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My experience running a tank dry.

I put ~190 hrs on a Swift that had Bendix injection (Lyc IO-320, then IO-360 engines) that had an STC'd aux tank. Standard practice on cross countries was to TO-main, switch to aux, run the aux dry, and switch back to main. You always knew within a few minutes when the aux would run dry, so you just monitored the fuel flow/pressure gauge & switched at the 1st drop in pressure & hit the boost pump. Yes, occasionally you could get distracted and the engine would cough/sputter before switching. The engine driven pump has no problem recovering; it'll just recover faster if the boost pump pushes fuel up there.

If the AFP pump is a gerotor or roller vane style pump (and it's almost certainly one or the other), the [AFP] statement makes no sense as written. Gerotor and roller-vane pumps are positive displacement pumps; they will self-prime at any level of lift you're likely to see in the planes we fly. Self-priming by definition means that there will be a bubble of air on the output side of the pump after the pump self primes; it means that the pump is pulling air through itself to get the gas up there. That air has to go somewhere; it doesn't just disappear. So....when the boost pump self-primes, there will always be a (temporary) bubble of air on the output side of the boost pump.

If AFP used a turbine style pump in that assembly, they made a grievous error in pump selection.

EDIT: Just realized what they might be talking about. Positive displacement pumps must have a regulator, to avoid damaging downstream stuff or stalling the pump. The regulator on that pump (and the other brands that are configured similarly) bypasses excess fuel *back to the intake of the pump*. I can see how the pump could fail to pump (gas), once there's air in the system around the pump. It's a lot easier to move air than fuel, so the pump *system* can vapor lock *itself*, if air ever gets in the line.

Something to think about, while flying over that forest, if you think there's ever any risk of unporting your fuel pickup while operating on the boost pump....

Would not be an issue, if the regulator bypass went back to the tank, as is done with the auto style injection systems that are gaining popularity on this forum.

So this is all good stuff. The operative question then is if the AFP has this problem, but your Swift pump (and presumably any stock RSA system e-pump) does not:
1)how do those pumps differ from the AFP
2)what make and model are those pumps
3)why would anyone choose to use anything but those pumps?

I havent decided on a boost pump, so this is an important issue for me, and until this thread, I hadnt even considered it an issue. Thanks for any help.

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Edit: Ok I get it. Weldon pumps are Piper stockers, 8120G or 8150s. I now get that the AFP is meant for EFI - guess I've been ignoring that, despite it being obvious. I now also get why the Andair pumps are the obvious go-to pumps for the RSA style inj for EAB. I'll leave this post here; maybe it'll help someone else in the future.
 
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Look carefully at the wording of the AFP warning:
"WARNING

Airflow Performance and Bendix/Precision fuel injection systems are non-returning systems. In the event that a tank is run dry in flight, an air lock will be formed on the out let of the pumps. It is possible that the auxiliary pump will not pick up fuel, as the auxiliary pump cannot create enough air pressure to over come the flow divider opening pressure, thus displacing the air and resume pumping fuel. It is not recommended to run a fuel tank dry in flight without adequate testing and proper documentation of the procedure for this operation."

To me, this reads as if they're talking about the stock engine driven pump, in addition to the electric aux pump. The statement goes on to say that the AFP aux pump can't make enough pressure to drive the air past the flow divider opening pressure. My understanding (I could be wrong) is that the flow divider operating pressure is at most a few psi (one of the reasons 'hot starts' are a pain; fuel boils in the injector lines and likely, in the feed to the flow divider, as well). The electric boost pump should be able to generate at least 30 psi; more than enough to open the flow divider. The only thing that makes sense to me is that the bolus of air is looping around the boost pump and its regulator circuit.

The most common 'old school' FI boost pump I'm familiar with is the Weldon.
https://www.weldonpumps.com/weldon-fuel-pumps

Very pricey and fairly heavy/big.

Look, the AFP (and other) experimental pumps obviously work quite well; I just have a hard time understanding the way they worded their warning.

to airguy:
On the issue of fuel heating, I asked Don at AFP that exact question several years ago via PM and his response was that they've tested at elevated temps and 'Even tests where 90 degree fuel was run in the pump continuously at idle flow was OK for 20 minutes or more'.

I've never seen any issue until this thread and seeing that warning, which got me thinking about a bolus of air 'looping' in the pump/regulator.
 
Look carefully at the wording of the AFP warning:
"WARNING

Yup I read it, and I get it. AFP is a better "RSA" inj. But the same pump warning is not present on the Weldon site nor the Andair site. Did they forget to tell us that? Are we being mislead? Or is AFP being over cautious with their product? Or worse? Dunno. Not enough information.

But I think since I have a Bendix, I'll stick with what Piper did. I'm gonna hazard that the designers knew pilots would run a tank dry, on purpose or not. And I'll hazard that they chose the weldon because it can push past dry lock. Or we'd have had a lot of planes in the dirt in the 60s, 70s, 80s etc.

