How Much Useable Fuel With Monroy Aux Fuel Tanks?

[GeneralT001]

It says that the Monroy Auxiliary Fuel Tanks (adds 29 US Gallons), for a total of 93 US Gallons Useable.

Scouring the POH it shows 66.5 U.S Gal with 64 U.S Gal usable.

So is my total fuel with the Aux tanks 66.5 + 29 = 94.5 with 93 useable?

 

Thanks

[LANCECASPER]

Great question. Short answer: I think Yes.

But longer answer: when you get the POH in hand for your specific airplane there should be a supplement in the back for your Monroy tanks. Since your Monroy tanks empty into your main tanks your unusable fuel should be confined to your mains. There should be a placard near your fuel gauges saying that X amount of gallons on the gauge really means that you have Y amount of fuel since you have the Monroy STC. Eventually at some point your gauges read accurate once the Monroys empty into the mains.

This is a beautifully simple way of adding fuel. On some airplanes with aux tanks there are extra pumps and valves that can be confusing, which can lead to accidents. Also the mechanical gauges on the wings are a nice way of verifying approximately how much is in each tank once they are down below 30 on each side.

I've had Monroy tanks on 4 different Mooneys and in my opinion it is the best speed mod, safety mod and economy mod ever for a Mooney: Speed in the sense that if you avoid a fuel stop and stay in the air your over all trip takes less time. Safety in that the only times you ever have too much fuel is if you are on fire (or over gross on take-off or landing). Economy in the sense that if you buy cheap fuel and can tanker it, you save money if your next stop is  more expensive or your home base is more expensive.

[GeneralT001]

1 hour ago, LANCECASPER said:

Great question. Short answer: I think Yes.

But longer answer: when you get the POH in hand for your specific airplane there should be a supplement in the back for your Monroy tanks. Since your Monroy tanks empty into your main tanks your unusable fuel should be confined to your mains. There should be a placard near your fuel gauges saying that X amount of gallons on the gauge really means that you have Y amount of fuel since you have the Monroy STC. Eventually at some point your gauges read accurate once the Monroys empty into the mains.

This is a beautifully simple way of adding fuel. On some airplanes with aux tanks there are extra pumps and valves that can be confusing, which can lead to accidents. Also the mechanical gauges on the wings are a nice way of verifying approximately how much is in each tank once they are down below 30 on each side.

I've had Monroy tanks on 4 different Mooneys and in my opinion it is the best speed mod, safety mod and economy mod ever for a Mooney: Speed in the sense that if you avoid a fuel stop and stay in the air your over all trip takes less time. Safety in that the only times you ever have too much fuel is if you are on fire (or over gross on take-off or landing). Economy in the sense that if you buy cheap fuel and can tanker it, you save money if your next stop is  more expensive or your home base is more expensive.

Great answer....thanks!!

[kortopates]

speed brakes, if installed, reduce the extended tank capacity. As Lance said, check the AFMS to get specifics.


Sent from my iPhone using Tapatalk

[carusoam]

Sometimes speed brakes are mounted to the back side of the spar….

Meaning, only the bolt heads are inside the tank…

You can probably see from the outside where the brakes are and the spar goes…

 

Keep in mind….

you want to verify the numbers, and the sensors for accuracy before relying on them….

 

Another variable is how full tanks are defined…. And how they get filled to be usable…

Start with the POH…

The limitations section has some interesting theoretical detail…

The fueling procedures also captures a few more details….

Monroy tanks are great to have…

If you add Ceis fuel level gauges… there is an interesting calibration procedure that covers many details like the speed brake volume difference…

Blasting off…. The first time…. It is really good to know that the fuel floats are not sticky, and any low level fuel alarms are actually working…

Some people test this stuff by emptying the tanks and refilling… good idea in this case….

Others gain the experience over time… while getting used to the plane and all of its quirks…

Often people discuss running tanks dry…

Why they do it, and why they don’t….

