One Account, Two Currencies
Climb and you convert speed into height. Dive and you convert it back. The exchange rate is fixed by gravity, and it is the same rate for every aeroplane ever built, because it is not a property of the aeroplane at all.
This is why a fighter pilot thinks about energy rather than about altitude or airspeed. Two aircraft can be at the same height and the same speed and one of them can be in serious trouble, because what matters is the total, and the total is the sum of the two.
The practical consequence is that climbing is never free and diving is never wasteful. Both are transfers. A pilot who climbs without understanding that has simply moved money from one pocket to another and paid a transaction fee in drag.
The Engine Changes the Rules
Without an engine the total only ever falls. A glider is a machine for spending energy slowly, and every manoeuvre costs some, so the whole skill is in choosing which spending buys the most distance.
With an engine the total can rise, but never for nothing. The engine adds energy at a rate set by the throttle, and the fuel it burns is a clock. Fly at full power and you climb and accelerate quickly and empty the tanks quickly. Ease back and you stretch the flight and give up the ability to climb.
That is the trade at the centre of Cargo, where the same lever sets height, speed and fuel burn at once. There is no setting that is good at all three, and the flight is a series of decisions about which of the three to be bad at right now.
How Pilots Actually Spend It
If height and speed are one account, the skill is in choosing the exchange rate. A glider pilot has a number for this and it is called the speed to fly, and it is not a fixed speed. It changes with the air the aeroplane is in.
Flying through sink, you want to get out of it, so you fly faster and accept the extra drag as the price of spending less time in bad air. Flying through lift, the opposite holds: slow down, because every second you are in rising air is a second you are being paid, and rushing through it throws money away. The same glider, the same afternoon, two different best speeds depending on what the air is doing.
That idea has a name in racing, where it is called dolphining. Rather than stopping to circle in every thermal, the pilot flies straight and pulls up gently in each patch of lift, letting the climb bleed the speed off, then lowers the nose again as the lift ends and lets the speed come back. Height is gained in small amounts rather than in circles, and the route stays pointed at the destination.
The same arithmetic runs in an aeroplane with an engine, it is just that the account refills. A jet crossing an ocean climbs as it burns fuel, because a lighter aeroplane needs less lift and therefore less drag, and the same thrust then buys more speed. Airliners do this constantly and the passengers never notice. The aeroplane is not being flown to a set of directions. It is being flown to a budget.
Which is why the games here do not give you a speed control. They give you a throttle and a nose, and the two of them between them decide where the energy goes. There is no third lever that means go faster, because on a real aeroplane there is not one either.
Running Out of Energy at the Wrong Moment
The reason pilots are trained so hard on energy is that the account can be emptied at a moment when refilling is not an option. Most of the ways a flight ends badly come down to an aeroplane that needed more energy than it had, at a height where there was no time to get more.
The classic is the turn back after an engine failure on takeoff. The aeroplane is low, slow and climbing, and turning it around costs energy it does not have. The turn is possible in the sense that the aeroplane will do it. What is not possible is doing it and arriving at the runway with anything left. Pilots who have tried it in light aircraft, in tests, have consistently come up short, which is why the training says land ahead and accept the field.
A stall on the base-to-final turn is the same story with a different cause. The pilot is low and slow, sees the runway is going to be missed, and pulls harder to stretch the turn. Pulling harder makes more lift, which makes more drag, which costs speed, and the aeroplane that was already near the critical angle goes past it. The wing lets go at exactly the height where there is nothing to trade for the recovery.
What both cases have in common is that the pilot was asking the aeroplane for performance it had already spent. The instruments were telling the truth the whole time. What was missing was the habit of asking what the manoeuvre costs before starting it, which is the same habit the games here are built to teach, and the same habit that makes them hard.
Why Dogfights Are Won With Energy
Two fighters of equal performance meet. The one with more total energy can choose whether to fight or leave, and the one with less cannot do either. That is the entire tactical situation, and it is decided before anyone fires.
A pilot who turns hard bleeds energy, because turning means angling the wing and angling the wing means drag. Every tight turn is a loan taken out against the future. Turn hard enough for long enough and the aeroplane is slow and low, which is the worst of both currencies at once.
Which is why Dogfight has no guns worth mentioning and no health bar. The fight is over when one aeroplane has spent its energy and the other has not, and the rest is administration.