I think its safe to say however that dry tanking an inj motor is not optimal, because its a lot of air to push thru the small inj lines; and restart when it comes, may not be as heart reviving (and perhaps not with enough instantaneous full power) as it is with a carb motor.
 
I think the intent of the air bolus warning was that the AFP cannot pump air to enough pressure to push the air through the flow divider and pick up fuel if the output is already pressurized. If the AFP pump can catch its prime with fuel, it can certainly push the air out the flow divider and through the injectors, I know because I tested that.

On the heat loop issue - Don tested for 100LL, but the issue is aggravated when running mogas with higher vapor pressure, especially with 91E10 autofuel winter blend. It was easy enough to install return tank lines, I took the safe path.
 
Have to admit reading only the first few posts on this thread before getting bored. Run out of fuel on purpose? Ridiculous.
 
Greg,

To be sure we're on the same page, are you talking about a 'typical' a/c injection system, and saying that you modified the AFP *boost* pump to return the bypassed fuel to the tank instead of back to the tank input?

Or are you talking about automotive style high pressure electronic injection (SDS, etc where there is no engine driven pump) where the norm is to return bypassed fuel to the tank?

Charlie
 
Did it today so I could calibrate a new fuel dipstick. Circling 4000' above 3 long runways, plenty of remaining fuel in other (right) tank. The fuel flow and pressure alarms went off at the same time, before any change in operation. Plenty of time to hit boost pump and switch tanks without so much as a hiccup. Total non-event, and reinforced the muscle-memory of what to do should it happen inadvertently. I am very fuel-conservative so I don't ever plan on being anywhere close to the limits, but the NTSB reports are full of people who never planned on being there. I also spent some time practicing crosswind landings in windy, gusty conditions. I did it today because I had plenty of outs, and never had to land, and did plenty of go-arounds. So that I will be better prepared if I do someday HAVE to make it happen. A little risk now to make me better prepared for a worse situation later.

I'm sure not everybody would want to do it, and that's fine, but for me it was preferable to draining fuel on the ground and the risks that go with that.

Chris
 
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Did it today so I could calibrate a new fuel dipstick. Circling 4000' above 3 long runways, plenty of remaining fuel in other (right) tank. The fuel flow and pressure alarms went off at the same time, before any change in operation. Plenty of time to hit boost pump and switch tanks without so much as a hiccup. Total non-event, and reinforced the muscle-memory of what to do should it happen inadvertently. I am very fuel-conservative so I don't ever plan on being anywhere close to the limits, but the NTSB reports are full of people who never planned on being there. I also spent some time practicing crosswind landings in windy, gusty conditions. I did it today because I had plenty of outs, and never had to land, and did plenty of go-arounds. So that I will be better prepared if I do someday HAVE to make it happen. A little risk now to make me better prepared for a worse situation later.

I'm sure not everybody would want to do it, and that's fine, but for me it was preferable to draining fuel on the ground and the risks that go with that.

Chris

I did the same thing back when I wanted to calibrate my dipstick (gets me within 3/10 gal at fill up). When the motor quit, I switched tanks without using the aux pump..... fired up in less than three seconds.
 
Why do you have to be flying to "run a tank dry"? Why not just drain most of the fuel, then disconnect the fuel line at the servo and run the engine pump until it sucks air? What's left, which you can measure by draining via the fuel drain, is now your "unusable fuel", and you can then proceed to fill the tank or calibrate your fuel senders or whatever.

I'm reminded of why the FAA many years ago advised instructors not to *actually* shut off the engine to "simulate" an in-flight shutdown...because there's the very real possibility of not getting it started again, thus turning a simulated emergency into a real one.

I used the procedure above on both tanks, and found unusable fuel << .1 gallons (just 2 or 3 fuel sample containers' worth), and calibrated both tanks. Easy peasy, no risk.

ETA: I was also taught that should the engine ever actually quit making noise, do these three things: Mixture rich, fuel pump on, switch tanks. I think it was Rod Machado who mentioned in a seminar, IIRC, that this would solve nearly all "the engine just quit" problems. Oh, and you should think seriously about landing ASAP, too :).
 
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If you've been switching tanks during the flight, why would you suspect that one tank suddenly would not feed? If that were a legitimate concern, then the only safe course would be to fly the entire flight on just one tank.

And as for the airline analogy... Jets have all kinds of automation in the fuel systems. By the way, back in DC-6/7 days, on very long range flights, they did indeed run the tanks dry in flight.

If you have been running with both mags the entire flight, why would you expect one to fail? You have two tanks, why would you remove one of the planes redundant features, ever? Anything can happens and it usually does when you least expect it.
 
Like I said, you don't. You can certainly do it on the ground. One way means a tiny risk of an engine-out landing. The other means the risk of a fire. We are all free to pick our poison..

