Arnt Karlsen wrote:
> ..one idea; try make the effectiveness'es a function of the propwash,
> or thrust initially, and from each engine. May help to get a feel for
> it, I'm not that sure this is the _right_ way to model it. Negative
> thrust (say on decent/approach, does not need negative prop pitch,
> only negative prop blade aoa) also has an impact on the tail surfaces.
My current thinking, actually, isn't to treat propellers specially at
all. Every surface (propeller, jet, wing, whatever) generates an
aerodynamic force, and every surface has a characteristic size. You
can use, with a little heuristic handwaving, to determine a downstream
wash field for each surface. Basically, how much air at ambient
density must be flowing through a "tube" the size of the surface to
create that force?
Then you get all sorts of nifty effects for free:
+ Propwash and jetwash, of course.
+ Asymmetric stalls when slipping, because the fuselage masks one
wing.
+ Loss of tail authority in T-tail aircraft during stall.
The hard part here is deciding what the wash field should look like.
It should spread out gradually along some vector between the global
velocity and the perturbed velocity, but which? Dunno. There is also
a potential performance issue, since the extra calculations will go as
O(N^2) in the number of surfaces; I think this isn't likely to be
significant in practice, though.
Andy
--
Andrew J. Ross NextBus Information Systems
Senior Software Engineer Emeryville, CA
[EMAIL PROTECTED] http://www.nextbus.com
"Men go crazy in conflagrations. They only get better one by one."
- Sting (misquoted)
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