Running tanks dry in cruise

flyingron said:
Knowing how much more you have by running it dry doesn't tell you how much "usable" fuel you have. Tanks are calibrated from full down to zero usable, not from bone dry up.
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Are you getting hung up on the syntax perhaps? We've been discussing what we're calling running tanks dry, but in reality I think most if not all of us are really discussing running tanks until the engine quits. When I say that I ran tanks dry regularly, it is very likely those tanks were not actually bone dry.

In fact I know they weren't bone dry because there were a few times that I would run a tank until the motor quit, then I would lay a wing over into a hard slip and see whether the tank or my thigh muscles would quit first. I only did it a few times but my thigh always quit first after 15 minutes or so. No one ever plans to get into a fuel exhaustion kind of situation, but good to know that if I ever found myself in one, putting it into a slip could buy me enough time to get somewhere suitable to put it down.
 
My dad did this in a Turbo Arrow III heading west into Cortez, CO over the mountains. He was unconcerned, but I was concerned when the engine stumbled a couple beats. But that was it.
 
I was taught to run them dry and it has never been an issue for me. I just have no reason to die on this particular hill, and hell, I am not even flying these days.
 
Run them dry. 4 tanks in the Comanche with two selectors. Out of each of 15gal tips, 15gallons are usable. There is a gradual fuel pressure drop when they are going dry and then I do the switch. I do brief any passengers but I normally don't kill the engine. Also have a fuel computer that is very accurate, normally to a 1/10gal.
 
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 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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Late to the party here, Tim, but I would consider coordinated flying to be more important than high side / low side in the pattern.

The position of the ball in the sight gauge during a turn will point to the direction the fuel will slosh, no?

i.e., my full drink on the tray table in the airliner doesn't usually spill when the pilot banks.
 
bradg33 said:
That's the truth. The NTSB records are full of Viking accidents that happened because the pilot flubbed up fuel management. 5 tanks, 2 selectors, and gauges that only show the level of the selected tank. Later models went to a 2-tank setup, but lots of early 4-5 tank models still flying.
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I’ve got an ‘89 Viking. 3 tanks (Left, Right, and Aux), 1 selector (Aux, Left, Right, Off). Much simplified over the earlier models.

I do run my tanks dry on long cross country flights. As others have said, I want to know where my fuel is. Taxi on Aux. Take off on Left or Right. Switch to the other main after an hour. Switch to Aux an hour later and run it dry. Switch back to left or right whichever has less and run it dry. All my fuel including reserves are now in one tank, and i have the max usable. I see no good reason to have a couple of gallons sloshing around in the other tanks. Certainly wouldn’t want to count on those gallons at the last minute.

The POH prohibits landing on the Aux, so I want to run it dry first.

I do have a Shadin Mini-Flo fuel totalizer, so I have a good idea exactly how much fuel I have, assuming I don’t have some sort of unexpected and/or undiscovered leak...


Sent from my iPhone using Tapatalk Pro
 
EdFred said:
And how do you know that at some point you don't develop a fuel leak before the fuel gets to the fuel transducer? Or the transducer goes bad. Had that happen on my JPI. And if those are the resistive float units they still aren't *that* accurate.
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There will be a puddle on the ground if the tanks are leaking.
My fuel flow is my primary and it’s very accurate.
I have wing mounted mechanical gauges as well, in case I lose power or need to verify JPI.
So I have 3 different ways to know my fuel levels: senders, fuel flow and wing mounted gauges...Not counting old fashion method of just calculating it.


Tom
 
MooneyDriver78 said:
There will be a puddle on the ground if the tanks are leaking.
My fuel flow is my primary and it’s very accurate.
I have wing mounted mechanical gauges as well, in case I lose power or need to verify JPI.
So I have 3 different ways to know my fuel levels: senders, fuel flow and wing mounted gauges...Not counting old fashion method of just calculating it.


Tom
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Only be a puddle on the ground if the leak doesn't develop in flight. And I didn't say tanks. Could be leaking anywhere between the tank and the transducer. And if you are calculating it (fuel used/time), how are you getting a verified usage without dry tanking? GIGO. My JPI fuel flow meter (was once reading 26gph cruise should be ~13) and gauges (original piper sending units and needles) have both been off - one would stick at 1/2 tank. So how do you know what you've got is accurate?
 
