Hey Mom,

Would it be stupid of me to ask what the difference is between turbocharged and supercharged?

Thanks,

Normally Aspirated But Curious

Let’s start simple. Both superchargers and turbochargers are forced induction systems. Induction just means the method by which we get air and fuel into the engine. After the fuel and air are mixed in the proper proportion (which will either happen in the carburetor or via fuel injection), we have to get that mixture into the cylinders. The more of that fuel/air mixture you can get into those combustion chambers, the more power you get. So far, so good, still simple, right? K. A supercharger is a device (which could be a blower or a compressor) that pressurizes or boosts the fuel/air mixture in the cylinders, allowing you to get more literal bang for the buck, or at least for the space. It allows you to force more fuel and air into those same cylinders than you otherwise could, thereby allowing your engine to produce more power. Or allowing you to maintain the same power at a higher altitude, since you can make up for the decreased air density you’d normally experience as you climb. There’s a couple of things you can accomplish here. If you’re boosting engine output-more power-YAY!, the airplane is referred to as ground-boosted, while a turbo normalized system keeps your sea level horsepower constant until you reach critical altitude (the altitude at which it can no longer provide enough pressure to maintain sea level performance). Once you pass critical altitude, performance decreases at the same rate it would for any normally aspirated (non supercharged) engine.

Now that we’ve got those basics out of the way, let’s address your original question about the difference between supercharging and turbocharging with this very abbreviated definition: A supercharger is an engine driven air pump or compressor meant to increase the pressure at the intake manifold.  A turbocharger is a variety of supercharger, specifically, one driven by exhaust gas. All turbochargers are superchargers, though there are other methods of supercharging an engine outside of turbocharging. Like what? Well, there are geared superchargers out there mechanically connected to the crankshaft via a single, dual, or multistage gearbox. For more detail on how these systems work, have a look at this article. Ooh, and this one, too.

Now let’s touch on why you want one. Check this out-let’s say you take your Cessna 182 out to Denver. You’ll use 65% more runway for takeoff than you would have at sea level. Turbo Skylane? Your takeoff distance will only increase by 25%. Not bad. Not bad at all. So, asks the astute pilot, why aren’t all aircraft engines supercharged? Well, turbocharging is gonna cost ya. A turbocharged engine is often nearly twice as expensive in the first place. That brand new turbo Skylane you’re taking to Denver, for example, will set you back $33K further than the standard version. Overhauls are significantly more expensive as well, and in most cases they come up a little more often than they would for a normally aspirated engine. TBO on the vanilla version of the Skylane vs the turbo happens to be the same (2000 hours for both the Lycoming IO-540-AB1A5 and the TIO-540-AK1A), though the difference between the IO-360 and the TIO-360 (2000 hours vs 1200 hours) is a little more typical.

Turbocharged engines get still more expensive when you mismanage them. Compress air and it’s temperature increases. Fail to manage that and you have an overheating problem. Overboosting your engine is also a possibility if you have a manual waste gate and aren’t paying close enough attention as you descend, for example.  And what happens when the darn thing goes awry? Well, it seems pilots aren’t necessarily getting as much training as they might for this type of situation. You might find this 2008 article about turbocharger failure helpful.  

Pilots who fly low and slow most of the time are likely to decide that the extra expense and maintenance might not be worth it. Are you the long cross country type, or a pilot who does a lot of flying out of high elevation fields? You’re just the one those engines are supercharged for. Just do read the book and pay attention, will you? Of course you will.

Don’t forget to do your homework,

Mom