 

GT, when you get a chance….  Add the details of your plane to your avatar area… I forgot which plane you have already… it is a great resource to use…

Best regards,

-a-

 

[Marc_B]

4 minutes ago, carusoam said:

If you add Ceis fuel level gauges… there is an interesting calibration procedure that covers many details like the speed brake volume difference…

Is there a specific procedure for this that increases accuracy? Or do you mean just adding fuel and letting equilibrate between the tanks between measurements? @carusoam where can I find details? Encore, speed brakes, monroy, cies. 

[carusoam]

20 minutes ago, Marc_B said:

Is there a specific procedure for this that increases accuracy? Or do you mean just adding fuel and letting equilibrate between the tanks between measurements? @carusoam where can I find details? Encore, speed brakes, monroy, cies. 

Probably one issue at a time….

The Encore was the most refined M20K ever…

The O1 has the speed brakes outside the fuel tanks…. It sounds nice if they were pushing directly on the spar…. Realistically holding the spar with a few bolts works pretty well too…. The O1 and Encore were built at the same time… in the same factory by the same people…

Ceis digital fuel floats have a higher accuracy by using more segments to get readings from… so their analog output is more accurate as well… we have the Ceis guy around here for more details…

Our standard analog fuel floats do an adequate job… right up to the point you install a digital readout with 0.1 gallon readings… 

POHs have come a long way over the years…. If you have the latest copy of the Encore’s POH… see how detailed their fuel system descriptions are… and how many locations the useable fuel is stated, and placarded in the plane…

On the panel, on the wing, and on the floor next to the selector valve….

The procedure for filling the tanks may also have been updated to reflect the 90s precision of getting real information into the customer’s hands…

See if your tanks have a reference for a full line, like the flapper valve… if you still have these installed…

Mr. Monroy still visits MS…. On occasion.

 

One change for TC’d birds… they don’t typically use the run the tank dry procedure…. Restarts of turbo engines can be challenging at higher altitudes… the TC slows, and becomes a mixture challenge….  Be familiar with your high altitude restarts either way…

Be able to avoid a turbo failure turning into an engine restart failure… if able…

 

Did I get what you were asking?

PP thoughts only, not a mechanic or CFI… or M20K owner like Paul (he has all of those and the CFII too…)

Best regards,

-a-

[Marc_B]

@carusoam I was curious about the “interesting calibration procedure” you mentioned. Wasn’t sure what you meant by that.

marc. 

[carusoam]

17 minutes ago, Marc_B said:

@carusoam I was curious about the “interesting calibration procedure” you mentioned. Wasn’t sure what you meant by that.

marc. 

Ceis has a gallon by gallon calibration procedure…

This relates float position to actual gallons on board…

Without this level of accuracy….  The floats would not be able to tell where the volume of the tank isn’t uniform with height…

like where chunks of the fuel volume are missing because there is a box-out for the speed brakes or other occurrence like that… Ceis has a great way of handling it…

Some other smaller quirks include spar caps, ribs and stringers, and other structural things inside the tank…and curved surfaces….

Our tanks are mostly rectangular with angled ends… pretty uniform with gallons vs. height…. There are clear advantages of using the actual geometry while doing the measuring…

 

Fill time is a real variable that doesn’t get accounted for with our equipment…

Fuel settling is a challenge caused by small holes in the ribs that allow for small bubbles of air to pass through….

It takes time for fuel to force air through the holes at the top of the ribs….

There are an extra couple of gallons at the top….

Something to get used to over time… usually.  Fill, wait, fill, wait… a few minutes each time… (for the O’s tanks, the O got long open, single compartment fuel tanks… one on each side.  Other planes got multiple tanks with hose between the main and extended compartment…)

Uneven surfaces are a quick challenge to recognize… most airport fueling areas are nice and level… except the one you are at when it is important… 

Multiple fuel caps because the extension is so far uphill compared to where the main tank’s cap is located…. Filling procedure becomes more important…

The O is simple… one fuel cap, that got relocated for the LBs…

Best regards,

-a-

 

[carusoam]

Hope this discussion is helpful for GT…. 
 

