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Old 12th May 2009, 17:09
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Pugilistic Animus
 
Join Date: Dec 2006
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just to add that without a derate or a flat rate

that thrust is [if i remember right] is about proportional to about N1^3.5
so if thrust or[ drag] decreases with altitude as thrust at any altitude =T[msl]*sqrt [pi]

at any temperature T [msl]* sqrt[theta]

pi = the pressure ratio
theta =temp. ratio


and it can be seen that the required N1 would be mathematically increased if necessary to counter drag until either a limiting rpm [ if N1 vs EPR limited] or a limiting temp. is achieved for non-accelerated flight

example: T[msl]*sqrt [sigma] ~N1^3.5...

...but for the purpose of meeting performance, N1 would increase to maintain the thrust required to meet performance [although Drag would decrease too] but for acceleration you need thrust GREATER than drag, for performance it's referred to a 'thrust required'

so you are correct

PA

Last edited by Pugilistic Animus; 15th May 2009 at 15:11. Reason: theta and pi are the correct designations, sigma is 'density altitude ratio
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