Fuel management

[Ulysse]

I am planning to fly frequently a route which will require a bit less than 60gal of fuel.
This leaves in theory 15 gal, enough to fly to the alternate + reserve
However, if I were to need these 15 gal of fuel, it would probably be in an emergency or stressful situation.
I'd rather have most of that fuel in one tank. 
My question is: when Mooney says "usable fuel" does this mean that once you have used 37 gal from one tank, the engine will stop or does it rather mean that you must switch tank at this point because the engine would be running some more minutes on the "unusable" fuel, approx 1.5 gal/tank?
Of course, I do not want to go to that limit, but I am wondering if I can safely use 35gal out of the theoretical 37.5 gal on each tank? 

Maybe I am wrong in thinking that I should have most of the fuel in one tank. What would you do ? (except a fuel stop enroute ;-) 

[dzeleski]

I would never push it anywhere near that close, I like to keep 20 gallons on board if that means stopping I stop. Even in my J thats 3-4 hours of flight time which is usually more then my bladder can handle anyways. Thats my personal opinion though.

Unusable is unusable, its the fuel remaining in the tank, lines, pump, etc that can no longer be pumped because its sucking air and pressure is not able to be maintained to keep the engine running. To answer directly yes in theory at 37 gallons the engine would start to stumble and shut down. Remember though these airplanes are hand built, there can be some variation between airplanes and tank shapes can change a bit overtime if any work has been done.

The best test you can do is run a tank until it starts to do this, then you know exactly when this will happen based on your FF/gauges. But you should do it to both tanks, they could be slightly different.

[DCarlton]

I'm not sure what I would do in this case if I were trying to use every drop.  Guessing an experienced CFI might have a recommendation.  Would you switch tanks to the 15 gal tank when you were on approach to your primary destination?  That's not a good time to run the tank dry.  I'll bet some people would run one tank completely dry enroute but I wouldn't do it.  I prefer to keep at least a half hour in each tank.  Will be interesting to see what others say.  

[PT20J]

[A64Pilot]

If for whatever reason your out and may need every drop, run one dry at cruise. then you KNOW all there is, is what’s in the one remaining tank, otherwise you’ll likely con your self into believing there is more fuel in the other tank than there is, when you get to the last tank, your more likely to divert.

‘If you fly a route that may have you using more fuel than your used to, have something that will compute fuel mileage, or do so yourself it’s simple math, that way when you find your using more fuel than planned due to unplanned winds or whatever you can either divert or slow down, slowing down a significant amount can often do astonishing things to range, and lean the hell out of it

Remmeber you can only have too much fuel if your on fire.

I think my usable capacity is 55 gls, but I use 50 for planning, and I don’t push that.

Go ahead and run one dry at cruise one day to see how much of a non event it is, when it starts spitting and stumbling, simply calmly reach down and select the other tank

Edited June 24, 2021 by A64Pilot

[Ragsf15e]

I’d also keep the entire reserve in one tank.  Run one dry in cruise or at least close enough to dry that you know you can’t switch back to it.  Does the 15 gallons still give you an hour endurance at cruise?  I suspect so, so I’d say that’s an acceptable reserve.  I would only use that with good weather, vfr diverts, and I would start to consider other things like how many runways are at my destination?  

[1964-M20E]

This is always an issue on long flights.  I fly the first hour on one tank and then run the second tank to empty. i.e. when the engine begins to lose power and switch back.  Then I know all usable fuel is in one tank in my case that is usually 17 gallons or about 1.9 hours of flying at cruise.  I evaluate my landing conditions at my destination and ETE to get there.  If I have to shoot an approach I already have a pre planned stop for fuel which is close to the area where I switch back to the first tank.  If the weather is clear and no approach is necessary I will continue on if I calculate I will still have about 10 gallons upon landing.

[David Lloyd]

Know your airplane.  I see you have a K, a turbocharged Continental engine.  It is different from the carbed Lycoming in my C.  Being turbocharged, it will restart after running a tank dry significantly different at FL240 versus 7000, and different from non-turbocharged engines even at 7000.  Part of the certification process requires a non-turbocharged engine to restart by only introduction of fuel in some period of time, I seem to remember 10 seconds.  Turbocharged, it was something like 30 seconds, but there may have been some altitude restrictions to go along with that.  It may not start at high altitude and require a descent to a lower altitude.

