Precautions when draining fuel from my aircraft

[mox499]

I would like to drain the fuel from my Just Escapade EAB Light Sport. It's a high wing, fabric over welded steel tube construction, with fiberglass fuel tanks in each wing. The tanks rest between fore and aft spars made of aluminum tubing, and are glued to the spars with epoxy.

The two tanks each feed a single aluminum header tank located behind the seats. There is a metal push-to-open drain valve at the bottom of the header tank, which I use to sample the fuel for water contamination. All the connections are by way of rubber fuel hose.

To drain the fuel down to the "minimum usable" level, I plan to lock the drain valve open and let the fuel run into a plastic funnel and into a plastic fuel can. Next, I'll re-weigh the plane, then calibrate my fuel tank dip stick as I return fuel to each wing tank through the filler port on top of the wing. I'd like to complete the whole procedure in my hangar, which is well ventilated, but has other airplanes in it.

Here are my questions for the forum:

1. Is there a risk in this procedure that a static charge could build up somewhere and create a spark that would result in a bad day for all concerned?

2. Should I run some kind of an electrical ground lead to prevent the spark?

3. If so, where should each end of this lead be connected?

4. Should this lead be heavy or light gage? Something in between? Does wire gage matter?

Thanks for your help on this.

John Smoyer
mox499@yahoo.com
N280MJ at N57

[FlyingRon]

You are 100% correct in your guess that there's a definite static problem with defeuling. I've seen two different defueling fires result in aircraft loss (the owner/pilot of one is sitting right next to me). Any time you have falling liquids you are going to generate static.

1. Drain things OUTSIDE the hangar.
2. Keep the distance the fuel falls to the minimum. If possible connect a conductive hose to the drain rather than letting it fall.
3. Bond everything. Bonding size isn't overly important. Good contact is.

Frankly, if you know what the USUABLE fuel is supposed to be, I'd not worry about getting it bone dry. What you want to do is add it in small increments until the tank is full and then work backwards from "absolute full / max usuable fuel" down. If you do it the other way, you have no clue if you're measuring useable or unusable fuel.

[Frank Giger]

1. Is there a risk in this procedure that a static charge could build up somewhere and create a spark that would result in a bad day for all concerned?

Yes, there is a small chance. A very small chance. But in aviation we tend not to like to take even small chances, as the penalties are very high when the odds are bucked.

2. Should I run some kind of an electrical ground lead to prevent the spark?

Absolutely. And make sure the can on the ground is grounded as well. Most tales of fires from gas cans involve them being in the beds of pickup trucks or otherwise not grounded.

3. If so, where should each end of this lead be connected?

Best place is exposed (non-painted) metal part of the aircraft. When in doubt, the exhaust pipe on the engine is a really good bet. The ground end has to be hooked, well, to the ground. Assuming you're pulling the aircraft out of the hangar and spinning it about to where the nose is now pointed in, I'd connect the ground from the exhaust to the metal plate the doors ride on at the front of the hangar or one of the metal posts of the hangar.

4. Should this lead be heavy or light gage? Something in between? Does wire gage matter?

Well, look at the ground wire they use on fuel trucks at the airport - it's not very big gauge at all. A poor man's solution is to use a heavy gauge wire with clips on both ends, also known as "jumper cables." Or strip the ends of an old outdoor extension cord.

[edit]

While I have been known to put a gallon or two into my little Nieuport in the hangar, I wouldn't do it if there were other aircraft in the hangar. The "best practice" of fueling and de-fuelling is to do it outside of hangars, a practice learned through hard experience.

[1600vw]

It sound like you are trying to find usable and unusable fuel. Is this what you are trying to find?

The FAA put out some info on how to check for usable fuel and unusable fuel. You do not do this with the airplane setting level.