EdFred said:
Only be a puddle on the ground if the leak doesn't develop in flight. And I didn't say tanks. Could be leaking anywhere between the tank and the transducer. And if you are calculating it (fuel used/time), how are you getting a verified usage without dry tanking? GIGO. My JPI fuel flow meter (was once reading 26gph cruise should be ~13) and gauges (original piper sending units and needles) have both been off - one would stick at 1/2 tank. So how do you know what you've got is accurate?
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I still have the wing mounted gauges.
 
@EdFred you keep coming up with these scenarios of what ifs... you have 4 tanks so you’ve got an advantage of staying on top of things but for a guy with 2 tanks, “What if” you burn all the fuel out of the left tank in X time... So you assume you have X fuel left in the Right tank... but ooooh ahhh a leak develops in that tank... It goes dry 20 minutes before you get to your runway... Whoops other tank is dry too... uh oh! Just a little Tongue-in-cheek there, bud.... Just trying to illustrate that nothing is fool proof... I understand your reasoning, and I can honestly say that if I wasn't nervous about deliberately causing my engine to lose power, I might use your method... I just don't see a reason with the type flying I do normally, which is well within the range of 1 to 1-1/4 tanks.

Also, side note, my POH says if you use that method, you should pull to idle to avoid an overspeed when the engine restarts... don't really understand the logic there, but it is in the POH...
 
flyingcheesehead said:
Those aren't for in-flight use, they're only designed to be accurate on the ground, where the Mooney sits 4.5º nose up.

Wing gauges are for ground, panel gauges are for flight.
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They are accurate enough, I’m not using them to figure out if I have 2.3 gallons. And I can always raise the nose 4.5° to get a more accurate reading. The lowest I gotten to is 14 gallons and that was sitting way too long.


Tom
 
FlySince9 said:
I understand your reasoning, and I can honestly say that if I wasn't nervous about deliberately causing my engine to lose power, I might use your method... I just don't see a reason with the type flying I do normally, which is well within the range of 1 to 1-1/4 tanks.
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There isn't a reason do to it in every type of flying, only some. If you don't have a reason to do it, don't. But at the same time being its nothing to be nervous about. I understand those who have never done it being nervous. People who have never been on a roller coaster are usually nervous their first time too. Doesn't mean its unsafe.

Also, side note, my POH says if you use that method, you should pull to idle to avoid an overspeed when the engine restarts... don't really understand the logic there, but it is in the POH...
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Constant speed prop I'm guess? As the engine torque ramps down, the prop governor is going to open up to try to maintain the same RPM. When the engine comes back, the prop pitch is going to be much more course than it was when the engine stopped making power, which could lead to the engine overspeeding until the governor catches up.[/user]
 
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FlySince9 said:
@EdFred you keep coming up with these scenarios of what ifs... you have 4 tanks so you’ve got an advantage of staying on top of things but for a guy with 2 tanks, “What if” you burn all the fuel out of the left tank in X time... So you assume you have X fuel left in the Right tank... but ooooh ahhh a leak develops in that tank... It goes dry 20 minutes before you get to your runway... Whoops other tank is dry too... uh oh! Just a little Tongue-in-cheek there, bud.... Just trying to illustrate that nothing is fool proof... I understand your reasoning, and I can honestly say that if I wasn't nervous about deliberately causing my engine to lose power, I might use your method... I just don't see a reason with the type flying I do normally, which is well within the range of 1 to 1-1/4 tanks.

Also, side note, my POH says if you use that method, you should pull to idle to avoid an overspeed when the engine restarts... don't really understand the logic there, but it is in the POH...
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Yeah, if you're never flying far enough to even switch tanks the whole discussion doesn't apply. 90%+ of my trips I dry tank at least the tips.
 
MooneyDriver78 said:
The possibility that
1. I spring a fuel leak
2. Fuel senders stick
3. Wing mounted stick
All the above in flight... I am more worried about colliding with a UFO....



Tom
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Well I did have a flight where 100% of my fuel information (stuck gauges, and bad info from fuel flow) was bad. It happens.
 
The law of primacy.
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That you'll believe over scientific evidence to the contrary what some inexpert instructor told you three decades ago?
 
flyingron said:
That you'll believe over scientific evidence to the contrary what some inexpert instructor told you three decades ago?
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One of the most dangerous things in aviation, IMHO. People who refuse to accept/believe things because an instructor once told them otherwise and they can't let go of it.
 
ElPaso Pilot said:
Late to the party here, Tim, but I would consider coordinated flying to be more important than high side / low side in the pattern.

