Bill,
I’m hoping one of our aero engineers will comment more
intelligently on your discussion/questions below, but let me give it a
start. At the speed our Lancairs fly, mass balancing the control surfaces
is important. Even small imbalances can lead to flutter, especially as the
hinges and multiple control system linkages wear a bit over time. I would
encourage you to balance especially the elevator and ailerons as well as you
can---after paint.
A number of builders have had the same problem with getting
enough weight in the tips so someone (Lancair?) developed a “bobweight”
that could be added to the control arms in the tail. I have not actually seen
one, but understand that it consists of a steel arm that attaches to the center
elevator hinge assembly and extends forward toward the front of the fuselage.
You can then add the necessary weight to the end to balance the total elevator assembly.
If one of you has used this system, could you elaborate?
Thanks,
Bob
There's an article in the EAA Experimenter about Paul
Lipp's 235. Among other mods he describes spring-loading the aileron
trim but using a trim tab for pitch.
The way I picture it is that a trim tab maintains
its relative effect with change in airspeed whereas spring loading will change.
(The spring would compress due to the additional load on the
surface, allowing the surface to deflect).
I don't know enough about the subject to say one way or the
other. My question is- do those with the spring-loaded pitch trim have to
adjust trim very often as their speed changes?
My reason for asking is that my IV-P elevators
are going to need more lead than I can pack into them. I've been thinking about
a spring-loaded system for trim so I can lose the weight of the trim tab and
MAC servo. What I have in mind would be a fiberglass leaf spring that
would act in both directions. Although I'd like to use a mechanical control I
may end up using a linear actuator (Velocity builders might recognize that
setup).
Looking for comments- Bill Wade