NASA
There are several advantages to flying at high altitude, such as decreased drag, faster true airspeed. And if you’re headed in the right direction, you can even enjoy higher tailwinds. However, there is one major drawback for normally aspirated engines: a lack of oxygen.
The High Altitude Problem
As you ascend in altitude, air pressure decreases rapidly. In fact, if you’re flying at 18,000 feet, half of the atmosphere is below you. This means there is less air for your engine to burn, resulting in a significant reduction in horsepower.
Solving the Thin Air Problem
Turbochargers are the solution for piston-driven engines to overcome the issue of thin air. They compress the intake air before it reaches the cylinder. By doing so, the engine can operate as if it were at sea level or lower, even at high altitudes.
How a Turbocharger Works
Turbochargers have three main components:
– Turbine: It is driven by the exhaust gas exiting the engine. As the exhaust passes over the turbine, it spins it. The more exhaust, the faster the turbine spins.
– Compressor: The compressor is responsible for drawing in air from outside the airplane, compressing it, and then delivering it to the engine. It spins due to the connection to the turbine through a shaft.
– Shaft: Connects the turbine and the compressor, allowing them to work together.
The Basics of a Turbocharger
The turbine starts spinning when the engine is started. The compressor then spins as well, as it is connected to the turbine. The compressor draws in air, compresses it, and transfers it into the engine. This process increases the air pressure in the intake manifold.
Wasting Air Through the Wastegate
Turbochargers are effective at increasing intake manifold pressure, but they can sometimes produce too much. To prevent damage to the engine, a wastegate is used. It regulates the amount of exhaust gas passing over the turbine, controlling the speed at which it spins. The faster the turbine spins, the more air enters the engine.
How Much Air Can Your Engine Handle?
The amount of air an engine can handle depends on the engine type. There are two main types of turbocharging: altitude turbocharging and ground boosting.
Altitude Turbocharging
Altitude turbocharging aims to keep the engine running like at sea level for as long as possible. Most altitude turbochargers maintain a manifold pressure of around 29-30 inches of mercury as the altitude increases. However, there is a critical altitude where the turbocharger can no longer compress enough air to maintain sea-level pressure. Beyond that altitude, less air enters the engine, resulting in a decrease in horsepower. But even at higher altitudes, it is still more efficient than a normally aspirated engine.
Ground Boosting
Ground boosting uses higher manifold pressures compared to altitude turbocharging. Boosted systems typically operate at pressures between 31-45 inches of mercury. The advantage is more horsepower output, but the disadvantage is increased heat.
Turbochargers and Their Heat Problems
Compressing air heats it up, which is a significant drawback of turbochargers. Aircraft engines already operate at high temperatures, and hot intake air makes it even worse. To solve this problem, many turbochargers use an intercooler. An intercooler acts like a mini air conditioner, cooling the hot air from the turbocharger to the engine, making the engine run more smoothly.
The High Altitude Advantage
Turbochargers are crucial for piston-driven airplanes to reach high altitudes and take advantage of strong tailwinds, higher true airspeed, and stunning views. They allow these planes to perform at their best in the challenging environment of high altitudes.
In conclusion, turbochargers play a vital role in enabling piston-driven aircraft to operate effectively at high altitudes, despite the challenges posed by the thin air. With their ability to compress air and overcome altitude-related limitations, they contribute to the performance and capabilities of these aircraft.
