Whether you’re a piston airplane owner or strictly a renter pilot, you have a vested interest in making sure the engine(s) of the plane(s) you fly perform as advertised. While the odds are that your powerplant(s) will function flawlessly, there are several steps you can take to further safeguard the health of your piston engine. Besides contributing to safety, such practices can help lower your maintenance bills and prolong the service life of your powerplant.
SMOOTH POWER CHANGES
Smooth inputs are about much more than just providing your passengers with a comfortable ride. A piston engine is loaded with moving parts, and any abrupt power changes can potentially throw these components out of whack. One of the possible consequences of rough operation is that you’ll dislodge the crankshaft’s counterweights, which is known as detuning. Detuning can lead to other possible component failures (discussed here), all of which are expensive to repair and could compromise flight safety. By employing smooth inputs, you’ll significantly reduce the chances of mechanical failure of your piston engine.
GRADUAL POWER REDUCTIONS
In addition to smooth power changes, piston engine pilots should take measures to make their power reductions in gradual increments. This is important to reduce the possibility of shock cooling the cylinders, which is most likely to occur during descent. When descending, less power is required than for cruise, so pilots typically reduce power in this stage. As power decreases, engine temperatures drop as well. Additionally, the descent angle results in increased airflow into the cowling, which further lowers the engine temperature.
In science class, you probably learned that many substances (particularly metals) expand with temperature increases and constrict as temperature drops. In a metal-heavy piston engine, abrupt temperature changes lead to expansion and retraction of several components. If these temperature swings occur too suddenly or too often, engine parts could expand/contract outside of their tolerance limits. As you can imagine, this is a situation you’ll want to avoid. When you fly, try to plan your descents so as to avoid making considerable power reductions in a short period of time.
Just as shock cooling is undesirable, you’ll also want to protect your piston engine from overheat situations. The most likely conditions to cause engine overheating occur under the high power, high angle of attack (AOA) configurations characteristic of takeoff and climb. Chief among your heat-related concerns is detonation, which is the explosive combustion of fuel in the cylinder. Excessive temperatures could also lead to preignition, which results from lingering hot spots in the cylinder that cause the fuel/air mixture to ignite prematurely in the four-stroke cycle. Either situation will likely cause engine roughness and possible damage to cylinder components.
To avoid heat-related problems, your best bet is to reduce your climb angle. Besides being easier on the engine, a shallower deck angle gives you better visibility and a quicker groundspeed. If practical, reduce the power setting to a more moderate level. When practicing high power, high AOA maneuvers like power on stalls and slow flight, enrichen the mixture to provide additional engine cooling. These practices are very easy to implement and can significantly reduce the engine’s operating temperatures.
In aviation, a little planning can pay big dividends in the life expectancy and overall health of your piston engine. With minor, easy-to-apply changes, you can profoundly reduce the chances of premature component wear or other unexpected surprises. Though already highly reliable and built for the rigors of flight, your engine can always benefit from a little TLC.