REFLECTOR: Lower winglets

[Alex Balic]

Keith,
You need to look at how the winglets  work to create yaw stability- the
cambered surfaces needs to face inboard, just like on the upper winglets-
you probably don't need the lowers at all, but if you do install them, you
do not want to have the "top" of the airfoil facing outboard, because this
will reduce yaw stability of your aircraft by some significant amount. The
upper winglets are designed to act against differing angles of attack (a
yawed condition) to straighten the flight path;
when the fuselage yaws, the leading winglet will now have a greater angle of
attack to the relative wind then the trailing winglet, this will generate
more lift on the leading, and less lift on the trailing, and since the
winglets are behind the CG of the aircraft, they will act upon the fuselage
to straighten the direction of flight- if you mount airfoils in reverse,
then they will cause exactly the opposite effect and your aircraft will
become inherently unstable in yaw- in other words, as the lower winglets see
differing angles of attack, they will act to displace this even further, the
greater this difference becomes, the stronger the tendency to yaw- not a
condition you want in any aircraft. Please reconsider your idea- even though
the lowers are pretty small, you don't want whatever force that they deliver
to be working against you.

Alex

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of KeithHallsten
Sent: Wednesday, August 04, 2004 8:49 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Lower winglets


I posted this a month ago, but it incited no comments.  Anyone care to share
an opinion?
Keith


----- Original Message -----
From: "KeithHallsten" <KeithHallsten at quiknet.com>
To: <reflector at tvbf.org>
Sent: Sunday, July 04, 2004 4:13 PM
Subject: REFLECTOR: Lower winglets


I was preparing to install my lower winglets yesterday, and was thinking
about installing them "backwards", so they push the air inboard on the
bottom of the wingtip, rather than outboard.  This would be accomplished by
installing the left lower winglet under the right wingtip, and vice-versa.
Although this theoretically has the potential to (very slightly) reduce the
induced drag, it would not look as good, since the lower and upper winglets
would not line up with each other, and the lower winglet would not fair in
below the rudder.  On the other hand, the trailing edge of the lower winglet
would be inboard of the rudder, so it could be fitted tightly to the wing
without interfering with the motion of the rudder.  Has anyone done this?

I suspect that the lower winglets may be so short as to have only a tiny
effect due to their "airfoil" shape.  Thus, it may not make any measurable
difference.  However, I'm one of those oddball "form follows function" guys
who would rather have a plane that looks a little wierd than accept less
than "optimal" design.

You may fire when ready!

Keith Hallsten


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