Fuel minimums

[VanGo]

The POH in Chapter 2 a note states “except for takeoff, fuel in the selected tank can be safely used until the quantity indicator reads empty …”

OK, what’s the minimum fuel for takeoff (or more likely a go around/missed approach) in a selected tank that can be safely used?   30 gallons (probably a lot less)? 5 gallons? I’ve never flown with that little fuel, & don’t intend to do so, but I’d like to know.  

After diverting to an alternate, I could imagine having only 10 gallons left ( 1 hour). Maybe 9 & 1 (& feeding off the 9) would be a safer go around than 5 & 5 in each tank (still allowing for one hour of fuel remaining).  

Someone told me 6 gallons was the minimum, but I can’t find that written anywhere.  

[Pinecone]

My POH (252/Encore) says the same thing.

I am firmly in the camp of rather have 9 + 1 than 5 + 5.

[BravoWhiskey]

I’m going on memory here but I think my POH says aircraft has not been tested for takeoffs using less than 15gal per wing.  I’ve landed with less than 10 in each but I don’t think I’d try to takeoff with that amount.  When I get below 15 in either wing my master warning comes on.

[Rick Junkin]

From Section 2 of the M20M POH:

 

I'm not knowledgable on how the M20K fuel tanks compare.

Cheers,
Rick

[LANCECASPER]

On 2/17/2024 at 12:24 PM, VanGo said:

The POH in Chapter 2 a note states “except for takeoff, fuel in the selected tank can be safely used until the quantity indicator reads empty …”

OK, what’s the minimum fuel for takeoff (or more likely a go around/missed approach) in a selected tank that can be safely used?   30 gallons (probably a lot less)? 5 gallons? I’ve never flown with that little fuel, & don’t intend to do so, but I’d like to know.  

After diverting to an alternate, I could imagine having only 10 gallons left ( 1 hour). Maybe 9 & 1 (& feeding off the 9) would be a safer go around than 5 & 5 in each tank (still allowing for one hour of fuel remaining).  

Someone told me 6 gallons was the minimum, but I can’t find that written anywhere.  

I wouldn't even go down that path of reasoning. What if turning to final causes an interruption in your fuel flow from the low tank in the turn? You don’t know exactly how much fuel you have in there no matter what fancy devices and what senders you have. Don’t err, but if you err  do it on the side of caution. I saw a low fuel light once on one tank early on in Mooney ownership and vowed never to have that happen again. Thankfully I was in the pattern, coming in after a long trip. The only time you have too much fuel is when you’re on fire. 

[BravoWhiskey]

25 minutes ago, LANCECASPER said:

I would even go down that path of reasoning. What if turning to final causes an interruption in your fuel flow from the low tank in the turn? You don’t know exactly how much fuel you have in there no matter what fancy devices and what senders you have. Don’t err, but if you err  do it on the side of caution. I saw a low fuel light once on one tank early on in Mooney ownership and vowed never to have that happen again. Thankfully I was in the pattern, coming in after a long trip. The only time you have too much fuel is when you’re on fire. 

My turns are so perfect the fuels thinks it’s in level flight

[Utah20Gflyer]

We should all be verifying there is fuel in the tanks before takeoff and to do that with the 52 gallon capacity tanks you need about 4-5 gallons to see the fuel when you pull the caps and look in.   So 5 gallons should be the baseline because otherwise you are placing complete reliance on the fuel gauges to be accurate.  

If your fuel sender float sticks and your sump drain is leaking you could end up with much less fuel that the fuel gauge indicates,  and this has been known to happen.  A fuel totalizer is a third data point to manage fuel.  I do all three - Visual check, accurate fuel gauges (CIES/aerospace logic) and use a fuel totalizer.  
 

Personally I like 8 gallons as a minimum.  

[hammdo]

I created a graduated stick to also measure visually too (from references here on MooneySpace)…

-Don

[kortopates]

Rick provided the correct answer which is in all the mid-bodies and long bodies. i don’t do much training in the vintage Mooney’s so can’t recall if min 12 gallons is listed. It’s not a limitation though, just a warning we’re a test pilot taking off with less than 12 on the tank we’re using. But regardless of model remember we’re all flying with the same wing despite some differences in unusable fuel - but that is another story.

With some of the loaded long bodies it can be a challenge maintaining over 12 gal in the tanks without getting over the max landing weight.


