Don's explanation of using crossed controls and what happens then seems
satifactory to me; as I understand it, he used crossed controls in some
aircraft to make a coordinated turn.
How about the original point Daryl made: the use of anybody wanting to fly a
flatter turn (cross-controlling would be a way to do that); Daryl seemed to
imply it's not a good idea; since I'm sure he knows a lot more about all
this then I do, and the use of a flattter tuns "seemed obvious" to me, his
remark made me wonder what the problem is ?
The article in question seems to contradict the necessity to make
coordinated turns:
"Most of the pilots tend to think it is necessary to make coordinated turns
with our sailplanes. [...] it's not necessarily the ideal think for our
models. Remember that we are looking for max or near max performance from
our planes and making coordinated turns while termalling can degrade the
performance of the wing. Many times when I'm doing fairly thight thermal
turns, I will actually be cross-controlling the plane (feeding in OPPOSITE
rudder) to work the inside wing harder and allow the wing to create more
lift. This situation of "adverse yaw" may look a little funny [...], but
it's a good way to create maximum lift in a given situation."
Stefan
> > > 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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