Well spotted Fred! What John says makes sense to me=0AGraham=0A=0A=0A=0A___
_____________________________=0A From: Fred Klein <fklein@orcasonline.com>
=0ATo: europa-list@matronics.com =0ASent: Saturday, 4 August 2012, 18:03=0A
Subject: Europa-List: seals for control surfaces=0A =0A=0AApropos the recen
t thread on this topic, I found an old posting by John Lawton which may be
enlightening:=0A=0AIn a message dated 5/9/2007 2:59:30 AM Eastern Daylight
Time,-europa-list@matronics.com-writes:=0A>My understanding is that pre
venting the air going over the flap, in-=0A>>cruise, reduces drag, result
ing in higher cruise speed, which I have-=0A>>experienced.- I don't hav
e the engineering background to completely-=0A>>understand what is happen
ing to the wing, in flight.- That's why I-=0A>>depend on the guys on th
e list to keep me straight.- I'm more of a "try-=0A>>it and see" kinda
guy... :)- John's advice is based on the success that-=0A>>the glider g
uys have had, sealing the gaps.- It seems to have worked on-=0A>>Baby B
lue, as well.- Continued testing will tell to what degree of-=0A>>advan
tage the seals make.- It may very well prove that the extra few-=0A>>kn
ots is not worth the float upon landing.- I won't know until I satisfy-
=0A>>myself that I've explored all the angles (and strip widths)... ;)=0A>
-=0A>Hey Jeff, et al,=0A>-=0A>The concept behind seals is pretty simple
. In flight the wing creates a low pressure area on the top and high pressu
re on the bottom.-(Bernoulli at it again)-This pressure differential wi
ll try to equalize through the gap in the flap area and the hinge line of t
he ailerons. This is also true to some extent on the rudder hinge line and
the-trim tabs when they are deflected.-This equalization causes drag, a
lot of drag. So, the idea behind seals, both flap gap and positive seals o
n ailerons (and rudder and trim tabs), is to prevent this pressure equaliza
tion.=0A>-=0A>On N245E I used PVC weather-strip to create the flap gap se
al. The size will depend on how big your gap is between the leading edge of
the flap and the flap closeout when retracted. Choose a foam that is sligh
tly thicker than the widest spot in the gap you have. The XS flap closeout
looks as if it were designed to be sealed, given the flat area at the botto
m 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 f
light, but still allow air to flow over the flap when extended. Use a foam
that crushes easily when the flap comes in contact with it. You-don't wan
t to use a foam that is too stiff or too thick or-else your flaps won't f
ully-retract. PVC weather-strip is-soft and pliable and works quite wel
l. It is also fairly UV resistant and is very cheap. It's available at any
hardware store in various thicknesses. We've found that open cell foams ten
d to not last
very long due to UV-and they don't seal as well as closed cell-foams l
ike PVC.-I also used weather-strip on the ends of my flaps so that they s
eal against the side of the fuselage when they are in the up position. Acco
rding to Bruce Carmichael, renowned Aerodynamicist who wrote a book on drag
reduction in homebuilts, the wing root/fuselage junction is another area o
f high drag on most airplanes. Sealing it up helps, too.=0A>-=0A>Aileron
seals are a bit more tricky to employ. Some folks apply Mylar strips over t
he hinge lines and think they've sealed their ailerons. This-is not-tru
e. Mylar-is not-a seal, but rather is applied-to help the boundary fl
ow stay attached over the hinge line.-Mylar is also somewhat cosmetic in
that-it hides the hinge line. At high speeds the Mylar will lift up off t
he wing due to the pressure equalization, thus negating the effects of any
sealing the Mylar might be offering. In some cases the Mylar will "buzz" at
high speeds.=0A>-=0A>For sealing ailerons you need to install what are k
nown as positive seals. These seals go from the leading edge of the aileron
to the rear of the closeout. There are commercially available materials fo
r this, including various types of cloth and Teflon tapes. Some folks even
use-cloth-tape along the length of the aileron on the undersurface. Thi
s is fine on low speed gliders, but I think at the speeds we fly this metho
d-likely creates more drag.-Personally, I like parachute cloth for maki
ng positive seals. Whatever you use it needs to be zero porosity, i.e., all
owing no airflow through the material. Parachute cloth is thin, flexible, z
ero porosity and-fits the bill here perfectly. Here at the 'Possum Werks
we use Parachute cloth almost exclusively to fabricate positive seals. (it
also helps that we have a parachute manufacturer a few miles down the road
that gives us their scraps)=0A>-=0A>First remove the aileron. Then, cut a
strip of parachute cloth about 3" wide exactly the length of the aileron.
The width you use might take some trial and error to get it right.-You do
n't want it so wide the-the material-bunches up when the aileron is-d
eflected. 2.5' to 3"-width should work on most Europas. Then, yellow cont
act cement is applied to the leading edge of the aileron, the rear of the c
loseout and the mating surfaces of the cloth. We use a brand of glue-call
ed Plio-bond. It's handy in that it comes in a small bottle with a brush ap
plicator.-3M also makes-good contact-cement if you can find it. Avoid
the water based stuff. It is crap.=0A>-=0A>Scuff the area to be glued wi
th 180 to-enhance the adhesion. Apply the glue in a swath about 3/8" wide
to both the seal, the aileron and closeout.-Use masking tape to keep you
r glue line to the prescribed width and remove the tape once the glue is dr
y.- You can also use the masking tape to provide a guide when you scuff t
he area to be glued, but wipe it with acetone to remove dust before putting
the-glue on.-Allow the glue to dry, usually about 20 minutes, remove t
he masking tape,-then stick the seal to the leading edge of the aileron f
irst, preferably while on your work bench. If you-screw something up Xyle
ne will remove the glue easily without harming your paint.-The next part
takes an extra set of hands.=0A>-=0A>With one person holding the aileron
close to the wing, attach the other half of the cloth to the closeout formi
ng an "S" pattern. Avoid wrinkles.-See this drawing for details:-http:/
/wingsandwheels.com/page28.htm=0A>-=0A>Then, reattach the aileron as you
would normally do. Check the throw and make sure you are not binding! If yo
u apply the seal correctly you will not even know it is there. I have also
sealed my rudder in a similar fashion as well as the trim tabs. They create
similar drag when deflected.=0A>-=0A>I can't say specifically-what imp
rovements have occurred in N245E as a result of the seals since I've not ev
er flown it without them. I can tell you that I exceed Europas published nu
mbers with a fixed pitch prop. I can also tell you that on gliders we gener
ally see 2 to 4 points increase in glide and a noticeable-decrease in sin
k rate, even on the old-"woodies",-after the application of seals.-In
power planes this translates to faster cruise, better climb rates-and be
tter fuel economy.=0A>-=0A>Anyway, hope it helps!=0A>=0A>Regards,=0A>-
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