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1. 10:06 AM - seals for control surfaces (Fred Klein)
2. 10:52 AM - Re: seals for control surfaces (Robert Borger)
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| Subject: | seals for control surfaces |
Apropos the recent thread on this topic, I found an old posting by
John Lawton which may be enlightening:
> In a message dated 5/9/2007 2:59:30 AM Eastern Daylight Time, europa-list@matronics.com
> writes:
> My understanding is that preventing the air going over the flap, in
> cruise, reduces drag, resulting in higher cruise speed, which I have
> experienced. I don't have the engineering background to completely
> understand what is happening to the wing, in flight. That's why I
> depend on the guys on the list to keep me straight. I'm more of a
> "try
> it and see" kinda guy... :) John's advice is based on the success
> that
> the glider guys have had, sealing the gaps. It seems to have worked
> on
> Baby Blue, as well. Continued testing will tell to what degree of
> advantage the seals make. It may very well prove that the extra few
> knots is not worth the float upon landing. I won't know until I
> satisfy
> myself that I've explored all the angles (and strip widths)... ;)
>
> Hey Jeff, et al,
>
> The concept behind seals is pretty simple. In flight the wing
> creates a low pressure area on the top and high pressure on the
> bottom. (Bernoulli at it again) This pressure differential will try
> to equalize through the gap in the flap area and the hinge line of
> the 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 on ailerons (and rudder and trim tabs), is to
> prevent this pressure equalization.
>
> On N245E I used PVC weather-strip to create the flap gap seal. 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
> slightly 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 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. Use a foam that crushes easily
> when the flap comes in contact with it. You don't want to use a foam
> that is too stiff or too thick or else your flaps won't fully
> retract. PVC weather-strip is soft and pliable and works quite well.
> 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 tend to not last very long due to UV and they don't seal
> as well as closed cell foams like PVC. I also used weather-strip on
> the ends of my flaps so that they seal against the side of the
> fuselage when they are in the up position. According to Bruce
> Carmichael, renowned Aerodynamicist who wrote a book on drag
> reduction in homebuilts, the wing root/fuselage junction is another
> area of high drag on most airplanes. Sealing it up helps, too.
>
> Aileron seals are a bit more tricky to employ. Some folks apply
> Mylar strips over the hinge lines and think they've sealed their
> ailerons. This is not true. Mylar is not a seal, but rather is
> applied to help the boundary flow 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 the 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.
>
> For sealing ailerons you need to install what are known as positive
> seals. These seals go from the leading edge of the aileron to the
> rear of the closeout. There are commercially available materials for
> this, including various types of cloth and Teflon tapes. Some folks
> even use cloth tape along the length of the aileron on the
> undersurface. This is fine on low speed gliders, but I think at the
> speeds we fly this method likely creates more drag. Personally, I
> like parachute cloth for making positive seals. Whatever you use it
> needs to be zero porosity, i.e., allowing no airflow through the
> material. Parachute cloth is thin, flexible, zero 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)
>
> 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 don't want it so wide
> the the material bunches up when the aileron is deflected. 2.5' to
> 3" width should work on most Europas. Then, yellow contact cement is
> applied to the leading edge of the aileron, the rear of the closeout
> and the mating surfaces of the cloth. We use a brand of glue called
> Plio-bond. It's handy in that it comes in a small bottle with a
> brush applicator. 3M also makes good contact cement if you can find
> it. Avoid the water based stuff. It is crap.
>
> Scuff the area to be glued with 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 your glue line to the
> prescribed width and remove the tape once the glue is dry. You can
> also use the masking tape to provide a guide when you scuff the 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
> the masking tape, then stick the seal to the leading edge of the
> aileron first, preferably while on your work bench. If you screw
> something up Xylene will remove the glue easily without harming your
> paint. The next part takes an extra set of hands.
>
> With one person holding the aileron close to the wing, attach the
> other half of the cloth to the closeout forming an "S" pattern.
> Avoid wrinkles. See this drawing for details: http://wingsandwheels.com/page28.htm
>
> Then, reattach the aileron as you would normally do. Check the throw
> and make sure you are not binding! If you 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.
>
> I can't say specifically what improvements have occurred in N245E as
> a result of the seals since I've not ever flown it without them. I
> can tell you that I exceed Europas published numbers with a fixed
> pitch prop. I can also tell you that on gliders we generally see 2
> to 4 points increase in glide and a noticeable decrease in sink
> rate, even on the old "woodies", after the application of seals. In
> power planes this translates to faster cruise, better climb rates
> and better fuel economy.
>
> Anyway, hope it helps!
