Elevator control: Pull-pull vs push rod

[george kennie]

Keith,
I'm using a little different system on my current, under construction,
ship than anything I've tried in the past. I've used pull-pull on
elevator in the past, and I like it, but you can still get trim changes
with temp changes as the fuse swells and contracts.What I'm trying this
time is to locate the elevator servo just ahead of the stab. I then
mount a piece of Dave Brown arrow shaft about a foot long running back
to the elevators with a bushing at EACH end with Y-rods exiting the fuse
to each elev half. I offset the servo to one side of the fuse so that
the end of the output arm is roughly in the center of the fuse.I connect
the servo output arm to the drive end of the pushrod with about a 2&1/2"
threaded end rod for adjustment.Being poor I use Rocket City clevises
which gives me additional adjustment as well as zero slop.As you can see
all links are very short guaranteeing that any trim changes will be
miniscule.
With the arrow shaft supported at BOTH ends there can be no side-to-side
movement assuring equal travel to each elev half.Also the parts are all
so small that the total weight of the system rivals the best pull-pull
set-up.I also installed the rudder servo at the same location and I will
use pull-pull on that.I can get away with this rearward installation as
my stab, on this airplane only weighs 1.8 oz.
You might have to throw the battery pak against the firewall, but I
thought this might be another option you might want to consider or a
modification thereof.
The rod bearings are nothing more than a couple of short pieces of brass
tubing so that the system is lighter and less complex than a bell-crank
unit.
Whatever you go with, good luck.
Georgie

Keith Black wrote:

> I'm in the process of building a new Aries and am trying to decide
> whether to use pull-pull or a push-rod on the elevator. I'd like to
> hear some opinions on which is the best way to go. I plan to go with
> pull-pull on the rudder, but I'm undecided on the elevator. The Aries
> requires no formers so there would be no problem with space in
> installing a pull-pull system for the elevator, however I know there
> are different theories as to which is the best approach. If you have
> an opinion please explain why you feel the way you do (weight, control
> accuracy, reliability, etc.). For those push-rod proponents I'd be
> very interested in hearing your opinion on the best approach to
> installing a push rod system. For example using a "Y" push rod with
> bushings, using an bell crank, etc. I look forward to hearing
> everyone's opinion. Thanks,Keith Black
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