Trimming a Kolb & Changing Elevator
Incidence
We had a problem with the FSII wanting
to act tail heavy, even though it wasn't. W & B were right
where they were supposed to be.
We initially trimmed out the tail heaviness
by drooping the ailerons. Drooping or reflexing the ailerons (or
flaps, or both) is basic SOP to trim a Kolb.
If a Kolb feels nose heavy, even when
it isn't, adjust the pushrods to raise the trailing edges of the
ailerons or flaps until it feels normal. Reflexing the ailerons
(or flaps) up moves the wing center of lift forward, & makes
it feel less nose heavy.
If it feels tail heavy even when it
isn't, lower the trailing edges of the ailerons or flaps. This
moves the wing center of lift aft, the tail comes up, the nose
goes down. Now it feels less tail heavy.
However, in order to get this particular
airplane trimmed correctly, it required so much aileron droop
that the ailerons felt heavy, which made sense, because now they
were always hanging down into the airflow, and under load. So
we decided to try raising the front of the stabilizer a little.
Nothing fancy, got a length of .080
x 3/4" steel strap from Tractor Supply, cut out four brackets,
and drilled three 3/16" holes in each bracket.
The middle hole in the new brackets
is used to bolt the new brackets to the original equipment welded
bracket through the original hole in the original bracket, the
one used for the stabilizer bolt. Fill the inside space tightly
with washers or a spacer bushing so that you can tighten it properly
without deforming the original bracket. Then you drill holes through
the original bracket and put another AN3 bolt through the bottom
to keep the new brackets from twisting or moving.
The final AN3 bolt goes through the
top hole which is above the original hole. You have now raised
the front of the elevator a bit and you ought to be good to go.
Note that it would be easy to put extra upper holes in the new
brackets so that you could test fly & adjust to find the optimum
location. We went about 7/8 of an inch up and got lucky. Your
results may vary...