Full Fuel Tanks

[gsxrpilot]

@201er likely knows as much and has more fuel management experience in Mooneys than anyone I know. And I'm in complete agreement with him on fuel management.

Unusable fuel is meaningless to me and I'm not about to take published numbers as fact when I'm sitting in the left seat at 12,000 or any other altitude. I'd like to know, and the only way to know is to periodically run a tank dry at altitude, in cruise and use that to accurately measure useable fuel and verify fuel flow, K value, etc.

1. I would never be in the pattern or maneuvering on an approach within +/- 2 or 3 gallons of useable fuel in my active tank. So if useable is different in straight & level vs maneuvering, is meaningless. 
2. Knowing the useable fuel in each tank allows me the luxury of flying further in cruise and arriving with more fuel in the selected tank on approach to my destination. I would rather have a 3 to 5 gallon cushion in my selected tank on approach rather than a 1 or 2 gallon cushion in each tank. I can only have one tank selected at a time and don't intend to be switching tanks in the landing environment anyway.
3. A landing with an hour fuel reserve is actually a lot less than an hour if it's split between two tanks and I'm not 100% sure I know the actual useful capacity of each tank. But landing with an hour fuel reserve all in my selected tank gives me much more comfort. 
4. Switching tanks based on fuel burned is more accurate and the math is easier, than switching tanks based on time.
5. Only switch tanks at altitude in cruise. I'll typically switch to my fullest (landing) tank at top of decent. 
6. It would appear from accident studies, that the risk associated with mismanaging fuel and running out is a much, much, higher than the risk of the engine not restarting after running a tank dry at altitude. Typically the first item on any Emergency Checklist for engine out is to switch tanks. Periodically running a tank dry ensures that you will always immediately recognize the effects of fuel starvation and that your instinctual reaction is to switch tanks.
7. Personal minimums are real and important for any pilot. And my personal minimums on fuel at destination are likely as conservative as anyone. The only difference is I like to KNOW where the fuel is and how much is useable. 10 gallons all together in a single tank is much more useful than the last 5 gallons sloshing around in each tank. So if my personal minimums for a VFR flight was 10 gallons, an additional 2 - 5 gallons in the other tank doesn't help me at all. It just means that my personal minimums are actually 15 gallons, 5 of which are useless. 
8. I like to go far in my Mooney. And useful load is always an issue. So while fuel is critically important, landing with an extra 3 or 4 gallons in the un-selected tank doesn't provide any safety and takes away from range and useful load.

*Rant off

Planning KBXM > KHYI tomorrow... 

[201er]

^Exactly

[Hank]

But none of this ranting helps the OP know when the tanks of his new-to-him Mooney are full . . . Mine doesn't have a filer neck or an anti-siphon flapper, so full is when the fuel is up to the opening; but if I'm not just about to depart, I leave ~1/2" air for thermal expansion.

[peevee]

14 minutes ago, Hank said:

But none of this ranting helps the OP know when the tanks of his new-to-him Mooney are full . . . Mine doesn't have a filer neck or an anti-siphon flapper, so full is when the fuel is up to the opening; but if I'm not just about to depart, I leave ~1/2" air for thermal expansion.

If you have the monroy tanks, it's apparently never full. I've spent a half hour trickling in go juice only to dump another 5 gallons in from a can the next day. It's ridiculously useless.

 

Making your own calibrated stick is the only way to know for sure.

[milotron]

The flapper precludes use of the stick, but it seems that draining to empty in flight and careful refuelling will be the best solution here. From there I can know empirically how much fuel is onboard at given visual milestones ( bottom of flap, bottom of fuel neck, wing level gauges, etc ). All of this is made worse by my home base fuelling area having an aggressively sloped drain in the middle meaning that the wings are virtually never level, let alone from fuelling imbalance between the wings.

I think once I can get a known baseline established with the totalizer, I can have more confidence in what is actually remaining, regardless of the panel gauges.

 

Thanks for the all the feedback on this; clearly my observations on the discrepancy between the various indicators is not unique, and that each airframe will have a slightly different 'full' volume.

[whiskytango]

Does anyone have a suggestion for telling line personnel how to fill the tanks completely on a K model with Monroy auxiliary tanks?  I have told them to top off all 4 tanks, and routinely find that the level in the auxiliary tanks is about 3 or 4 inches below the cap.  This is a real annoyance when I am trying to plan a long flight without an intermediate stop for fuel.