My C, I recently ran a tank dry both to observe fuel pressure indications, restarting when the tank was changed, what the tank indication would be when empty, how accurate was the fuel flow gauge and how many gallons would be required to fill that tank.  In level fight, as the tank neared empty, the fuel pressure dropped from 4 psi to near 0 psi.  I stepped on the rudder pedal to slosh the remaining fuel toward the fuel pickup and the pressure came back to 4 psi for 10 or 15 seconds and began dropping again.  At that point I turned on the electric pump and a little more pressure on that rudder and the pressure came up to 6 psi over the next minute it began dropping again.  I released all the rudder pressure and the engine quit within a few seconds. Pulled the throttle and prop back some, switched tanks and about the same time there was a fuel pressure indication, the engine was running.  Fuel pressure took about 10 seconds to stabilize.  Every bit of that including pressure indications were expected.  The fuel gauge for that tank read 0.  At the self-service fuel pump, that tank took 27.6 gallons, the O&N bladder is placarded 27.4 gallons useable.  Supposedly there is 1.25 gallons unuseable fuel per tank.  Maybe with full rudder I could have used half of that, maybe one day.  My fuel totalizer showed almost 29 gallons used, about the error I had already figured, something I need to adjust one day.  Okay, nothing unexpected here.

I spent a lot of time in a F33A Bonanza with a fuel injected Continental engine, an IO-520, later an IO-550.  I did similar to above with the Bo, ran the 40 gallon tank dry several times.  The tanks were placarded as 37 gallons useable.  In level and smooth flight, each time a tank was run dry, right or left, it would require 40.1 to 40.4 gallons to fill.  I did not play with the rudder, ball was in the center.  Differing from the carbed engine that gave an indication of running out of fuel, in the Bo as soon as the fuel pressure gauge dropped any at all, before I could reach the electric fuel pump switch the engine was windmilling.  That quick.  I've read that other people have seen the fuel pressure drop and catch it before it quits.  Not my experience.  Pulled the throttle and prop back some, switched tanks, richened the mixture a little and within a few seconds the engine was running.

The reason for pulling the throttle and prop back some prior to switching tanks, is the engine might start making a bunch of power suddenly and will overrev before the prop governor can react.  Pull 'em back so that won't happen.

The OP was looking for a technique that would have the majority of fuel in one tank for landing.  We flew to see the wife's parents in New Mexico several dozen times. Trying for only one fuel stop, my goal was the same: land with a good amount of fuel in one tank, didn't matter about the other.  For a long trip in the Bo, I would always depart on the right tank, use 10 gallons, switch and use 20 gallons from the left, switch back to the right and run it down to the bottom, switch back to the right which now had 17 gallons "useable" and land on that tank.  Wife saw what I was doing at some point, watching the fuel pressure with hand on the selector and told me in that voice (you know it) "You better not run a tank dry with me in this airplane."  Never did with her in the plane, a side benefit to knowing your airplane.  I used that tank switching strategy in that airplane for thousands of hours, including shorter trips.  I always knew where my fuel was.

In my C, a similar strategy will be adopted for a long range trip.  Maybe 10 from the left, 15 from the right, left tank to the bottom, land on the right.  Figure out a strategy and write it down.  Follow it.  If you don't want to try running a tank dry, go a low as you care or dare.  How many gallons remained?  What did the tank gauge indicate?  How did that match with your fuel flow totalizer?  Know the answer to these questions before trying to stretch your range on a long distance trip.

 

[Yetti]

If you are going to make a left hand landing keep more fuel in the right tank, so when you turn, you don't unport the fuel.    If you are going to crash keep more fuel in the left tank since you have to exit the right wing.

[ArtVandelay]

If you are going to make a left hand landing keep more fuel in the right tank, so when you turn, you don't unport the fuel.    If you are going to crash keep more fuel in the left tank since you have to exit the right wing.

If you make a coordinated turn, you shouldn’t have to worry about unporting the fuel.

[Yetti]

7 minutes ago, ArtVandelay said:

If you make a coordinated turn, you shouldn’t have to worry about unporting the fuel.

Agreed, but we are talking about the edges of envelopes

[201Mooniac]

2 hours ago, Yetti said:

If you are going to crash keep more fuel in the left tank since you have to exit the right wing.

If you can plan that far ahead of the crash, maybe just either run out of fuel so no fire at all or just don't fly that day

[ArtVandelay]

If you can plan that far ahead of the crash, maybe just either run out of fuel so no fire at all or just don't fly that day

Switch to right tank, start dumping fuel using gasolator drain. I wonder how long will that take?

[Yetti]

44 minutes ago, ArtVandelay said:

Switch to right tank, start dumping fuel using gasolator drain. I wonder how long will that take?

You don't have a fuel dump switch?    As a practice when just putting around the state I only keep 10 gallons in the right tank.   Just a little pre planning

[carusoam]

On 6/24/2021 at 4:42 PM, David Lloyd said:

Know your airplane. 

 

While reading all of the advice within this thread….

