to a "both" system which, I think, helps some pilots forget about fuel until its all gone.

 

George,

I have a plenty of mogas and "pop" bottles. Testing the return flow at idle is definately something I plan to do once the system is plumbed. If you'd like to come over and hold the stop watch you'd be most welcome.

 

Regards,

John

[Jim Sower]

John,

Another consideration that makes your "Right = Main; Left = Reserve" design even more bulletproof is a "vent check valve" that they use in Velocities - it's a check valve that is closed when there is zero or positive pressure (like you're on the ground or flying with ram air) in the vent system. It opens to cabin pressure if the relative pressure (vent line pressure <=> cabin pressure goes negative. You have ram air vent to your strakes when the vent lines are open. You have cabin air to the strakes if a "dirt dauber" takes up residence in your vent(s).

 

YOU'RE HOME FREE!!!

 

If you installed a screen over the blister, theres NO WAY any trash can get into your fuel system that would block a 3/8" (or much less a 1/2") fuel line. Anything that could get through the screen will pass through the pump and get caught in the filter.

 

Parallel fuel pumps. You could have one filter upstream from the pump and the other downstream if you want. Mount filters vertically so they can't accumulate moisture.

 

Facet pump transfers from bottom of Reserve tank into the return line just before it enters the top of the Main tank. Facet pump lights a light when it's running so you're MUCH less likely to over fill the Main and vent fuel overboard. When the Reserve runs dry, the Facet pumps air bubbles into the return fuel until you notice that the Reserve is empty and turn it off (like, so what?).

 

Fuel management task amounts to turning on the Facet pump from time to time to [nearly] top off the Main. If it fails, you've lost what's left in the reserve. When the transfer pump does fail, it's loss becomes obvious when you still have a nearly full Main tank. You've lost only the untransferred fuel in the Reserve tank.

 

Return (hot?) fuel goes to the Main tank where it has maximum opportunity to cool, not to a small sump where it gets recirculated almost immediately.

 

We've solved blocked vents above. Even if you don't use the check valves, a blocked Main vent will still "suck" fuel from the vented Reserve tank through the Facet pump. A blocked Reserve vent will seriously reduce transfer but perhaps not prevent it altogether; you can transfer until the Facet won't suck hard enough to overcome the vacuum in the Reserve tank. When you turn off the Facet, air will tend to leak (through fuel cap, vent restriction, etc.) and reduce the vacuum. Then you can use the Facet a little more. In any event, any blockage will be obvious in plenty of time to divert somewhere and fix it. NO vent blockage can go undetected long enough to cause a problem.

 

The (my) problem with sump tanks is based on my own experience with my Velocity not transferring evenly (and sometimes not transferring at all from one strake). The Velocity fleet is rife with assymetric transfer problems, some worse than others. It's either a significant design defect in the Velocity or an inherent problem with sumps. But even if the strakes transferred perfectly to the sump, you'd still have the possibility of recirculating fuel before it had time to cool sufficiently.

 

If I were you, I'd lose the gascolators. You can't avoid a low spot in the fuel line somewhere between the Main tank and the fuel pumps. Install a drain there if you must I see no particular value in it. Parking on your nose will put all the water over the strake drains. If you forget to drain your strakes on preflight, the water will, when you raise the nose, run straight to the blister, straight to the engine. You can't possibly get from your parking place to the runway on the fuel in the lines and the filter. Main tank water will ALWAYS reach the engine almost immediately after start.

 

If you set up the lines to the injectors so that secondaries come out of the bottom of the rail and primarys out the top, you can't accumulate water in the rail, and a reasonable slug of water might not fill the whole rail so you might only lose half your injectors.

 

Worst case is that for some reason, you drain the water from the Main but not the Reserve so that water from the Reserve goes to the engine sometime enroute when you begin transfer. This problem (draining the Main tank but not the Reserve) is worse than not transferring from the Reserve at all, or not noticing problems with the Facet. It cam ONLY happen if you're IFR (there is "no visual reference to the horizon" when you've got your head up your ass )).

 

I think you're on the home stretch. Very low parts count (fewer failure modes), minimal plumbing and wiring (minimal failure modes), simple, economical and very easy to evolve from should you feel the need.

 

Think I'll do mine that way too .... Jim S.

[John Slade]

>I think you're on the home stretch.

Yea right. Unfortunately, the theory didnt work out in practice. Either that, or it just didnt "feel right". I'm part way through installing the system and I don't like it. Too many connections, T fittings and pumps.

 

I'm rethinking the whole thing. Here's plan 9f...

 

I'm going to re-install the plans weatherhead manual valve in the seatback and use it to switch the return. The feed is already switched by the electric pumps being on or off, so I'll be able to draw and feed from either tank. This system is a bit more pipe, but an even lower parts count.

 

Of course there's the fuel management issue of switching pumps but forgetting to switch returns. I dont see that being an issue. Doing both at the same time will be an easy habit to learn. Certainly less of an issue than remembering to turn off the transfer pump. I'll probably fit a couple of microswitches to warn about crossfeed. Unless I plumb a "both" position for the return I guess I wont be able to have both pumps on when taking off with both tanks full to the brim, but other than that I have my redundant fuel system back.

 

If anyone sees any problems, I'd like to hear them.

 

John Slade