One of the maintenance items I checked out on Saturday was the tailwheel steering. There was a very illuminating thread on the Vans Air Force forums recently. The original poster had ground looped his RV–8 while landing in a moderate right crosswind. Luckily, nothing was damaged except his ego. He wasn’t 100% sure what had triggered the ground loop, but he suspected that the tailwheel may have unlocked from the tailwheel steering during rollout.
The ensuing discussion was quite interesting, as it highlighted a potential issue with single-are tailwheel steering linkages, as is fitted to our RV–8. It seems that the typical geometry of these linkages puts the bellcrank at the tailwheel pivot at a different angle than the rudder horn where the front end of the linkage attaches. This results in more tailwheel travel to one side than to the other, and this may cause the linkage to unlock at full rudder travel.
I check our tailwheel on Saturday, and sure enough, full left rudder turns the tailwheel far enough that the unlocking cam disengages it from the bellcrank at the pivot. In principle, the tailwheel should remain locked to the linkage at full rudder, unless you tap the brake to tighten up the turn, in which case the spring in the linkage allows the wheel to turn further, causing it to unlock.
I played around with the available adjustment in the linkage, but it was not possible to set it up so that it would remain locked at both full right and full left travel. I studied the geometry and concluded that there are two possible fixes.
- Purchase or fabricate a tailwheel pivot bellcrank that has the end of the arm swept back further, so the line between the pivot and the end of the arm is parallel to a line between the rudder hinge and the forward end of the steering linkage.
- Purchase a longer rod end for the steering linkage and drill a new hole for the front end of the arm. The new hole would be further ahead on the rudder horn, which would make the angle between the rudder hinge and the linkage arm attachment close to parallel to the angle between the tailwheel pivot and the aft end of the linkage arm.
Note: This issue is not present if the builder uses the two chains and springs that Van supplies with the kit. I had tried those, but found that the chains hit the bottom of the rudder fairing, which prompted me to switch to the single-arm steering linkage.