Breakfast today has turned into brunch as all three model variations had a
higher
velocity of 75m/sec (150kt) applied; and revealed an interesting anomaly.
Its not certain or being ruled out that at the higher air speed an acoustic
pressure
wave is detected traveling rearward along the fuselage belly aft of the
main gear. (the fully enclosed fairing does not exhibit this trait).
Other results on the acoustic aspect shows db levels increasing some 50%; the
loudest
areas being where deflected free stream air at the lower engine cowl fairing
rejoins slower moving air exiting the engine bay area; some 105db; quite
audible over everything... installing a trailing fence may reduce this turbulent
corridor.
The pressure wave though is interesting, at 70-80db it would be noticeable and
the cause of it would likely be related to the flutter of turbulence created by
air passing over and behind the cylindrical shape of the tyre. As Bud mentions
above there is also the added element of air escaping the gaps of the fairing
and exposed main gear rejoining faster moving air... The belly of the fuselage
is quite flexible and is likely oscillating enough to cause annoying pressure
pulses within the cockpit.
Employing fairing fences might provide an answer to the above situation.
Regarding Drag and Lift comparatives at 150kt, standard and semi enclosed setups
were identical in Drag with the later giving up 3.0kg of Lift; again the tyre
is removed from the free stream... The fully enclosed setup provides some 3.0kg
Drag reduction and gives up 2.0kg of Lift.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510682#510682
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