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PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL AGK question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

General knowledge final test two question two

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Marko created the topic: General knowledge final test two question two

Hi all just a quick question. To increase cylinder head temperatures on descent The answer states you add power and decrease the rate of descent by maintaining or reducing a speed which reduces heat loss. If you add power and decrease the rate of descent Wouldn’t you either speed up In a dive or start to climb by slowing down and adding power.
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Marko replied the topic: General knowledge final test two question two

Just had a rethink is it because you are on the backside of the broc/brod curve and need more power the slower you go?
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bobtait replied the topic: General knowledge final test two question two

That looks a bit odd to me. Can you give us a page reference to help us find the question you are talking about please.
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Marko replied the topic: General knowledge final test two question two

Final test number two page 149 question number two answer is c c page 159
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bobtait replied the topic: General knowledge final test two question two

The question is directed at the problem of 'thermal shock'. It's most likely to be the result of a long power-off descent from high altitude.

If a piston engine cools too rapidly during a long descent, the rate of heat loss needs to be reduced. If power is increased, more heat will be produced, and if airspeed is reduced, less heat will be carried away in the passing airflow. Both of those actions will slow down the cooling rate. Of course this would also result in a reduction in the rate of descent which would just have to be accepted.

In general aviation it could occur in parachute dropping operations, The piston-engine aircraft climbs at max rate to 14.000 ft, the jumpers exit and the aircraft makes a rapid power-off descent. This causes very rapid cooling of the cylinders that may eventually lead to cracked cylinders and/or valve damage.
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Marko replied the topic: General knowledge final test two question two

Thanks for that explanation bob
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