The position of the ball in the sight gauge during a turn will point to the direction the fuel will slosh, no?

i.e., my full drink on the tray table in the airliner doesn't usually spill when the pilot banks.
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True dat...but I don't hesitate to kick the plane into a full deflection slip of I'm high on final...or base to final...and if flying a LH pattern I always kick the nose to the right when I do this.
 
I'd like to hear from one or more of the many IAs we have here on what running a mechanical fuel pump dry does to the diaphragm. My guess is that an argument may be posed that it isn't "dry" long enough to matter. I'm just asking.
 
tmyers said:
I could be wrong, and often am, but I think most of us are simply comfortable with what we were taught in primary flight school and that is ingrained in our brains. Not gonna change anyone's way of thinking on the subject.
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Likely some of that. But I've interpreted this thread as being more of a debate between:

Those who have done it, know how well it works, and understand that it's no big deal.

vs.

Those who haven't (or at least haven't more than once or twice) and are skeeerd.
 
EdFred said:
The only way to know an accurate fuel burn is to run a tank dry.

Scenario: You always leave a half an hour of fuel in your fuel tank and don't dry tank. But how do you know there's a half hour of fuel in your tank? Maybe the primer line stuck open, maybe the fuel flow sender isn't accurate. So, you launch on your cross country flight in my plane. You have 4 tanks. Two wing tanks, and two tip tanks. So your plan is to land with 2 hours of fuel (out of possible 7 hours of fuel). You burn off the tip tanks, and leave what you believe to be a half hour of fuel left in each one. You burn off the left main, and leave what you believe to be a half hour of fuel left in the tank. But what you didn't know is that your draining more fuel from the tanks than you expected, and you made the switch, not with 30 minutes of fuel left in the tank, but 30 seconds of fuel left in the tank, and you happened to switch over just before it was going to run out. But you "know" there's 30 minutes left in each of the three tanks.

So you're flying along on the right main, and you have planned that you will be landing with just short of 30 minutes of fuel in the right main tank. Perfect, you still have 90 minutes of fuel in the other tanks. So you're on a long straight in and about 10 miles out. No problem, you planned have at least 25 minutes in the last tank, and another 90 in the other three. Suddenly, the engine quits 6 minutes short of the field. You freak out because you have never dry tanked. You start to lose altitude, and finally switch to the left tank. Engine comes back to life, and then quits only a few seconds later. You switch to the left tip tank. Again the engine comes back to life, and then quits shortly thereafter. Last tank, same thing. You can see the runway, but it's slowly disappearing behind the trees.

NTSB report: No post impact fire. No fuel found in any of the tanks.

Now, had you run any one of those tanks dry, you would have known that the fuel burn was higher than what you had planned for, and your almost 2 hours of fuel reserve was in fact 2 minutes. You could have stopped 16 airports back, and you would have been able to see your family waiting for you at your destination rather than them seeing you disappear into the trees 3 miles short of the runway.

So how exactly is your way safer?
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I agree. I used to run tip tanks till I had about 30 minutes remaining ,then back to mains. But I always time them so I know what should be used. One time, over mountains the engine quit when I should have had 30 minutes left. My fuel burn was much higher because I didn't have it leaned as normal. Now I just run out the tips first, and by timing them, I know when to expect empty, and when I see the fuel pressure bounce, change tanks. This confirms my expected fuel burn rate each time.
 
I NEVER run my tank dry in cruise! But.....oh I have an old 150f and both tanks are connected together and the selector is only On/Off. Run one tank dry in cruise and I may as well just flip that selector!
 
Timbeck2 said:
I'd like to hear from one or more of the many IAs we have here on what running a mechanical fuel pump dry does to the diaphragm. My guess is that an argument may be posed that it isn't "dry" long enough to matter. I'm just asking.
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Not an IA or A&P, just a schmuck. But I did once have a phone conversation with one of the developers of the aux tank STC that was installed on the banner plane I was flying at the time.

The aux tanks had electric transfer pumps which were controlled by a pair of momentary switches. The assumption was the switches had to be momentary so you wouldn't forget and leave them on and burn up the pump. But in that plane the switches were installed on each side overhead panel near the fuel gauges and the pumps took about 15-20 minutes to move 10 gallons. So you had to fly holding a switch on the overhead panel for 15 minutes every time you needed to get to your aux fuel. Needless to say we got our hands on some small medical elastic bands that were grippy enough to hold the switches up.