Chris

Quite right!

....except..... your life insurance policy will probably be voided when they find out that you intentionally caused your engine to stop in the air.

I know I know. I too hate to make life decisions based on what the ins co might or might not do. But to not at least consider that (in todays world) is to not fully evaluate all the risk and consequences. And we all pay for insurance whether we like it or not.

Just points to ponder, not fingers to point.
 
AFP Injection and air bolus

probably not a good SOP, but the AFP injection system with a purge valve installed should alleviate concerns about an air bolus preventing fuel flow. open the purge valve and air pressure in the system should be vented back into the fuel tank allowing fuel to flow. close the valve and fuel should be moving thru the flow divider as desired.

disclaimer: I've never tried this as I haven't run a tank dry in flight and make it a practice to never operate the purge valve control in flight (other than the occasional touch to make sure it's all the way in - call it OCD). if I ever do mistakenly run a tank dry and get an air bolus, hopefully I'll be able to report back in with the results...
 
I have to admit that I have a complacency to fuel starvation because it's not something that I worry about on cross country flights :eek: . My body simply can't sit in any small plane for more than 2.5 maybe 3 hours top. If I don't have to empty my own tank, I do have to land, get out and stretch. I talk to people all the time that talk about their plane's range.... I have a human factor range :D
So I just make sure that after 2 hours or so I start looking for a nice airport to land, get fuel, and rest for a few minutes. I've gone all over the country and always expect that my "planned flight" will be changed for one reason or another but one thing stays constant, you have to go when you have to go. :D
 
Surprise

To anyone who has never had an engine shut down in flight, whether intentional or not. You have a surprise waiting. No matter how well you practice for the event, I seriously doubt you will be as prepared for it as you think you are.

If a pilot has been exposed to engine shutdowns a few times in the air, they tend to be more competent and in control of the situation when it happens unexpected.

Instructor simulations of pulling the throttle to idle did not fully prepare me.

Should it be practiced to intentionally gain the experience? The argument is you are exposing some intentional risk to gain experience for a higher risk situation that is unintentional.

Not everyone will want to gain certain experience levels. There are levels of experience that I gained by choice at a young age that no longer look like wise choices to me now. But I still value the experiences....:)
 
Ive heard the "two tanks = redundancy" thing several times in this thread now and I believe this is just one way of twisting a circumstance to justify ones own bias. The fact is, there are very very few circumstances where more than one fuel tank is preferred. The vast majority of the time the use of multiple tanks is a DESIGN COMPROMISE. Van did not add a second tank to increase safety, he did it because it is preferable to having a 42 gallon single tank within the confines of an RV. If a single tank meets the mission of the aircraft, that is almost always the preferred method. Those that think multiple tanks = redundancy must think the early Staggerwing with its myriad of tanks and multiple selector valves is really safe! Keep it real, people!

I've also heard the term "running a tank dry" twisted into some ridiculous hyperbole in this thread. Reading some responders, you would think those that do this run a tank dry, the engine quits, and after gliding for some time the pilot tries a relight. Nonsense. In many cases, its just a slight dip in fuel pressure that signals the end of fuel in that tank and the passengers dont even know the event happened.

Lots of talk about FAR mandated fuel "reserve" in this thread too. Reading this thread one might believe that landing with XX fuel is a requirement. Also nonsense. You must PLAN to land with reserve, but even the FAA knows that plans change. I dont care how much planning you did, what kind of on board weather magic you have, you still cant forecast the corporate jet landing gear up on your planned destination airport and closing it down just before your arrival (for example). Sometimes through no fault of your own, you will be flying on your "reserve" fuel for a bit. This is not an emergency, and you are not going to get "violated" for dipping into this reserve. Assuming you are eating into that 30 minutes, do you think its better to have less than 2 gallons above each pickup, or 4 gallons above 1?

Also lots of comments about people's personal range being considerably less than the aircraft. If this is your choice, then I agree there is no need to run a tank out as a fuel management tool. Put another way, your opinion does not count in this discussion. You need to realize that while your own "personal duration" is to land every 2 hours, some of your RV bretheren opperate their airplanes over water and may not EVEN SEE land for 2 hours. These are very capable airplanes, and some of us extract all the capability we can out of them. It does not neccessarily make us "unsafe" just because we choose to do so.

The bottom line is that consolidating fuel in this manner is SOP for many circumstances (including Certified aircraft and piston airliners in some cases), and has been done for generations of pilots. I have done it on EVERY airplane I've flown at one time or another and consider it a useful and safe tool for extracting maximum range out of the aircraft. If that is not within your personal comfort zone, so be it, but consider this fact: There are SCORES of our brethren pilots who would NEVER fly an RV because they are "Experimental" and therefore "unsafe". And trust me, they have much more solid statistics to back up that decision.

