Hi Chris,
The dimpled ribbing is primarily to add stiffness and prevent
oil-canning. Piper learned, to their dismay, in the 1960s, that raised
ribs, stamped into the sheet metal, led to transverse fatigue cracking.
When they changed to dimpled ribs, the problem was greatly diminished.
The classic vortex generator installation has the small vanes installed
in pairs, with the leading edges slightly inclined toward each other.
These produce counter-rotating vortices which energize the boundary
layer to reduce airflow separation. DeHavilland apparently felt that the
flow had enough angularity of its own, so installed them in parallel.
Jim Nichols
Tullahoma, TN USA
On 6/15/2016 4:34 PM, ChrisB wrote:
Thanks for those ideas and pictures, Jim. And why was the rudder ribbed? Was
it only for strength, or did it produce its own vortices and increase the
rudder's effectiveness?
Chris
C M I Barker | Gamlingay
On 15 Jun 2016, at 20:14, Jim Nichols <jhnichols@xxxxxxxxxxxxx> wrote:
Apparently the sky divers' Twin Otter is undergoing maintenance, so they
brought in a replacement today. This is Serial Number 66, from 1966.
http://www.gallery.leica-users.org/v/OldNick/Another+Twin+Otter.tif.html
The DeHavilland Twin Otter is loved and respected for its abilities and its
handling. To understand how this was achieved, one must look at the details
that DeHavilland worked into the design. An example pictured here are the
vortex generators that energize the airflow in the corner between the fin and
stabilizer to increase the response of the rudder and elevator.
http://www.gallery.leica-users.org/v/OldNick/Vortex+Generators+on+Twin+Otter.tif.html
Fuji X-E1 and Leica Summaron 35/3.5
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