It makes no difference about what method you use…

Until you have defined what is useable fuel in YOUR plane…

Everything has probably changed, from the hardware used, to the accuracy of the documents that came with the plane…

Know the limits to filling the plane… to the top…

Know the limits to emptying the plane… at the bottom…

Know when to change tanks…

Know how much to leave in each tank…

Know that Mooney pilots haven’t made running out of fuel impossible… yet…

You don’t have to be an engineer to fill a tank with precision… one gallon at a time… marking a stick as you go… 

You don’t have to be a test pilot to follow the procedure to run a tank dry…. There is an ordinary procedure to follow for this…

Know where your fuel pick-ups are… 

Know that your selector valve is working properly…

Know the important steps if you have a turbo and fly at high altitudes…

 

All of this is under David Lloyd’s excellent advice above….  
 

If you need a hand with any of this… CFIs make great council!

Many of our planes are similar to each other… but, no two are exactly identical… until proven so…

So Ulysses…. Plan on spending some time with your tanks and procedures before going off into the wild blue expecting it to work correctly because some document said it will work… or guy on the internet said it should…   There are just too many variables that may have changed prior to your ownership…

By going through all the details… you prove to yourself you haven’t missed a change in volume that may have occurred…  or found a filled rib hole… there are many and they are tiny… and are susceptible to being filled by sealant…

Getting to know your plane is something to look forward to…  

PP thoughts only, not a CFI…

Best regards,

 -a-

[Ulysse]

Many thanks for all the advice here. I learnt a lot from all the contributions.

I must say I am impressed by @David Lloyd's maestria !

[carusoam]

MS word of the day… supplied by Ulysses…

https://www.collinsdictionary.com/dictionary/italian-english/maestria

Thus… making David,  El Maestro!

Or something akin to that…

Thanks for playing long…

Best regards,

-a-

[N201MKTurbo]

When I commuted, I would routinely start a cross country with less than 15 gallons on board. It all comes down to knowing your consumption and your capacity. 

While commuting on a 90 mile commute, every second counts. The amount of time it takes to open and close the hangar doors is important. If I fueled up on every flight, I might as well drive, it comes down to splitting hairs. The time it takes to refuel is equal to 15 miles of driving. On a 90 mile commute the plane only saves 10 minutes or so. My legs were typically 28-32 min depending on the winds. I would start the trip with 10 gallons on board. I could usually get 9 legs between refueling. I wouldn't start a leg unless there was 1/4 inch of gas in both tanks looking straight down from the gas caps. I did this for 20 years without incident.

 

[David Lloyd]

Not a 90 mile commute but another benefit to knowing your airplane is being able to buy the majority of your fuel at the less expensive pump.  For years my average leg was 2 1/2 hours.  Fuel at my airport was always less than where I went.  Oh dark thirty on Monday morning I would top the tanks with cheap fuel(?) prior to departure.  Depending on the forecast at home, I would order only the amount expensive fuel that would leave me with an hour of fuel arriving home.  That typically worked out to $20-$30 savings every week.  Year after year.  Okay, a few times every year I would top the tanks away due to iffy weather at home.  Always be safe.  Know your plane.

[Ulysse]

On 6/28/2021 at 4:35 AM, carusoam said:

MS word of the day… supplied by Ulysses…

I thought "maestria" was almost universal !

On 6/28/2021 at 4:57 AM, N201MKTurbo said:

I would routinely start a cross country with less than 15 gallons on board

another maestro! 

I do not have the expertise (maestria !) to confidently fly to the limits. I think I'll learn how to fly LOP in my plane and see if it allows me to extend the range.

[Ragsf15e]

2 hours ago, Ulysse said:

I thought "maestria" was almost universal !

another maestro! 

I do not have the expertise (maestria !) to confidently fly to the limits. I think I'll learn how to fly LOP in my plane and see if it allows me to extend the range.

Lop will definitely extend your range at the cost of a couple minutes per trip.  Do you have egt readout on all 4 cylinders?

[DXB]

On 6/24/2021 at 4:42 PM, David Lloyd said:

Know your airplane.  I see you have a K, a turbocharged Continental engine.  It is different from the carbed Lycoming in my C.  Being turbocharged, it will restart after running a tank dry significantly different at FL240 versus 7000, and different from non-turbocharged engines even at 7000.  Part of the certification process requires a non-turbocharged engine to restart by only introduction of fuel in some period of time, I seem to remember 10 seconds.  Turbocharged, it was something like 30 seconds, but there may have been some altitude restrictions to go along with that.  It may not start at high altitude and require a descent to a lower altitude.

