Hello all,

I am a new Comanche owner and love everything about my new plane except for draining the fuel sumps. The center drain tube is inconvenient to say the least. I am wondering if any of you who have much more experience with a Comanche than I have figured out a good way to drain/check fuel with minimal spillage or waste. Right now I am just using a rather large container that I guesstimate where to put it and hope for the best. Anyone have a good solution?

Thanks.

Hi Ron,

Congratulations and welcome!!

I use a 30 gallon sterile container from Walmart, slide it under, sump, check for water and dirt and then reuse gas in the tow that gets the twin in and out of the hangar.

If you search the forum there are folks who have done significantly more elegant solutions. see the upper right corner.

Hi Ron,
Welcome to the forum.
Here is the solution that I found, a baking pan where I made two holes for the tow bar.
I placed it under the drain tube and works great… except when you are alone, outside and its windy!

I use a small glass cup. I made a box that gets the cup to the right height. I than drain a little from all 4 tanks. If all is good than I proceed. In the event of water, I would have to narrow down which tank.

All,
Just a quick refresher on how our Comanche fuel systems work. There is NO TANK SUMP in any tank. All of the fuel that is in a tank will drain out of the tank. Some of our sub type (Twin, 250, 260 400) aircraft have a value of fuel labled "unusable" but this is simply a function of certification, as all fuel will drain from all tanks if the aircraft is in a somewhat level attitude. When "sumping" the aircraft, you are only draining the gascolator or strainer bowl. Only fuel that passes through the strainer gets filtered. In order to get fuel to pass through the filter the fuel must be sucked through it, thus the engine must be running (or you have a really big fuel leak somewhere downstream). So, the best time to actually sump the aircraft is After a flight, or after there has been fuel sucked through the strainer.

Now, the question of checking the fuel after refilling the tanks. Unless you are willing to dump a significant amount of dead dino juice out of the belly of your aircraft, sumping each tank does absolutly nothing more than you did after you shut down. Think about this for a minute. In order to actually see what is in a tank, assuming the fuel line was not totally dry before you refilled it, you will have to allow whatever is in the tank to settle, then you will have to drain enough fuel out of that "tank" so that all of the exisiting fuel in the line from the tank to the selector is cleared, and then you have to drain additional fuel to see whats in the tank. Mains have shorter lines than aux tanks, but in order to do the whole process on a 4 tank aircraft, you are looking at sumping a total of about 2 gallons to get an accurate tank sample. Obviously, unless you suspect that a large abount of contaminents are present from a pump, this process is not cost effective or practical.

If you truly are worried about fuel contamination, it is a better practice to treat that at the source by using a fuel filter funnel or something similar. If your aircraft is outside in the rain, you can prevent water contamination by ensuring that your gas caps are proper and tight, that the tank filler covers have good gaskets, and that the scupper drain for the filter well is free and clear of bugs, old paint and garbage. Be aware that the twins aux tanks are particularly susseptable to attracting water if the outer door gasket is bad. The tank vent actually protrudes into the filler neck causing a not so round surface that you are trying to plug with a round cap. Of all the tanks on all of our aircraft, the most likely to see water contamination is an Aux tank on a twin.

-Zach

Hi Zach,

Thanks for the explanation.

Can you run me through exactly what you do before flight with regards to the 'sumping the fuel'. If I understand you correctly are you saying that there is no real value in draining a couple of ounces from one tank, changing tanks and draining a couple more ounces?

Cheers,

James.

Yes, draining a few oz from each selector position is really a waste of effort unless you are going to drain lots of fuel. I drain post flight and do not drain during preflight. Looking at the post flight sample will show you what was collected out of whatever tank(s) that were used in flight.

Zach

Zach, that was a very clear explanation, thank you.

Will, in your view, make sense then to sump one main tank, lets say 30 seconds, take off with that one and then, when you switch tanks at altitude deal with any potential water problems under better circumstances that at take off?

Andres,
Yes, that would certainly be an acceptable and effective way to deal with the issue.

The fact remains, that unless you have significant contamination, if your strainer bowl is cleared, it will absorb its volume of contamination before there is any issue with the engine operating. If anyone out there is finding significant water or other contamination in any of their birds, it needs to be addressed. It is not normal to find anything but fuel in a sample of a properly cared for Comanche under normal circumstances.

-Zach

Thank you Zach.
I have never found any water in my tanks, besides my aircraft is always hangared, however I worry about condensation when I go to the sea side, where it is hot and humid and then you have to drop from 12,000 ft to sea level in about 40 miles.

