Why Are Cars Turned Off to Refill But Planes Do it in Mid-Air?

Fuel is transferred to fighter jets by another military aircraft known as the tanker during flight by aerial refueling, which is also known as mid-air refueling or tanking.

This process extends the time in the air for the receiving aircraft. Because the receiving aircraft may be refueled while in the air, it is possible to take off with a larger payload, such as weaponry, cargo, or troops.

But couldn’t this process be dangerous? I was always told to turn off my car during a refill at the gas station. Isn’t it the same thing? How could the fighter jet get refueled while its engine is ON and not getting on fire?

Air refueling procedures

Source: By Tech Sgt Shane A. Cuomo, U.S. Air Force / wiki commons

The probe-and-drogue refueling system and the flying boom are the two types of refueling systems available. A third option is a hybrid of the first two. The two most important are explained below:

1- The probe-and-drogue approach can be more easily adapted to current aircraft because of its simplicity. A lengthy hose is unrolled from the wingtip or the fuselage by the engineer. The hose has what seems to be a windsock-shaped basket or drogue attached to the end.

Source: Research Gate

The receiver pilot must place a retractable probe into the basket or drogue once the hose has been extended to its maximum length. The nose of the aircraft is equipped with a retractable probe for easy access. The probe must be softly maneuvered by the engineer and the receiver pilot in order for it to latch onto the basket.

Source: wikipedia F35 probe-and-drogue

2- The flying boom technique necessitates using a separate operator stationed at the rear of the tank in order to be effective. He places a telescopic tube into a receptacle at the front of the receiver plane.

Source: Research Gate

When the boom latches, a signal is transmitted to the tanker, telling it to start pumping aviation gas. Compared to the probe-and-drogue, the flying boom has a higher fuel capacity. This works well for big planes with huge fuel tanks.

Isn’t this process dangerous?

We are always taught that when we reach the gas station to refuel our cars, to turn OFF the engine. This is a safety precaution to avoid any accidents. But why do we have to do this while fighter jets are easily refueling while flying in the air? There are two possible reasons behind this:

1- Type of the fuel:

Source: somagnews

Refueling a car while the engine is running and refueling a fighter aircraft while it is in the air are basically the same, but with one critical difference: the kind of fuel utilized.

Source: iStock

Cars often run on gasoline, which has a lower flash point of around -43°C, which means it is a highly flammable fuel. This is the point at which a vapor is formed around the fuel, this vapor is what causes the combustion of the fuel when exposed to an open flame. As a result, the fuel will likely get unexpectedly ignited, resulting in the whole fuel tank catching fire.

Source: Greg Bishop / flickr

For fighter jets, fuels with a higher flash point are used: JP5 has a flash point temperature of 60°C, whereas JP8 has a flash point temperature of 38°C. Catching fire is less likely to occur when using a higher flash point gasoline. Additionally, higher elevations in the air provide lower temperatures, which further minimizes the dangers.

2- Low probability risk:

Refueling your car while it’s running isn’t all that risky! Adding extra gasoline has no effect on the process because your engine is still taking fuel from the bottom of the tank. There are countries where refueling running cars is completely unregulated, and this is the norm.

So, what’s the point of the rule then? According to one theory, requiring a person to start the car makes them less willing to drive off with a nozzle in their tank and pulling the gasoline line loose, which could end up deadly. Another possibility is that you may spill petrol when filling up your car, creating a vapor cloud that could be ignited by a running engine. This probability is extremely small, but it still does exist.

This is a “1-in-10,000” probability to occur. If something happens once in 10 thousand cases, it may seem little, but if ten thousand people take that risk, the odds worsen dramatically. With over ten million individuals filling up their cars every day in the United States, even the tiniest chance becomes an almost certain catastrophe.

Source: U.S. Air Force photo/Senior Airman Ashley J. Thum / dvidshub

Fascinating fact: Aircraft are handled like Sedans when refueled on the ground, with engines completely switched off throughout the process. When refueling planes on the ground, there are actually additional safeguards in place. Aside from that, when planes are refueled, a fire truck is usually stationed nearby to deal with any accidents that may occur.

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