Using physics to fuel safely

A few weeks ago I received an email with a cartoon of a mature lady sitting back with a glass of wine. The caption read, “Another perfect day, and I never had to use algebra once.”

I smiled a little, but then got to thinking about how much we use math and science in our everyday life. And I started to wonder why people look down on their time in school taking these courses as a waste of time, because, in actuality, we use math and science many times every day.

For example, when we fill up our aircraft or automobile, we use physics and chemistry to keep us safe.

One of the laws of physics is that when you transfer a nonconductive fluid — read 100LL, autogas, and Jet-A — a static electrical charge builds up. This charge can cause a spark, and we all know that sparks and fuel do not mix well.

So what keeps us from blowing up every time we refuel our planes or car?

The first thing is that all dispensing hoses are supposed to have a conductive strip in them so that the hose will provide a grounding path to dissipate any static build up. The second safety measure is that a hydrocarbon fuel will not burn in a liquid state. It must be vaporized and mixed with oxygen in the air.

There are limits to the air-to-fuel ratio that will burn. For example, if you fill a beaker half full of 100LL and hold a spark plug 5 feet away and spark it, probably nothing will happen because the air-to-fuel ratio is too lean. Now if you put the spark plug just above the surface down in the beaker, (I strongly recommend that you not try this at home, just take my word for it) and spark it, usually nothing will happen because the air-to-fuel ratio is too rich to burn. So when you refuel your plane or car with 100LL or auto gas, the air-to-fuel ratio at the fill neck is too rich to burn.

Conversely, when refueling with Jet-A or diesel, the air-to-fuel ratio at the fill neck is usually too lean to burn. (This is why you should never mix auto gas and diesel because it may put you in an explosive range, but that is another story.)

When you refuel your car, it is usually not in an open area and the fuel door and fill neck are kind of sheltered. But on an aircraft, the fill neck is usually on top of the wing and you refuel in an open area. This can cause wind turbulence that can “lean out” the air-to-fuel ratio at the neck and put it into the combustible zone.

Now add the fact that the refueling rate for aircraft is usually higher, which increases static generation, and many people hold the nozzle to see how full the tank is, you have more potential for problems. This is why we always recommend using a bonding strap to dissipate the static build-up when refueling an aircraft.

We all agree that an aircraft should have a bonding cable attached to it when refueling, but where do you attach the bonding cable?

I do not know of any GA aircraft that has an identified bonding terminal. Some people use the exhaust and others the landing struts. But the big question is, is there conductivity between the place you are attaching the bonding strap and the fill neck?

If you have some time, you may want to see if there is conductivity between your fill neck and where you usually attach the bonding cable.

Do it carefully by always attaching to the fill neck first so that you do not cause a spark — because sparks and fuel are not a good combination.

The future of fuels

Fuel is the lifeblood of aircraft and pilots. Most aircraft need it to power their engines; pilots need it, in the form of oxygen and proper nutrition, to power themselves. The November issues of General Aviation News will turn the spotlight on fuels — all kinds — and look at the current state of affairs, as well as what we can expect

As always, we’d love to hear from our readers. Email General Aviation News Editor Janice Wood with your feedback.

Questions abound on FAA’s news about alternative fuels


Was it only me, or did anyone else find the press release by the FAA announcing that it has selected four fuels for further testing to replace 100LL this fall to be a bit peculiar?  In case you you missed it, the official press release from the FAA is here. Articles also appeared on this site, General Aviation News, and from the EAA.

None of the articles answered any of the obvious questions that came immediately to my mind, for instance:

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STC in the works for G100UL


While the government begins its testing of four potential 100LL replacements, George Braly and Tim Roehl of General Aviation Modifications Inc. in Oklahoma just finished up yet another test of their unleaded 100-octane avgas — G100UL — at Embry-Riddle Aeronautical University.

The fuel underwent flight testing and engine block testing in one of the school’s carbureted 172s.

“No issues were found,” Roehl reports. “We just lack a couple of other tests to complete our first STC on the 172.”

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Four alternative fuels to undergo testing

WASHINGTON, D.C – The FAA has selected four unleaded fuels for the first phase of testing at the FAA’s William J. Hughes Technical Center. The goal is for government and industry to work together to have a new unleaded fuel that reduces lead emissions for general aviation by 2018.

Shell and TOTAL, with one fuel each, and Swift Fuels, with two fuels, will now work with the FAA on phase-one testing, which will begin this fall and conclude in fall 2015.

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FAA receives unleaded fuels proposals

WASHINGTON, D.C. – The FAA reports it has received 10 replacement fuel proposals from producers Afton Chemical Company, Avgas LLC, Shell, Swift Fuels and a consortium of BP, TOTAL and Hjelmco, for further evaluation in the Piston Aviation Fuels Initiative (PAFI), an industry-government initiative designed to help the general aviation industry transition to an unleaded aviation gasoline.

The FAA will now assess the viability of the candidate fuels to determine which fuels may be part of the first phase of laboratory testing at the FAA’s William J. Hughes Technical Center. The goal is for government and industry to work together to have a new unleaded fuel by 2018, according to FAA officials.

“We’re committed to getting harmful lead out of general aviation fuel,” said Transportation Secretary Anthony Foxx. “This work will benefit the environment and provide a safe and available fuel for our general aviation community.”

There are approximately 167,000 general aviation aircraft in the United States that rely on 100LL aviation gasoline for safe operation. It is the only remaining transportation fuel in the United States that contains the addition of lead, a toxic substance, to create the very high octane levels needed for high-performance aircraft.

PAFI was established to facilitate the development and deployment of a new unleaded aviation gasoline with the least impact on the existing piston-engine aircraft fleet. PAFI will play a key role in the testing and deployment of an unleaded fuel across the existing general aviation fleet, FAA officials note.

Congress authorized $6 million for the fiscal year 2014 budget to support the PAFI test program at the FAA Technical Center.

“The FAA, the general aviation community and the Environmental Protection Agency are focused on this issue, and we look forward to collaborating with fuel producers to make an unleaded aviation gasoline available for the general aviation fleet,” said FAA Administrator Michael Huerta.

On June 10, 2013, the FAA asked fuel producers to submit proposals for replacement fuels by July 1, 2014. The goal is to identify, select, and provide fleetwide certification for fuels determined to have the lowest impact on the general aviation fleet.

The FAA will analyze the candidate fuels in terms of their impact on the existing fleet, the production and distribution infrastructure, their impact on the environment, their toxicology and the cost of aircraft operations.

By Sept. 1, 2014, the FAA will select several of the fuels for phase-one laboratory and rig testing. Based on the results of the phase one testing, the FAA anticipates that two or three fuels will be selected for phase-two engine and aircraft testing. That testing will generate standardized qualification and certification data for candidate fuels, along with property and performance data.

For more information: