Calculated fuel on board versus indicated fuel on board

[GeeBee]

I've spent many minutes with my hand on the fuel selectors of twin Cessnas and Navajos getting every last drop of fuel out of the aux tanks for max range. The last thing you want to do is have to go back to a tank with a few gallons in it. So the answer is, yes, the fuel pressure will start to wiggle when. the tanks starts to empty. I've never had the engine quit, but I've seen the needle start to wiggle.

 

[MooneyMark]

Thanks for all the replies! I'm taking it all in. I think I'll run both tanks dry (not on the same flight...), take notes and compare gauges readings while refuelling. 

[KRviator]

I often run a tank dry in my RV and it is a total non-event. Fuel pressure drops, RPM drops a few hundred, and recovers in a few seconds after switching to the full tank. Of note, FAR23 certificated aircraft have to demonstrate continued safe operation after running a tank dry...

Here's a video of it happening showing the indications on the EMS. Ignore the hunting volts & amps, the PP alternator went bad & was replaced with a B&C unit... 

Edited July 15, 2020 by KRviator

[ArtVandelay]

Takeoff in Both?

Not in a Mooney.

 

I prefer to limit the tank switching to 1 a little over half way there. Our planes fly fine with fuel tanks out of balance.

[Bob - S50]

1 hour ago, irishpilot said:

Running tanks dry is a non-issue at alt. FP, RPM, will decrease, you'll also feel and hear it. Done right, engine never stops. I know within +-5 min when the tank should be dry.

In order to max long rang flying in a Mooney, a technique is to run dry a tank as you'll know your reserve in the other. If you have 5 hrs of calculated flying time at your fuel flow (including your VFR/IFR reserve), You'd do this:

Takeoff in Both
1:00 - Left
2:00 - Right

At this point you should have two hours left of flying time.

3:00 - (Hack clock) Left til dry
If you get 1:20 out of the tank, you have 1:15 in the right tank til dry, so you have 45 min left to land with VFR reserve or 30 min with IFR reserve.

4:15 - Right
5:00 - Land

This technique was taught to me by my original instructor who was a C-46 pilot flying the Hump during WWII. It works in all GA planes that have Both/L/R selectors and it takes the guesswork out of innacurate tanks (think old Cessna bouncing guages).

I do this with my JPI enabled Bravo with very accurate guages when long XC. When flying long range XC in the Bravo, it is possible to put in more than the 89.9 gals the POH says which throws off the JPI totalizer. Although the fuel senders in the tanks are accurate, I fly off of time and FF and base wx diverts on most conservative numbers (ie if I'm burning 18.5 gph, I round up to 19).

Note: this is a technique only. There are other techniques. Pick one that doesn't rely solely on technology so that when stuff fails, you still know how much fuel is left in the tanks. Fuel-related GA mishaps are preventable. Never get into, "I can push past this fuel stop because my tanks show good."

Fly safe!

Sent from my Pixel 3a using Tapatalk
 

Having accurate fuel gauges, I do this:  Switch tanks as needed to keep them within 5 gallons of each other on a quantity that is divisible by 5.  When one tank is at 15 gallons and I switch to the other, I run the other side down to 12 instead of 10.  At that point I switch back to the tank with 15 and stay on that tank until it is empty or until I'm about to enter the pattern for landing.  That way I know I have at least 12 gallons in the active tank for pattern work.  Similar to the K mentioned earlier, my J has a caution about extreme maneuvers with less than 8 gallons.

[irishpilot]

Takeoff in Both?
Not in a Mooney.
 
I prefer to limit the tank switching to 1 a little over half way there. Our planes fly fine with fuel tanks out of balance.

Yep, that is what happens when I write when I can't sleep. That was gravity feed technique. My b. I still do that technique for L/R.

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[irishpilot]

Having accurate fuel gauges, I do this:  Switch tanks as needed to keep them within 5 gallons of each other on a quantity that is divisible by 5.  When one tank is at 15 gallons and I switch to the other, I run the other side down to 12 instead of 10.  At that point I switch back to the tank with 15 and stay on that tank until it is empty or until I'm about to enter the pattern for landing.  That way I know I have at least 12 gallons in the active tank for pattern work.  Similar to the K mentioned earlier, my J has a caution about extreme maneuvers with less than 8 gallons.

That's a good technique!

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[GMBrown]

I was flying my Grumman Cheetah back from Loreto, Baja, at 8500 feet when suddenly the only sound I heard was silent whoosh of air going over my canopy.  It was that sudden.  The dents from my passenger gripping the arm rest so hard are probably still there.  I switched the tanks and turned on the fuel pump and the engine came back immediately.  No hesitation.  

[carusoam]

Nice video, KR...

The instruments clearly read 0 liters on board that tank...

the FuelP runs perfectly well, until there is no fuel left...as it drops rapidly from 10 to 1.... as the valve gets flopped...

Thanks for sharing the detail...

What makes it edgy for the old certified planes... you never know what could possibly sneak into the individual system until you try it... most often it works as designed... perfectly...

A few times around here the valve gets stuck.... something that gives plenty of warning prior to failure...

Best regards,

-a-

[jlunseth]

On 7/13/2020 at 7:13 PM, gsxrpilot said:

The tanks in the M20K are a real pain in the ass to fill properly.

Ain’t that the truth. I always know when my FBO has new line staff because there is a 10 gallon empty “hole” under the anti-siphon valve, instead of a full tank. Yesterday I was in Billings MT explaining to a line guy how he needed to fill the tank and that I needed all the fuel I could get for my next leg. We took that cap off and filler neck was full to the brim with fuel, although I had just flown nearly four hours and there was only ten gallons in the tank.

I always check the fuel myself, always. And I always punch the anti-siphon valve down with the stick of the fuel sump. With the valve open, if I can’t see tank fuel slushing around I make them bring the truck out and do it again.  Invariably, we can put in anywhere from 10-20 more gallons.

PS Bear in mind that ten gallons is nearly an hour’s worth of fuel, I use 11.1-.3 in normal cruise flight. So that is a lot of safety factor left out of the tanks.

Edited July 17, 2020 by jlunseth

[ArtVandelay]

Do jet guys have this problem? I never seen a jet pilot sump the tanks, check fuels visually, or ever use a self serve pump.

[N231BN]

Do jet guys have this problem? I never seen a jet pilot sump the tanks, check fuels visually, or ever use a self serve pump.

Don't wanna smell like jet fuel.

[GeeBee]

Oh, believe me I have had fuel problems in jets.

One time the gauges would not show quantity because the gauges indicated "contamination". The mechanics said it was an error, drained the sumps,  pulled the drip sticks and said the fuel amount was correct. I said, "Humor me and do a Millipore check on the fuel truck. Millipore failed and upon further inspection they found a sweater left in the truck tank by a repairman. Those fibers would have clogged the fuel filters, no telling what would have happened.

Another time, I found a fuel cap left off a 737 basic after it came out of maintenance. They did have overwing fueling provision on early Boeings.  For whatever reason, most airlines do not include a "cap check" in the walk around.

Fuel quantity verification comes in. the form of a "fuel slip".  The slip shows the beginning quantity, the quantity after servicing, the gallons pumped and the fuel density times the gallons pumped which should be very close  to the difference between the before and after service quantities. I could not get the gallons x fuel density to match up. Then it hit me. There was no way in the middle of January in Chicago that fuel density was 6.7 lbs/gal. Upon further investigation we found that procedures require a density check, twice a day, it had not been done in 3 weeks.

Let me not even begin to talk about gauge inoperative fueling, which is messed up 90% of the time unless you go down and supervise it personally. The most common error is not taking a pre-service stick reading.  If you don't do it right, and you don't match your serviced quantity with your sticks, you end up with this.

 

Edited July 17, 2020 by GeeBee
Spelling

[GeeBee]

Oh and on the "self service"? There is only one guy who services my Mooney....me. I may let you stand there and hold the nozzle, but no one fuels my airplane unless I am there.

 

[carusoam]

The gimli glider had a meter stick in place of a yard stick... to aid with their mistake making exercise...
 

There are only a few airliners that have run out of fuel...  our NYC area has air Avianca... inability to let ATC know their fuel situation...

https://en.wikipedia.org/wiki/Avianca_Flight_52

 

If these guys can goof it up...

PP thoughts only, not an airliner fuel expert...
 

Best regards,

-a-

[MooneyMark]

La Mia Flight 2933 comes to mind too, these guys took off knowing they had insufficient fuel, needed to hold en ran out and crashed.

[GeeBee]

8 hours ago, carusoam said:

The gimli glider had a meter stick in place of a yard stick... to aid with their mistake making exercise...
 

There are only a few airliners that have run out of fuel...  our NYC area has air Avianca... inability to let ATC know their fuel situation...

https://en.wikipedia.org/wiki/Avianca_Flight_52

 

If these guys can goof it up...

PP thoughts only, not an airliner fuel expert...
 

Best regards,

-a-

It is correct they had a unit conversion problem, but that is a cop out., This is why you compare the "pre-service reading" to the "post service reading" x the fuel density per unit of volume. That way, ANY error is shown and indeed magnified regardless of units. The mistake servicing personnel make (and was made in this case) is to simply fuel to the mark on the drip or magna stick. Once you have done that you have "lost the tank" because a continuous "volume pumped" vs quantity shown (regardless if it was a stick or gauge) has been lost. Your only out at that point is to empty the tank and re-service with a known volume.  Hopefully you have room in another tank to pump the lost tank over, then an operative gauge to measure it and pump it back. If not you are going to be tankering some fuel. 

This should be our way on our airplanes too. We should be always comparing the pre-service quantity to the post service and the volume pumped. Not simply pumping to a mark. That way any over consumption is noted and cause ascertained. 

[carusoam]

La Mia...

https://en.wikipedia.org/wiki/LaMia_Flight_2933

Quite a tragedy.

Best regards,

-a-

[GeeBee]

I never understand why pilots are so reluctant to declare low fuel states and emergencies. About 3 years ago, I had to declare minimum fuel after a thunderstorm exploded over my destination while on approach. After the missed I could not get ATC to clear me to my alternate, I literally was on a 100 mile downwind from the destination I just blew out. Things happen quickly when you are burning fuel so don't delay. I finally declared "MINIMUM FUEL". These days things happen PDQ when you do that. I was not only declared direct to my alternate, center cleared me for "any approach" at my alternate before I talked to Approach. When I talked to approach, they just asked what approach I was executing and did I want the visual to the parallel instead. I said, "Nope, we're locking her up on the ILS for an auto land. If we go around, it will be an emergency declaration." We landed with 40 minutes of fuel.

 

[Warren]

On 7/14/2020 at 9:01 AM, gsxrpilot said:

 

Hi Paul,  do you see the FP flicker or drop prior? Had an aux tank in a Pitts, you could see FP fluctuate prior to sucking air. 
-Matt

I run a tank dry multiple times a year on longer flights.  There is a significant difference between running a tank dry LOP vs. ROP.

When ROP, the FF reduces and the engine starts to surge - change tanks and in less than 10 sec everything is back to normal.

LOP is a whole different story.  Already lean means that any reduction in FF causes the fire to go out.  Switch tanks and it will recover but it is more dramatic and takes longer to get going again - 20-30 seconds which is a long time to wait for a restart.  I have never had to use the boost pump to get a restart and have not attempted this above FL180.

In general things are much smoother when ROP.  I regularly operate lean but when my low fuel light goes on I know I have about 15 mins of fuel and I switch to ROP until I have switched tanks.

If you are doing this at altitude, make sure you are familiar with the restart procedure in case you have trouble.  If the turbo spins down and the MP is much lower, you will be very rich — probably too rich for a restart.  Read the restart procedure, but the main focus is leaning the fuel flow to an ignitable fuel ratio.

I also make sure I am within gliding distance of an airport — just in case the worst happens.

Warren

[donkaye]

On 7/15/2020 at 2:09 AM, MooneyMark said:

Thanks for all the replies! I'm taking it all in. I think I'll run both tanks dry (not on the same flight...), take notes and compare gauges readings while refuelling. 

I had thought that the only time the fuel gauges need to read accurately was when they read zero.  The FAA kindly reminded me that was not the case, after a student's airplane we were training in turned out to have fuel gauges frozen in place.  Part of the requirements for airworthiness in the US is having working fuel gauges (90.205(b)(9)).  Yours are not working correctly.  In the US your airplane would not be airworthy.  I would have your fuel gauges or fuel system repaired or you are asking for trouble.

[MooneyMark]

Hmmm, well you could be right. Strickt adherence to that one would ground most GA airplanes. As most of them have crap fuel gauges.

I wouldn’t say the gauges are ‘not working’, they are just very pessimistic the last 15 gallons and have been pretty reliable at that for the past 22 years the Mooney has been in my family.

[Ibra]

On 7/15/2020 at 2:20 PM, Bob - S50 said:

Similar to the K mentioned earlier, my J has a caution about extreme maneuvers with less than 8 gallons.

The good news if you are sideslipping that hard on final to stave the engine, you really don’t need engine power  well maybe for a go-around when you are past 1/2 of the runway but....

Edited July 19, 2020 by Ibra

[GeeBee]

On 7/17/2020 at 12:21 PM, GeeBee said:

Oh and on the "self service"? There is only one guy who services my Mooney....me. I may let you stand there and hold the nozzle, but no one fuels my airplane unless I am there.

 

Another lesson on why you never leave the fueling process

https://www.avweb.com/aviation-news/misfueling-cited-in-alaska-commander-crash/

 

[ArtVandelay]

Oh and on the "self service"? There is only one guy who services my Mooney....me. I may let you stand there and hold the nozzle, but no one fuels my airplane unless I am there.
 

Don’t go to San Carlos (KSQL), fuel is not onsite, truck comes from somewhere at some point to fill the planes.