Battson
Moderator
After more than 300hrs of intensive backcountry flying including countless landings on riverbeds, unimproved airstrips, and places which weren't meant for 4-place aircraft - we wore out our tailwheel retaining bracket AKA hat bracket.
The bracket was understrength for this kind of work. It steadily deformed under the load, and had snapped one of the bolts in the process through bending stress. The bracket loosened off enough that it was allowing the springs too much room to free-play and bounce.
There was a lot of corrosion too, and combined with the bends in the metal bracket, I worried about Stress Corrosion Cracking.
We decided on an very simple upgrade, at the cost of three hours work.
We used a mild steel plate and some thin AN washers as spacers, these are the sacrificial parts; and two pieces of a NAS bolt for the retainers - which should last a long time.
We were certain to leave enough room for a slight amount of movement, so the leaf springs can slide over each other. Overtightened, the leaf spring would become much too springy and transfer more stress to the fuselage.
You can see where I had to relieve the cylindrical parts to allow the tailwheel steering horns to travel. The cylindrical parts are indexed against the leaf spring, to prevent them rotating.
If you haven't drilled the holes in the fuselage bracket yet, then you could reduce the size of the barrels somewhat.
The whole assembly needs to allow a little room for the spring to move around (vertical axis) IF you are going to be landing or taxiing on very rough stuff. On flat surfaces it doesn't seem to matter. The original bracket works fine, and there seems to be no need to leave room for the springs to move.
This time I have used rattle can etch primer, so I can repaint the parts easily and regularly. The two pot paint system with undercoat was strong, but was not durable and easily chipped from stones / debris impact; the two pot system is harder to reapply.
The bracket was understrength for this kind of work. It steadily deformed under the load, and had snapped one of the bolts in the process through bending stress. The bracket loosened off enough that it was allowing the springs too much room to free-play and bounce.
There was a lot of corrosion too, and combined with the bends in the metal bracket, I worried about Stress Corrosion Cracking.
We decided on an very simple upgrade, at the cost of three hours work.
We used a mild steel plate and some thin AN washers as spacers, these are the sacrificial parts; and two pieces of a NAS bolt for the retainers - which should last a long time.
We were certain to leave enough room for a slight amount of movement, so the leaf springs can slide over each other. Overtightened, the leaf spring would become much too springy and transfer more stress to the fuselage.
You can see where I had to relieve the cylindrical parts to allow the tailwheel steering horns to travel. The cylindrical parts are indexed against the leaf spring, to prevent them rotating.
If you haven't drilled the holes in the fuselage bracket yet, then you could reduce the size of the barrels somewhat.
The whole assembly needs to allow a little room for the spring to move around (vertical axis) IF you are going to be landing or taxiing on very rough stuff. On flat surfaces it doesn't seem to matter. The original bracket works fine, and there seems to be no need to leave room for the springs to move.
This time I have used rattle can etch primer, so I can repaint the parts easily and regularly. The two pot paint system with undercoat was strong, but was not durable and easily chipped from stones / debris impact; the two pot system is harder to reapply.
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I defer to Jonathan's experience on that.
