Frans...indented comments below...Fred
On Aug 6, 2012, at 1:58 PM, Frans Veldman wrote:
> >
>
> On 08/06/2012 04:18 PM, Fred Klein wrote:
>
>>> How much air is going to this gap with the flaps extended? Is it
>>> possible to make the underside of the wing flush with the flaps
>>> when the
>>> flaps are retracted?
>>
>> ..."possible"...but not necessarily desireable...this type of gap
>> seal
>> was installed on Cessna 180s with decidedly mixed results...
>
> I know it was an option on Cessna's but I didn't know about the mixed
> results.
>
>>> This would reduce the size of the gap with the flaps extended, does
>>> this have consequences?
>>
>> I would think so, and not necessarily positive. I'd classify the
>> Europa
>> flap as a "slotted flap" which is generally designed to allow
>> substantial airflow thru the slot which I believe is intended to
>> promote
>> the attachment of the boundary layer to the upper surface of the
>> flap...a good thing, no?
>
> Yes. But the current slot is a 90 degree corner,
true 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 flow
up thru the slot...
> and apperently you can also put cell foam in it as a seal. Id
> doesn't look like it allows lot of air through.
well...I guess "a lot" depends upon one's point of
view...recognise
that the air is 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.
> That's why I wondered whether some "lip" at the bottom
> of this slot would make things different.
On my plane, such a "lip"...if it is intended to provide a
smooth,
continuous bridge over the gap between flap and wing when flap is
retracted...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 that width it would seriously degrade the air
flow thru the slot w/ flap deployed.
>
>> I would think that if the compressible flap gap seal which John
>> Lawton
>> recommends was sliced from a circular rod of closed cell foam
>> (known as
>> "backer rod" and used in the US for sealing the joint between
>> concrete
>> and the sill plate of a wood wall) would have minimal disruption of
>> airflow thru the slot.
>
> Yes, but he mentions in the email that "the XS-wing looks like it has
> been designed with a seal in mind, because it has a flat area at the
> bottom of the slot."
Lawton wrote:
The XS flap closeout looks as if it were designed to be sealed, given
the flat area at the bottom rear of the closeout. 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.
Notice that John does not advocate placing the compressible
foam
seal at the lowermost portion of the flat 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 the
lower.surface of the wing. This location, at least on my plane, is the
place where the "slot" is narrowest when the flap is retracted, and
widest when the flap is deployed. Thus the location is optimal for
using the thinnest seal w/ minimal interference of air flow when flap
is deployed. I plan to use3/8" diameter backer rod sliced in half.
> But 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
> as what he means.
When 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.
Indeed, gap at the literal "bottom of the slot" which
would include
the radii of the closeout and the forwardmost portion of the lower
surface of the flat on my plane would require that 1.5" to 2" wide
"lip".
>> As you can read from my use of terms that I have only a fuzzy
>> awareness
>> of this stuff, so take my comments with a grain of salt.
>
> Same here. I hope to find someone who can shed some more light onto
> this
> matter.
Piry we don't have a resident aerodynamicist to keep us
luftmensch
in chek,
Fred
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