[mox499]

Thanks to all of you for the excellent and fast responses. Frank's suggestion of jumper cables is right on. Based on these replies, I'll do the procedure in front of the hangar, running jumper cables from the handle of the plastic gas can and from the plane's exhaust pipe to the hangar door frame. I'll connect a hose from the drain valve to the bottom of the gas can. It'll be electrically conductive hose if I can find it. Otherwise, I'll connect one end of a wire to the valve, and the other end to the handle on the gas can.

In reference to 1600vw's reply, I'm doing this because I want to measure the weight and CG of the airplane with minimum useable fuel. I figure I'll be at that point when the plane is sitting on its tricycle gear, is on level ground, and no more fuel is coming out of the header tank. After I have the weight, I'll return fuel to each tank, a gallon at a time, and calibrate the dip stick at each gallon.

Thanks again for your excellent and timely inputs, folks.

[1600vw]

Thanks to all of you for the excellent and fast responses. Frank's suggestion of jumper cables is right on. Based on these replies, I'll do the procedure in front of the hangar, running jumper cables from the handle of the plastic gas can and from the plane's exhaust pipe to the hangar door frame. I'll connect a hose from the drain valve to the bottom of the gas can. It'll be electrically conductive hose if I can find it. Otherwise, I'll connect one end of a wire to the valve, and the other end to the handle on the gas can.

In reference to 1600vw's reply, I'm doing this because I want to measure the weight and CG of the airplane with minimum useable fuel. I figure I'll be at that point when the plane is sitting on its tricycle gear, is on level ground, and no more fuel is coming out of the header tank. After I have the weight, I'll return fuel to each tank, a gallon at a time, and calibrate the dip stick at each gallon.

Thanks again for your excellent and timely inputs, folks.

You need to do fuel flow test to determine usable and unusable fuel. This needs to be done at both a nose high attitude and a nose low attitude. Only then will you know your usable and unusable fuel load. This is so very important that you do these test, the FAA a few years ago had or made a big ordeal about this. They put out a notice or form showing what needs to be done to determine usable and unusable fuel.

Without me going into all this please look for this info and follow it to the letter.

1600vw

[1600vw]

fuel flow and unusable fuel check: This series of tests is designed to ensure that the aircraftengine will get enough fuel to run properly in all normal flight attitudes. The recommended testsare intended to duplicate the conditions found in a maximum power climb near the edge of apower-on stall, a maximum rate of descent with power off and full flaps at the top of the whiteairspeed arc, or in a plane with no flaps, at the top of the green arc. Lastly, the tests verify thatfuel flow remains steady in a slip with low fuel.

All of these are normal flight attitudes. Fuel flowduring aerobatic maneuvers is not considered.Page 4 of 14P.O. Box 3086 Oshkosh, WI 54903-3086 | Tel 920.426.4800 | Fax 920.426.6560 | www.EAA.orgAny good fuel system will incorporate these important elements:1) Adequate capacity and adequately-sized fuel and vent lines for the engine being used.Typically fuel lines will be 3/8” and vent lines will be ¼”. Fuel quantity depends on the demandsof engine.2) Some way to remove water and other contamination from the fuel tank (sump drain, fuelfilter, gascolator, etc.)3) Fuel and vent line routing that will not allow water or sediment to collect in any lowpoints. Unavoidable low points need their own drains.4) A means of insuring adequate fuel flow to the engine in case the main fuel pump fails.Gravity fed systems without pumps do not need backups, but other systems do. The failure of afuel pump should not cause an engine failure.5) Some reasonable assurance through testing that the fuel system will work properly in allnormal flight attitudes.

