Running tanks dry in cruise

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zbrown5

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Zach
looking for thoughts and words of wisdom on running a tank dry on a long cross country. I’ve never done this before. But, how else to maximize fuel range and leave the max amount in the last tank for approach, landing, missed approach, etc? Is the method to run her til the engine quits and immediately switch tanks? Any thing to be worried about from a sediment/ contamination standpoint or getting air in the line such that the engine won’t re-light? How much uncomfortable silence is expected before she fires again? Plane is a 63 debonair.
 
If you're going to do this, experiment over an airport.

In my carbureted RV-6, I try to catch the fuel pressure drop when the tank runs dry but have had the engine stop when I didn't notice the pressure fluctuation. A quick tank change and a few seconds on the boost pump and the engine comes back to life. 5-10 seconds, tops.

YMMV.
 
zbrown5 said:
looking for thoughts and words of wisdom on running a tank dry on a long cross country. I’ve never done this before. But, how else to maximize fuel range and leave the max amount in the last tank for approach, landing, missed approach, etc? Is the method to run her til the engine quits and immediately switch tanks? Any thing to be worried about from a sediment/ contamination standpoint or getting air in the line such that the engine won’t re-light? How much uncomfortable silence is expected before she fires again? Plane is a 63 debonair.
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IBT-NTSB-R !!
 
In my K35 Bonanza I routinely ran the aux tanks until the fuel pressure needle started to quiver. If I was ready for it and switched at the first twitch of the needle, there was usually no noticeable stumble or burp from the engine. The fuel injection system pulled fuel from the aux tanks at about double the engine's fuel consumption, and returned the excess to the left main. So every minute I could squeeze from the aux tanks meant two minutes of usable fuel for maneuvering and landing.
 
Kenny Phillips said:
Note that the author doesn't suggest that you use that as a normal operational procedure, but that you do it to find out your actual usable tank capacity.
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He says he has used it routinely on maximum range flights. That is mentioned near both the beginning and end of the article.
 
Kenny Phillips said:
Note that the author doesn't suggest that you use that as a normal operational procedure, but that you do it to find out your actual usable tank capacity.
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Yupp, whether you use this routinely or not, the first time I am trying this, I am going to be on top of an airport just to see how she reacts
 
FAR 23.955(e) Multiple fuel tanks. For reciprocating engines that are supplied with fuel from more than one tank, if engine power loss becomes apparent due to fuel depletion from the tank selected, it must be possible after switching to any full tank, in level flight, to obtain 75 percent maximum continuous power on that engine in not more than -
(1) 10 seconds for naturally aspirated single engine airplanes;
(2) 20 seconds for turbocharged single engine airplanes, provided that 75 percent maximum continuous naturally aspirated power is regained within 10 seconds; or
(3) 20 seconds for multiengine airplanes.​

FAR 25.951(a) Each fuel system must be constructed and arranged to ensure a flow of fuel at a rate and pressure established for proper engine and auxiliary power unit functioning under each likely operating condition, including any maneuver for which certification is requested and during which the engine or auxiliary power unit is permitted to be in operation.
(b) Each fuel system must be arranged so that any air which is introduced into the system will not result in -
(1) Power interruption for more than 20 seconds for reciprocating engines; or
(2) Flameout for turbine engines.​

The earlier CAR 3.4221(d) had an even stronger requirement for single-engine airplanes:
If an engine can be supplied with fuel from more than one tank, it shall be possible to regain the full power and fuel pressure of that engine in not more than 10 seconds (for single-engine airplanes) or 20 seconds (for multiengine airplanes) after switching to any full tank after engine malfunction becomes apparent due to the depletion of the fuel supply in any tank from which the engine can be fed. Compliance with this provision shall be demonstrated in level flight.​
 
Ravioli said:
I wonder what @Katamarino thinks of this topic. He's probably leading the league for PoA extended range piston single flight.
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To be honest, not a huge amount of experience on this one. On yesterday's flight, my aircraft was set up with 5 tanks. 4 in the wings - 2 aux tanks that are pump fed into the main tanks (so you can run them dry into the mains) and the ferry tank. The ferry tank (nominally 160 gallons but I have not been able to fit that much in to it!) is fed into the left main by two redundant fuel pumps. While I did run the ferry tank dry, it doesn't feed the engine directly (although can in an emergency), so it wasn't an issue; I landed with about 15-20 gallons each side in the mains. Going to dip the tanks this morning and see exactly.

If I had needed to, I would not have been too concerned about running one main dry and being ready to switch straight over to the other. I have done this in a Maule in Egypt and it was a non-event. A bit nerve-racking through.
 
Brad Smith said:
Some aircraft have hot start issues and may not relight quickly or the remaining amount in the tank is water. You figure it out. I don't like running the tanks dry in any aircraft and certainly wouldn't reccomend it.
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Not an issue as water is denser than avgas.

