Message-Id: <3.0.3.32.19981229184934.02d5a70c@olsusa.com>
Date: Tue, 29 Dec 1998 18:49:34 -0500
To: lancair.list@olsusa.com
From: Marvin Kaye <marvkaye@olsusa.com>
Subject: Re: Flaperons and things
In-Reply-To: <19981228084441.10296.qmail@www04.netaddress.usa.net>
Mime-Version: 1.0

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Posted for Scott Dahlgren <dahlgren@itsnet.com>:

Dan wrote:
>>>
"It seems that if reflexing the flaps lets us go so much faster and
reduces the stress on part of the wing at the same time, reflexing
the whole wing could only help."
<<<

On lift: some very high wing loaded aircraft are built with "drooping
ailerons" which allows both ailerons to droop down a few degrees (normally
independent of flap position) once the flaps are deployed past a certain
value. this gains you a little bit of additional lift (around 5% max for 
the 320 under ideal conditions). Since the tips are open on one side, they
produce very little lift in comparison to the main wing anyway (elliptical
lift). another way to look at a wing is that the aspect ratio decreases as
you move outboard. The tips would need very high angles of attack (or flap
deflection) to generate any lift at all. This makes for very dangerous and
tricky flight due to the potential for tip stall.

on reflex: most aircraft wings (including the Lancair's) have twist in the
wings to reflex the tips and keep the tips from stalling, so the tips are
typically unloaded in flight. one reason reflexing the flaps can help is
because it makes the flapped segment of the wing more closely match the
tips effective angle of attack and even out the lift (make it more
elliptical).  Reflex also allows you to tailor your airfoils camber into
the drag bucket of the laminar airfoil, which is unique to individual
flight reimes.   Reflexing does reduce the pitching moment of the airfoil,
and subsequently the load on the tail and induced drag which can be a
significant portion of the total drag of the wings. The modified NLF
airfoil used by the LIV does have a high pitching moment, but the modified
nasa6300 series on (my old) 320 has a low pitching moment for a laminar
flow airfoil. I heard something (rumor?) once about Lancair putting the NLF
airfoil on the 320/360 and was curious to hear if the newer models were
using it?   One thing to keep in mind when the flaps are Reflexed, is that
the tips are more prone to stall on landing which can be fatal.  positive
flap deflection helps prevent this.

Let's invent like Thomas Edison who said:" I never invented anything, I
just improved on what was already known".

Scott