Fw: REFLECTOR:Lower Winglets

Greg Poole reflector@tvbf.org
Fri, 30 Jan 2004 08:41:51 +1100


>From one of my aircraft designer mates.....


Subject: Re: REFLECTOR:Lower Winglets


> hi Greg,
> The lower winglet design on the Velocity is more a wingtip skid than a
lower
> Whitcombe winglet. The upper winglet design is more somewhere to put the
> rudder than a Whitcombe winglet.
> An efficient design would have a winglet span of only 20% of the main wing
> semi-span with the leading edge of the upper winglet starting at the
thickest
> point of the main wing profile and ending behind the main wing trailing
edge.
> The winglet is more tapered and sweptback than the original wing and the
> airfoil section changes the camber forward towards the tip( geometric
> washout).
> The lower Whitcombe tip should be 5% of the wing semi-span (from
memory)and
> start before the leading edge of the wing, ending at the thickest point of
> the main wing airfoil section. The upper winglet has the airfoil as a bent
up
> version as the main wing whereas the lower winglet is opposite with the
main
> camber facing the fuselage.
> Modern design also cant the winglet out at 30 degrees to reduce the
bending
> moment and pressure area at the winglet root.
> I hope this gives you a bit of an idea as to winglet designs,
> Ray
>
> On Wed, 28 Jan 2004 17:40:13 +1100, Greg Poole wrote
> > Al,
> >
> > Most of the designs of effective lower winglets as appear on other
> > aircraft, kick the winglet out at a decent angle (rather than up and
> > down) and have more of a tapered shape - I would love to know the
> > reasons why the Velocity is different in this regard...can anybody
> > shed any light? ....Could be better visual aesthetics I suppose.
> >
> > Forever curious!
> >
> > Greg in Sydney.
> >   ----- Original Message ----- 
> >   From: Al Gietzen
> >   To: reflector@tvbf.org
> >   Sent: Wednesday, January 28, 2004 4:59 PM
> >   Subject: RE: REFLECTOR:Lower Winglets
> >
> >   One notable result of not having the lower winglet is increased
> > speed,
> >
> >   which doesn't quite jibe with the above discourse?
> >
> >   Scott
> >
> >   Oh, I think it could.  Airfoils producing a force cause drag.  The
> > winglets cause drag, but they produce a force we need for handling
> > and stability.  I'd expect the Velocity lower winglets to cause drag
> > at cruise without much in the way of offsetting benefit.  Apparently
> > there is some handling benefit at lower speeds.
> >
> >   Do you have any with/without data about the increased cruise speed?
> >
> >   Al
>
>
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