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Rear Longeron

Several pilots have reported deformed lower aft longerons.


It is not uncommon for taildragger aircraft being used off-airport to experience damage to the rear fuselage. The Bearhawk is no different. The original tailwheel leaf springs had their own issues and tended to bend occasionally. A stinger was introduced with the Bravo model, however this too has it's own set of issues. There are a number of contributing factors.



The Issue


The aft fuselage is designed to handle stress from the tailwheel when it is aligned longitudinally, and in a vertical plane, such as in a normal landing.


However while taxying, when the tailwheel is swiveled at 90º to the fuselage, it may introduce a torsional moment to the lower aft longerons. If the wheel then encounters a rock or hole a shock may be transmitted forward and can result in bent longerons. It manifests as loose fabric in the area underneath the tailplane that is noticeable upon inspection.


The Fix


Bob Barrows issued an engineering notice to address the issue that involves welding a strengthening plate between the lower longerons. Obviously this is not a small job and can involve significant down time, therefore is best addressed during construction. How successful the fix is will become more apparent once a number of repairs have in service for a reasonable amount of time.


Avoidance


There are a number of things that may help minimize the possibility of damage in this area, particularly when taxying over rough ground.


- Avoid tight turns on rough ground.

- Taxy the aircraft to the takeoff position before loading it.

- Shut the engine down on the airstrip and push the aircraft off into rough areas.

- Apply down elevator (with caution) to reduce the loading on the tailwheel while turning.

- A right turn may help lighten the tailwheel in some circumstances (due to precession) with a clockwise rotating prop.



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