|
|
Another related question: I walked around a Citation
the other day and noticed that the rudder has a T-shaped aluminum extrusion
riveted to the trailing edge of the rudder - looked like a "fix" to get more
rudder sensitivity by simulating a wider trailing edge, compensating for
boundary layer thickness, just like our ailerons. Why do our elevators and
rudders have pointed trailing edges while the ailerons have blunt ones?
Gary Casey
Gary has a good question and I have been asking this for a long time. The Aerodynamic drag formula shows that the trailing edge radius is related to drag by the CUBE of the radius. The radius times itself and times itself again. That is huge, so that is why you see sharp trailing edges. On the Lancair ailerons the trailing edge is blunted to make a small cord surface act like it is longer/bigger without increasing the effort to much compared to a longer cord aileron. Remember that many fighters that fly at these speeds have hydraulic boost to move the ailerons enough to get a fast roll rates. My guess is that Lance wanted heavier/more effective roll controls and didn't care about the drag increase on the ailerons.
The rudder is a different issue. At slow speeds you can only move the rudder so far before it stalls or becomes less effective. Then you add VG's to reattach the boundary or have a second hinge, like double slotted flaps, or put the deflector plate at the trailing edge which I think deflects the high pressure side air more, giving more rudder effect at full deflection. It looks very dragy but it is way out back and probably is in separated air while in cruise but must cause some drag and is less complicated than the other choices.
While parked my drag is the lowest,
Jim Hergert
N6XE, "An Sex Y" L4P
|
|