>
> Regards,
>
> John Lawton
Message 2
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| Subject: | Re: seals for control surfaces |
Fred,
Thanks for digging this up. Very informative. Now, if I could just get
my 914 running right=85
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop.
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger@mac.com
On Aug 4, 2012, at 12:03 PM, Fred Klein <fklein@orcasonline.com> wrote:
Apropos the recent thread on this topic, I found an old posting by John
Lawton which may be enlightening:
> In a message dated 5/9/2007 2:59:30 AM Eastern Daylight Time,
europa-list@matronics.com writes:
> My understanding is that preventing the air going over the flap, in
> cruise, reduces drag, resulting in higher cruise speed, which I have
> experienced. I don't have the engineering background to completely
> understand what is happening to the wing, in flight. That's why I
> depend on the guys on the list to keep me straight. I'm more of a
"try
> it and see" kinda guy... :) John's advice is based on the success
that
> the glider guys have had, sealing the gaps. It seems to have worked
on
> Baby Blue, as well. Continued testing will tell to what degree of
> advantage the seals make. It may very well prove that the extra few
> knots is not worth the float upon landing. I won't know until I
satisfy
> myself that I've explored all the angles (and strip widths)... ;)
>
> Hey Jeff, et al,
>
> The concept behind seals is pretty simple. In flight the wing creates
a low pressure area on the top and high pressure on the bottom.
(Bernoulli at it again) This pressure differential will try to equalize
through the gap in the flap area and the hinge line of the 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 on
ailerons (and rudder and trim tabs), is to prevent this pressure
equalization.
>
> On N245E I used PVC weather-strip to create the flap gap seal. 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
slightly 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 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. Use a foam that crushes easily when the flap comes in contact
with it. You don't want to use a foam that is too stiff or too thick or
else your flaps won't fully retract. PVC weather-strip is soft and
pliable and works quite well. 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 tend to not last very long due to UV
and they don't seal as well as closed cell foams like PVC. I also used
weather-strip on the ends of my flaps so that they seal against the side
of the fuselage when they are in the up position. According to Bruce
Carmichael, renowned Aerodynamicist who wrote a book on drag reduction
in homebuilts, the wing root/fuselage junction is another area of high
drag on most airplanes. Sealing it up helps, too.
>
> Aileron seals are a bit more tricky to employ. Some folks apply Mylar
strips over the hinge lines and think they've sealed their ailerons.
This is not true. Mylar is not a seal, but rather is applied to help the
boundary flow 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 the 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.
>
> For sealing ailerons you need to install what are known as positive
seals. These seals go from the leading edge of the aileron to the rear
of the closeout. There are commercially available materials for this,
including various types of cloth and Teflon tapes. Some folks even use
cloth tape along the length of the aileron on the undersurface. This is
fine on low speed gliders, but I think at the speeds we fly this method
likely creates more drag. Personally, I like parachute cloth for making
positive seals. Whatever you use it needs to be zero porosity, i.e.,
allowing no airflow through the material. Parachute cloth is thin,
flexible, zero 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)
>
> 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 don't want it so wide the the
material bunches up when the aileron is deflected. 2.5' to 3" width
should work on most Europas. Then, yellow contact cement is applied to
the leading edge of the aileron, the rear of the closeout and the mating
surfaces of the cloth. We use a brand of glue called Plio-bond. It's
handy in that it comes in a small bottle with a brush applicator. 3M
also makes good contact cement if you can find it. Avoid the water based
stuff. It is crap.
>
> Scuff the area to be glued with 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 your glue line to the prescribed
width and remove the tape once the glue is dry. You can also use the
masking tape to provide a guide when you scuff the 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 the masking tape, then
stick the seal to the leading edge of the aileron first, preferably
while on your work bench. If you screw something up Xylene will remove
the glue easily without harming your paint. The next part takes an extra
set of hands.
>
> With one person holding the aileron close to the wing, attach the
other half of the cloth to the closeout forming an "S" pattern. Avoid
wrinkles. See this drawing for details:
http://wingsandwheels.com/page28.htm
>
> Then, reattach the aileron as you would normally do. Check the throw
and make sure you are not binding! If you 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.
>
> I can't say specifically what improvements have occurred in N245E as a
result of the seals since I've not ever flown it without them. I can
tell you that I exceed Europas published numbers with a fixed pitch
prop. I can also tell you that on gliders we generally see 2 to 4 points
increase in glide and a noticeable decrease in sink rate, even on the
old "woodies", after the application of seals. In power planes this
translates to faster cruise, better climb rates and better fuel economy.
>
> Anyway, hope it helps!
>
> Regards,
>
> John Lawton
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