I don't recall why I was on the phone with the aux tank guy, but while I was talking to him I asked about the concern of running an aux tank dry and burning up the pump. He explained that the pumps need pressure on the input side in order to push fuel through to the output side. When there is no more pressure on the input side i.e. no more fuel coming in, the fuel that's in the impeller will not pump out and instead just sits there in the spinning impeller. So it never really gets dry. Leave it running long enough, and it will eventually heat up and burn the pump up, but it would take an hour or more. Go ahead and run em' dry and don't worry about it was pretty much what he told me.

Of course that was in reference to the particular pumps used in that particular STC. I have no idea if other fuel pumps work the same way.
 
Timbeck2 said:
I was specifically referring to a mechanical/engine driven pump.
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Understood. But knowing that its possible to build a fuel pump that can run for many minutes with no fuel flowing through it without failing, it does make one wonder why an aircraft manufacturer would utilize a fuel pump that can be damaged by running for a few seconds without any fuel flowing.
 
EdFred said:
And how do you know that at some point you don't develop a fuel leak before the fuel gets to the fuel transducer? Or the transducer goes bad. Had that happen on my JPI. And if those are the resistive float units they still aren't *that* accurate.
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If it’s primary it’s not calculating from fuel flow and JPI recommends the digital senders. There is also another setup with CEIS senders that is accurate to .1 gal or some ridiculous number like that if you with their digital senders.
 
That's what I have. I have digital CIES senders with an Aerospace Logic digital fuel gauge. In the near future, I'll also have an Electronics International engine monitor with digital fuel flow.
 
Timbeck2 said:
That's what I have. I have digital CIES senders with an Aerospace Logic digital fuel gauge. In the near future, I'll also have an Electronics International engine monitor with digital fuel flow.
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I have the JPI for fuel flow and going with your set up this annual
 
Juliet Hotel said:
Understood. But knowing that its possible to build a fuel pump that can run for many minutes with no fuel flowing through it without failing, it does make one wonder why an aircraft manufacturer would utilize a fuel pump that can be damaged by running for a few seconds without any fuel flowing.
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I never said anything about damage, I just want someone with more knowledge than I have to explain what happens (if anything) to a mechanical engine driven fuel pump at high rpm to be run dry.
 
Timbeck2 said:
I never said anything about damage, I just want someone with more knowledge than I have to explain what happens (if anything) to a mechanical engine driven fuel pump at high rpm to be run dry.
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It’s a pretty simple device. I can’t imagine that it would even notice if it were dry for a few seconds.

Screen Shot 2019-03-19 at 7.19.36 AM.png
 
Timbeck2 said:
I never said anything about damage, I just want someone with more knowledge than I have to explain what happens (if anything) to a mechanical engine driven fuel pump at high rpm to be run dry.
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Well with all due respect, if you're not talking about damage then what are you talking about? Are you concerned that running a fuel pump dry for a few seconds might cause the fuel pump to become stronger and more evil? Or make it join a religious cult?
 
SOP in my Bonanza right out of the manual, run off left main 1 hour then run the other 3 tanks dry. This leaves the left main full with 17 gallons usable remaining because of the pressure carb return line.

If I'm paying attention I can see the fuel pressure fluctuation about a minute before it quits but if I miss it and it quits I bet it's less than one second before I've switched tanks and it's running again. With non pilot passengers I set a timer and switch early. I really like looking in a dry tank to inspect for debris and then seeing that it takes the correct amount to fill. In level flight I can use all 20 from the aux and right main, I think the 17 usable is for turns and approach attitude.

Dan
 
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Great discussion. I think I'll stick with the C-172N I flew yesterday. 50 gal usable, 8.3 gal/hr in cruise = about 6 hours fuel. Put the selector on Both and fly. A 3 hour bladder says that if I gas up every time I land on a long XC I'll never run out of gas in the plane. The club's other C-172 and C-182 are similar, more gas than bladder. :p

I did have to worry about this when the club had its Arrow, but that had far more range than the longest XC flights I took with it, too.

Have fun!
 
This is a great discussion. Learning on Cessnas with "Both" selectors, this is not something that I had to worry about, but it's a good procedure in certain planes and cases. I've starved a plane (on purpose, over the airport) of fuel before to see how it restarts. Complete non-event, even if you let it windmill for a few seconds. I've also had a fuel sender fail on me in a low-wing 2 tank airplane. Ended up using as much fuel as I dared in that tank before switching to the other to get to destination with a known quantity of fuel in the other tank. In retrospect, i should have taken it to empty, but this was before I experimented with aerial restarts.
 
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