252 with Monroy Tanks Dip Stick Info

[Pinecone]

Attached is the information to figure out how much fuel is in your tanks.  My plane is a  1986 252 with Monroy aux tanks and speed brakes.  The main filler is placarded at 37.8 gallons and the aux fillers at 14.5 gallons.   

I ran the right tank until the engine sputtered.  Then I added fuel 2.5 gallons at a time.   To measure, I used a Universal Fuel Hawk and a Fuel Stik.  The Fuel Hawk is the clear plastic tube you stick in and cover the end with your thumb.  The Fuel Stik is a tube with a float that you insert and then read how much of the float rides up.  I also measured the Fuel Hawk level in inches.  I also have the sight gauge readings for my airplane.  I will be sending the Fuel Stik info to the company, as the offer to generate a custom scale to insert in the device.

I found that I could see fuel at 7.5 gallons, but I could not get a reliable measurement, so the chart starts at 10 gallons.  I could see a wash of fuel in the aux at 25.0 gallons, but could not get a reading.  Notice that even though I am placarded at 52.3 gallons useable, I got more than 54 gallons in the tank.  I set my JPI to show fully fueled at 104 gallons useable, so I will have a bit of reserve in my pocket.

One other interesting thing was, even when the fuel was almost full at the aux filler, when I added fuel, I could hear air bubbling out of the main.  I would have thought that the main would be filled a long time before the aux got to the top.

 

Universal Fuel Hawk - https://www.mypilotstore.com/MyPilotStore/sep/1177?gclid=EAIaIQobChMIo8eww-ic_QIVBrjICh10RQJAEAQYASABEgIdLPD_BwE

Universal Fuel Stik - http://fuelstik.com/product/fuelstik/

Enjoy

Fuel Measurements.pdf

[1980Mooney]

7 hours ago, Pinecone said:

One other interesting thing was, even when the fuel was almost full at the aux filler, when I added fuel, I could hear air bubbling out of the main.  I would have thought that the main would be filled a long time before the aux got to the top.

If the prior owners retained the paperwork, you should have a 60+ page binder from Monroy Aerospace with the STC, installation instructions and drawings.  You can see that the tubing connecting the long range tanks to the mains are only about 3/8 in. ID.  There is only a few inches of head pushing the avgas from the Aux to the Main - however you are filling the Aux with an approx 1 inch hose under pressure at about 15-20 GPM.  If you have the Aux empty and fill the Mains to the lip and wait the level will drop slowly as the head pushes some fuel to the Aux.  So if you then fill the Aux to the lip it, being higher, will push the fuel slowly back to the Main.

Also when you stick the Aux tank, where do you position the tube relative to the tank opening? - the bottom of the tank (the wing) slopes - so you will get a different level depending on where the stick rests.  Do you center the stick in the tank opening or align it adjacent one side or the other?

[Pinecone]

1)  I waited at least 5 minutes between each addition of 2.5 gallons.  I also checked, waited a minute or two and checked again to make sure it was not changing.

2)  I used the same location for each reading.  For the Fuel Hawk, I used the inner, aft cutout in the cap mount.  For the Fuel Stik, I put it at the after center of the opening.  Due to the flaps and the size of the Fuel Stik, this worked best.

3)  Yes, I understand that they are connected and it takes time for the fuel to move from one tank to the other.

[Will.iam]

13 hours ago, Pinecone said:

Attached is the information to figure out how much fuel is in your tanks.  My plane is a  1986 252 with Monroy aux tanks and speed brakes.  The main filler is placarded at 37.8 gallons and the aux fillers at 14.5 gallons.   

I ran the right tank until the engine sputtered.  Then I added fuel 2.5 gallons at a time.   To measure, I used a Universal Fuel Hawk and a Fuel Stik.  The Fuel Hawk is the clear plastic tube you stick in and cover the end with your thumb.  The Fuel Stik is a tube with a float that you insert and then read how much of the float rides up.  I also measured the Fuel Hawk level in inches.  I also have the sight gauge readings for my airplane.  I will be sending the Fuel Stik info to the company, as the offer to generate a custom scale to insert in the device.

