Parley mentions "(G)round effect" - the often-experienced phenomenon
resulting from the downward deflection of airflow over a wing.
Downward-deflected airflow does happen and in this case it can have
significant effect on our landing technique.
Aerodynamicists use both surfaces of an airfoil to get what they want.
This is seen on the "New" AS50** airfoils designed for the KR-2. As we
know, these are laminar flow airfoils intended to generate less drag
than the older airfoil, and the way it is achieved is by maximizing the
"laminar run" over the forward portion of the airfoil. The air is not
accelerated much, not asked to do too much too soon, keeping its local
pressure as high as possible for as long as possible over the surface of
the wing. If the velocity increases beyond a certain point, the pressure
drop makes the flow more likely to "trip" to turbulent resulting in
increased drag. So this means that the forward part of the airfoil is
not generating much lift at all. Most of it happens in the aft portion
of the airfoil, past where it starts to thin, my eyeball guesstimate is
from about the 45% point aft. If you follow the top surface, it drops
away around the 60%-65% point, and then rises again at about 85%. I
suspect that is for pressure recovery, which results in less drag than
if the surface followed a more parabolic curve. The bottom surface has a
cusp that intersects the chord line at about 95% and then diverges
again, below the chord line. That's where the airflow along the bottom
surface is deflected downward, and where much of the lift created by the
airfoil's bottom surface comes from. And Ashok is an aerodynamicist -
shouldn't he know better about that bottom surface business? That's a
joke. My point is that all the stuff we have discussed is always in play
when an airplane is flying, and to try to separate or rank certain
characteristics, or components such as one airfoil surface over the
other, is not always simple. My $.02.
Many gliders have airfoils that look similar to the AS50** airfoils, and
the intention is that they work the same way. They exhibit low drag at
higher speeds and good lift at low speeds, relatively high pitching
moments due to the center of lift well back from the 25% chord, and
sometimes stiff aileron feel due to them being aerodynamically loaded on
the bottom surface at all airspeeds. I'd be interested to hear from
anybody in the KR community who has flown new and old airfoils on the
same fuselage or new and old on airplanes with similar powerplants &
weights re: difference in aileron feel.
Chris K
On 4/23/2019 8:58 AM, Parley T Byington via KRnet wrote:
For all those who do NOT believe in the Bernoulli theory, I would suggest you
try this simple experiment: take an ordinary teaspoon and dangle it from the
handle so that the curved surface just comes in contact with a stream of
running water and watch what happens. Yes water is much more dense than air
but the principle is the same with a airfoil. The difference is that the
median that it is traveling through, air versus water, is much thinner and
therefor has to be moving faster to achieve the equivalent force.
Yes there is some lift created due to the angle of incidence and the resulting
downward deflection (this is one of the causes of what is called “ ROUND
EFFECT”) of air produced due to the forward movement of said airfoil through
that median BUT the vast majority of the lift created is due to the
differential in air pressure that is created due to Bernoulli’s theory.
_______________________________________________
Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/.
Please see LIST RULES and KRnet info at http://www.krnet.org/info.html.
see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change
options.
To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
