[NSRCA-discussion] Annhedral Stab

[J N Hiller]

Thanks Matt, as with any other design change it needs to be tried to
understand the effect. I always felt that the bottom running stab in
knife-edge or the outer stab when the fuselage is yawed is more effective
than the other side and dominate. In the old days I was able to balance
knife-edge pitch by adjusting one elevator up and the other down. When an
annhedral stab is yawed it becomes unbalanced resulting in a pitch force
change towards the top of the fuselage. If this were true it should also
produce a slight roll with yaw. I will probably never understand as much
about pattern plane design as I would like, I just try things. It either
gets better or it gets worse and this is only one of many design
considerations.
OH that rolling circle stuff makes my head hurt. An analog processor would
probably help or one about thirty years younger.
Jim

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of
rcmaster199 at aol.com
Sent: Sunday, April 20, 2008 12:43 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] Annhedral Stab

Jim,

Most would say that anhedral stabs are hype......

I prefer to call them a viable option for pattern models and here're my
thoughts on the subject. First off, fundamentally, they don't change how the
wing is stabilized in pitch compared to a flat stab...same physics apply.
Anhedral area however is the resultant of two component areas, horizontal
which dominates and a vertical which adds to the already eixsting vertical
stabilizer area. It may be thought as area added to the ventral side of the
fuse without adding a subfin. This often helps settle some unwanted thrust
vector forces namely the much cussed and discussed dredded pitch to belly
with top rudder. Does it always work as prescribed? Does anything in our
sport ever always work as prescribed?

Rolling circles may be helped with anhedral in the stab. When the anhedral
angle is "just right", there is no region during rotation (X degrees from
horizontal) that completely blanks out the stab as can happen with flat
stabs. Does is do wonders? I don't think so but it certainly does not hurt.

My new design will have anhedral in its stab (7-8 degrees)

Cheers,

MattK


-----Original Message-----
From: J N Hiller <jnhiller at earthlink.net>
To: NSRCA Mailing List <nsrca-discussion at lists.nsrca.org>
Sent: Sun, 20 Apr 2008 2:01 pm
Subject: [NSRCA-discussion] Annhedral Stab



Can I open a discussion on why some designs have an annhedral stab?  Was it
to lower the effective flying height of the stab to reduce the wing  to stab
vertical offset and knife edge belly pitch, or is there some other  reason?
Jim Hiller    _______________________________________________
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