There may be some helpful info exposed, to consider… or look into deeper.

Best regards,

-a-

[Marc_B]

M20C/E/F/J/K roughly correlate to 17 gal w/o speed brakes, or 14.5 gal with speed brakes.  My total measured was 104.8 gal (not 104.5).  I'm sure there are some variation from aircraft to aircraft, but Monroy also spelled out procedures for measuring amount of fuel in Aux tank with dipstick to correlate to a rough fuel amount.  I haven't had a chance to really see how accurate this is, but from flying and fueling it's surprisingly close.  Since this all drains inboard I think all Aux fuel would be usable?  Does anyone know if there is any low point that holds fuel with the aux tank that doesn't drain into the mains?

AuxTanksVolumes.pdf

[LANCECASPER]

3 minutes ago, philip_g said:

Above about 25g a side, the fuel gauge were worthless with the monroys, they just read full. We made a calibrated stick by adding 5g at a time and letting it settle after we ran a tank dry intentionally. That helped some. Guess we just got used to not really knowing how much gas we really had between 50g and 100

 

Having a fuel totalizer on the panel and then writing down levels every time you switch tanks helps keep a very exact idea of what fuel you have on board and in each tank. Once you have burned off the fuel in the Monroys then your gauges read correctly, but I still like keeping track since it is amazing when you fill up how close your calculations are. 

[philip_g]

5 minutes ago, LANCECASPER said:

Having a fuel totalizer on the panel and then writing down levels every time you switch tanks helps keep a very exact idea of what fuel you have on board and in each tank. Once you have burned off the fuel in the Monroys then your gauges read correctly, but I still like keeping track since it is amazing when you fill up how close your calculations are. 

That's great if you have an hour to get the tanks totally full to start. Or until you forget one time to update the fuel. We had a jpi that replaced the factory gauges. I get this. It was still a pain in the ass. On a j it's not worth the hassle. On the rocket it was a necessity

Edited December 20, 2021 by philip_g

[carusoam]

Way cool avatar update GT!

 

-a-

[carusoam]

Unusable fuel can be found pooling in the area below, and inboard of the main fuel tanks’s sump drain/valve…

If the extended tanks have the same arrangement… there may be about a cup of fuel, water, dirt, hanging around below the drain… and lower than the fuel pick-up…

It is a challenge of geometry for plane builders…

 

It is always good karma to check the design of the drain valves to make sure you have the right one… there are many similar designs that don’t have their internal plumbing the same… this changes the height of the fuel that actually gets drained out…

Also look for extra sealant that may be on the drain holes… depending on the skill of the last person to do sealant maintenance…

 

PP thoughts only,

-a-

[Danb]

On 12/20/2021 at 1:44 PM, LANCECASPER said:

Having a fuel totalizer on the panel and then writing down levels every time you switch tanks helps keep a very exact idea of what fuel you have on board and in each tank. Once you have burned off the fuel in the Monroys then your gauges read correctly, but I still like keeping track since it is amazing when you fill up how close your calculations are. 

L, having a G1000  like your on trips I chart my beginning fuel/gal used/ remaining fuel each 30 minutes/GPH/MAP/RPMs and TIT. Comparing to the fuel totalizer on the 1000. My calculations generally agree with the totalizer. We don’t have much to do up there anyway when things are calm.

 

[LANCECASPER]

9 minutes ago, FlyingDude said:

I do that, but there are imperfections:

- my jpi allows to reset it to full tank amounts (mains only or all 4) when you fill up the tanks, or add a certain number if you just add a known amount. In the reset method, you need to be damn accurate as to fill the tanks to the same level every time. If you fill it to 82gl level but reset it to 84gl, 2gl in 84 don't matter much but they count when you think you have 6 gl left (~30-45min legal reserve). In the addition method, small inaccuracies in the pump readings pile up over time (assuming that your totalizer is error-free).

- the totalizer doesn't account for any leaks... Rare, but what if?

That's why it's good to have fuel gauges wiggling around and becoming relatively accurate towards empty...

