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In your dreams, you need only gossamer wings to fly, but the waking world calls for a more realistic form of propulsion. Like many vehicles, aircraft rely upon the internal-combustion engine. And even though you may have heard that aircraft piston engines are dinosaurs compared to "modern" powerplants, that's not entirely the case. Aero engines use lightweight materials, some of which are only now common among automobiles. It's true that today's cars make extensive use of computer control to improve efficiency - and aircraft steadfastly do not - but on the whole, airborne and ground-bound powerplants are more alike than they are different.

Internal-combustion engines share this lineage because they work on the same principle: Take the latent energy in chemicals and turn it into motion. Ignite a mixture of fuel and air above a moveable piston that is attached to a rotatable shaft, connect a propeller at one end, and you're nearly aloft. Aircraft engines, like the vast majority of gasoline engines, are of the four-cycle (sometimes called four-stroke) variety, invented by Nicolaus August Otto in 1876. This system gets its name because the engine uses pistons that must make four up/down motions to complete the cycle.

You may also have heard this kind of engine called reciprocating - that's because the pistons move in one direction, stop, move in the opposite direction, stop, and repeat the cycle. Can you think of engines that don't have major reciprocating components? Try these: Turbine engines' major parts rotate continuously in one direction, as do the moving parts inside a Mazda rotary engine.

Before we get into the hard parts - literally, as in discussing the actual bits and pieces of an aircraft engine - let's follow the cycles for a simplified version of what's happening more than 80 times a second at the front of your airplane. (Yes, this is the theory portion; roll your eyes once and be done with it.) The fuel in the aircraft's tanks is supplied to the engine, where it is mixed with air (at a ratio of about 14 parts air to each part fuel). This mixture of fuel and air - hence the name for the red knob in the cockpit - is routed to the cylinder through a collection of tubes called a manifold, regulated by a valve just inside the cylinder head. Inside these cylinders slide pistons, which take up the entire width of the cylinder, like pennies dropped into a coin roll. As the piston moves down, the first or intake stroke draws this fuel/air mixture into the cylinder.

Then the piston moves upward in the cylinder, forcing this air-and-fuel mixture into an ever-smaller space. This is known as the compression stroke. The fuel and air are squeezed into a space about one-eighth the original size, making the mixture volatile - meaning that it is much more ready to combust than in its "relaxed" state. The spark plugs produce a brief electrical discharge - er, it's a spark - which ignites the fuel/air mixture. This causes the combustibles to expand in the cylinder, pushing the piston downward in the power stroke. Incidentally, combustion is not an explosion per se, but a controlled burn, like a match head igniting. The final exhaust stroke sees the piston rising again in the cylinder as the exhaust valve opens, pushing the burned gases out through the exhaust system.

Enough theory for today, then. All internal-combustion, four-stroke engines follow this format - intake, compression, ignition, exhaust - but aircraft engines differ from auto engines in many ways. For one thing, aero engines are predominantly of the air-cooled variety. That is, those holes in the front of the cowling adjacent to the propeller admit ambient air, which is then carefully routed over and around the cylinders. These cylinders pass the heat generated by combustion into that air flowing and swirling around fine-pitched fins.

The choice of cooling medium is just one aspect of the aircraft engine that would seem utterly alien to an automotive engineer. For simplicity and redundancy of systems, the aircraft engine's spark plugs - two per cylinder - are triggered not by a computer but by a pair of totally self-contained magnetos. Yes, like the old Ford tractor your uncle is always telling you about. Make fun of them if you wish, but mags have the advantage of being separate from the aircraft's electrical system, so a dead battery or a failed alternator will not cause an engine shutdown.

Not only are aircraft engine systems vastly different from your car's, but also the powerplants are built with divergent goals. Cars need to have cheap, easily produced engines. Airplanes need, above all, engines of minimal weight and maximum reliability. Look at the Lycoming O-320 on page 34.

This is perhaps the prototypical aircraft engine - four cylinders, air-cooled, carbureted, robust, extremely common. And simple. It's been said that an ideal design is as simple as possible, and not one iota simpler.

From an engineering standpoint, the Lycoming eschews technical idealism for ease of service, and parts commonality. For example, each of its four cylinders is identical and bolted to the cast-aluminum crankcase so as to facilitate removing one cylinder at a time for maintenance or repair. This is important: Aircraft cylinders live a hard life, and it's not unusual to repair or replace one or more cylinders before the engine has reached its (mostly theoretical) time between overhaul (TBO) interval. This is called topping the engine, because the cylinders are considered part of the "top end," while everything below the point where the cylinders mate to the crankcase is called the "bottom end." Never mind that the cylinders are lying on their sides.

The single camshaft that opens the two valves per cylinder - the minimum you need for a four-stroke engine, against the four-valve- per-cylinder designs that you see in even the lowliest of economy cars - shares activating lobes for opposing cylinders wherever possible. A single carburetor is bolted to the bottom of the oil pan, inside which is a container sealed from the oil supply that branches off into four intake tubes. In this way, the warm oil helps to keep the carb warm and prevent icing. The prop is bolted directly to the front of the crankshaft, while the opposite end terminates in a robust gear that drives the camshaft, both magnetos, the oil pump, and any accessories such as a vacuum pump or back-up alternator. It's a straightforward system, with the minimum parts to do the job.

Such has been the aero-engine status quo for the better part of 50 years, but advances are on the horizon. There are computer-controlled systems in the works - and one now available - for high-end engines that automate the mixture control and provide more efficient operation. And diesel engines are showing some promise, with manufacturers around the world working toward small, light, efficient aero diesels. Why so much effort? The diesel carries two main benefits - it is inherently fuel-efficient, and it can run on Jet A fuel, which is widely available around the globe. Three decades ago, prognosticators said we'd be flying behind ultra-efficient turbine engines in every airplane from the plushest business cocoons to the lowliest trainer. Of course, that's a Star Trek-like parallel reality that we don't enjoy - at least not yet. But you can dream.