How Long Will the Engine Run with Fuel Selector OFF

[Hank]

Anthony,that's why you need to know how much fuel is in each tank before departure, and how much you use from each in flight. I try to keep my hour reserve all in ine tank; they're each good for about 2:30 at cruise, but the one with takeoff and climb runs a little shorter (it was 2:25 to the first cough once). My longest leg so far was 4:40, and I had 11 gallons left, or 1:12-ish. Always land on the fullest tank, i.e., the one with the reserve hour in it.

[carusoam]

Shaking my head, I didn't know what I didn't know...  (That's why I'm sharing this)

I wish we had MS back in Y2K...

checked the fuel in the tanks, visually, and was doing pattern work testing a new generator installation.  Brief flights.

thinking there has got to be enough fuel with two tanks.  If one runs out, go to the other....

Could of used a stick.  It would have said zero...

Could have used a totalizer if I had a few AMU...

Could have used my head.  Got distracted by the 'just switch tanks' idea....

the switch over took about 10 seconds.  Kind of a long 10 seconds...

Best regards,

-a-

[MyNameIsNobody]

19 hours ago, CJpilot316 said:

In a 172, within a minute or two of startup.

Also in a 152.  I was training with my 1000 hour 19 year old instructor and when I pulled mixture to cut-off it came off in my hand...He went "I don't know what to do"...I said "I will shut the fuel off".  He smiled and the plane shut down in about a minute.  Also had fuel prime come off while on night flight cross-country...

[MitchS]

I am another one that sets the fuel as part of the pre-flight.  I still pull the drain on both sides, but I make sure that I leave it at the proper tank before I sit down.

One funny thing in the checklist that came with my plane was a warning about "Do not change fuel selector just before takeoff".  I found that one interesting.

[carusoam]

Another thing related to pre-flight and fuel, including both tanks...

1) The pull ring does empty from the tank that is selected...

2) It makes sense to drain fuel from both sides.  In the event water has entered the tank that you are not drawing from.

3) The challenge with using the pull ring is...  The fuel that is sampled, lands on the ground.  If water is present, the pilot may not know it, and may not have cleared it all.

4) Rumor says: a sample cup can be used in the central drain under the fuselage to capture a sample to see if water is present.  Go back inside to switch the valve, sample again.

5) there are a couple of things that go wrong at the top of the tank that allows water to enter.

  - Seals age

  - Caps get mis adjusted

  - Mild steel fuel necks rust

This idea makes more sense after you are parked outside during a rainstorm.... 

Best regards,

-a-

[M20F]

13 hours ago, DXB said:

It makes sense to me that the answer here would be longer for carb'd engines with  float bowl reservoirs than fuel injected.  It would be interesting to kill the engine this way at cruise power (on the ground, of course) with an engine monitor that you could then pull the data from.  In theory, fuel pressure and fuel flow annunciators should give some decent interval of warning, at least in the carb'd setting, before the bowl empties and the engine quits?  This would also be nice warning right after the tank empties and might also be a tool to run one tank completely dry intentionally on a carb'd plane  to maximize range without having to deal with the stumble while you switch tanks?

On a related note, my C STILL has intermittent issues with the fuel pressure dropping to 0.0 in climb at WOT after I turn off the boost pump.  I've come up with detailed trouble shooting lists and begged a good MSC and one other shop to investigate, only to get the same response: "meh...carbed low wing planes do that."   What reassures me more is that when I pull the data off the JPI in every case, the WOT fuel flow doesn't budge when fuel pressure goes to zero.  I've only gone a max of 30 seconds with the 0 FP reading before I noticed and turned the boost pump back on, so the bowl might not empty, but the fuel flow should have dropped if pressure was really zero.  I think it's just that the pressure transducer sits much higher than the main fuel line and/or there is intermittent vapor lock in the fuel pressure line.   Sample FF vs FP trace below.   

I usually get the same issue on my F climbing through 14000 feet or so.  Intermittent vapor lock is what I have determined and the boost pump fixes it.  It fixes itself usually prior to leveling off.  The first few times it did it though it got my attention.  

How long it takes for fuel to kick in when you run a tank dry is interesting between models as well.   I used to fly a Cherokee 6 and if you ran the inboards dry and switched to the outboards it really took forever for it to kick back up.  

