Modifications to the tail-wheel of the Chinook
One problem I had was that it was possible for the tail-wheel to swing past
center. This mangled the spring, and put a terrible load on the rudder cables.
It also made it impossible to steer, and took a large blast of throttle to get it
out of this condition. See above.
The plane could be flown, but was very sensitive to steer. Longer control
arms slowed the steering response and allowed me to land in a cross-wind.
It was still very unstable when trying to follow a very straight line. With such
a large amount of trail, and negative caster, I could push the rudder with my
little finger and steer the tail-wheel. The original design is inherently unstable
and the plane does not want to go straight.
I machined an aluminum bracket to fit into the end of the body tube. The bracket had some
positive caster angle on it and two saddle clamps held the original steel pivot tube.
( Later, by turning over the wheel fork, I was able to gain another inch of ground
clearance.)
I also added some aluminum axle nuts that are smooth and tightened with a cross-bar. ASAP
supplies a very slick tow-bar for moving the plane around. ( I modified the tow-bar by adding
a bend and extension, so the elevator is not scratched.)
Control arms are slightly longer than original.
The original tailwheel as supplied by
ASAP
This also puts weight on the rudder
bearing
Castor angle with plenty of trail makes it track
accurate and true.
If your Chinook seems a bit squirrely, this might help.
This tail-wheel was made from the original. The added machined parts are new control arms,
saddle clamps, and a "machined from solid" mounting plate to fit into the body tube.
The mounting plate was made from a rectangular chunk of aluminum that was held at an angle in the
lathe chuck. The more angle, the more caster you will have, and the straighter it will track. The
aluminum was machined to slide into the body tube. Holes were then drilled and tapped to secure
this mounting plate in the body tube with 1/4-28 screws.
The saddle clamps were made by bolting to rectangular hunks of aluminum together, then boring a
hole on the center line.
Lightening holes were drilled as much as possible to keep the weight down. Adds about one pound.
You are not alone:

When I first got my Chinook +2 put together, I at first thought something was wrong with me, in that I could not land it in cross-winds or hold it in a straight line with the tail down
at 30 MPH. My first experience at just a slow taxi got me into an oscillation where the tail wheel went full lock to lock. The plane was steering ME !  It went into a ground loop so
fast and so violent, and I hadn't fastened my seatbelt as I was only going to taxi, that I was almost thrown from the plane.
Anxious to fly the plane, I flew the plane the first year by lengthening the control arms to slow the steering and give me some mechanical advantage over the tail-wheel and allowed
me to hold it straight by force. It also prevented the over center or past center condition that would lock it up if turned too tight. For most folks that can't do machine work, the
longer arms will give you a usable aircraft.
Changing the caster angle is the real fix and makes it handle great on the ground. 25 MPH cross-winds are no problem now.

Other tail-wheel problems I have had in 550 hours are:
  •        Wheel bearings. Worn out two sets. Water and mud take their toll, and replacements should be sealed bearings, not shielded.
  •        Tire can get knocked eccentric on the wheel. The plastic tube they give you does not fit tight to the tire. This gives an out-of-round condition that can really make some
    vibration. I made a new wheel flange spacer from aluminum that fits tight. There really should be a spacer between the wheel bearing inner races on the axle, and if I have
    anymore trouble with bearings I will fix this. ASAP no longer supplies this tail wheel as tires are not available.
  •        The tail-wheel takes a real beating as there is a LOT of weight on it. If you carry passengers, it is worse, so yearly greasing of the thrust bearing is a must.
Take-off is very easy in cross-winds if bungee are tight and a good tail-wheel.

The Chinook +2 is an extremely rugged little airplane. Very roomy pilots seat and fantastic load flying capacity.
Very fast, easy to build, dependable and it holds up over time. I don't think there is any contest between Chinook and a Challenger.
My parking brake is just a bungee hooked to the split handles as shown.
Grass runways are perfect for the Chinook.
Note: The fork has been reversed since
these photos were taken. This moved the
wheel down about an inch. The axle hole is
not drilled on the center line of the 4 bolts.
ASAP no longer supplies this wheel. I found a very
good 8 inch by 1 7/8 inch replacement wheel from a
"RAZOR" scooter front wheel. 1 pound less weight,
too. (Plastic split rim.)