Operation Notice from Bob about Fuel Tanks on Systems with Fuel Pumps

[jaredyates]

Operation Notice

The Bearhawk Fuel System as shown in the Bearhawk Book is designed for use without a fuel pump.
If a fuel pump is used, extra care in flying is required so that neither main tanks become unported, as a fuel pump would rather suck air than fuel.
If one tank is very low and the other is not very low, set the fuel selector on the fullest tank and fly the plan as not to unport that tank.
A header tank (3 gal) could be used to solve this problem, but fuel in the cockpit can be a safety issue. (Vent the header tank to both main tanks)

[robcaldwell]

Operation Notice

"The Bearhawk Fuel System as shown in the Bearhawk Book is designed for use without a fuel pump..."

Does this include the engine driven fuel pump?

[Mark Goldberg]

Yes. Any fuel pump. Mark

[svyolo]

I kind of think this is a bit of an overly broad disclaimer, and it might cause a lot of confusion.

Also, if you think about it, what is the difference between being in an uncoordinated bank, and un-porting one side, and being in a climb or descent, and un-porting one or both fore and aft fuel pickups? I don't see any.

If you are going to run multiple fuel pickups, either with a "Both" setting on a fuel valve, or fore and aft fuel pickups in the same tank, the fuel system (or the input to the fuel pump) must be continually fed by gravity. If you are sucking fuel into the pump, I can't remember the correct term (scavenging?), and you are running multiple fuel pickups, you risk sucking air if a fuel pickup gets un-ported.

[Archer39J]

Well it's the easiest solution from a designer's standpoint that's for sure. But yeah, confusing for those who use any kind of pump and very broad, and yeah same effect in pitch. I think we pretty much ferreted out the sucking pump as the necessary culprit in unporting mishaps.

[svyolo]

Does the Model 5 have 3/8" fuel lines, or Bob spec 1/2"?

[Collin Campbell]

The Model 5 uses 3/8" lines. At least that is how Bob had me do the prototype.

[Pbruce]

I thought all 0-360s and O-540s had a mechanical fuel pump. Am I mistaken? I’m sure I could be since my knowledge is quite thin in this area. Does anyone run without one? Thanks

[zkelley2]

Neither need one if you can gravity feed 150% of the fuel burn at takeoff power in the least favorable pitch attitude. That's what the AC calls for.

The carbs themselves don't need any fuel pressure, so as long as you can get fuel to them they work.

There are people here that don't run fuel pumps.

[swpilot3]

I don't have any fuel pumps on my O-540.

[svyolo]

I thought about this for a couple of days and I think Bob is correct writing this notice the way he did. There is no way he can come up with every permutation of pumped engines and write a notice for all of them.

I think if I was writing it, it would just say: The BH fuel system was designed to gravity feed a carburetor on an engine up to 300 hp. Each builder should conduct a fuel flow test according to AC 43 to verify their installed system is compliant. Any use of the fuel system for other than a gravity fed carburetor, is up to the individual builder to ascertain its' correct function.

[zkelley2]

Ya, to me, the fuel system seems like an ancillary item that is up to the builder, not the kit maker/designer. Almost like if they were recommending one way to wire an electrical system over another. He cannot possibly account for all the things people are going to want/come up with. Although fuel starvation is the #1 cause of E-AB engine failures.

Even with his design it seems like it's 50/50 whether you can get sufficient fuel flow based on the way individual builders interpret how it's supposed to be, fittings used, etc.

[Sir Newton]

I am quickly become addicted to this forum. 100% Refer to the requirements layout by the manufacturer of the fuel system.

[Pbruce]

Thanks everyone. For my perspective, so I can measure the risks against something I’m familiar with, does a 172 have a mechanical pump? Say a 1970-1980 vintage with a lycoming 0-320?

Just trying to figure out if I buy an engine with a mechanical pump am I increasing safety by removing it? (Assuming I am meeting the 150% of max flow rule in the worst pitch attitude)

[zkelley2]

Assuming it's still an o-320 and not injected then no. None of the high wing carbed cessnas have pumps.

[Pbruce]

Good to know. I assumed otherwise. If you have a mechanical pump on your engine, is it safer to leave it on or remove it? Opinions?

[whee]

Some Cessnas have a fuel pump but I can’t think of one that came that way from the factory. The ones that have them are like a C170 or early 172 that have an O360 installed in place of the O300.

As has been said, if your fuel system will flow 150% of the volume needed at max power and worst case AOA via gravity then there is no need for a fuel pump. If it will not then you’ll need to modify you fuel system to get that 150%. Most builders install a fuel pump since that is the easiest.

