The ratio of travel affects only stick force gradient. Is the tab
approx. in trail at the speed where you're experiencing the phugoid?
Looking at my manual, they say in trail with tailplanes in the "zero
position," w/o defining that. The typical case in cruise, since
there's downwashed air flowing over the tail, is about level with A/C
in cruise A of A. I'm guessing that if the tab is significantly down,
the tail's effectiveness will be reduced. Were it me, in flight I'd
measure stick distance from the seat structure and note tab pos. on
the indicator. Then replicate that on the ground.
Also, all-flying tails are greatly affected by mass balance, and
Dykins points that out in his book. How's the balance? I believe
it's any aft heaviness that's of interest here.
Doesn't sound like CG is the problem, but longitudinal instability is
experienced with an aft CG. In further desperation, I'd try near most
forward CG (burning fuel move CG fwd), which solo, just needs weighty
stuff on the passenger side floor.
Regards,
Fred F., A063
Dave DeFord wrote:
>
> I should have mentioned that the ratio of tab travel to tailplane travel is
> right at the minimum end of the allowable range specified by Europa.
>
> We haven't noticed any change in the effect with different CG locations,
> though some might exist. In any case, we are happy with our existing empty
> CG, as there is no loading arrangement below 1370 lbs gross that is too far
> forward, and a single 170 lb pilot can carry up to 73 lbs of bags with full
> fuel.
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