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[MikeOH]

From an old POH for an F.  Looks like don't slip with less than 8 gallons:

 

[Will.iam]

Easiest way to verify what your airplane can do is go up to altitude you feel safe over an airport say 4000ft and practice a climb pitch like when you take off on a tank that has the level o f fuel you want to verify. I know my low fuel lights come on at around 3.5 gallons as that is how much lower my fuel totalizer goes down from the time the liw fuel light comes on and the engine starts sputtering due to no gas in that tank. Switch to the other tank and land. Fill up the empty tank and go test the other tank. In the same fashion i have verified from a takeoff pitch attitude at 4000ft that 5 gallons in the tank and i could still climb at that low of fuel level. I double that as my personal limit of 10 gallons. Every plane was built just a little bit differently so a test is really the only way i know to find out. 

[Z W]

I've landed a couple of times with a low fuel light on one side, and the other tank reading between 5-10 gallons.  Once on purpose which convinced me not to do that again.  The second time, more recently, after getting shorted on a fuel order and then hitting greater than forecast headwinds.  Both times made me extremely uncomfortable.  I greatly prefer to get extra fuel, or stop for more. 

The M20K doesn't take much fuel to get there - 12 more gallons gives you an hour of time and 160+ miles of range.  The stock 75 gallon tanks give you 6.25 hours of flight and 1,000 miles of range, and unless you're hauling 4 adult males, the plane can usually be flown easily within W&B with 75 gallons on board.  It's the most efficient model in the fleet for this.  I don't see a lot of reason to be landing, taking off, or going around with less than 12 gallons in both tanks, so I don't do it.

My thoughts only.  Your experience may vary.

[jlunseth]

Yup, the 231 POH has the same warning. It also states, "Except for takeoff, fuel in the selected tank can be safely used until the quantity indicator reads empty (top of red line) for all other coordinated flight conditions." [Emphasis added.] Level or nose down and coordinated you are ok. ZW said it right, there is so much range with full tanks there is really no reason to get down to 0 in one and 10 in the other wing in the very efficient 231. I did it once on a trip from KFCM to Asheville, NC back in the day when I was flying ROP all the time, but if you fly LOP at cruise there is no good reason. Even if you get up into the flight levels and have to fly ROP, now your range per gallon is around 175 nm plus the tailwind that caused you to go up there in the first place.

[Pinecone]

20 hours ago, LANCECASPER said:

I would even go down that path of reasoning. What if turning to final causes an interruption in your fuel flow from the low tank in the turn? 

If that happens, you are not using your rudder properly.

Coordinated turn, the fuel in the tanks is the same as in straight and level flight.

[Pinecone]

Aren't the fuel pickups at the aft inside corner of the tanks?

If so, I would be more worried about descending as the fuel would move forward.

But I am not too worried.  It is very unlikely I will ever try to take off with less than 15 - 20 gallons in at least one tank.

[Shadrach]

20 hours ago, Utah20Gflyer said:

We should all be verifying there is fuel in the tanks before takeoff and to do that with the 52 gallon capacity tanks you need about 4-5 gallons to see the fuel when you pull the caps and look in.   So 5 gallons should be the baseline because otherwise you are placing complete reliance on the fuel gauges to be accurate.  

If your fuel sender float sticks and your sump drain is leaking you could end up with much less fuel that the fuel gauge indicates,  and this has been known to happen.  A fuel totalizer is a third data point to manage fuel.  I do all three - Visual check, accurate fuel gauges (CIES/aerospace logic) and use a fuel totalizer.  
 

Personally I like 8 gallons as a minimum.  

For the 64gal tanks it’s closer to 10 gallons before fuel is visible through the filler. In terms of a starvation incident for a given amount of fuel, I would think that descent to landing would be the attitude with the greatest chance of unporting a low tank.

[EarthboundMisfit]

Haven't seen it mentioned yet, so I'll take a different tack (fearful, theory-only types might like to look away). This approach will require thought and self-consideration (or mental rehearsal) on your part, but will give you confidence in your machine and its equipment.

 

If you're trying to discover the actual figures for your aircraft, here's an exercise you could try.  Take off with a low amount of fuel in one wing, but plenty in the other.  In straight and level cruise, preferably with George the autopilot driving, set the fuel selector to the low fuel wing.  Prepare your mind for the engine to stop. Remain calm. As your fuel quantity gauge reads zero, watch your EGT gauge: it reads zero as the fire goes out, and CHT's will trend downwards.  Wait a minute, look at that windmilling propeller, observe how the plane still flies, savour the experience. Notice how the prop doesn't stop turning, and recall that air and spark are still present in the combustion chamber, and that you've only removed fuel from the equation. Calmly switch to the other (high fuel) tank.  As fuel meets air and spark again, combustion resumes (confirmed by EGT numbers again) and you can feel safe and satisfied knowing that all conforming engines are required to behave this way. Return to land, and when you get back to your hangar, drain the remaining fuel from the "low" wing.  That will be the amount of fuel (in that side) you cannot depart on. Repeat for the other side.