And that's why I mentioned at the end of that post that, "Once you have burned off the fuel in the Monroys then your gauges read correctly"

[LANCECASPER]

15 minutes ago, FlyingDude said:

Yes. So you agree with me...

I have a placard that says "don't rely only on totalizer". They put it over the gauges. They should've put it rightover the jpi actually  

I agree with you on the fact that your totalizer may not be set up correctly.

If the K factor is set up properly in the programming,  the totalizer will be extremely accurate, which will be noticed when you fill up. Keeping track of it over time (comparing the total fuel shown used on the totalizer vs. the fill up) will help to adjust the K factor if it's not originally set up properly in the programming. A properly set up totalizer will be much more accurate than factory gauges.

The totalizer, the panel gauges and the wing gauges all help to give a good picture.

[LANCECASPER]

1 hour ago, FlyingDude said:

My totalizer is spot on, but I don't always fill the tanks to the same level when I "fill her up". If I'm filling up before a long flight, I stuff gas all the way up to the cap. That's 86gl. 90 total minus the 4 unusable. If I'm filling up a few days before a trip, especially in the summer, I leave 1-2cm right under the ext cap level in case it gets hot and I don't want fuel dripping from the vents. So that's ~84 gl in my plane, which is what I reset the jpi to. But, do I always exactly fill it to the same exact point? I doubt it.

Before I redid my tank, it started with leaking 1gl/week to dripping 1gl/2 days. The totalizer doesn't account for that.

You see where I'm getting at? I'm not discussing the accuracy of totalizers. I'm pointing out the starting point of totalizer accounting and any undesired losses.

I understand completely about not always filling it up. Glad to hear that the totalizer is spot on. If that's the case then just "add" the amount of fuel that you put in by using that function on the the totalizer. I've used Hoskins, Shadin and JPI totalizers on Mooneys over the last 30 years and found them to be very accurate and useful, but good record keeping is essential. They are not the only tool, but one important tool we have for fuel management.

The tank that you refer to - i agree, the totalizer wouldn't account for that. But a much more important point -  it should have remained completely empty at the rate it was leaking, since it was not airworthy with fuel in it according to the maintenance manual. Paul in Willmar and Edison in Fort Lauderdale have both mentioned that many times people have to ferry their airplanes to them using one tank for that reason. 

 

[carusoam]

Everything is good, until… the leak is upstream of the FF sensor…

In this case… the fuel is getting away, without being accounted for by the FF sensor…

in an ideal world… the totalizer and your fuel levels agree with each other…

If they don’t… you probably forgot to reset the FF totalizer… or you fuel has leaked out the sump drain… or fuel cap…

 

At least with the fuel cap… it leaves a big blue visible indicator as a signal…  the fuel sump won’t leave a visible indicator… until after you are on the ground…

+1 for having just enough excess fuel… thanks José!

Best regards,

-a-

[aviatoreb]

8 hours ago, carusoam said:

At least with the fuel cap… it leaves a big blue visible indicator as a signal…  

Unless your airplane is dark blue....

I did have a fuel leak immediately after repainting that was one spot where my initial tank reseal had an issue (which was fixed under warranty).  Initially there was talk of repairing the paint.  But honestly - you cannot see it even if you try - its on the underside of the wing, and even lying there on my crawler looking up to where I know the leak was (a few years ago now), I see nothing.  I know because I just relaxed the plane top and bottom last month.  I found the leak because - it was enough to drop on the floor.

[FlyingDude]

20 minutes ago, aviatoreb said:

there was talk of repairing the paint

Did the dye in the fuel damage your paint?

[aviatoreb]

1 hour ago, FlyingDude said:

Did the dye in the fuel damage your paint?

It doesn't seem so - looks perfect.  And the paint color itself is so similar to the dye color that there is no discoloration that I can see.

[aviatoreb]

3 hours ago, FlyingDude said:

Did the dye in the fuel damage your paint?

...oh and plus its on the underside of the wing, where one rarely looks anyway.