I found that I could see fuel at 7.5 gallons, but I could not get a reliable measurement, so the chart starts at 10 gallons.  I could see a wash of fuel in the aux at 25.0 gallons, but could not get a reading.  Notice that even though I am placarded at 52.3 gallons useable, I got more than 54 gallons in the tank.  I set my JPI to show fully fueled at 104 gallons useable, so I will have a bit of reserve in my pocket.

One other interesting thing was, even when the fuel was almost full at the aux filler, when I added fuel, I could hear air bubbling out of the main.  I would have thought that the main would be filled a long time before the aux got to the top.

 

Universal Fuel Hawk - https://www.mypilotstore.com/MyPilotStore/sep/1177?gclid=EAIaIQobChMIo8eww-ic_QIVBrjICh10RQJAEAQYASABEgIdLPD_BwE

Universal Fuel Stik - http://fuelstik.com/product/fuelstik/

Enjoy

Fuel Measurements.pdf 52.97 kB · 14 downloads

Thanks for your detailed analysis of fuel levels as i too have the monroy extended tanks and i get a reliable 10 15 20 reading but 25 30 and 35 are not due to the flow into the aux tank. I will top off the inner tank then quickly fill the aux so that I minimize the amount of flow out to the aux but even then i can burp the aux tank literally 15+ times adding fuel with each time being less of an amount and i say 15+ as i stopped there as i had managed to squeeze in 104 gallons not including the 5 gallons i had in the other tank and if there was any fuel left in the tank i ran dry so i know i had at least 109+ so i was comfortable with setting my jpi for 105 as full tanks as i can easily get that with only a few burps instead of the 15 which had diminishing returns of adding fuel. 

[carusoam]

Pinecone…

When you get a chance…

post a pic of where you stick the tank…

I appreciate the logic…

It might be something that we can standardize on…. 

 

MS logic rules!

Best regards,

-a-

[Z W]

I went through this exercise once.  If you fill the mains to the cap, then fill the aux, on our plane anyways, the pressure will start pushing fuel out of the inspection plate on top of the wing nearest the fuselage.  Good way to find out where your tanks might be leaky.

Keeping track of all 4 tanks with a dipstick requires a lot of patience, waiting after fueling for the fuel to equalize, and a calculator, unless you're better than me at doing math in your head.  90% or more of the time, I fill the mains and go.  Leaves you with 75 gallons, plenty of useful load for 1-3 people with bags, and the answer to "How much fuel do I have?" is 6+ hours and more than enough.  The sight gauges become pretty accurate under 25 gallons or so.  

I also have found the tanks will hold more than the placarded 105 gallons if you're patient while filling.  But again, it starts leaking out the top of the wings and sloshing out the vents, so not for long.  Also, with 105 on board, there's not much useful load left for anything but the pilot, so not a lot of reason to do this on many flights.  Good for flying to Alaska without stopping in Canada, heading out to the islands, or setting endurance records, I guess.  It is cool to have a plane that's able to use essentially all of its useful load on fuel if you want though.  Makes for an amazingly capable machine at 11.5 GPH and 175 knots.

[Pinecone]

I can get a picture of the aux filler port and the locations I used later today.  I can't get a picture of the main filler, as the tanks are FULL.

And yes, I discovered a leaking screw from having totally full tanks.  

As for keeping track, my thoughts are to dip after landing to see what is in the each tank, then I will just put in what I want to get to where I need to be.  The only caveat, if you think you have over 42 gallons, open and dip the aux FIRST.

Actually, opening and dipping the aux filler first is probably a good habit to get into.  If there is enough fuel to get a reading, you don't need to dip the main filler.  And if there isn't, you can then dip the main, or use the sight gauge.

I need to do the same on the left tank to check the sight gauge readings.