[Chris In Milwaukee]

It’s funny because my Maule had a fuel pump but not a single reference how to use it in the POH. don’t think I ever used it.

[rv8bldr]

I use the electric pump in my Maule M5-235C to bring the fuel pressure up to 5 lbs before start. Three pumps of the throttle then gives me all the prime I need. That's all I use it for because it is on the checklist I inherited from the previous owner.

[zkelley2]

It’s funny because my Maule had a fuel pump but not a single reference how to use it in the POH. don’t think I ever used it.

Every Maule I've seen has an engine driven pump with electric backup. If you need a mechanical pump a backup is required.

If you have(need) a mechanical pump the electric should be on for all takeoffs, landings and any other critical phase of flight where a short interruption of power while you get it figured out and the electric pump on would turn out bad.

[JimParker256]

Every Maule I've seen has an engine driven pump with electric backup. If you need a mechanical pump a backup is required.

If you have(need) a mechanical pump the electric should be on for all takeoffs, landings and any other critical phase of flight where a short interruption of power while you get it figured out and the electric pump on would turn out bad.

Having recently experienced the failure of an engine-driven fuel pump in my buddy's Piper Cherokee 160, it made me really think about this whole "aux" fuel pump situation. We had been in flight for a while when he said "Oh, I never did my level-off checklist..." He ran the checklist, and one item was "Fuel Pump - OFF". He turned it off, and 3-4 seconds later the engine faltered and quit. He looked at me with big eyes, and I said "Well, you might wanna turn that fuel pump back on..." He did, and power was restored within a couple of seconds. In hindsight, the mechanical pump had failed at some point after the runup, and we had been running strictly off the electric pump for an unknown amount of time. That's what it's there for, of course, but it left us both feeling a bit "queasy"...

The checklist for his plane calls for the electric pump to be turned ON (and look for a rise in fuel pressure) BEFORE you start the engine (which automatically activates the engine-driven pump). You then turn it OFF for the pre-takeoff engine runup / mag checks (to ensure the engine-driven pump is working as well). Just before takeoff, you turn it back ON and it stays ON until you reach your cruise altitude – precisely to guard against the failure of that engine-driven pump – as we experienced. The electric pump kept the engine running for us – until he turned it OFF...

If he had never turned the electric pump off, we would have been blissfully ignorant of the failure of the engine-driven pump – at least until the electric pump failed! Or until the next engine runup was done – assuming he actually did that complete "before takeoff" checklist prior to every flight – even the 2nd or 3rd flight of the day. And prior to the events that day, he told me no use for doing the complete runup / mag-check, fuel pump check, etc. prior to every flight, and only did them for the first flight of the day. Now he has "seen the light" and performs that complete checklist for every flight!

So I'm now looking over the checklist I developed for my airplane (experimental, so no "factory" checklist), with an eye to ensure I'm able to 'validate' even the redundant systems in the plane somehow. My plane does NOT have an electric fuel pump. It's high-wing, so it shouldn't need one. Except for the fact that the header itself is below the seat, so it's an "uphill" run to the engine from there. I'd be OK feeding from the wing tanks, but once I hit the 2.5 gallon (1/2 hour) "reserve" in that header, I'm entirely dependent on the engine-driven pump. If it ever quits, so will the engine. Adding an electric pump is on my horizon... And my checklist will be modified to ensure I'm getting fuel pressure with the electric pump ON, well before starting the engine.

As the Rotax is shut down by turning off the ignition system (no mixture control to pull), I shut one side off, and wait 3-5 seconds before I shut off the other side. That's to ensure the P-lead is actually grounded by the "off" position on both circuits. By alternating which side I turn off first on each flight, I check both systems on a regular basis. Even on the Citabria that I used to own, I would occasionally shut down using the ignition switches instead of pulling the mixture, just to ensure those P-leads really were grounded properly. Cheap insurance for the day someone pulls the prop through – accidentally or on purpose...

[zkelley2]

Having recently experienced the failure of an engine-driven fuel pump in my buddy's Piper Cherokee 160, it made me really think about this whole "aux" fuel pump situation. We had been in flight for a while when he said "Oh, I never did my level-off checklist..." He ran the checklist, and one item was "Fuel Pump - OFF". He turned it off, and 3-4 seconds later the engine faltered and quit. He looked at me with big eyes, and I said "Well, you might wanna turn that fuel pump back on..." He did, and power was restored within a couple of seconds. In hindsight, the mechanical pump had failed at some point after the runup, and we had been running strictly off the electric pump for an unknown amount of time. That's what it's there for, of course, but it left us both feeling a bit "queasy"...