There are two basic standards that may apply to any particular aircraft. If the aircraft has agravity fuel system, then that fuel system needs to provide 150% of maximum fuel flow in thesetests. Gravity systems use either no fuel pump or a fuel pump that must rely on gravity as thebackup if that pump fails. Typically these are high-wing aircraft, but some low-wing airplanesalso have gravity systems. These aircraft have carburetors rather than fuel injection systems.If the airplane is fuel injected, an engine-driven fuel pump AND a back-up or auxiliary fuelpump will be needed. These are called pressure systems, and they must flow at least 125% ofmaximum fuel flow in these tests.After determining the type of system (pressure or gravity) determine what the maximum fuel flowis for the aircraft. The manufacturer of the engine may provide a maximum fuel flow at fullpower or it may list horsepower and specific fuel consumption (also called brake specific fuelconsumption or simply BSFC). Lycoming, for example lists BSFC for each engine in apublication it calls “Detailed Engine Specifications,” which are available from theirpublications department for each major engine type.If the BSFC for the engine is unavailable use the conservative figure of .55. The fuel flow for anyparticular engine is simply Horsepower x BSFC. This gives is in pounds (not gallons) per hour.This needs to be converted to ounces per minute so it can be easily measured.Here is a sample calculation:The Lycoming O-320-D1A engine produces 160 hp. It has a BSFC of .51 pounds/hp hour. Simplymultiply 160 times .51 to get 81.6 pounds per hour, the maximum fuel flow at full power. Thendivide pounds by 6 to get gallons per hour of 13.6. Next multiply by the fuel system factor of125% or 150% and get 17 or 20 gallons/hour, depending on the type of fuel system.Page 5 of 14P.O. Box 3086 Oshkosh, WI 54903-3086 | Tel 920.426.4800 | Fax 920.426.6560 | www.EAA.orgContinuing on, divide gallons per hour by 60 to get gallons per minute and then multiply by 128to get ounces per minute. The results are 43 or 36 ounces per minute, depending on the fuelsystem.

[1600vw]

All of this can be simplified with these formulas:Gravity: HP x BSFC x 1.5 x .36 + Ounces/minute orPressure: HP x BSFC x 1.25 x .36 + Ounces/minuteThe first test is the maximum power in level flight test. For this test, level the aircraft both sideto-sideand front-to-back. Then place one gallon of fuel in each tank. Be sure to shut the fuelvalve off. Next, disconnect the fuel line where it goes into the carburetor or fuel injection servo.If the exit to the fuel line will not easily reach the measuring container, the fuel line may beextended as long as the exit point is at the same level as the carburetor or fuel servo input fitting.Open the fuel valve to verify fuel flow. Turn on the fuel pump if the airplane has a pressuresystem. Be sure to catch the fuel flowing out of the line and have a fire extinguisher handy incase of an accident. If no fuel flows when you open the valve, then add another gallon to eachtank and try again until fuel begins to flow.With fuel flow established open the valve for one minute and see how much fuel flows out. Thenlet fuel flow out of the line until no more comes out. Measure this fuel and subtract it from whatwas put in the tanks to determine unusable fuel. Compare the fuel drained in one minute to thenumber calculated previously. As long as it is equal to this number or more the test result issufficient.Do not run the engine during this test! Record the results of these tests in the builder’s log.The completion of this test will be a sufficient evaluation of the fuel system if ALL of thefollowing conditions are met:1) The kit manufacturer has designed and tested a fuel system for this aircraft and found itto provide adequate fuel flow in all normal flight attitudes.2) The fuel system has been installed in this aircraft that matches exactly the kitmanufacturer’s design, including the fuel lines, fuel tank, fuel valves and drains, fuel pumps, andvent system.3) An engine approved by the kit manufacturer has been installed.If any of these conditions have not been met then the following fuel tests should be performed:Maximum Climb Test. With the level flight test complete proceed to the climbing flight test.