If you want to argue the relative safety of running a tank dry at high altitude as a means of fuel consolidation so you can stay high and go long vs penetrating the terminal environment, managing the climb and descent every 2 hours, all the while tankering 120 pounds of fuel you never intend to use, well, we could go round and round all day.

Consolidating fuel is proven and effective... If you want to tell us about your bladder issues, there are other forums for that. But please don't try to pull the "safety card"
 
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The OP did it accidentally - the thread quickly turned into a debate over a "planned event". Many of us know that the planned event makes it a "non-event".
 
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Literally what the OP described happened, to be fair...

Well....I guess it depends on how you interpret the phrase, 'for some time' as meaning 'the instant the engine quit', or 'many seconds', or 'several minutes', etc.

The OP said the interval from engine windmill to relight was not much more than 3 seconds.

Let's be real, if we're going to discuss this rationally.
 
The OP did it accidentally - the thread quickly turned into a debate over a "planned event". Many of us know that the planned event makes it a "non-event".

Sure, but as that's literally what he described happening it wasn't "nonsense" as you say. A planned event maybe, but not a smart event. You do you though...

Well....I guess it depends on how you interpret the phrase, 'for some time' as meaning 'the instant the engine quit', or 'many seconds', or 'several minutes', etc.

The OP said the interval from engine windmill to relight was not much more than 3 seconds.

Let's be real, if we're going to discuss this rationally.

Just pointing out this is what was literally described. Let's be real though, intentionally running a tank dry during a flight is ridiculous, unnecessary at best and negligent at worst. But like any population there is a bell-curve...

Stay safe and manage your fuel properly.
 
Greg,

To be sure we're on the same page, are you talking about a 'typical' a/c injection system, and saying that you modified the AFP *boost* pump to return the bypassed fuel to the tank instead of back to the tank input?

Or are you talking about automotive style high pressure electronic injection (SDS, etc where there is no engine driven pump) where the norm is to return bypassed fuel to the tank?

Charlie

I'm running dual AFP pumps, one from each tank, with no engine-driven pump. Each AFP pump has a return back to it's source tank, switching tanks is done electrically by switching pumps. The pumps output tees together through check valves and goes forward to a standard Bendix injection system.
 
...Let's be real though, intentionally running a tank dry during a flight is ridiculous, unnecessary at best and negligent at worst...

For many pilots, the thought of screwing an airplane together in your basement then flying it night/IFR is "...ridiculous, unnecessary at best and negligent at worst". Yet many on this forum do exactly that. Personally, night/IFR is WAY outside my risk threshold, but I sure am not about to call those that do it "ridiculous" or "negligent". It's an insult.

Don't let personal bias taint an otherwise practical discussion.
 
Due to my impatience and boneheaded fuel expectations I managed to run a tank dry on a recent long cross country.

I knew the left tank was getting close to being empty but I thought it would get me another 10-15 minutes along before I switched to the right tank. I was about 20 minutes from home with rapidly diminishing daylight at 3500 ft. "The fuel in the right tank would be enough to get me home with reserves", was my thinking before the left tank went dry.

I did not think it would happen but suddenly the engine quit with the prop windmilling at a good clip. I was pretty quick to switch tanks and after about 3 long seconds the engine restarted. I don't remember if I pushed in the mixture and turned on the boost pump but was very relieved that the power came back on.

So...do I fly on, confident that the right tank would carry me through a darkening sky to my destination? No. I finally made a wise decision and diverted 9 miles to an airport I knew had SS fuel. I made it home later than I planned and logged some night flying and and a landing. I would have gotten home sooner if I had just topped off the tanks before I left in the first place. :(

Lesson Learned: After 11 years and 1100 hrs with my RV9, overconfidence, impatience, and complacency are real dangers. I'm glad this happened. It needed to happen and I am a better pilot for it.

If you are cruising along and run out of fuel, don't touch anything.... just switch tanks and be sure the valve is in position, then switch on the fuel pump. It will probably be running before you get to the switch and confirm it. DO NOT mess with the mixture..... it was running fine, it just needs fuel.

When I ran a tank dry to figure unusable fuel and calibrate my dip stick, I didn't lose any altitude during the engine out, the plane just slowed down for under 3 seconds.
 
For many pilots, the thought of screwing an airplane together in your basement then flying it night/IFR is "...ridiculous, unnecessary at best and negligent at worst". Yet many on this forum do exactly that. Personally, night/IFR is WAY outside my risk threshold, but I sure am not about to call those that do it "ridiculous" or "negligent". It's an insult.

Don't let personal bias taint an otherwise practical discussion.

Just so we understand, I'm addressing those advocating intentionally running a tank dry because they feel it is best to use all the available fuel in that tank prior to entering the detestation airport environment. The logic being that when you switch to the second tank, which at this point also apparently has minimum fuel, you're less likely to run out while doing airport ops. This actually makes sense if you find yourself running low on fuel... Unintentionally.