[201er]

Just now, whiskytango said:

Does anyone have a suggestion for telling line personnel how to fill the tanks completely on a K model with Monroy auxiliary tanks?  I have told them to top off all 4 tanks, and routinely find that the level in the auxiliary tanks is about 3 or 4 inches below the cap.  This is a real annoyance when I am trying to plan a long flight without an intermediate stop for fuel.

That's probably not cause they didn't top it but because some time went by and the level went down. You're still at the full fuel capacity, just it spread out and came down a bit.

[carusoam]

Ever have Fuel come out the vent like a C152...? (Known for thermal expansion problems with full tanks...)

 

1) It can happen with a Mooney, but the hill you parked on will be unusually noticeable.

2) the dihedral of the Mooney is quite large compared to the C152.

3) The tank's vent is uphill a few inches above the fuel cap.

 

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4) the fuel pick-up is towards the trailing edge of the wing... this means, when you are on descent for final approach, the fuel is going to move away from the pick-up... Fortunately while going down hill, you have gravity working in your favor...

5) My M20C's fuel gauges could not discern which tanks had five gallons in it or not.... selecting the tank with the most fuel was harder to do than expected...

------------

6) Importance of the length of the crosswind runway...

• When you stick a valve on departure, the next runway that becomes available is the cross wind runway on your left (or right)...
• when you don't know if the engine is going to continue to deliver power, it is comforting to know that runway was is really long...

--------------

7) telling a line man that you have four tanks probably over simplifies the situation...

• Interconnected tanks have a lot of fuel movement and air displacement going on...
• Your plane has a specific filling procedure that is unknown to most Mooney owners, never mind a lineman at any airport...

8) George/AOPA had developed a business card for fuel filling instructions, with all the important details for your plane.

• If you want it done right, leave instructions everywhere...
• i usually oversee the filling procedure out of caution. Too easy to get jet fuel accidently...

 

Best regards,

-a-

[jaylw314]

42 minutes ago, Hank said:

But none of this ranting helps the OP know when the tanks of his new-to-him Mooney are full . . . Mine doesn't have a filer neck or an anti-siphon flapper, so full is when the fuel is up to the opening; but if I'm not just about to depart, I leave ~1/2" air for thermal expansion.

I've always filled to the filler cap neck and maybe overshot a couple times, but I've never seen anything come out of the tank vents.  I think I remember somebody saying the fuel vents are at the very outboard ends of the fuel tank, which are bit higher than the filler cap, so leaving an extra 1/2" might be overkill.  Well, at least to keep it from coming out the fuel vents, but I did have fuel come out the filler cap when I opened it on a hot day 

[peevee]

1 hour ago, 201er said:

That's probably not cause they didn't top it but because some time went by and the level went down. You're still at the full fuel capacity, just it spread out and came down a bit.

This makes no sense. It's full but there's air in it because it settled? Mmmmnoo

You have to fill the monroys painfully slowly as you push air out the vent line.

[201er]

23 minutes ago, peevee said:

This makes no sense. It's full but there's air in it because it settled? Mmmmnoo

You have to fill the monroys painfully slowly as you push air out the vent line.

You will get to at or above certified full fuel just by filling it quickly. It will look full to the brim but settle down as it fills out in a few hours. If you choose to fuel slowly or add more after it settles, that is a bonus, beyond certified full fuel, capacity.

It is one of the reasons it's impossible to measure fuel with total accuracy on Monroy equipped Mooneys.

[Guest]

Sure glad I fly a Piper Comanche, refuelling a Mooney seems as difficult as flying one.  When I fill the tanks and there is no air left the tanks are full and it doesn't settle to some new imaginary "certified full" level.

Clarence

[gsengle]

Sure glad I fly a Piper Comanche, refuelling a Mooney seems as difficult as flying one.  When I fill the tanks and there is no air left the tanks are full and it doesn't settle to some new imaginary "certified full" level.
Clarence

No such nonsense on my R without extended range tanks


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[gsxrpilot]

I don't have the Monroy tanks, but just a stock standard 252. And it's frustrating as hell to get the tanks full. I'm never quite sure if I'm full or not. The best I can do is fill to a number on the wing gauges. On this trip to Maine and back, we're very heavily loaded so I've been just filling to the 30 in both tanks. 

