Stefan Smets asks:
>Ok, I'll ask the stupid question then :-) :
The only "stupid" question is one that you should have asked, but didn't! ;-)
> > or to fly flatter turns (although I'll never understand why anyone would
>do that)
>
>I would guess to lose less lift in the turn ?
>Sometimes I try to level the wings a bit while turning by cross-controlling
>the ailerons the other direction than the turn. I've even read about that in
>different magazines.
>Judging from what you wrote, there is something wrong with that ?
There's a difference between using crossed controls and having an
uncoordinated turn. I've flown a number of full-scale aircraft where I
found it was necessary to use crossed controls ("top aileron" plus "bottom"
rudder, typically) in order to keep the ball centered. Two that come to
mind a re a 7AC Aeronca Champion, and a Schweitzer 2-22.
In a turn there are a lot of unsymmetrical things happening to various
parts of the airplane. In particular, the airflow is now curved (the amount
of which and the significance of that curvature depends on the aircraft in
question, its flying weight, and the details of the turn being flown), and
the local airspeeds along the wing are different. In a good HLG, it's
possible that the airspeed at the outboard wingtip could be twice the
airspeed at the inboard tip. This means that the inboard
tip's Reynolds number is half that of the outboard tip, and it also needs
to develop four times the lift coefficient of the outboard tip! At the same
time, the lower airspeed can reduce its parasite drag in comparison to the
outboard tip.
The net result of all of this can, in some cases, result in the airplane
wanting to roll into a steeper
bank angle ("overbanking tendency"), while at the same time yawing toward
the outside of the turn. A combination of aileron towards the outside of
the turn ("top" aileron; this increases both the camber and the angle of
attack of the inside wingtip so that it can make that extra lift
coefficient needed to balance the extra airspeed of the outboard tip), and
enough into-the-turn ("bottom") rudder deflection to counteract the yaw is
needed to balance these effects. Without these "crossed" control inputs,
the airplane will not fly a coordinated turn.
Note, this phenomenon may or may not exist for a particular aircraft and
flight condition. I've flown other aircraft that did not need these control
inputs. It all depends on how the various factors and forces add up. The
bottom line is that you should use whatever control inputs are needed to
make your airplane "straighten up and fly right"!
Don Stackhouse @ DJ Aerotech
[EMAIL PROTECTED]
http://www.djaerotech.com
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