Forthis test put the aircraft in a nose-up position to simulate a maximum climb. Here are somepossible ways to determine the required angle:Consult with the kit or plans designer or measure the angle in a similar aircraft using a Smartlevel. Then add 5 degrees to that number for the test. If that number is unavailable, use 25degrees for the test and later verify that angle in Phase I flight testing. Don’t add 5 degrees tothe 25 degree number.Page 6 of 14P.O. Box 3086 Oshkosh, WI 54903-3086 | Tel 920.426.4800 | Fax 920.426.6560 | www.EAA.orgWith the angle established position the aircraft at that angle by some combination of raising thenose and/or lowering the tail. Get some help to do this safely. A hole or ditch may be available tolower the tail. Do not dig a hole on the airport property without the permission of the airportmanager. A flatbed tow truck may be useful to raise and lower the plane for these fuel tests.Repeat the fuel flow test as before. Do not run the engine during this test. Record the results inthe builders’ log. Note – the unusable fuel quantity may be more in this configuration.The Maximum Descent Test. This test is similar to the previous tests but with the nose down.Again, determine the down angle, which should be the angle in a full-flaps, power-off descent atthe top of the white arc (Vfe), or if no flaps a power-off descent at the top of the green arc (Vno).As before consult the designer for this angle, or measure the angle in a similar plane, or assume15 degrees and verify it later in flight testing. You do not need to add an extra 5 degrees for thistest.As before, carefully position the plane at the proper down angle. Take care to avoid damage tothe aircraft or injury to people. Conduct the fuel flow test as before. A fuel flow of 25% ofmaximum is sufficient for this test, due to the lower fuel flow required in a power-off descent.Do not run the engine during this test. Record the results in the builder’s log.

The Maximum Slip Test. This test cannot be conducted on the ground; it must be done in flight.While flying over an airport at a safe altitude, burn off fuel until the fuel remaining equals theamount of fuel needed to sustain 75% power for 45 minutes. Then place the aircraft in a landingconfiguration and slow to 1.3 Vso.Consult with the airplane designer regarding any limitations on slipping with flaps extended!Perform a maximum-rudder-deflection slip to the right and hold for 30 seconds. Then repeat tothe left. During this test no loss of fuel pressure or engine power should occur. If it does, landsafely, add fuel and repeat the test until a minimum safe amount of fuel can be determined.Record results in builder’s log book.Insufficient Fuel Flow. If fuel flow is insufficient in any of these tests here are some possiblethings to consider. Also use AC43.13.1B as a reference in addition to the manufacturer’s design.1) Any small piece of debris left in a fuel line can significantly reduce fuel flow. Thisespecially likely to occur with rubber or rubber lined fuel lines. Be sure all fuel lines and tanksare perfectly clean prior to final assembly. Be sure no small flap of rubber is left in any rubberfuel line.2) More fittings create more flow loss in a fuel system. Reduce the number of fittings andvalves as much as possible. Simplify the fuel system whenever it is possible and safe to do so.3) Try to replace 90 degree fittings with 45 degree fittings if possible, or better yet replaceangle fittings with sweeping bends in fuel lines.Page 7 of 14P.O. Box 3086 Oshkosh, WI 54903-3086 | Tel 920.426.4800 | Fax 920.426.6560 | www.EAA.org4) Consider installing a header tank if fuel flow cannot be maintained in any normal flightattitude.

Many manufacturers of aircraft kits will perform these tests for their builders and make theresults available. If the fuel system is installed exactly as per the kit manufacturer’srecommendations in every detail, only the level flight test would be necessary. Exactly the samemeans even to the fuel flow sensor and the venting system, especially the venting system. If any ofthese tests are not performed it should be noted in the builder’s log, citing manufacturer’s testingwhere appropriate.The level fuel system test, at a minimum, should be repeated whenever there is any addition to ormodification of the fuel system, after which an appropriate entry should be made in the aircraftlog book.This language was developed by EAA’s Homebuilt Aircraft Council as a comprehensive guideto fuel flow testing, a critical system test

[stewartb]

Static spark is a very real threat. Grounding has nothing to do with anything here. I drain usable fuel through the gascolater using a hose that runs into a metal fuel can. A bonding wire is attached from airplane to can. I only de-fuel outdoors and always stay nearby with an extinguisher in easy reach.

Here's an old video that's worth watching. https://m.youtube.com/watch?v=2sSqzLPMb4s

[wyoranch]

Excellent video...
Besides the excellent information
1) Brought back memories of grade school in the late 60's early 70's
2) I laughed at the opening as the woman was un buttoning her blouse and hiking up her skirt as I was thinking this is going to be VERY educational

Rick