In my M20C, fueling was so easy. Even though it was only 52 gallons, it was nice to spend 10 minutes on the ground and KNOW I was departing with 52 gallons.

With the K it's often a guess.

[Guest]

Just now, gsengle said:

 

No such nonsense on my R without extended range tanks


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Yours must be defective, it sounds normal with some Mooneys.

Clarence

[gsengle]

Yours must be defective, it sounds normal with some Mooneys.
Clarence

And besides I almost never put the full 89 gallons on board. That's a whole lot especially climbing out of a small field.


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[carusoam]

Visual inspection of fuel level...  Little glass windows would be awesome...

Two 'full' lines one on each wing would work...

My O1 is as easy to fill as my M20C...

Filling to 101 gallons takes a few minutes extra to allow air to escape. It's like having a big air bubble get caught in there...

the 252 must have some baffling, baffling issues internal to the tank.  Internal ribs have to allow air to flow out of the system.

Similarly the ribs have to allow fuel to move from one side of the ribs to the other...

It would take looking up what the ribs look like as they would have fuel drain holes at the bottom and air drain holes at the top. Probably bent shapes during part forming leaving gaps at the bottom and top of the tanks...

 

@Piloto your thoughts?

Best regards,

-a-

[peevee]

3 hours ago, 201er said:

You will get to at or above certified full fuel just by filling it quickly. It will look full to the brim but settle down as it fills out in a few hours. If you choose to fuel slowly or add more after it settles, that is a bonus, beyond certified full fuel, capacity.

It is one of the reasons it's impossible to measure fuel with total accuracy on Monroy equipped Mooneys.

 

We don't get anywhere near the 103 or 108 capacity without some serious effort.

You certainly don't just top it off to the neck's and walk away.

[kortopates]

I don't have the Monroy tanks, but just a stock standard 252. And it's frustrating as hell to get the tanks full. I'm never quite sure if I'm full or not. The best I can do is fill to a number on the wing gauges. On this trip to Maine and back, we're very heavily loaded so I've been just filling to the 30 in both tanks. 
In my M20C, fueling was so easy. Even though it was only 52 gallons, it was nice to spend 10 minutes on the ground and KNOW I was departing with 52 gallons.
With the K it's often a guess.

That's only true if filling above the factories definition of full which is at the base of the filler neck. After you're recent re-seal didn't you find you got factory rated capacity at the base of the filler neck?


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[Guest]

SB M20-230A is relevant to this,

http://www.mooney.com/en/sb/M20-230A.pdf

[Danb]

I've had L/R tank for 11 yrs, I fill them up and have about 120 gal, then if needed can painstakingly fill to the skin and have about 130. There's a lot of leeway telling the lineman to fill it up. On long trips I have to examine them after there filled.

[milotron]

10 minutes ago, M20Doc said:

SB M20-230A is relevant to this,

http://www.mooney.com/en/sb/M20-230A.pdf

Thanks Clarence.

 

Interesting that the M20K has 2 big dedicated antislosh valves, while all others use a series of holes to allow for fuel equalization at the bottom of one of the ribs.

[kortopates]

Thanks Clarence.

 

Interesting that the M20K has 2 big dedicated antislosh valves, while all others use a series of holes to allow for fuel equalization at the bottom of one of the ribs.

So does the M20K - no different than J really (except the wet area in the K is a bit larger) but the issue is with the small holes in the top of the ribs, not the bottom. They get mistakenly or accidentally blocked by patch repairs and then trap air and prevent people from getting rated fuel capacity. And without the knowledge of the pilot if they don't drain the tank to empty and fill to see what it really takes.

 

 

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[gsxrpilot]

46 minutes ago, kortopates said:

That's only true if filling above the factories definition of full which is at the base of the filler neck. After you're recent re-seal didn't you find you got factory rated capacity at the base of the filler neck?

I've only topped off the tanks one time and it seemed that they would only hold about 73 or 73.5 and that was up past the base of the filler neck. We haven't calibrated the fuel gauges in the JPI yet so we'll get a chance to check it again.

[Guest]

Maybe there are a few gallons of PRC sealant steeling some of your tank capacity?

Clarence