Small Tail Stinson Floatplane Fin Options
The aux fins (finlets) I've installed are p/n
U-3901002A, Univairs replacement for the original Stinson aux seaplane
108-3901002 for 108 models up to dash 2. The original fin is no longer available
and it's just as well. The Type Certificate A-767 states that aux fin/s (item
207) are required equipment on all 108's except the dash 3. I know some fellows
that have flown without but I wouldn't recommend it.
The only things going for the single fin are:
- It's cheap, you can have mine for a song.
- It's lighter, 4 lbs vs. 8 lbs for the finlets.
- It's easier to install and less likely to cause stress fractures.
- Not in the way when we pick up the plane with the float dolly
- Not in the way when the wind blows tail into the dock.
- Looks a little nicer... I think so.
- Doesn't go under water when you start the takeoff roll.
- Provides equal stability to the larger single fin in flight but doesn't interfere with turning in strong wind as much. This is due to the fins being located on the same lateral level as the primary fin. If you imagine the tail section from the side, you can imagine how much more the wind will effect the single fin. I am now able to turn in winds that I previously was not.
The only real down-side to the finlets is that they are relatively expensive, a bit heavier, and they tend to vibrate a bit which can cause some problems with cracks in the horizontal stabilizer tip former. Not the end of the world and well worth it in my opinion.
With floats and fins installed the plane is actually more stable then on wheels. It's a real pleasure to fly.
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