If you do this intentionally then you have failed to adequately plan for the intended flight and indeed are in violation of the FARs. It is poor aeronautical decision making, not a personal preference.

Night IFR is an issue of personal preference.

Don't let pride prevent you from becoming a better pilot.
 
Just so we understand, I'm addressing those advocating intentionally running a tank dry because they feel it is best to use all the available fuel in that tank prior to entering the detestation airport environment. The logic being that when you switch to the second tank, which at this point also apparently has minimum fuel, you're less likely to run out while doing airport ops. This actually makes sense if you find yourself running low on fuel... Unintentionally.

If you do this intentionally then you have failed to adequately plan for the intended flight and indeed are in violation of the FARs. It is poor aeronautical decision making, not a personal preference.

Night IFR is an issue of personal preference.

Don't let pride prevent you from becoming a better pilot.

I can have 6 gallons aboard - fuel for >45 minutes in normal conditions and an hour or more if I'm descending from a mid/high altitude leg on a cross country.

With analog fuel gauges, it is difficult to know how evenly that fuel is distributed between tanks. In my opinion, it is better to manage fuel so all of the remaining fuel is in one tank. Then, I don't need to worry that I'm feeding from the tank with a 2 gallons in it, rather than the one with 4 gallons.
 
Just so we understand, I'm addressing those advocating intentionally running a tank dry because they feel it is best to use all the available fuel in that tank prior to entering the detestation airport environment. The logic being that when you switch to the second tank, which at this point also apparently has minimum fuel, you're less likely to run out while doing airport ops. This actually makes sense if you find yourself running low on fuel... Unintentionally...


Well as long as you put it that way, we are probably in agreement. I have not heard anyone advocate such a thing in this thread, but what some of us do to maximize the utility of the airplane is as follows:

Assuming you are a typical pilot and retained some semblence of balance between tanks- before switching to your "last" tank, ensure the tank you are on has consumed ALL usable fuel - either by running it into the stumble, a fuel pressure flux, intuition, or Oija board - so that your remaining tank is indeed your LAST tank - both mentally and actually. If you do the planning right, this tank will have enough fuel to descend and land at your intended airport IN ADDITION TO the FAA "minimum". This will ensure that you maximized the utility of the airplane, have as much headroom above the pickup tube as possible, and will have removed the need to fumble for one last desperate switch if things do go wrong at the last second and have to burn some of that FAA mandated minimum - unintentionally.

I am glad to see that we are in agreement concerning responsible airmanship.
 
Not sure if this scenario has been mentioned but when beginning a descent after a cross country flight one day, the remaining fuel in the lower level tank (tank not in use) was around 5 gal or so. This is more than 1/2 of the legal reserves. When the nose was pointed down for the descent, the low fuel level alarm (which was set around 3 gal) sounded. So I reset it. but with every turn, change in pitch it would restart and became distracting during a busy time in flight. At the time I knew how to acknowledge the alarm but not to disable it and didn't have the time to figure it out. Two takeaways:

1) Low fuel levels while known/planned may become distracting events, and
2) The last few gallons of fuel may be useable when cruising in level flight, but may not be relied on when descending/maneuvering for landing.

For these reasons, I would prefer to have all remaining useable fuel in one tank, acknowledge/disable the low fuel level alarm for the abandoned tank and continue the flight normally like in the old days where there was only one tank on the aircraft.

Bevan
 
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Not sure if this scenario has been mentioned but when beginning a descent after a cross country flight one day, the remaining fuel in the lower level tank (tank not in use) was around 5 gal or so. This is more than 1/2 of the legal reserves. When the nose was pointed down for the descent, the low fuel level alarm (which was set around 3 gal) sounded. So I reset it. but with every turn, change in pitch it would restart and became distracting during a busy time in flight. At the time I knew how to acknowledge the alarm but not to disable it and didn't have the time to figure it out...

This scenario illustrates EXACTLY why some of us consolodate fuel for descent and landing following a max range cross country leg. The fuel level above the pickup is the only thing important - not the total qty on board. 3 gallons per side is far more risky than 6 in one.
 
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This scenario illustrates EXACTLY why some of us consolodate fuel for descent and landing. The fuel level above the pickup is the only thing important - not the total qty on board. 3 gallons per side is far more risky than 6 in one.

I completely agree and with your prior post too. We typically don't have a transfer pump in our RVs so fuel management has to be done with advance planning. Not a biggee but takes some planning.

I wish there was a "like" button on this forum.

Bevan
 
AFP Warning Conclusion

From AFP:

"WARNING

Airflow Performance and Bendix/Precision fuel injection systems are non-returning systems. In the event that a tank is run dry in flight, an air lock will be formed on the out let of the pumps. It is possible that the auxiliary pump will not pick up fuel, as the auxiliary pump cannot create enough air pressure to over come the flow divider opening pressure, thus displacing the air and resume pumping fuel. It is not recommended to run a fuel tank dry in flight without adequate testing and proper documentation of the procedure for this operation."

