Summary: airfoil families and planform selections DO matter, even on hand
launch
birds.
A little empirical data for you. I recently had to bag a new set of tails
for
the Kluge and a second set for the new Splooge. The Splooge requires the
tail
halves to mount individually and directly to the CF/Al boom, which involves
gluing and then wrapping with some glass. Not being one who enjoys tail
failures, I'm always looking for ways to beef things up.
The Kluge originally used a 5% section made from mirroring the top surface
of a
thinned 7003, which I created because its max thickness point is well
forward
and the LE has some roundness to it. However, I had also got some templates
for
a fin section which had to this point gone unused. The fin section was a
derivitave of a mirrored RG-14 top section, created to maximize thickness at
the
joining area. The LE is sharper, the section reaches max thick later, and
sustains a high thickness for a fair portion of the chord; ya know, that
whole
broader, deeper thing. Seemed like the thing to try for the new
Kluge/Splooge
tails since I figured it would help make that boom/tail joint a little
stronger.
The chord of the root template is a little larger than on my original tails,
so
I cut the span down just a hair while retaining the original tip section in
order to maintain the prescribed tail area. I think it's still around 5%,
but
the chord is bigger so thickness might be increased a super tiny bit. Moving
surfaces are identical in area and the routed hinge line is the same width.
Surface finish and weight is the same as well. So the only things that
really
changed were span, planform and root airfoil.
The rest of the Kluge fuse is damn near identical to where it started, and
incidence was brought into spec over a friendly camper's burner on June 3. I
can
honestly say that I see a significant change in the handling qualities of
this
plane. I've lost snappiness in entering turns (poly, by the way) and
cleanliness
at max deflection. Although I can't perceive a worsening of the dead-band
issue,
the handling has definitely changed for the worse. As far as the planform
change
goes, I would think that the slight increase in taper would tend to work in
the
right direction, enabling the tail to be effective at more angles of attack.
Also, the slightly increased chord should have cleaned things up due to the
improved Re. Since the surfaces were identical in size, the hingeline
effectively moves farther aft as a percent of the root, which could
encourage
the max-deflection problem I see. The rest gets back to the sharp LE and the
sustained thickness. The quick fix would be to take a sanding block to the
LE,
the right one would be to replace the tails.
Due to these perceptions, I can no longer agree with the idea that tail
sections
are irrelevant at the Reynolds numbers HLG tails fly in. Keep it as thin as
your
joining method will allow, keep the thickness very far forward, keep plenty
of
volume up near the LE and get that hingeline as far forward as the effects
of
rigging and servo slop will allow.
And then you'll be stylin!
Derek
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