[carusoam]

Mooney fuel tanks are overall pretty simple…

The M20K got the most complex fuel system we have…

from flapper valves, and overflow tanks, to the location of the range extension tanks…

then there are the hidden o-rings in each fuel cap…

then there is the whole priming system evolution…

Kinda the price of greatness…. 
 

best regards,

-a-

[Pinecone]

OK, as requested, here are pictures of the locations I used the two devices.  You can see how large the Fuel Stik is and why, due to the flapper I used dead after to reduce how far you have to push the flapper in.  The pictures are of the aux filler.

 

[DonMuncy]

I wonder how many MSers are like me about fuel measuring? I like to know that my dip stick and my gauges are accurate down to the gallon. However this is an academic exercise for me. If I am flight planning and get down to anything approaching 10 or 12 gallons, I am going to plan something different. If I am flying, it is even worse. I have had my plane for 22+ years, and have seen only one low fuel light on one tank come on. That, or course, doesn't count when I ran a tank dry intentionally, to make my fuel stick. 

Except for my crazy desire to know it is precise, I doubt if it would ever make a difference if all my measuring devices were off 10 gallons.

[Pinecone]

I originally was going to do it in 1 gallon increments.   But decided 2.5 gallons was easier and close enough.

I did run a tank to the low fuel light in December.  I was going to be somewhat low on fuel on landing, and my preference is to have as much as possible in1 tank versus spilt between two.  I was not tight as to run one tank dry, but I did want to run it down a bit.

And again, my use of this is to see how much fuel in in the plane to determine how much to add based on the next leg and W&B concerns.

 

If you are interested, the reason 2.5 increments was easier is:  I have 5 each 5 gallon jugs. I filled all 5 up with 55 gallons each.  Since if there is less than 5 gallons in a tank, I don't care how much less, I poured one jug into the tank.  I then took a full one and poured half into the empty one.  This was easy to check, as I set the two jugs next to each other to see that the levels matched.  Add the 2.5 gallons into the tank, wait for the levels to settle, measure, repeat.

[Z W]

I've only seen the low fuel light once.  It was near the end of a trip, in the dark, about 10NM off shore over the Gulf of Mexico due to ATC routing.  I switched to the other tank which had, supposedly, about 15 gallons left.  In theory that, plus the 4 gallons in my low tank, was good for another 2 hours of flight at descent fuel flows with 1 hour remaining in the flight, giving me a 1 hour reserve, to land with about 10 gallons on board.  That was planned, as I had 3 adults on board and was stretching for range.

I landed short and bought some gas when that low fuel light came on.  Didn't care for that feeling and don't plan to see that low fuel light again.  I plan my fuel much more conservatively now, and don't really ever see less than 10 gallons on each side.  Reliable amounts of usable fuel in both tanks is a redundancy I put a value on.  I'm probably extra cautious in part because of the difficulty in being precise with the extended tank setup.

[Pinecone]

My next step will be to run the tank down to the low fuel light, then fill to see how much is actually in the tank at the low fuel light.

[rickseeman]

I want to do the same. Please post your results. Thanks

[Pinecone]

Low fuel light is adjustable, so you need to do your own and do both sides. 

 

SEPARATELY.

 

[Will.iam]

From low fuel light coming on to running dry at 10gph took 23 mins but that can’t be relied upon as when the low fuel light comes on varies from time to time. I have also pressed to test the low fuel light to verify the bulb didn’t burn out one time as my mental calculation and fuel flow totalizer both said i should be about empty but the low fuel light had not come on. After the test lit up both low fuel lights for each tank, when i released the test button the tank with low fuel the light then stayed on so i didn’t know when it ahould have except the engine started sputtering before the usual 23 mins where up. 

[Pinecone]

There is also an adjustment of the low fuel light activation point, so every plane and even left to right is likely to be different.  You need to test YOUR plane, both sides.

[geoffb]

thanks for doing this, it's been on my to-do list

Miss Piggy is heavy enough that for any sort of short field work I need to consider fuel very closely.  In the E it was simple.