 

Polite discussion welcomed.

[Will.iam]

5 hours ago, EarthboundMisfit said:

Haven't seen it mentioned yet, so I'll take a different tack (fearful, theory-only types might like to look away). This approach will require thought and self-consideration (or mental rehearsal) on your part, but will give you confidence in your machine and it's equipment.

 

If you're trying to discover the actual figures for your aircraft, here's an exercise you could try.  Take off with a low amount of fuel in one wing, but plenty in the other.  In straight and level cruise, preferably with George the autopilot driving, set the fuel selector to the low fuel wing.  Prepare your mind for the engine to stop. Remain calm. As your fuel quantity gauge reads zero, watch your EGT gauge: it reads zero as the fire goes out, and CHT's will trend downwards.  Wait a minute, look at that windmilling propeller, observe how the plane still flies, savour the experience. Notice how the prop doesn't stop turning, and recall that air and spark are still present in the combustion chamber, and that you've only removed fuel from the equation. Calmly switch to the other (high fuel) tank.  As fuel meets air and spark again, combustion resumes (confirmed by EGT numbers again) and you can feel safe and satisfied knowing that all conforming engines are required to behave this way. Return to land, and when you get back to your hangar, drain the remaining fuel from the "low" wing.  That will be the amount of fuel (in that side) you cannot depart on. Repeat for the other side.

 

Polite discussion welcomed.

Or just goto the gas pump and see how much gas you can put in. In my case the 37.8 main and 14.5 aux when the main and aux were both full i had pumped 53 gallons or more than what was certified to hold so either the gas pump was not recording fuel accurately or i can put more fuel in that what it’s suppose to hold so if there was any unusable fuel it was very little when it ran dry. I think the 3.5 unusable fuel limit comes from flying the airplane at normal climb and or descent angles and still reliably keep fuel going to the engine. 
there was a video about a mooney pilot that ran out of gas as he was gliding down to an airport he was about to land short and hit an obstacle but when he pulled back and traded some air speed for a slight climb there was enough fuel left that sloshed back and the engine sputtered to life and gave him enough of a boost to make the end of the runway. I bet if he checked his tanks afterwards he would have less than the 3.5 unusable fuel amount. Same reason so many have said and i agree i would rather have 10 gallons in one tank than 5 gallons each side. 

[cliffy]

Point of reference-  D/C model, 52 gal total (26 a side),  filling from dead empty (drained) EXACTLY 26 gallons each side right to the steel lip.

PoR #2- I use a stick to check each tank before every flight to double check the "indicated" quantity on my Dynon at start up. Always within 2 gallons

Stick graduated every 5 gallons- interpret between marks.  

99% of the time I leave with full tanks regardless of the flight distance Sometimes it bites me in the behind when I can't purchase the min to avoid charges. 

I usually (on longer trips 2+ hrs) make a reasonableness check after each hour by reading tank quantity and subtracting what I know I should have burned 

to what is in the tanks (NOT what is shown as burned on the computer) as I have made many many flights and measured how much went back in  after each flight. 

Just like we all learned in basic flight training. Works for everything from J-3s to Boeings. We knew what we should have burned each hour and subtracted from what we had on board at the start and compared to the indicated quantity remaining each hour or each waypoint crossing.

Did it on over water trips in big stuff, do it still on spam cans today. Its called "flight planning". 

How many still do it today? I wonder. 

Prediction from a Jurassic pilot- Glass panels and Autopilots have dumbed down flying so much that we will have a problem in the future (if not now). 

Those who have learned only on glass panels/A/Ps know not what they don't know and its not their fault. JMO

But glass panels may also be as much a safety improvement to aviation in total as the jet engine was to commercial flying in the 60s.

Jet engines transformed the safety paradigm of commercial aviation. Of that there is no doubt.  

But just like jet engines- sometime the panel will go dark-not often but sometime- What will you do then?

