On 04/11/2010 11:54 AM, Kingsley Hurst wrote:
>> Again, this is no indication of trim. The trim determines (after
>> balancing out the aerodynamic forces) the position of the tailplane, and
>> the trim tabs will always remain in the same relative position to the
>> tail plane.
>
> Are you saying that for a given aircraft, if you fly at AUW with CG at
> its forward limit, the trim tab will be in the same position relative to
> the tailplane as when at AUW with the CG at its rearmost limit?
Yep. You say it correctly. The trim tab will remain in the same position
relative to the tailplane at all times.
If you change the trim, you introduce imbalance, and the tailplane moves
to another position to restore the balance again, i.e. get into the same
position relative to the trim tab. It is this "balance seeking movement"
which eases the forces on the stick.
You can easily see this on the ground, as for every trim tab position
you can find a tailplane position where the trim tab lines up with the
tailplane.
In flight, the trim tab position is always in the same relative position
to the tailplane.
I always assumed that this position would be straight in line with the
tailplane, but apperently this balance is found when the trim tab is
somewhat deflected upwards...
I thought that the tail plane was supposed to be aerodynamically
neutral, but this is not so. With the trim tab deflected up, there is
more force acting upon the underside of the tailplane than on the upperside.
Anyone with an explanation for this?
Frans
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