Not to say condensation doesn't happen, but I haven't seen it in any Comanche, including my turbo twin after flying in the flight levels for 4+ hrs and descending into the Florida humidity. Here's why I think it doesn't happen. Even if you are at altitude, you need to be there a long time to cold soak a full tank of fuel. If you are there a long time, then you don't have much cold soaked fuel and it will warm very quickly. In burning the fuel, you have sucked dry air from altitude into the tank through the tank vents. So, even though you may see some external condensation for a short period on the bottom of the wing after landing, the air in the tank is significantly less humid than the air you are descending into. Even if you do get some condensation in the tank on descent, the sloshing of the fuel should knock it loose and it will wind up in the sump drain to be expelled on a post flight drain. Once the temperatures are normalized(and this happens very quickly), there is very little chance of further condensation, especially if you fill your tanks post flight.

-Zach

Thanks Guys..... This is an excellent post and very helpful! Zach, I always enjoy your posts! Thanks for sharing your knowledge!

Ed

This thread is broader now so I'll add my 2 cents on sumping in general.

The times in 44 tears of having it in the family that I have seen condensation in the Twin's tanks are few but worth noting. We usually found it on pre-flight but not always and I really don't like that hiccup sound - even with two engines.

About 15 year ago we were on the return from visiting ill father-in-law. I was PIC and the trip was so stressful, I forgot to sump. Auxes were partially full. Halfway home on a very cold day, the engines take turns hiccupng. I mentally cursed myself and I haven't let it happen since. The pitot cover stays on until fuel has been sumped.

We sump before the first flight of the day and after the last one. We have yet to find any contamination in post flight sumping.

Pre-flight sumping we have occasionally found water and before I had all the bladders and hoses replaced, we found some tiny specks. Fuel caps and fuel door gaskets do wear over time. Water in the fuel is the first indication that something needs attention that we get.

More than once, while hangared, dirt daubers have elected to make their new home in the sump tubes - overnight occurrences. Really slows down the departure process but better find9ng the problem at the home airprot.

When all tanks were in good shape, we would get condensation in partially full bladder tanks we'd left less than full for useful load reasons. I used to rock the plane, wait and then sump the fuel.

The Miller wet wing tanks, Webco nacelle tanks and tip tanks are much more likely to sump garbage/water in descending sequence despite being topped off.

I've attached our sump process. Hope it helps.

Couldn't get the file to attach so here is the cut and paste.

N3322G FUEL HYGIENE

This is the process we use to sump fuel on our Twin Comanche. It has evolved from the methods we were taught. The results are that the fuel sump screens are remarkably clean at each 50 hour AD inspection – so much so that shops have commented upon their cleanliness. Sumped fuel has been entirely water and debris free for almost two years or more of flying. I should mention that all bladders were replaced in 2009/2010, fuel door seals are fresh and I do my best to keep the fuel caps in good condition. When home, the aircraft is hangared in Texas where the heat eats rubber for lunch.

1. Before the first flight, place 30 gallon sterlite bin bottom under sump drain lines (or something that will catch fuel)
2. Start with selectors on main tanks
3. Sump right main by holding up rear sump drain
4. While holding sump open, change to right aux (notice movement of mechanism in sump area)
5. While holding sump open, change right selector to crossfeed
6. Release sump drain
7. Return selector to right main
8. Sump left main by holding up forward sump drain
9. While holding sump open, change to left aux (notice movement of mechanism in sump area)
10. While holding sump open, change left selector to crossfeed
11. Release sump drain
12. Return selector to left main
a. If fuel in tips - with selector on right aux, turn on master and switch to right tip
b. Sump right tip by holding up rear sump drain
c. Return switch to aux
d. Return selector to right main
e. If fuel in tips - with selector on left aux, turn on master and switch to left tip
f. Sump left tip by holding up forward sump drain
g. Return switch to aux, master off
h. Return selector to left main
13. Check fuel in bin. If debris, individually sump tanks until sumped fuel is clean
a. If fuel in tips, sump right tip external sump on tip
b. If fuel in tips, sump left tip external sump on tip
c. If nacelle tanks have fuel sump at external sump valves both sides
d. If Miller wet wings have fuel, sump at external sump valve on both sides
14. Fly
15. Fuel main and aux tanks (and any other desired tanks)
16. After last flight of day, sump main and aux tanks again.

Zach hit the key!
Fuel tanks not filled post-flight and stored in unheated conditions are prone to water accumulation from
temp changes in cool/cold weather. Daytime temps go up, air can hold more humidity, nighttime temps go down
and humidity in air inside tanks turns to condensation.
Solution? Heated hangar and/or full tanks.
Works for me.
Steen
PS Excellent description of fuel tank sumping by Zach!!