Hot and cold engines

Dunk the hot tray under cold water and watch it buckle.

Under normal operation an aero engine will have high temperatures during high-power application, typically takeoff and climb, and lower temperatures with low power use such as during descent.

All pilots concerned about the long-term health of their engines should work to flatten out those high and low-temperature peaks.

To do that there are different techniques for different engines. In his book Aircraft Engine Operating Guide, Kas Thomas makes the statement: “In a trainer aircraft with a stout, reliable powerplant unencumbered by wastegates, controllable propellers, prop reduction gearing, dynamic counterweights, etc, it is acceptable simply to yank the throttle back and head downward.

Unfortunately, what’s good enough for the Cessna 150 is not good enough for the Navajo Chieftain. Getting the high-performance engine back to earth without doing damage calls for a bit more expertise. ” I agree but as I write my school’s Cessna 152 is in the maintenance shop having engine work done as a consequence of a hard life subjected to hot and cold temperatures.

That is the norm with a trainer aircraft engine – in effect, it is the cost of doing business.

Looking after the temperatures of an aero engine begins at startup and continues right through to shutdown. An aero engine is a mass of steel and aluminium and both have different heat expansion rates. There is no point in starting an engine then demanding power from it while one part of the engine is hot and another part stone cold.

Let the thing warm up. After startup is a good time to pick up the ATIS, check the flight controls including the flaps, set up the avionics or tickle up the GPS. All the while the whole engine is warming up.

Now move off – but do you need a massive application of power or just enough to get the aircraft rolling? At the run-up bay face the aircraft into wind.

Late model Cessna 182s have very deep cowl intakes, making it vital to point them into the wind to get maximum air intake while on the ground.

The mag check does not mean going from a high rpm setting to a sudden full cut for the idle check.

In an ideal world the engine will be ready for takeoff power application when the oil temperature is into the green.

Climbing out – can the engine be held at full throttle until it reaches cruise altitude or does the manufacturer recommend bringing the power back at say 300ft? This will help reduce the engine temperature.

Into the cruise – and is the pilot aware of what power settings to use in cruise as per the pilot’s operating manual? Are the cowl flaps, if fitted, raised to both increase the speed and help control the engine temperature, controlling the temperature peaks? Still in the cruise, leaning the engine reduces fuel wastage and controls the temperature by way of the EGT, if fitted, or by the traditional power-loss-increasemixture method.

For the descent, it is time to be concerned with the engine temperature backing off. This is where an engine-conscious pilot will think ahead before reducing power. In a recent flight review the owner of the subject Beech A36 wanted to reduce power gradually and only partially during a practice forced landing to try and reduce the low temperature trough. I agreed with him all the way.

Thinking ahead and backing off the power gradually will progressively lower the engine temperature and prevent shock-cooling.

The classic examples would have to be glider tow aircraft and skydiving aircraft, which involve full power to altitude and then low power to get back on the ground ASAP. The technique here is to educate the pilots operating the aircraft to gradually reduce power and engine temperatures to prevent shock-cooling.

After landing you can still be engine-conscious. Can you roll through and take just a bit longer to get to the chock point and in so doing let the engine cool down a bit more? This is critical with turbocharged engines.

Engines may only be engines but with care and foresight hot and cold peaks can be smoothed, resulting in a more reliable engine less likely to need costly major repairs. n Contact Dave by email at flyer02@optusnet. com. au