So try it safely before you need it.



So what is the conclusion about this warning. I really do not want to have an off-airport landing just because I unported a fuel pickup. Do I need to add a purge valve?

Thanks / Ron B.
 
Way too funny

Fellas, I had a C45 for ten years - that thing had 5 tanks - 6 if you really know the plane. My std OP was to take off on the mains (75gal ea) and swap to the nose tank (48gal) in the climb. So somewhere around 1hr I had to be ready as both engines were running off the same tank. I always caught that one, but the next tank was the aft wing tanks - with the L tank feeding the L engine and the R tank feeding the r engine. Both aft wing tanks held 25gal, so if done correctly, both engines would quit at the same time. The way to outsmart yourself is to switch one engine to its main for 5 min, then back to the aux, so at least BOTH wouldn't quit at the same time...except they did once: I had a non-familiar CP flying the thing at about 10500MSL, and my usual CP was in the left front seat. When the rt engine quit (right on time, I might add) my Fancy CP threw up his hands and said YOU HAVE IT! I put his hands back on the yoke and told him I was gonna restart the rt engine. My normal CP in the PAX seat started laughing - he said don't you notice something? I said no, not really - he said 'there is no yaw! BOTH engines have quit!' and continued laughing. Now my Fancy CP was really worried until the rt engine came back to life - displaying its power with a large yaw - and I got another YOU GOT IT! I put his hands back on the yoke and I told him I was now gonna start the LEFT engine and we would continue on our trip to OSH. I also asked him to put his feet on the rudder pedals..oh did we have some laughs about that trip - still do.

And I still run the left tank dry when flying cross country: the return to is the right tank.

My point is: run 'em dry so you know exactly what you have left - AND what's the point of carrying fuel around that you don't use? Most of the time it is a non-event - especially when you catch the fuel pressure needle wobble and do it without letting the engine quit.

I doubt you will have as much fun was we did on that OSH trip, but you get used to the quiet when the tank runs dry..
 
So what is the conclusion about this warning. I really do not want to have an off-airport landing just because I unported a fuel pickup. Do I need to add a purge valve?

Thanks / Ron B.

I too try to consolidate my fuel in one tank when I need max endurance, but this has always worried me so I'm not running till my engine quits.

However, if you know you're about out of fuel in the tank, the fuel pressure will tell you you're out or almost out before the engine quits. The only time I've ran my tank "empty" I was trying to stretch a 700+ mile cross country to non-stop with a 30ish knot tailwind. I was watching the fuel section of my EFIS pretty close once I got below one gallon on the display. About a minute after it read 0 the fuel pressure started behaving erratically, presumably as the pickup was just beginning to suck a little air. That was good enough for me; boost pump on and switch tanks. The engine never showed any indications anything had changed.
 
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I'm another in the 'be prepared & don't sweat it' camp. I'd never tell someone else to do something they can't get comfortable with, but it's a very common practice in some circles. I flew a Swift for a couple of years that had aux fuel. SOP: Take off on main, switch to aux. Watch time, when fuel pressure needle wiggles, switch to main & run boost pump until pressure stabilizes. If you do get sloppy, it just gets a little quieter until you do the switch/boost pump thing, then the engine re-lights on its own.

Note that the equation may change a bit if you're using one of the 'new' boost pumps that use an auto style gerotor or roller-vane pump+regulator/bypass. In the alt engine world I frequent, the same pump is used, but with a separate regulator that returns to the tank instead of looping back to the pump inlet, as is done with the current crop of 'boost pumps'. One frequent practice is to notch the disc in the regulator valve slightly, so that a small quantity of fuel always flows back to the tank even if there's no pressure in the regulator to open the valve. This becomes an 'air bleed' if the pump ever sucks air. The pump has no problem moving air; this just gets the air out of the system quicker so that the pump can pull fuel back to its inlet. That trick won't work with the new a/c 'boost pumps', since they return the bypass to their own inlet.

The 'tank dry' stress can be eliminated by feeding the engine from just one tank. Separate transfer pump to move fuel from any aux tanks. This is how my alt engine (with automotive style injection) powered -7 will be set up. It's a very common setup, both in light planes and (I'm told) in turbine hardware.

