> In a static situation the tailplanes are counterbalanced by the
> counterbalance weight, the moments for which are transmitted through the TP
> pins. Any g loading increases these loads proportionately.Any shock loads
> (counterbalance weight coming up against the upper stop) have a similar
> magnifying affect.
>
> Interesting thread this! No concrete solutions yet though.
>
> Duncan McFadyean
I gotta be careful in encroaching on technical details in this group,
lest others really understand this stuff! No doubt about the banging
the mass balance weight against stops, nor G-loaded flight. In static
load, the center of mass of the tailplanes is aft of the hinge line
(the torque tube), but I figured just a few pounds rotational force.
In flight, same effect, but plus/minus wherever the center of lift is
relative to the hinge line. In level cruise flight, the pressure
distribution is typically graphed for a laminar shape like this is
supposed to balance out the static aft heaviness. I picture low
pounds of rotational force on any of the components, until you pull
G's, where center of lift shifts really fwd (giving you desired stick
force gradient), and that should stress the parts.
Cruise is where she spends most of the time, and low values of steady
pressure on the parts shouldn't mash metal, no? That's why I was
thinking about conditions where the thing is pounded and twisted,
because that adds the multiplier effect of inertia. I recall the trim
tab beef-up mod where something was breaking the welds on the tab
drive pins, blamed on start-up shaking.
As an aside, this relationship of lift-center to hinge line makes
stabilators a tricky balancing act, and fixed surfaces with elevators
are an easier out. It's covered in Don Dykins' book on the Europa,
and a chapter in Horner's book on lift. Stability, stick force
gradient, and low-speed tail effectiveness are affected too,
especially in a short-coupled airplane with greatly effective flaps
(airflow change), making tail area and wing distance further things to
play with. Or so they say. But in terms of flight characteristics
Dykins apparently got it right?
Regards,
Fred F.
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