by Steve Busby, Aerolite Flight Services
The tail spring for the Bearhawk Patrol and Model B Bearhawk 4-Place has two pre-drilled holes, one at each end, to accept AN4 bolts. The socket for the spring, on the fuselage, has a hole pre drilled as well, so its a simple matter of lining up and bolting. The tail wheel has two holes so you will need to drill the second one once the spring is inserted. Make sure the tailwheel is properly standing vertical with no leaning to a side before drilling. And confirm the final hole sizes/bolts required by referring the the plans.
The spring is made of 17-4 Stainless Steel hardened to approx 44 Rc. Though it is tough, it can still be drilled. Use a new HSS drill bit, turning slow with steady pressure and some form of cutting fluid. A cobalt drill bit is preferable (NOT carbide) as it handles the hard, tempered material better.
Builder video from Ken:
Builder Bruce Case drew this nice diagram of Bob’s tailwheel assembly:
Bearhawk Tailwheel Exploded Diagram
This process is not this simple. You need to verify that the pilot hole in your fuselage were drilled in a way to orient the tailwheel perfectly vertical. My holes were not which required slightly rotating the stinger and developing a bushing system to accurately drill through the tailpost and hardened stinger. If the tailwheel is not mounted perfectly vertical you are creating a plane that want to ground loop.
good to know, thanks for posting
Video does tell a bigger story and gives the reader/viewer a better I idea of whats going on
The tailwheel spring mount for the round spring on the Bearhawk-B measures out with a set of calipers at 3/8” interior diameter at .3725with calipers. The An4-16 is loose. A AN5-16A is likely the correct fit. Also, it appears that this is mounted with a fiber locking nut. Is this correct?