Charlie
 
I've seen the fuel pressure twitch giving time to switch tanks. I have also experienced in the same plane the engine quitting suddenly with no warning. Every time, just switched tanks and 5-7 seconds later the engine would be running. IO-550. A Bonanza has 37 gallon usable tanks. Every time one was run dry it took 40.6 gallons to refill. 3.6 gallons extra fuel on a long trip.
Pretty sure it was a 1965 Mooney POH that suggested fuel management on a long trip was run one hour fuel from one tank, switch and run the 2nd tank dry, then switch back to the first tank. Gotta look that up. Yep, so many words, that's what it says. Download an old POH on Mooneyspace. Used this method for many long trips.
I have not run a tank dry on my AFP injected RV7. Pretty sure it will restart with switching a tank as long as my mechanical pump is working. Pretty sure it will not restart if my mechanical pump is not working.
 
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I had cause to fly to Queensland and back today (7.5 hours total), and as is usual on long flights ran the tank dry. Only this time, I had the foresight to actually film it to prove there's nothing to be scared of, at least in my -9...

The engine setup is an ECI OX-340S, Sensenich GA prop, Rotec TBI and dual PMags.

The most obvious thing experienced is the loss of the exhaust note but switching tanks brings things back to normal in a matter of seconds. I did film it on the return leg, but it isn't as obvious as this one, as I switched tanks a few seconds earlier. And I am still trouble-shooting the alternator output hunting... :confused:

https://youtu.be/PSexkSe8gl8
 
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balancing the load

You know your mission better than I do, but don't you want to balance the load a bit by changing tanks every 30/45/60 minutes or something like that? What I do is fly on the right tank while the minute hand is on the right side of my watch (minutes 0-29) and on the left tank when minute hand is on the left side (minutes 30-59). Seems that there is some additional (unnecessary?) risk in staying on one tank until it's dry, then changing tanks. Just my 0.000003 BTC.
 
With 41 gallons in the wings, I personally don't see a reason to let it run dry. For me, it's WAY out of my zone of comfort for the engine to sputter for whatEVER reason. I've read these post and learn something each time I'm on VAF. The thought that 6 in one is better than 3 in each and the only fuel that matters is the fuel ABOVE the pickup tube.... good lessons!
I keep an eye on fuel flow and try to keep the tanks close equal. I do think of problems when switching tanks and try to avoid it over vast areas of trees. I'll delay until theres a nice field/airport halfway close.
On a XCTY, I'll run the left tank low and like to arrive with no less than 5 or six in the right tank.... only because patterns are usually left. (I know in coordinated turns in doesn't matter).
I keep track at fill ups of what the red cube says and actual. Usually within 1 gallon and sometimes it's within a few tenths. Gives one the confidence to press on.
A look at times... by the time I've burned 30 gallons or so, for my plane that usually carries me about 3 1/2 hours... 650 miles... down the road. By then, I'll have the red lights going off in my head to empty MY tank!
 
To get max range, depleting a tank(s) completely has been common for decades.

It cannot be good for a motor to go from cruise power to off to cruise power again. I prefer to switch with a couple gallons left and then if I need max range, when I am within the GPS glide range ring of an airport, switch to the low tank and stare at the pressure gauge. I have been amazed at how long it can take to deplete that last little bit from the low tank. I may have to go back and forth as I overfly several airports but in the odd event I let it quit and even more improbable scenario that it fails to restart, I know I can dead stick. Remember Murphy lives in the ether.

This used to be a much bigger issue with old analog gauges but with our digital fuel flow totalizers, we may be splitting hairs to squeeze that last gallon.

P.S. I felt a little inferior when the RV-10 I bought was a 250 hp O-540 but I have been around a long time and all this debate about hot starting and AFP models and EFI makes my head hurt. It sure is nice to stroke the throttle a couple times and she starts. And if I run a tank dry, I am sure it will run again (barring Murphy’s mischief).
 
So what is the conclusion about this warning. I really do not want to have an off-airport landing just because I unported a fuel pickup. Do I need to add a purge valve?

Thanks / Ron B.

Thanks for all of the thoughtful replies about fuel management, but my question is really about what happens if you unport a fuel pickup - for whatever reason. For example, say I had a fuel line crack at the connection to the pickup of the right tank and sucked air until the engine quit before I noticed a problem existed. Could I switch to the left tank and restart, or will the system be air-locked (as suggested in AFP's warning)?

Thank / Ron B.
 
Flight Test

Hi Ron,

You won't know until you flight test. You have two options: design a flight test with appropriate risk mitigation considerations after you consult with the AFP engineer(s) or never run a tank dry because flight test data is unavailable. If a system failure occurs and you haven't tested, well you are definitely a test pilot at that point and have no choice but to finish the experiment!

FAR 23 certification criteria do require the ability to run a tank dry and restart, but those criteria do not apply to EAB types. While it is best if the fuel system is plumbed strictly in accordance with the designer's instructions, there are simply too many variables to to make any assumption, thus the requirement to properly test your airplane.

Unfortunately, every RV is unique, and while there are excellent lessons that apply (our community is an outstanding "brain trust"), each airplane has to be tested. Such is the nature of EAB aviation.

