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Critical Altitude and Full Throttle Height

  • sydpilot
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sydpilot created the topic: Critical Altitude and Full Throttle Height

Hello Bob,
I'm having trouble comprehending the difference between the two. The definitions from page 4.6 of your book state.

CA - The height above which a particular nominated manifold pressure can no longer be maintained.
FTH - The height above which a particular manifold pressure is no longer available at full throttle.

Page 4.2 says full throttle height or CA is the height above which the rated boost cannot be maintained, even at full throttle.

Confused, confused.

Thank you.
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bobtait replied the topic: Critical Altitude and Full Throttle Height

Every turbo charged engine has a rated boost which is the maximum manifold pressure permitted for that engine. It is marked as a red line on the manifold pressure gauge. Because the ambient density drops with altitude, there will always be an altitude beyond which it will be impossible to obtain the rated boost. That is called critical altitude.

However the aircraft is still capable of climbing beyond that altitude but the manifold pressure available at full throttle will be less than rated boost. For every value of manifold pressure there will be some other altitude beyond which that particular manifold pressure will no longer be available. So every value of manifold pressure has its own full throttle height. Critical altitude is simply full throttle height for rated boost i.e. the red line on the manifold pressure gauge.
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  • sydpilot
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sydpilot replied the topic: Critical Altitude and Full Throttle Height

Thanks Bob!
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