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Air Inlets Calculations?

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Air Inlets Calculations?

Old 30th Oct 2008, 08:54
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Join Date: May 2005
Location: Singapore
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Air Inlets Calculations?

Hi guys,

Is there anyone who could shed some light on how do we calculate the drag caused by the ram air inlet under an a/c belly.Do we use the Drag Polar equation to calculate the amount of drag?

To what extent can the pack 1 & 2 air inlet and air conditioning bay cool air inlet affect the aircraft performance?Is the drag caused by these inlets significant enough to cause a dip in performance or is it negligible?I've attached the link which shows the location of these inlets.

Vibes is offline  
Old 31st Oct 2008, 04:19
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Join Date: Sep 2002
Location: La Belle Province
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Originally Posted by Vibes View Post
Hi guys,

Is there anyone who could shed some light on how do we calculate the drag caused by the ram air inlet under an a/c belly.Do we use the Drag Polar equation to calculate the amount of drag?

To what extent can the pack 1 & 2 air inlet and air conditioning bay cool air inlet affect the aircraft performance?Is the drag caused by these inlets significant enough to cause a dip in performance or is it negligible?I've attached the link which shows the location of these inlets.
That's a rather large picture!

To answer the two questions:

1. No. Drag polars relate to lift/drag relationships. Those naca scoops are producing no lift, so it's not a drag polar issue. A very simplistic way is to take the inlet flow and assume it is brought to rest inside the aircraft (or, if you like, accelerated from rest to the aircraft speed) and calculate the force resulting. There's a well know book by Hoerner on Drag which gives all kinds of empirical methods for just such calculations.

2. I don't know, but I rather doubt it; they'll have been designed for minimum impact.
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