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Old 9th May 2009, 14:01
  #439 (permalink)  
Graviman
 
Join Date: Nov 2004
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Dave,

I would be more convinced if the maths was there to back up your pictogram logic.

In the code i mention, actually designed for cooling fans, i have assumed that each streamline passes through the fan then through a cooling pack before accelerating away as thrust. Along each streamline total pressure (static+dynamic) must sum to zero, although will increase through the fan and decrease through the cooler. What is really happening is that a different streamline leaves the same position in a different direction as the aerofoil passes, but that would require a full 3D vortex panel model (ie much bigger matrix). It is early days but the results tie up well with testing. After i finish my OU physics degree i intend to adapt it for high speed helicopter design studies like yours.

The typical assumption in textbooks of total pressure being uniform under the rotor disk is just that: an assumption. It allows momentum methods to calculate a figure of merit, but beyond that does not tell you what the aerodynamics look like. The 1g lift must remain constant by definition. What changes is the power required to achieve that lift. A pusher prop will require less power than a puller prop, but will increase power required by the rotor. Total power requirement all balance out so that Lift=Weight and Thrust=Drag...

With equal respect, i would say that a refresher on first principles of aerodynamic theory would allow discussions of performance quantities rather than qualities for your project. The discussion about pressure increase below rotor in ground effect made me go away and do some reading to understand which of my assumptions were wrong.

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RJS, interesting technical detail about X2 swashplate layout.

Last edited by Graviman; 11th May 2009 at 11:48. Reason: Dave reading way too much into my response to his questions.
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