You might consider engaging with an EAA Flight Advisor or test pilot to help meet your objective. Drop a PM or email if there is anything I can do to help you out.

Cheers,

Vac
 
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Hi Ron,

You won't know until you flight test. You have two options: design a flight test with appropriate risk mitigation considerations after you consult with the AFP engineer(s) or never run a tank dry because flight test data is unavailable. If a system failure occurs and you haven't tested, well you are definitely a test pilot at that point and have no choice but to finish the experiment!

FAR 23 certification criteria do require the ability to run a tank dry and restart, but those criteria do not apply to EAB types. While it is best if the fuel system is plumbed strictly in accordance with the designer's instructions, there are simply too many variables to to make any assumption, thus the requirement to properly test your airplane.

Unfortunately, every RV is unique, and while there are excellent lessons that apply (our community is an outstanding "brain trust"), each airplane has to be tested. Such is the nature of EAB aviation.

You might consider engaging with an EAA Flight Advisor or test pilot to help meet your objective. Drop a PM or email if there is anything I can do to help you out.

Cheers,

Vac


Thanks for the great response Vac. AFP also recommends testing, however since my fuel system (including the AFP pump) is built per plans, perhaps someone on this forum has already tested this scenario and can share their experience? Nonetheless, I will test on my plane as you suggest.

Thanks again, Ron B.
 
I find my bladder endurance is much less than my fuel capacity so this is rarely an issue. But I've run a tank dry before. Never quite planned on it but was squeezing the last drop o a long leg. Had plenty in the other tank. Engine coughed and when I switched tanks was purring again before I could even hit the boost pump. Not FI which may have helped.
 
For those of you that want to run one tank dry (for whatever reason), you may want to take a look at this low fuel sensor. Ive just discovered this and got me thinking that if it was put into the tank at the very bottom or in the fuel line via a tee fitting (perhaps in the wing root area), it would give you advance notice that the "big bubble" is coming and that it is time to switch tanks, before that big bubble makes its way past the fuel selector. Just a thought.

http://www.aircraftextras.com/LowFuelSensor.htm

Bevan
 
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It cannot be good for a motor to go from cruise power to off to cruise power again.

If this were true, just imagine the abuse you put on your car's engine - Idle at the light until it turns green. Hit the gas and rev up to 4000 RPM. Push in the clutch, back to idle, shift gears/release clutch and back to 4000 RPM again - repeat, repeat... I won't belabor this, but most cars do this millions of times in their 150,000 mile life. Same goes for starting and stopping the engine withing a few seconds. The oil pressure doesn't even drop more than 10-20 PSI.

Larry
 
Running a tank

I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.
 
I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.

Yes running one tank to empty without using the other is dangerous, as in your situation you can't be sure the other side is useable. However, even a simple balancing of fuel mitigates this risk.

My typical fuel management is burn from the right tank until it reads 11 gal, switch to left until 5 remaining (if I need max endurance this is where I'd run to 0), then back to right tank to land which still has about 90 min at cruise.
 
An alternative to the sensor suggested by Bevan:
http://www.pillarpointelectronics.com/kits.html

These sensors are used fairly widely in the Glasair Glastar/Sportsman fleet. If you think there is lots of gnashing of teeth and hand wringing over fuel management here in the RV world, with only two tanks to choose from, you'd go nuts with a Glastar (with long range fuel) or Sportsman with its 4 fuel tanks and 2 header tanks! :)

For those who are curious... The low fuel sensor is often installed between the Aux and Main fuel tanks in each wing. Aux holds 10 gallons, main holds 15, so 25 gallons in each wing. The only way fuel gets from the Aux to the Main is by actuating an electric transfer pump. Since many of the Aux tank installations have no fuel quantity gauge one has to rely on timing the run-time of the transfer pumps. Fly on a main tank for an hour or so, then pump from the Aux tank to the Main tank and monitor the main tank fuel gauge to ensure fuel is transferring. Pretty simple. The optical fuel sensor is used to automatically turn off the transfer pump so it doesn't burn out by pumping air instead of fuel.

Header tanks are installed below each wing root to ensure unporting a tank, especially in a prolonged, steep descent, is a non-event. Fuel pickups are in the aft end of the main tanks so a prolonged nose-low condition could cause unporting if there is very little fuel in the tanks. The half gallon or so in the header tank ensures the engine keeps running.
 
I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.

Maybe if you wish to continue your run past 52 years you could invest in a fuel tester cup. Then you can check for water in the tank. This might even be an obvious thing to do when it hasn't been raining a lot. The other thing that might extend your life expectancy would be to check both tanks on the ground.
 
ice

...The other thing that might extend your life expectancy would be to check both tanks on the ground.
I may be interpreting what was written, but it sounds like the water froze in the tank, so testing the fuel might not have picked this up. I could be wrong of course. It's something that I don't believe I've ever experienced, but will keep an eye out for.
 
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