Shock cooling refers to the theory that damage to engines (particularly air-cooled aviation piston engines) may occur because of an excessively rapid decrease in temperature. Air-cooled engines rely on the circulation of air directly over hot parts of the engine to cool them. ...

The situation where rapid cooling arises is on descent from altitude. In this condition, less power is demanded of the engine (it is throttled back) so it is developing much less heat. In a descent, the plane's airspeed increases, simultaneously increasing the cooling rate of the engine. As metals expand and contract under temperature changes, dimensional changes in the engine may exceed tolerance limits.

Damage from shock cooling most commonly manifest itself as stuck valves [1] and some have attributed cracked cylinders to shock cooling as well. 4-stroke engines, of either spark ignition or compression ignition varieties, use poppet valves to allow air (or an air/fuel mixture) into the cylinder and exhaust gases out. ...

A single cylinder head temperature (CHT) sensor, or in more sophisticated installations, an array of sensors (one for each cylinder) may be employed to monitor the temperature and cooling rate of the engine, usually through a simple gauge or a bar-graph style graphical display. Spoilers on the wings may also be deployed to lose lift without having to reduce engine power substantially. Not to be confused with censure, censer, or censor. ... This KLM cityhopper Fokker 70 still has its spoilers deployed (the cream-coloured panels projecting above the top surface of the wing) after landing at Bristol International Airport, England. ...

Kas Thomas, a respected aviation engine expert, believes that "shock-cooling is not a major contributor to cylinder head cracking".

While the subject is controversial and hotly debated, many believe shock cooling, as commonly explained, is nothing but a myth. This position is supported by the fact twin engine planes commonly experience ideal conditions for shock cooling during simulated, single engine failures, yet statistically show no difference in wear or damage distribution between engines. Furthermore, others believe shock cooling is actually the cause of rapid throttle changes of super cooled fuel from high altitude flight, during decent into a very hot engine cylinder; where rich of peak (ROP) operation is considered the norm. In fact, it is well established this behavior can contribute to excessive component wear and even damage; wear and damage which is typically associated with "shock cooling". Given the two commonly available data points, it strongly suggests shock cooling is nothing but a myth, at least in the context as commonly explained. Nonetheless, the topic will remain highly controversial and surely continue to be hotly debated well into the future. For other uses, see Myth (disambiguation). ... ROP or RoP may stand for: ROP - or Shawn Salliotte is my hero. ...

External links

• Shock Cooling: ¿Myth or Reality? at AvWeb.com