>I have made the plywood mock-up of John Moran's tail wheel steering
>and rudder arm.
>I am unable to get the stop drive to function. If stops on rudder arm
>push tailwheel arm to original stops, rudder arm cannot then reach
>the original stops. If stops not fitted, springs will have to do
>this.
I have now completed construction of my revision of the tailwheel drive and it
functions as originally envisioned. Unfortunately, I apparently didn't make
the expected operation clear and in also there are a couple of additional
things which cropped up as detailed below.
The stops on the bottom of the idler plate eyebolts are meant to limit the
differential between the rudder and tailwheel to a maximum of about 15 degrees
thus ensuring tailwheel steering (degraded) if the springs should fail as well
as to limit spring compression.
Recall that the idler plate is driven directly by the cables from the pedals.
To limit rudder deflection to that specified in Europa's manual, the tailwheel
mount's stops were extended upward so that the rear of the idler plate -
shaped to copy the rear of the tailwheel arm - would contact this extended
stop exactly as the original tailwheel arm contacted the stop built into the
tailwheel mount. I used one of the pieces sawed out of LG02A and filed it so
that it fit snugly into the top of the tailwheel mount by about 1/2 its
thickness. The protruding part was filed to match and extend the stops. A
piece of scrap 1/8 stainless was shaped to fit below the tailwheel mount
between the bulkhead and the bearing. A threaded tube was sized to fit between
these two pieces and secured with 10-32 screws/Locktite.
Thus, the idler plate drives the rudder as in the original design, including
limit stops. The tailwheel arm is linked to the idler plate by the springs on
long 8-32 bolts (threads removed where contact with eyebolt occurs by filing
while spinning in a drill press). If the rudder is deflected more than about
15 degrees from the tailwheel's direction, the stops on the eyebolt force the
tailwheel to follow further pedal deflection in that direction. Once the idler
plate contacts the limit stops, the last 15 degrees of tailwheel deflection is
by spring force plus aerodynamic force produced by the rudder. Ultimate
tailwheel deflection is limited by the original stops.
A friend from the local EAA chapter is a retired tool & die maker who helped
immensely by making the collar for the tailwheel shaft. He refined my crude
concept by making a steel shoulder washer which retains the idler plate,
provides the bearing surface, and is recessed on the top to allow the nut to
go in so the hole for the cotter pin is accessible. He also faced about 1/16
inch off the nut to ensure an easy fit of this cotter pin. The bearing area
of this shoulder washer was made 0.005 thicker than the idler plate to give a
nice fit without binding. Even without lubrication the overall assembly works
smoothly.
The hole through the tailwheel bulkhead for the rudder pushrod was enlarged
upward about 1/4 inch to accommodate the slightly higher position of the idler
plate compared to the tailwheel arm.
The eyebolts were welded into the tailwheel arm using TIG. The 1 inch square
steel piece used to form the cup for the rudder bolt head was arc welded.
Weight of the overall assembly is 12 ounces, which could be reduced by cutting
away extraneous parts of the idler plate.
The remaining questions are, of course, the required strength of the springs
and how it will handle on the ground. This will have to be resolved
experimentally once the overall project is finished, hopefully in the summer.
Thanks for the interest.
Regards, John A044 Newtown, CT
|