Fred, hopefully Ivan might have an opinion on this, I know he's been away b
ut should-be-back now. Ivan?=0AIf you look at the definitive digital co
ordinates of the-section-you will see first of all-that-the bottom
surface is not flat but slightly convex,=0Aso there is a slight reflex at
the trailing edge. This will have an effect on drag in the cruise. I think
it's important to have smooth airflow through the gap=0Awhen the flap is de
ployed to keep airflow attached over the flap. I don't think we need to sea
l the LE of the flap flap up because we aren't looking for optimum lift=0Aw
e want minimum drag in any case the pressure top and bottom will be almost
equal at this point. The control surfaces are different, here we want more
effect without increasing drag.=0AGraham=0A=0A=0A__________________________
______=0A From: Fred Klein <fklein@orcasonline.com>=0ATo: europa-list@matro
nics.com =0ASent: Tuesday, 7 August 2012, 3:11=0ASubject: Re: Europa-List:
seals for control surfaces=0A =0A=0AFrans...indented comments below...Fred
=0A=0A=0AOn Aug 6, 2012, at 1:58 PM, Frans Veldman wrote:=0A=0A--> Europa-L
ist message posted by: Frans Veldman <frans@privatepilots.nl>=0A>=0A>On 08/
06/2012 04:18 PM, Fred Klein wrote:=0A>=0A>=0A>How much air is going to thi
s gap with the flaps extended? Is it=0A>>>=0A>possible to make the undersid
e of the wing flush with the flaps when the=0A>>>=0A>flaps are retracted?
=0A>>>=0A>=0A>>=0A>..."possible"...but not necessarily desireable...this ty
pe of gap seal=0A>>=0A>was installed on Cessna 180s with decidedly mixed re
sults...=0A>>=0A>I know it was an option on Cessna's but I didn't know abou
t the mixed=0A>results.=0A>=0A>=0A>This would reduce the size of the gap wi
th the flaps extended, does=0A>>>=0A>this have consequences?=0A>>>=0A>=0A>>
=0A>I would think so, and not necessarily positive. I'd classify the Europa
=0A>>=0A>flap as a "slotted flap" which is generally designed to allow=0A>>
=0A>substantial airflow thru the slot which I believe is intended to promot
e=0A>>=0A>the attachment of the boundary layer to the upper surface of the
=0A>>=0A>flap...a good thing, no?=0A>>=0A>Yes. But the current slot is a 90
degree corner, =0A=0Atrue enough...but I measure the radius of the corner
of the closeout at about 3/8" and the radius of the forward portion of the
lower surface of the flap at approximately 3/4" which invite the air to flo
w up thru the slot...=0A=0Aand apperently you can-also put cell foam in i
t as a seal. Id doesn't look like it allows lot-of air through.=0Awell...
I guess "a lot" depends upon one's point of view...recognise that the air i
s flowing from high pressure / low velocity to low pressure / high velocity
so I'd say that a lot of air is being sucked up into the gap and blown out
the rear across the top surface of the flap.-=0A=0A=0AThat's why I wonde
red whether some "lip" at the bottom=0A>of this slot would make things diff
erent.=0A>=0AOn my plane, such a "lip"...if it is intended to provide a smo
oth, continuous bridge over the gap between flap and wing when flap is retr
acted...would have to be between 1.5" and 2" wide, and stiff enough so that
it would not just get sucked up into the gap the first time the flaps are
deployed...and if it were sufficiently stiff, it would seem to me that at t
hat width it would seriously degrade the air flow thru the slot w/ flap dep
loyed.=0A=0A=0A>=0A>I would think that if the compressible flap gap seal wh
ich John Lawton=0A>>=0A>recommends was sliced from a circular rod of closed
cell foam (known as=0A>>=0A>"backer rod" and used in the US for sealing th
e joint between concrete=0A>>=0A>and the sill plate of a wood wall) would h
ave minimal disruption of=0A>>=0A>airflow thru the slot.=0A>>=0A>Yes, but h
e mentions in the email that "the XS-wing looks like it has=0A>been designe
d with a seal in mind, because it has a flat area at the=0A>bottom of the s
lot." =0A=0ALawton wrote:=0A=0AThe XS flap closeout looks as if it were des
igned to be sealed, given the flat area at the bottom rear-of the closeou
t. If you apply the foam strip to the area where the flap "noses" into the
closeout when up it will seal this area for cruise flight, but still allow
air to flow over the flap when extended.=0A=0ANotice that John does not adv
ocate placing the compressible foam seal at the lowermost portion of the fl
at area but rather "where the flap 'noses' into the closeout" when flap is
in the retracted position; on my plane, this location is about 1" up from t
he lower.surface of the wing. This location, at least on my plane, is the p
lace where the "slot" is narrowest when the flap is retracted, and widest w
hen the flap is deployed. Thus the location is optimal for using the thinne
st seal w/ minimal interference of air flow when flap is deployed. I plan t
o use3/8" diameter backer rod sliced in half.=0A=0ABut at the bottom of the
slot the gap is at its-widest point, far too wide for a foam seal. So I'
m a bit confused here=0A>as what he means.=0A>=0AWhen John wrote "bottom of
the slot", I did not infer that he intended the literally lowest point of
the slot but rather the portion of the closeout which is flat and vertical.
=0A=0AIndeed, gap at the literal "bottom of the slot" which would include t
he radii of the closeout and the forwardmost portion of the lower surface o
f the flat on my plane would require that 1.5" to 2" wide "lip".=0A=0A=0AAs
you can read from my use of terms that I have only a fuzzy awareness=0A>>
=0A>of this stuff, so take my comments with a grain of salt.=0A>>=0A>Same h
ere. I hope to find someone who can shed some more light onto this=0A>matte
r.=0A>=0APiry we don't have a resident aerodynamicist to keep us luftmensch
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