My C, I recently ran a tank dry both to observe fuel pressure indications, restarting when the tank was changed, what the tank indication would be when empty, how accurate was the fuel flow gauge and how many gallons would be required to fill that tank.  In level fight, as the tank neared empty, the fuel pressure dropped from 4 psi to near 0 psi.  I stepped on the rudder pedal to slosh the remaining fuel toward the fuel pickup and the pressure came back to 4 psi for 10 or 15 seconds and began dropping again.  At that point I turned on the electric pump and a little more pressure on that rudder and the pressure came up to 6 psi over the next minute it began dropping again.  I released all the rudder pressure and the engine quit within a few seconds. Pulled the throttle and prop back some, switched tanks and about the same time there was a fuel pressure indication, the engine was running.  Fuel pressure took about 10 seconds to stabilize.  Every bit of that including pressure indications were expected.  The fuel gauge for that tank read 0.  At the self-service fuel pump, that tank took 27.6 gallons, the O&N bladder is placarded 27.4 gallons useable.  Supposedly there is 1.25 gallons unuseable fuel per tank.  Maybe with full rudder I could have used half of that, maybe one day.  My fuel totalizer showed almost 29 gallons used, about the error I had already figured, something I need to adjust one day.  Okay, nothing unexpected here.

I spent a lot of time in a F33A Bonanza with a fuel injected Continental engine, an IO-520, later an IO-550.  I did similar to above with the Bo, ran the 40 gallon tank dry several times.  The tanks were placarded as 37 gallons useable.  In level and smooth flight, each time a tank was run dry, right or left, it would require 40.1 to 40.4 gallons to fill.  I did not play with the rudder, ball was in the center.  Differing from the carbed engine that gave an indication of running out of fuel, in the Bo as soon as the fuel pressure gauge dropped any at all, before I could reach the electric fuel pump switch the engine was windmilling.  That quick.  I've read that other people have seen the fuel pressure drop and catch it before it quits.  Not my experience.  Pulled the throttle and prop back some, switched tanks, richened the mixture a little and within a few seconds the engine was running.

The reason for pulling the throttle and prop back some prior to switching tanks, is the engine might start making a bunch of power suddenly and will overrev before the prop governor can react.  Pull 'em back so that won't happen.

The OP was looking for a technique that would have the majority of fuel in one tank for landing.  We flew to see the wife's parents in New Mexico several dozen times. Trying for only one fuel stop, my goal was the same: land with a good amount of fuel in one tank, didn't matter about the other.  For a long trip in the Bo, I would always depart on the right tank, use 10 gallons, switch and use 20 gallons from the left, switch back to the right and run it down to the bottom, switch back to the right which now had 17 gallons "useable" and land on that tank.  Wife saw what I was doing at some point, watching the fuel pressure with hand on the selector and told me in that voice (you know it) "You better not run a tank dry with me in this airplane."  Never did with her in the plane, a side benefit to knowing your airplane.  I used that tank switching strategy in that airplane for thousands of hours, including shorter trips.  I always knew where my fuel was.

In my C, a similar strategy will be adopted for a long range trip.  Maybe 10 from the left, 15 from the right, left tank to the bottom, land on the right.  Figure out a strategy and write it down.  Follow it.  If you don't want to try running a tank dry, go a low as you care or dare.  How many gallons remained?  What did the tank gauge indicate?  How did that match with your fuel flow totalizer?  Know the answer to these questions before trying to stretch your range on a long distance trip.

 

Great guidance, and good info for my C that has the same setup with bladders.  Also thank you for detailing the experience of running tanks dry so I don't have to try it out myself    My '68 POH describes running one tank dry as the SOP before making the final switch to the other tank  .   With fuel flow and digital senders as modern instrumentation, I see little need to do that unless I really get myself into a bind.

 

[Skates97]

59 minutes ago, DXB said:

Great guidance, and good info for my C that has the same setup with bladders.  Also thank you for detailing the experience of running tanks dry so I don't have to try it out myself    My '68 POH describes running one tank dry as the SOP before making the final switch to the other tank  .   With fuel flow and digital senders as modern instrumentation, I see little need to do that unless I really get myself into a bind.

 

I do this on every long cross country. Take off on one tank, switch after one hour, un that one dry, then switch back. It ensures I have all fuel available in one tank. Exceptions are if I am descending before running it dry and then I switch at the top of descent, I don't want to be doing that on approach. Running it dry is no big deal in our O-360's. Because there is fuel in the carb bowl you can watch the fuel pressure start dropping and switch tanks before the engine will even stumble. For a brief moment you will see your fuel flow jump as the carb bowl is filled back up but then the fuel flow will go back to normal.

[PT20J]

Don’t forget that many autopilots have fuel imbalance limitations. From the GFC 500 AFMS…

[Ulysse]

4 hours ago, Ragsf15e said:

Do you have egt readout on all 4 cylinders?

yes, I have Garmin EIS on all 6 cylinders