In a message dated 12/4/2003 5:25:30 PM Central Standard Time,
dfs155@earthlink.net writes:
I've related here before an episode wherein I encountered a really
big cloud
of bugs that apparently had glue for guts. I found that upon
leveling out
for cruise, I couldn't seem to get up to my normal IAS (I
thought maybe the
nose gear had been trapped, partly extended, by the nose
gear door - a
problem I had for a while early on). Tried recycling the gear
but didn't
help. Landed and found the leading edges coated with what felt
like sand
paper (Billions and Billions of squashed bugs). Once cleaned off,
the
problem went away. Don't remember the exact loss of IAS (maybe 20 kts)
but
was enough to get one's attention. I can only assume it was caused by
loss
of laminar flow.
Dan and Cy,
One of the design characteristics of the 235/320/360 wing
(NLF-0215F) is that loss of laminar flow should only cause a rise in drag
and little or no loss of lift.
In the 2003 Kittyhawk to OSH x-ctry race, the descent into ARR (Chicago
check point) resulted in the pickup of billions and billions of bilious green
splats on any surface exposed to the air. I lost about 6 Kts IAS on the
remaining leg to OSH and Mark Ravinski, in close trail of Larry Henney (a few
minutes in front of me), called off their formation flight race since Mark
couldn't see much thru the bug-goo covered canopy. I think your wing
contamination was worse than ours.
On one of my trips to the annual Labor Day Lancair fly-in, I encountered
smoke from the usual seasonal forest fires (smoke was present up to 15,000 feet)
as I flew over South Dakota and Monanta and made an overnight stop at
Bozeman. Parking to the South, I had a good view down the wing into the
setting sun. I saw overlapping v-marks, left by the smokey air,
emanating from the bugs picked up leaving an Iowa refueling stop. The
included angle of each vee was about 60 degrees and the smoke trails
extended over what appeared to be 50% of the chord. If only I had
taken a picture of the wing.
The Navy performed laminar flow tests and found that leading edge
contaminations closer than 1 inch apart destroyed the laminar flow.
----
Jarret and Jack,
Jarret wrote:
<<
We all know that Lance designed our Lnc2's w/
the NLF-0215
airfoil, which is a natural laminar airfoil. The problem arises
when we as
the builders built this a/c w/ this airfoil. There is no way that
we are
all getting our outter skins to form this airfoil exactly. If memory
serves
correct the 0215 has NLF [natural laminar flow] out to about 55%
chord
--> In best case wind tunnel conditions <-- and I think that is
the
key. In the real world we are probably only getting 35-40% NLF so if
a
person was to put their VG's at 25-30% chord there would be little effect
to
the laminar flow characteristics. The reason I feel we are only getting
the
little NLF that we are is because of the variables in leading edge
shape as
well as skin waviness and ruffness[not to mention bugs, rain or
paint
chips]. Not to sound like the total pessimist, the 0215 is a great
airfoil
and even though it is being used in the higher end of its intended
Re#
[remember this airframe/wing was originally intended to be flown w/
an
0-200]. Another point which I can't remember what the effect was, is
the
reflexing of the flaps, this enables us to fly at a different AOA
than
optimum and which I believe [don't quote me] isn't helping our NLF
situation
either.>>
If you are interested, our wing is based on the following research:
Some of the design characteristics are to achieve about 40%
chord laminar flow (LF) on the upper surface and 60% on the lower (yes, the
bottom of the wing is important). The airfoil (NLF-0215F) uses the reflexed flap
for for several things. Control of the pitching moment of the high camber
airfoil and re-attachment of the turbulent air flow to reduce profile drag.
Care must be taken in the corner formed at the intersection to the flap and wing
trailing edge so that separation does not occur there. The wing was also
designed for an efficient transition area from LF to turbulent boundary layer.
Note that there are low drag turbulent boundary layer wings with "interesting"
characteristics. The minimum profile drag occurs at an AOA of 1.52*
(experimental wing). Yada...Yada...Yada....
Conclusion:
Put some oil on your wing, go fly, interpret the results - much like
reading tea leaves. You will be impressed.
Scott
Krueger
MotorMouth, Charlatan, Bon Vivant, Escapee, Etcetera...
"...as
we know, there are known knowns; there are things we know we know. We also know
there are known unknowns; that is to say we know there are some things we do not
know. But there are also unknown unknowns - the ones we don't know we don't
know." D. Rumsfeld