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Over Sensitive Rudder

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BBerson

Light Plane Philosopher
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Not only careless but illegal. The aux stabs or ventral fins are part of the float STC and are required. Cessna had a modification kit to eliminate the ventral fin; it involved a non-linear rudder return spring system that increased breakout forces enormously and improved directional stability while on floats.
Interesting. I thought the only good way to improve the directional stability was added tail area.
Some seaplanes have used VG,s also, to improve stability.
 

Dan Thomas

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Sep 17, 2008
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5,409
Interesting. I thought the only good way to improve the directional stability was added tail area.
Some seaplanes have used VG,s also, to improve stability.
I forgot to mention that the kit only applied to 185s, and 180s with the larger dorsal fin. The later 180s had that fin, and some earlier models were retrofitted with it.

The rudder, without the non-linear return spring system, would deflect in an unintentional slip, like a lot of airplanes will do. You can apply some aileron and get the adverse yaw in a lot of airplanes and with your feet lightly on the pedals you can feel the rudder deflecting toward the opposite side. The non-linear return spring system made that rudder pretty stiff in the neutral position so that it acted like additional keel area. Floatplanes, because of the large side area of the floats ahead of the CG, have more adverse yaw and can slip a little too aggressively and can get into control difficulties without some added yaw stability.

The Jodels were originally designed with the one-piece rudder/vertical fin. The whole thing moves. There is no other fin area. The plans called for a spring-loaded rudder bar return/centering device. I still have it in one of my junkboxes; it was made but never installed. We just used plain return springs. In turbulence, the tail wags considerably and you can feel the pedals moving. If you put your feet firmly against them and hold them still, the wagging mostly stops; the rudder is acting as a fixed fin.
 

Pops

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I forgot to mention that the kit only applied to 185s, and 180s with the larger dorsal fin. The later 180s had that fin, and some earlier models were retrofitted with it.

The rudder, without the non-linear return spring system, would deflect in an unintentional slip, like a lot of airplanes will do. You can apply some aileron and get the adverse yaw in a lot of airplanes and with your feet lightly on the pedals you can feel the rudder deflecting toward the opposite side. The non-linear return spring system made that rudder pretty stiff in the neutral position so that it acted like additional keel area. Floatplanes, because of the large side area of the floats ahead of the CG, have more adverse yaw and can slip a little too aggressively and can get into control difficulties without some added yaw stability.

The Jodels were originally designed with the one-piece rudder/vertical fin. The whole thing moves. There is no other fin area. The plans called for a spring-loaded rudder bar return/centering device. I still have it in one of my junkboxes; it was made but never installed. We just used plain return springs. In turbulence, the tail wags considerably and you can feel the pedals moving. If you put your feet firmly against them and hold them still, the wagging mostly stops; the rudder is acting as a fixed fin.
My Falconar F-12 did not have any tailwag. The Falconar has a separate fin and very large rudder not like the Jodels. The F-12A had a swept fin and rudder. Glad mine was not a A. It handled turbulence very, very good. If you was just starting to feel the bumps, it was rough for most others. It was quite, smooth, and fast, felt as smooth as a light twin. Stall speed was 65-68 mph but with the wing so low to the ground, The ground effect in landing was large. Approach at single place 80 mph and not any less to not get in the high sink rate. Approach heavy 85 mph. Gross wt ROC of 1700 fpm and single place of 2200 fpm with a cruise of 150 mph. Loved that airplane.
 
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