The "few pounds of rotational force" is the weight of the counterbalance
times the length of the arm it sits on. Same difference in trimmed flight
where any air-load eccentricity is reacted by the effect of the trim tabs.
Duncan mcFadyean
On Thursday, January 17, 2002 3:08 AM, Fred Fillinger
[SMTP:fillinger@ameritech.net] wrote:
> > 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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