What happens when a tank empties on a fuel injected engine

flyingron said:
What makes no sense? You can't pump out of an empty tank and pumps won't draw fuel if they're sucking air. Basic experiment: get two straws. Stick one in a glass of your favorite beverage. Leave the other out in the air. Try sucking from both at the same time.
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We're talking about a gravity fed system, right? It's a simple concept. Do you ever tilt a beer can up to get the last swallow?
 
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brcase said:
A few years ago I did a test on a 1966 182 (O-470), because I wasn't entirely confident the Usable fuel was as published. So on a Cross country flight I planned it such that if ran on the Right tank, IIRC, so that it was nearly empty at my destination (my home airport). Then at about 4000 feet I orbited the airport until I ran the right tank dry...
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Pelican's Perch #7:
Run That Fuel Tank Dry!
John Deakin

AVweb's John Deakin takes aim at yet another OWT (Old Wive's Tale). While running a fuel tank dry in your recip powered plane may serve to increase your heart rate, John explains why it's not such a bad thing at all, and it is probably a really good idea for most of us. In fact, John explains why it's one of the first things you ought to do with a new plane and how it could save your life someday...

https://www.avweb.com/news/pelican/182044-1.html
 
So when you get air in the lines because of fuel starvation, then switch tanks, does the boost pump take care of priming the pump and pushing the air through the system? Will the engine driven pump do the same thing if the prop is windmilling? What condition would cause the engine not to fire (yes, assuming that there was fuel in the other tank!)? No gravity feed in my plane. I definitely see the merit of trying this out while orbiting over a nice friendly airport.
 
Again, the certification requirement requires the engine to restart within 10 seconds on a non-turbo'd single engine plane after the fuel is switched to a tank with fuel in it. So to respond to Jim's comment, the engine stops, but it should come back if you switch to a tank with fuel in it.

Note that ten seconds can seem like forever. As I stated a dozen replies ago, the boost pump may be required and even if not, it may speed up the situation.

Really about the only difference between a carb'd engine and a fuel injected one is that the engine will die faster when the tank is run dry (or switched off0 as there's no reservoir of fuel in the carb bowl.
 
N1783M said:
I was cruising at 10,500
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Well, there ya have it. I mistakenly remembered an AD, but later found that it only affects 172s, and apparently not 182s.
The one requiring switching to single tank in cruise, above 5000'msl.
 
GlennAB1 said:
Fuel management.
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I used to fly 172 with both option, no one ever said to switch tanks and run it left or right as a best practice. In all my flights I saw the both option drains the fuel from both tanks and they were pretty close. Why bother changing tanks when there is both option? What am I . Missing?

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WannFly said:
I used to fly 172 with both option, no one ever said to switch tanks and run it left or right as a best practice. In all my flights I saw the both option drains the fuel from both tanks and they were pretty close. Why bother changing tanks when there is both option? What am I . Missing?
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From the C-172 TCDS (3A12), required placards:

K. Near fuel selector valve on models with serial numbers 28000 through 17258855 [all 172s delivered before November 20, 1969], except those with Cessna Kit No. SK-172-31B or SK-172-32 installed:
"SWITCH TO SINGLE TANK OPERATION IMMEDIATELY UPON REACHING CRUISE ALTITUDES ABOVE 5000 FEET."​

The referenced Service Kits (-31 for standard tanks, -32 for long-range tanks) add vent tubes to the fuel lines in the aft doorpost area. "This change was made to prevent the possibility of vapor formation in the fuel lines when operating at high altitudes under certain unusual conditions of temperature and humidity."

Cessna 172 aircraft built after November 1969 have the vent tube installed at the factory, and do not require the placard.
 
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WannFly said:
I used to fly 172 with both option, no one ever said to switch tanks and run it left or right as a best practice. In all my flights I saw the both option drains the fuel from both tanks and they were pretty close. Why bother changing tanks when there is both option? What am I . Missing? Tapatalk
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Fuel management; monitor fuel quantity. Why would you purposely leave it on both and totally deplete one tank? That doesn't sound like a best practice.
 
WannFly said:
I used to fly 172 with both option, no one ever said to switch tanks and run it left or right as a best practice. In all my flights I saw the both option drains the fuel from both tanks and they were pretty close. Why bother changing tanks when there is both option? What am I missing?
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From a post I made in January:

The single-tank operation on old 172s was a result of some engine power loss events that Cessna blamed on vapor lock in the fuel lines under certain conditions of altitude, temperature and humidity. What humidity does I have no idea. Anyhow, they had two service bulletins on in the late '60s and a service kit to fix it. That kit involved installing tees in the vent crossover tube above the headliner behind the front spar carrythough and a couple more in the fuel lines above the doorsills where the fuel moves out of the tanks and back and down behind the aft doorposts. The idea was to let any vapor bubbles that formed to escape into the vent line.

Cessna tested the original system using clear plastic lines and a movie camera to try to spot how the vapor formed and what it did to the fuel flow. They weren't able to get vapors to form on their own, so they had to introduce some air and see what it did. They designed the fix based on that. They never were able to confirm that the power loss complaints were due to vapor lock in that area, but that was the most likely spot.

From their info in the service bulletins, I inferred that vapor might form there if hot and high enough, since the head pressure is at a minimum there. A bubble in the line might want to move upward at the same rate as the fuel is travelling downward, so it is, in effect, a partial blockage in the line. That, I think, is why it was OK in climb (lots of fuel flow at high power that carries the air to the carb where it is vented through the bowl vent) or in single-tank operation in cruise (maintains a good rate of fuel flow in the line, twice that it would be if on Both). Cessna installed the modified system in 172s from 1969 and on, IIRC.
 
GlennAB1 said:
Fuel management; monitor fuel quantity. Why would you purposely leave it on both and totally deplete one tank? That doesn't sound like a best practice.
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My question is , how do u leave in both and deplete just one tank unless there is something wrong? I understand monitoring fuel and how it's being consumed is required.

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