Dorsal fin leading-edge curvature / sharpness

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addaon

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Anyone have opinions or documents on this? On one side (in my particular design) it's constrained by blending nicely into the vertical tail, but the forward point, where it intersects the fuselage, is pretty unconstrained. Take it to minimum bending radius of the aluminum skin? Keep it uniform along the dorsal? Other?
 

WonderousMountain

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My thought is for a petite strake ahead of the junction.
Some of them really extend forward and I can't endorse
those. You don't want excess skin surface in a transition.

CA-61 Strake tail.jpg
 

BJC

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The dorsal fin, as BB said, should have a sharp edge for maximum effectiveness in damping / countering yaw. The opposing consideration is how it looks, and whether or not a sharp edge will hinder ground handling.


BJC
 

Mad MAC

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The other point being that having a sharpish LE on the dosal fin is ensuring that is consistently sheds vortexes from the same location which improves the constancy of the handling (power on / off etc etc). This may not be the case using a large or non constant LE radius.
 

Riggerrob

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In the extreme form, look at all the sharp-edged dorsal fins, ventral fins, ventral strakes, strakes ahead of horizontal stabilizers, etc. installed on aerobatic military trainers (Beechcraft Turbo Mentor and AT-6 Texan II, French Epsilon, all the Pilatus trainers, etc.) to improve stall performance. Cessna T-37, Canadiar Tutor and Beechcraft Sundowner (in RCAF service ever grew strakes on their noses to improve spin recoveries.
At risk of over-simplification, a sharp edged strake converts the entire aft fuselage into a larger fin that generates negligible drag in cruise, but contributes massive amounts "straightening" force at large yaw angles (e.g. spin).
 

Riggerrob

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When considering spin characteritsics, a smooth, round or oval aft fuselage is the worst configuration for spin recovery (think Spitfire).
Compare this with the boxy aft fuselage on Beechcraft Mentor, then look at all the extra strakes added to the Turbo Mentor. Most modern military trainers also have entire FLOCKS of strakes, fins, vortex generators, etc. all perform the same function as sharp, square corners.
 

Bill-Higdon

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When considering spin characteritsics, a smooth, round or oval aft fuselage is the worst configuration for spin recovery (think Spitfire).
Compare this with the boxy aft fuselage on Beechcraft Mentor, then look at all the extra strakes added to the Turbo Mentor. Most modern military trainers also have entire FLOCKS of strakes, fins, vortex generators, etc. all perform the same function as sharp, square corners.
Think T-37 with out the fixes
 
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