What happens when you fly upside down in a fighter jet? Does everything fall-up and hit the windshield?
That’s a great question. As fighter pilots, we go upside down all the time. However, we rarely maneuver the jet so that objects float, or “fall-up.” When we turn, we start by rolling in the direction we want to go, and then we pull back on the stick. This means the G-Force is straight down and into the seat. At our peak of 9G’s, it feels like a car is parked on your chest, and, while it’s extremely difficult to withstand, everything falls in the same direction as it does on the ground. Even when we go upside down, we’re applying back-stick pressure and maintaining positive-G.
Check out this video of a pilot pouring Redbull into a cup, all while doing a barrel roll:
The reason we usually pull positive-G’s is that it’s most comfortable for the pilot. Our natural environment is 1G–if you’ve ever hung upside down, that’s negative 1G, and for most people, it’s an uncomfortable experience. The human body is just not built to pull large amounts of negative-G’s. Worse still, our G-suits don’t help with negative-G’s either.
When pulling positive-G’s, blood is being pulled from your brain into your arms and legs. If you lose too much, you can pass out, and in a single-seat fighter that can often mean death. Therefore, we wear G-suits designed to squeeze our legs and force the blood back into our brain. When we pull negative-G’s, the opposite is true–an excess amount of blood pools in our brains which can eventually cause retinal damage and hemorrhagic stroke. Unfortunately, short of a G-suit around your neck (not the best idea), you can’t stop this flow of blood.
In addition to the discomfort, visibility plays a large factor in why we pull positive-Gs. The bubble canopy on top of the aircraft gives a near unlimited view from the horizon as far back as your neck can stretch. It often feels like you are floating in a chair, which is why we don’t say we’re hopping in the jet, but instead say we’re strapping the jet on our backs. When looking down through, the nose of the aircraft blocks nearly all our visibility. Because maintaining sight is critical to fighting another aircraft, it’s advantageous to pull the adversary towards the top of the canopy, which means pulling positive-Gs.
Now, I can already hear it: let’s get the pilot out of there and move on to autonomous drones that can pull in whatever direction they want. For multiple reasons, that isn’t going to happen for several decades, but even after we transition, drones won’t be performing high negative-G turns.
Making a great aircraft is about balancing hundreds of competing variables. One of the most important is weight: By favoring one axis for G’s, engineers can save a significant amount of structural mass. Additionally, with the incredible roll rates of modern figures, it takes on the order of half-a-second to roll inverted and change what would be a negative-G pushover into a positive-G turn. With that small advantage, it’s not worth the high cost in weight and engineering.
Feature image courtesy of F-35 Lightning II Joint Program Office