I do it fairly commonly on max range trips. Much more comfortable landing with 12 gallons when I know that all 12 gallons are in the selected tank vs split across two. I have a very accurate totalizer (usually accurate to the half gallon on 92 gallons usable) and fuel tank gauges that are much less accurate (within 5 gallons, probably less but certainly not 0.5 gallon accurate).

It’s no big deal to switch tanks at the first sign of a burble. Just be prepared for it, have boost pump on and brief any passengers so they don’t freak out. On my plane, there is virtually no risk of not restarting even if I let the engine fully die out (which I don’t) since the prop will keep turning, it still has spark and all you need to do is reintroduce fuel and it keeps on going like nothing happened.

It’s a total non event and makes for a much safer approach and landing. I don’t do it routinely or in IMC simply because I have higher fuel reserves usually and it would be a bad idea to have one dry tank and one with 25+ gallons in it.
 
I do it fairly often myself. Never had an issue with the engine coming back to life. However, I try not to do it if I have passengers. Although I may brief the passenger about it if I don't think they'll be particularly bothered by it.

Like others, I tend to watch the fuel pressure and try to switch just before the sputter.
 
I don't intentionally run a tank dry with passengers onboard for obvious reasons.

Solo in a C-340 once, I was at altitude and set up for cruise. I had more than enough fuel in the main tanks for the short trip so I decided to see how much was in the auxiliary tanks. I switched, and 15 seconds later I found out how much air was in the auxiliaries..... I mean both engines quit like the mags had been shut off.

Quickly switched back to the mains and both engines came back to life within seconds. And then a quick check of the seat.....clean.!!! :lol::lol:
 
RudyP said:
Not an issue as water is denser than avgas.

I do it fairly commonly on max range trips. Much more comfortable landing with 12 gallons when I know that all 12 gallons are in the selected tank vs split across two. I have a very accurate totalizer (usually accurate to the half gallon on 92 gallons usable) and fuel tank gauges that are much less accurate (within 5 gallons, probably less but certainly not 0.5 gallon accurate).
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I’m curious to know what input feeds your totalizer versus your tank gauges that accounts for the disparity between them.
 
I suppose the fuel flow transducers are more accurate than the fuel level transducers. So, if the totalizer is set to the fuel quantity when you sticked the tanks, and that matched the gauges, the inflight totalizer fuel remaining would typically be more accurate than the fuel gauge.

Suppose + 2 if's = SWAG. YMMV :)
 
Regardless of my opinion on the subject, I was taught to run the tank dry. If you are keeping track you should know within a five or ten minutes of when you need to switch. As soon as you hear a slight stumble switch tanks. Did it for years with no issues, YMMV.

Sent from my SM-N920V using Tapatalk
 
kyleb said:
If you're going to do this, experiment over an airport.

In my carbureted RV-6, I try to catch the fuel pressure drop when the tank runs dry but have had the engine stop when I didn't notice the pressure fluctuation. A quick tank change and a few seconds on the boost pump and the engine comes back to life. 5-10 seconds, tops.

YMMV.
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Would be the longest 5-10 seconds of your life


Sent from my iPad using Tapatalk
 
I'm probably an "overswitcher."

I fly on the tank the minute hand of my watch is pointing to. So I switch every 30 minutes (~5 gallons). It's a habit from training in low wings.

Probably the extreme opposite of flying a tank dry, right?
 
Passengers are not amused. Very important to brief them. I have done it maybe 3 times on long x/c. No problems. I generally try to stop every 3 1/2 to 4 hours anyway, and my plane's range can easily exceed 6 hours, so stopping for additional fuel is not a problem. I always try to land with 1 hour reserve which allows me a margin for bad weather or headwinds more than forecast.
 
The DA40 has a max imbalance of 8 gallons. Since it burns about 9-10gph and I never land with less than an hour of gas, running a tank dry in that plane would mean I'm doing something very wrong.
 
When I was working from Georgia to Ohio to Wisconsin to Louisiana and all points in between, I dry tanked at least once a week. It added over 30 minutes of reserve. Since my aircraft is gravity feed, I'd alway dry tank the left tank if going into a standard pattern airport. That way the tank with fuel was on the high side when flying the pattern. Needed? I don't know, but I assumed it was a easy precaution to take.
 
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Ravioli said:
I suppose the fuel flow transducers are more accurate than the fuel level transducers. So, if the totalizer is set to the fuel quantity when you sticked the tanks, and that matched the gauges, the inflight totalizer fuel remaining would typically be more accurate than the fuel gauge.

Suppose + 2 if's = SWAG. YMMV :)
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It may just be semantics but that sounds more like a fuel calculator than the totalizers that I am familiar with.
 
SkyDog58 said:
It may just be semantics but that sounds more like a fuel calculator than the totalizers that I am familiar with.
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Probably - Maybe fuel computer? Like a Shadin or Matronics FuelChec
 
timwinters said:
When I was working from Georgia to Ohio to Wisconsin to Louisiana and all points in between, I dry tanked at least once a week. It added up to 45 minutes of reserve of which I only counted on 30 of. Since my aircraft is gravity feed, I'd alway dry tank the left tank if going into a standard pattern airport. That way the tank with fuel was on the high side when flying the pattern. Needed? I don't know, but I assumed it was a easy precaution to take.
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Interesting thought, never thought about it, but I guess it could happen that you are low on left tank, and the right one is already dry, during your left hand pattern the gas could go away from the lines. That would definitely be a bad day
 
John Deakin has a strong opinion that you SHOULD run them dry. Me, I try to avoid it. The engine is SUPPOSED to always restart once the fuel is restored and frankly I've never experienced otherwise, but it does come for a tense few seconds.

I
 
This topic has led me to do some fuel tank measuring on my new airplane:

With both tanks completely empty and the plane sitting on all three wheels, I'll add one gallon at a time in each tank and measure the depth of the fuel with a dipstick. With the stick vertical and touching the bottom of the tank and the rear of the filler neck, I'll make marks for every gallon in each tank, alternately. I'll also take a photo of the respective fuel gauge after each gallon.

Since my useful load is restricted by my body weight being 70 pounds higher than it was last time I flew a C-140 (getting old and fat sucks), I'll need to know exactly how much fuel is in my tanks in order to stay under max gross weight with a (skinny) passenger!

Following that endeavor, I'll fly the plane on a smooth day and run each tank dry (on separate flights, of course) to see how the fuel gauge indicates in the level, in flight attitude. That will also make me familiar with how the plane reacts with an empty tank.

I plan to take my little airplane on many long flights in the future, so fuel management will be a primary consideration in my flight planning. I believe in using every drop of fuel to get where you are going and I also believe in knowing exactly how much fuel you have in order to make it.

This should be fun. :D:cool:
 
simtech said:
I've come close to running a tank dry and to be honest my thoughts were at that time, if I run this tank dry and I have a problem suddenly with the next tank I'm screwed. So I just manage the tanks evenly and if I have to stop I stop.
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Some switch too much as in L-R-L-R rather than

L-R then leave it on right for the next cycle since you are now balanced (L-R-R-L-L-R). Never got to the last one in the Tiger previously, but changed 8 gallon intervals which was near an hour in cruise.
 
If the flight is more than two and a half hours long I'm dry tanking not once, but twice, because I always burn off the tips first and I have about 2 and 1/2 hours of fuel in the tip tanks.
 
simtech said:
I've come close to running a tank dry and to be honest my thoughts were at that time, if I run this tank dry and I have a problem suddenly with the next tank I'm screwed. So I just manage the tanks evenly and if I have to stop I stop.
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This. Good grief. Stop for fuel or get a longer range plane. ;)
 
At the 135 carrier I flew a piston twin for, our SOP was to run a tank dry.
 
Rockymountain said:
This. Good grief. Stop for fuel or get a longer range plane. ;)
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It's really not a big deal, at least in my plane it's not.

I have an EI FP5-L fuel flow and when it starts "wagging out" I switch the tanks. Typically the engine doesn't even sputter.

But, on the rare occasion that I miss it, the engine comes back to life in just a few seconds, five on the outside. But I know exactly where my fuel selector is without hunting for it! :)

Edit: By "wagging out" I mean the flow will start oscillating wildly. I typically burn about 11 GPM in cruise and, as the fuel lines start sucking air, the flow will drop to 5...jump up to 20...drop to 3...etc. My fuel flow transducer is on the primary side of the gascolator so, since it is a mini-tank, the actual flow to the engine is yet to be disrupted and it doesn't even sputter.
 
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zbrown5 said:
looking for thoughts and words of wisdom on running a tank dry on a long cross country. I’ve never done this before. But, how else to maximize fuel range and leave the max amount in the last tank for approach, landing, missed approach, etc? Is the method to run her til the engine quits and immediately switch tanks? Any thing to be worried about from a sediment/ contamination standpoint or getting air in the line such that the engine won’t re-light? How much uncomfortable silence is expected before she fires again? Plane is a 63 debonair.
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-- it's a certification requirement for the engine to re-start
- with a fuel totalizer and a fuel pressure gauge you will know when the tank runs dry before it happens and you can change tanks the second the pressure drops. The engine will maybe stumble and surge for a second, but it will never shut down alltogether
- tell your passengers that that the engine will lose thrust for a couple of seconds while you change tanks
- don't touch nothing ! You can flip on the boost pump if it makes you feel better, but leave the throttle and mixture alone
- NOT running a tank dry on a long cross country is the unsafe thing to do.

There I said it.
 
The Owners Manual for my 1970 Mooney says to takeoff and fly for one hour; switch tanks and fly that tank dry; then switch back to the first tank. Keep track of the flight time on the second tank, you niw have one hour's less flight time left.

But I switch every hour, wjth 2-1/2 hours+ in each tank. Will come really close to 3 hours each. I've run a tank dry twice, once by accident, and it started right back up.
 
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