The gorilla in the room? What happens when the GPS system goes down? (This probably needs a separate thread itself) 

[N201MKTurbo]

`When I was commuting to Tucson almost every day, I wouldn't leave unless both tanks had fuel under the gas cap. with the edge of the fuel below the center of the hole there was 5 gallons in that tank. did this for 20 years without issue. The flight was normally 28 min. There was a few times when the gas pumps at 57AZ were broken and I had to fly to KAVQ to get fuel. That was a bit of pucker factor. It is about a 5 min flight, but it is downhill the whole way. As soon as you get airborne, you can coast to AVQ (well, almost)

[Nokomis449]

When an old friend was a young man and his family owned an FBO, his dad dropped him off after dark at an airport where someone had left their rental plane, to ferry it back to the home airport.  Friend was concerned there wasn't enough fuel in it to make it back, and there was no fuel available.  The dad said there was plenty in the tanks, and get going [cue crack of whip].  So friend took off in the dark, planning to run one tank dry and finish the flight with the other.  About halfway the first tank ran dry and he switched; no problem.  But 5 or 10 miles short of the destination, the other tank went dry.  So he banked the plane to pool the unusable fuel under the port, and the engine came back to life.  When that stopped working he switched tanks and banked the other way and was able to complete the flight.  

As Mark Twain said, “Good decisions come from experience. Experience comes from bad decisions.”

I've often wondered if any of the "ran out of fuel and landed short of the runway" pilots have tried this.

(DISCLAIMER: I do not recommend nor endorse this behavior or my friend's dad.)

[Will.iam]

59 minutes ago, Nokomis449 said:

When an old friend was a young man and his family owned an FBO, his dad dropped him off after dark at an airport where someone had left their rental plane, to ferry it back to the home airport.  Friend was concerned there wasn't enough fuel in it to make it back, and there was no fuel available.  The dad said there was plenty in the tanks, and get going [cue crack of whip].  So friend took off in the dark, planning to run one tank dry and finish the flight with the other.  About halfway the first tank ran dry and he switched; no problem.  But 5 or 10 miles short of the destination, the other tank went dry.  So he banked the plane to pool the unusable fuel under the port, and the engine came back to life.  When that stopped working he switched tanks and banked the other way and was able to complete the flight.  

As Mark Twain said, “Good decisions come from experience. Experience comes from bad decisions.”

I've often wondered if any of the "ran out of fuel and landed short of the runway" pilots have tried this.

(DISCLAIMER: I do not recommend nor endorse this behavior or my friend's dad.)

The ironic part is did the friend know to do this from previous experience or learned it from another pilot that had done this?  The airforce had an A-10 that lost both engines and instead of punching out and parachuting to ground the pilot chose to deadstick it and land on the runway thus saving an airforce asset. The word spread around the squadron and later a different pilot had the same loss of both engines and instead of punching out since he knew another pilot had saved a plane he chose to try and save a plane but crashed on landing and died. The airforce had to re-emphasis that the risk to save an asset was too great to the loss of life and to punch out was the required procedure. 

[N201MKTurbo]

There were two A-10 mechanics at the air show manning one of the Air Force booths. I asked him what takes the most maintenance on an A-10. He said “That’s easy, wheels and brakes” 

[A64Pilot]

17 hours ago, EarthboundMisfit said:

Haven't seen it mentioned yet, so I'll take a different tack (fearful, theory-only types might like to look away). This approach will require thought and self-consideration (or mental rehearsal) on your part, but will give you confidence in your machine and it's equipment.

 

If you're trying to discover the actual figures for your aircraft, here's an exercise you could try.  Take off with a low amount of fuel in one wing, but plenty in the other.  In straight and level cruise, preferably with George the autopilot driving, set the fuel selector to the low fuel wing.  Prepare your mind for the engine to stop. Remain calm. As your fuel quantity gauge reads zero, watch your EGT gauge: it reads zero as the fire goes out, and CHT's will trend downwards.  Wait a minute, look at that windmilling propeller, observe how the plane still flies, savour the experience. Notice how the prop doesn't stop turning, and recall that air and spark are still present in the combustion chamber, and that you've only removed fuel from the equation. Calmly switch to the other (high fuel) tank.  As fuel meets air and spark again, combustion resumes (confirmed by EGT numbers again) and you can feel safe and satisfied knowing that all conforming engines are required to behave this way. Return to land, and when you get back to your hangar, drain the remaining fuel from the "low" wing.  That will be the amount of fuel (in that side) you cannot depart on. Repeat for the other side.

 

Polite discussion welcomed.

That works for a NA engine, it’s my understanding that a turbo at altitude it’s a little more complex, but if managed correctly it will come back

[Danb]

On 2/17/2024 at 10:00 PM, kortopates said:

Rick provided the correct answer which is in all the mid-bodies and long bodies. i don’t do much training in the vintage Mooney’s so can’t recall if min 12 gallons is listed. It’s not a limitation though, just a warning we’re a test pilot taking off with less than 12 on the tank we’re using. But regardless of model remember we’re all flying with the same wing despite some differences in unusable fuel - but that is another story.

With some of the loaded long bodies it can be a challenge maintaining over 12 gal in the tanks without getting over the max landing weight.


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You lost me on that one Paul..