The checklist for his plane calls for the electric pump to be turned ON (and look for a rise in fuel pressure) BEFORE you start the engine (which automatically activates the engine-driven pump). You then turn it OFF for the pre-takeoff engine runup / mag checks (to ensure the engine-driven pump is working as well). Just before takeoff, you turn it back ON and it stays ON until you reach your cruise altitude – precisely to guard against the failure of that engine-driven pump – as we experienced. The electric pump kept the engine running for us – until he turned it OFF...

If he had never turned the electric pump off, we would have been blissfully ignorant of the failure of the engine-driven pump – at least until the electric pump failed! Or until the next engine runup was done – assuming he actually did that complete "before takeoff" checklist prior to every flight – even the 2nd or 3rd flight of the day. And prior to the events that day, he told me no use for doing the complete runup / mag-check, fuel pump check, etc. prior to every flight, and only did them for the first flight of the day. Now he has "seen the light" and performs that complete checklist for every flight!

So I'm now looking over the checklist I developed for my airplane (experimental, so no "factory" checklist), with an eye to ensure I'm able to 'validate' even the redundant systems in the plane somehow. My plane does NOT have an electric fuel pump. It's high-wing, so it shouldn't need one. Except for the fact that the header itself is below the seat, so it's an "uphill" run to the engine from there. I'd be OK feeding from the wing tanks, but once I hit the 2.5 gallon (1/2 hour) "reserve" in that header, I'm entirely dependent on the engine-driven pump. If it ever quits, so will the engine. Adding an electric pump is on my horizon... And my checklist will be modified to ensure I'm getting fuel pressure with the electric pump ON, well before starting the engine.

As the Rotax is shut down by turning off the ignition system (no mixture control to pull), I shut one side off, and wait 3-5 seconds before I shut off the other side. That's to ensure the P-lead is actually grounded by the "off" position on both circuits. By alternating which side I turn off first on each flight, I check both systems on a regular basis. Even on the Citabria that I used to own, I would occasionally shut down using the ignition switches instead of pulling the mixture, just to ensure those P-leads really were grounded properly. Cheap insurance for the day someone pulls the prop through – accidentally or on purpose...

This is why the backup is always on for a critical phase of flight. You don't want that happening at 400ft.

So you say you have a mechanical pump. If you actually need that pump for the engine to run in any way at all, you MUST have the backup. Even on a rotax. I'd get one in there ASAP. I wouldn't fly again until you do. Or consider that 2.5gal unusable, but I'm pretty sure the carbd rotax needs the pump to run properly regardless of the head pressure from tanks. I think the issue is putting enough fuel through the failed mechanical pump. They're like $100. If you're high wing or not is irrelevant in of itself. Plenty of high wing planes have pumps. It has everything to do with if you can get the fuel to the carb ALWAYS.
If you don't need the pump, I'd take it off.

Most commercial shops mag checks are on the runup and shut down checklists. On shutdown it lets you know if a mag is hot, or if one is bad and you can fix it before you go to fly next and now can't.

[Battson]

If you have(need) a mechanical pump the electric should be on for all takeoffs, landings and any other critical phase of flight where a short interruption of power while you get it figured out and the electric pump on would turn out bad.

See that has always been my assumption too, however I found it doesn't hold in all cases. I always check the POH. Some require boost pumps OFF at certain times.
For some reason I thought some Maules were like this. Or maybe I am thinking about the high and low pressure pump switches in the Cessna

[zkelley2]

I would think you're thinking of the Continental style fuel injection with a high and low and it does need to be in it's correct position. I cannot think of how a carb or Bendix FI would have an issue with a boost pump on, and very bad outcomes with it off.

Some Maule's run the TCM IO-360, and that would then be the case there, but the lycoming's seem to be most common.

[Battson]

Good notes - thank you

[PaulSA]

I've been thinking about this......

Is the inference that unporting ANY of the four ports is going to cause air to be sucked to the engine? In which case, a few questions:

Should I put the aircraft in (say) the landing attitude and see what the minimum fuel in the tanks is to keep the forward port covered and then make that "unusable" fuel?

OR

Is it counterproductive to have 4 ports? Should I blank off the forward ports?

OR

Should I run LEFT/RIGHT instead of BOTH?

OR

Should I fit a header tank?

OR

Should I not really worry? - I'm sure there are plenty of IO powered Bearhawks flying quite happily.