I understand the general “how” aspect in that the planes use a special fuel line to get the fuel to the plane.
How can they do it safely with the engine on however? Thinking about refuelling a car you have to turn your engine off, when a plane/helicopter refuels mid flight they obviously have their engine on. Is there differences in how they get/store fuel that makes it safer or just differences in the type of engine?
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I don’t think it’s safer than refueling a car with the engine on, but the danger is tolerated because it’s not particularly large, and the benefit is deemed worth the risk. That’s why you only really see it on military aircraft. It allows you some flexibility in circumstances where you might not have a friendly base at which to land and refuel.
The biggest danger present in a car that’s absent with mid-air refueling is that the driver is usually the one getting out of the car to put the fuel in, and leaving the car running without someone in control brings in a whole new category of potential dangerous situations, like a kid or pet knocking the transmission into gear.
This is mostly my opinion and guesswork:
When refuelling your car there is almost no chance of a fire traveling back from the engine into the tank. The risk is rather with an errant spark igniting the fumes building up around the stations. Given the number of refuelling actions each adding a bit of gasoline fumes this builds up.
With a jet refuelling there’s less chance for that. The hose down to the jet is empty until it has contact with the port, and drains before disconnecting. And even if there were fumes to escape they are “blown away” by a 800km/h wind (cruising speed of a KC-135 Stratotanker).
Refueling a car while the engine is on is not particularly dangerous. With a normal car, a normal engine, I can’t really think of any situations where something might go wrong.
Gas stations just want to minimize risks as much as they can. Engines are still metal blocks with explosions and heat.
It’s more about total times and training than risk
There are hundreds of millions of cars being fueled by complete amateurs. There are only about 1000 aerial tankers all crewed by professionals with training on what to do if something isn’t right
If the odds of an incident while refueling a car that is on is 1 in a million and you have 100M cars refueling every day that’s 100 incidents per day or 36,500 per year!
Around the entire world there will be maybe 100k aerial refueling attempts per year, even at 10x higher risks you’re at just 1 incident per year
Danger = odds of something bad x number of attempts
Rare problems with common tasks will pop up a lot but common problems with rare tasks will still be rare
Aircraft are meticulously maintained. Cars on the other hand is a crap shoot. Most modern cars have little to zero risk of catching fire while fueling, especially with a functional vapor recovery system on the pumps.
Let’s turn the clocks back forty years ago. Most pumps didn’t have any vapor control systems, most cars had spark plug wires and carburetors. Some still had points ignition. Not everyone had new cars, much like today. Spark leak, engine back fire (out the carb or exhaust), along with all the fuel vapors on a hot windless day could have the potential for disaster.
The biggest risk, even today, is getting in and out the car while fueling. Static electric shocks have the potential to light fuel vapors and most people don’t ground themselves until they’ve reached the fuel pump.
If you do find yourself at the gas station and your pump is on fire with the hose in the tank, let it stay in the car and shut off the pump by pushing up on the flapper where you store the nozzle. Do not panic and pull out the hose to spray fire at others.
Fuel in liquid form really doesn’t burn. It’s only when it vaporizes and mixes with air that it burns. The only way fueling presents a danger to aircraft is if the fuel is atomized and then ingested by the engine. During midair refueling there are safety interlocks to prevent this, and even if some fuel leaked, the air stream would carry it away before a significant amount could be ingested.
A car uses petrol. Petrol can ignite easily at 15Celsius, any object or spark, even your clothing static charge can set petrol on fire. The exhaust pipe of a piston engine, diesel or petrol, is hot enough to ignite petrol vapours. Even in winter, the petrol stored in the ground may be hot enough to make flammable vapours.
Kerosene for aircraft is not that flammable, it makes flammable vapors at 65celsius, that’s not a temperature you find in flight, not in the tanks, not in the air. The only ignition you can have is a electrostatic spark while the two aircraft touch eachother. That contact and spark happens in the beginning of the fueling, before the parts are fully connected. Aircraft engines are hot only inside, if you spray fuel on the engine inlet you don’t have a fire. If you spray the outer part, there are cowlings that prevent fuel to get into the compartment, and the inside of it is not that hot. The only part of the engine that can set it on fire is the exhaust, but if you are flying, any exhaust covered in kerosene on fire is not a risk. Air will just blow the flame away from the plane.
The only case that we can make is a helicopter refueling. But the fueling probe is mounted so low that a fuel spill will not go on the engines. Not in normal condition. While there is a video on the internet where the heli does a strange move and cuts the supply line, spraying itself in fuel. Still no ignition happened.
There is a risk. It’s very remote. This type of refueling is done only after special training, and only in military, where taking risks is normal as you signed up for it. Military is itself a dangerous job, whatever is your role.
For civil, air refueling and external tanks are completely forbidden, no matter the situation.
There isn’t a problem putting gas in a running car. But gasoline vapors are flammable and a running car could have an electric short somewhere. So it’s just an extra safety margin. Jet fuel doesn’t give off as much volatile vapors.
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