[Marauder]

On February 16, 2016 at 2:16 PM, Marauder said: I can tell you what I experienced. It was the reason I changed my checklist to include the "fullest" tank a couple of times.

I got distracted as I was doing the pre-start checklist. I had started moving the handle and let go of it to help a passenger with their seat belt. It ended up in the "off" position.

It was after a warm start. It started, I did a systems check including a quick mag check. I entered the runway and got to around 50 KIAS when it quit. So, my guess, 2 maybe 3 minutes.

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Holy Guacamole Batman! I'll bet you check it now!  

You betcha. I get cold sweats thinking about what could have happened.

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[Hank]

3 hours ago, daver328 said:

And I never "whip it around hard" lining up with centerline before takeoff, nice and easy - boost pump already on before making that line-up turn ...

I used to back taxi, make a hard right turn and pause briefly to check the DG and passengers, glance at the radio/GPS, hit the mic and go.

[Wildhorsesracing]

I made it to ~50 ft AGL, right after I retracted the gear it ran out of fuel.  In my case the selector wasn't in the off position but "almost" in the fullest tank position.  At 1st glance it looked like it was pointed at the fullest tank but was not fully in the detent. 

Once the engine went silent I checked the boost pump: it was on so I decided to switch to the other tank, that's when I realized it wasn't in the full tank detent.  I now put my keys in the selector when I am doing the pre-flight and before the key goes in the switch I verify that the selector is in the detent of the fullest tank.

[Shadrach]

15 minutes ago, Wildhorsesracing said:

I made it to ~50 ft AGL, right after I retracted the gear it ran out of fuel.  In my case the selector wasn't in the off position but "almost" in the fullest tank position.  At 1st glance it looked like it was pointed at the fullest tank but was not fully in the detent. 

Once the engine went silent I checked the boost pump: it was on so I decided to switch to the other tank, that's when I realized it wasn't in the full tank detent.  I now put my keys in the selector when I am doing the pre-flight and before the key goes in the switch I verify that the selector is in the detent of the fullest tank.

Wait, so you had a fuel starvation incident while configuring for climb at 50'agl and were able to restart before grinding metal?

[Wildhorsesracing]

Just now, Shadrach said:

Wait, so you had a fuel starvation incident while configuring for climb at 50'agl and were able to restart before grinding metal?

Yes, I leveled off with the idea that I was going to land on what was left of the 5000' runway or on the golf course at the end.  The engine was silent but windmilling so once I restored the fuel supply it refired almost immediately.  I managed to keep it at roughly 50' AGL but if I had taken any longer I would've probably run out of altitude.

FWIW - I have also run out of fuel on one tank and the same thing happened once I switched tanks, engine refired instantly.

[Shadrach]

35 minutes ago, Wildhorsesracing said:

Yes, I leveled off with the idea that I was going to land on what was left of the 5000' runway or on the golf course at the end.  The engine was silent but windmilling so once I restored the fuel supply it refired almost immediately.  I managed to keep it at roughly 50' AGL but if I had taken any longer I would've probably run out of altitude.

FWIW - I have also run out of fuel on one tank and the same thing happened once I switched tanks, engine refired instantly.

I've run a tank dry many times in cruise. Given that at lift off and gear retraction you're typically well below best glide speed, I figured it'd be pretty hairy. Of course with an "Johnson bar" bird you can drop the gear faster than you can say "oh $hit".

[Wildhorsesracing]

9 hours ago, Shadrach said:

I've run a tank dry many times in cruise. Given that at lift off and gear retraction you're typically well below best glide speed, I figured it'd be pretty hairy. Of course with an "Johnson bar" bird you can drop the gear faster than you can say "oh $hit".

I was picking the plane up from getting new windows installed and my A&P heard the engine quit on takeoff and his assistant said he was jumping up and down watching me yelling "Put the gear down!!! Put the gear down!!!" LOL!

I stayed in the pattern to make sure that was the only problem, he went to his radio in the hangar and asked "Jim, do you need to land to change underwear?"

[steingar]

10 hours ago, Shadrach said:

Of course with an "Johnson bar" bird you can drop the gear faster than you can say "oh $hit".

Yeah, ain't that nice?

[Shadrach]

16 minutes ago, steingar said:

Yeah, ain't that nice?

It is! To be fair the electric gear birds are pretty fast as well.

[ArtVandelay]

Just now, Shadrach said: Wait, so you had a fuel starvation incident while configuring for climb at 50'agl and were able to restart before grinding metal?

Yes, I leveled off with the idea that I was going to land on what was left of the 5000' runway or on the golf course at the end.  The engine was silent but windmilling so once I restored the fuel supply it refired almost immediately.  I managed to keep it at roughly 50' AGL but if I had taken any longer I would've probably run out of altitude.

FWIW - I have also run out of fuel on one tank and the same thing happened once I switched tanks, engine refired instantly.

Fuel injected or carburetor?

[Yetti]

22 hours ago, carusoam said:

Another thing related to pre-flight and fuel, including both tanks...

1) The pull ring does empty from the tank that is selected...

2) It makes sense to drain fuel from both sides.  In the event water has entered the tank that you are not drawing from.

3) The challenge with using the pull ring is...  The fuel that is sampled, lands on the ground.  If water is present, the pilot may not know it, and may not have cleared it all.

4) Raw fuel on the ground in a hanger seems like a bad idea

5)  I have a proper length piece of tubing(floor to drain) that goes into a glass mason jar

6) The tug gets the sampled gas.

 

 

[Hank]

I sump my tanks after pulling out of the hangar . . . It makes great weed killer.

[Wildhorsesracing]

5 hours ago, teejayevans said:

Fuel injected or carburetor?

'62 M20C - Carburetor - O-360 

[Hank]

8 hours ago, Shadrach said:

It is! To be fair the electric gear birds are pretty fast as well.

I timed mine during annual, ~5 seconds up and 3 seconds down, while jacked up in the hangar.

Wheeee!!

[Shadrach]

I tested this during Taxi yesterday. At a well leaned 1000rpm my engine ran for 34 seconds after the fuel was turned off. It must have created tremendous vacuum in the line because it restarted the instant I turned the selector back to left. That is to say say it was like flipping a switch. I was surprised at how the engine was back to life in an instant, no coughing or sputtering, just right back on line.

[Raptor05121]

This reminds me of my first time flying a 172. Going from 0 hours to PPL, I flew nothing but a 152 with a simple on/off lever. Then I transitioned into a PA-28 with left/right/off. So I've got about 40 hours in each now, and then my friend wheels out a 172 and asks me to take him up. I review the POH speeds, and taxi it off to the pump. I fill it up and sump, then fire it up and it runs, diesels, and shuts off. I then drained the battery trying to start it up. Turns out, the markings on the fuel selector were worn off and with the lever in the middle to where I thought "both" was, was actually off. It ran for about 60-90 seconds for the taxi so that sounds about right at idle.

[M20F]

55 minutes ago, Shadrach said:

It must have created tremendous vacuum in the line because it restarted the instant I turned the selector back to left. That is to say say it was like flipping a switch. I was surprised at how the engine was back to life in an instant, no coughing or sputtering, just right back on line.

If  I run for example left tank dry, land, refill left, start on the right, and the flip to the left it coughs and sputters a fair amount.  It doesn't die and after 4-5 seconds its smooth again.  That may be just coincidental to mine but your results may not always be the same.

[Shadrach]

14 hours ago, M20F said:

If  I run for example left tank dry, land, refill left, start on the right, and the flip to the left it coughs and sputters a fair amount.  It doesn't die and after 4-5 seconds its smooth again.  That may be just coincidental to mine but your results may not always be the same.

Agreed, I often run a tank dry on a long XC in the interest on concentrating fuel in one place. When I do, I always test fuel system continuity before departure.

[Raptor05121]

29 minutes ago, Hyett6420 said:

In the cockpit, there is a "fuel sump drain" with a ring pull on my 1986 M20J.  I have never used it.  It appears to drain the fuel aka a Cessna or Piper out of the tube in the cowling, but I have not worked out how to pull the ring, runaround at high speed to the front plane put a beaker underneath the pipe, run back again, close the pull ring.....you get the gist.

what on earth is it for and how the hell do you test it?

Andrew

Its an actual sump for the selctor itself. You can have someone stand underneath it and cup it, or just pull and hope if anything was in there, is now out.