tuft testing

I was reading and saw a picture of a wing being tuft tested. I was
wondering, since I do not have a clue, how much difference the tape holding
the tufts would cause. In the picture it appears that 1/2 inch blue masking
tape was used and it was torn rather than cut. The tufts were spaced a
couple of inches apart and there were seven rows and eight columns. His
results were that the wing was not showing any separation. Just wondering
if there are accepted methods of doing this type of testing? How would you
determine where to test? Any discussion and comments would be appreciated.

On Wed, 27 Oct 2004 15:56:11 GMT, "keepitrunning"
wrote:

I was reading and saw a picture of a wing being tuft tested. I was
wondering, since I do not have a clue, how much difference the tape holding
the tufts would cause. In the picture it appears that 1/2 inch blue masking
tape was used and it was torn rather than cut. The tufts were spaced a
couple of inches apart and there were seven rows and eight columns. His
results were that the wing was not showing any separation. Just wondering
if there are accepted methods of doing this type of testing? How would you
determine where to test? Any discussion and comments would be appreciated.

tufting is useful for checking that flows are remaining laminar and in
trying to identify drag sources due to turbulence.

you use a tape which can be peeled off without ripping up the paint.
vinyl gaffer tape is ideal. the wool is any contrasting colour and at
about 8ply thickness. the tuft is about 6-8 inches long.

you tape about an inch or so of the wool. the tape should remain
within the boundary layer with the wool getting out into the airstream
eventually.

accepted methods? nah, use whatever works. it isnt rocket science.

where to test? anywhere which looks like further improvement is
possible. it should be obvious but you need to tuft where you can see
or photograph the tufts. if you cant see the tufts you will need
another aircraft to formate in flight.

what do you find out? well sometimes nothing but often you get to see
what the air is doing.

try a few tufts on the bonnet and windscreen of your car.
Stealth Pilot

Here is a link to a photo from last month's tuft-testing on my
Velocity with hopes that some clue would appear as to why my engine
cooling is worse than marginal. Tape was duct tape and some was on
for several months (waiting for weather, photographer, digital camera,
photoplane, etc...) and was a pain-in-the-butt to remove.
For the test, the left (pilot) side NACA has two VGs, the right side
none.

http://img35.exs.cx/img35/5182/HPIM0430.jpg

Sid Knox

Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ

http://img35.exs.cx/img35/5182/HPIM0430.jpg

"keepitrunning" wrote in message . com...
I was reading and saw a picture of a wing being tuft tested. I was
wondering, since I do not have a clue, how much difference the tape holding
the tufts would cause. In the picture it appears that 1/2 inch blue masking
tape was used and it was torn rather than cut. The tufts were spaced a
couple of inches apart and there were seven rows and eight columns. His
results were that the wing was not showing any separation. Just wondering
if there are accepted methods of doing this type of testing? How would you
determine where to test? Any discussion and comments would be appreciated.

"sidk" wrote in message
om...
Here is a link to a photo from last month's tuft-testing on my
Velocity with hopes that some clue would appear as to why my engine
cooling is worse than marginal. Tape was duct tape and some was on
for several months (waiting for weather, photographer, digital camera,
photoplane, etc...) and was a pain-in-the-butt to remove.
For the test, the left (pilot) side NACA has two VGs, the right side
none.

http://img35.exs.cx/img35/5182/HPIM0430.jpg

Sid Knox

Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ

http://img35.exs.cx/img35/5182/HPIM0430.jpg

Interesting. I'm sure you have researched the data that shows NACA
submerged inlets are poor at cooling applications, where the pressure
required for good flow, are relatively high?

Wouldn't a scoop, ala upside-down P-51 scoop do much better, with low drag,
also?

Did you try naphtha, (lighter fluid)?

I made the mistake of leaving duct tape on a vehicle too long once, and I
commiserate. Slow steady progress with plenty of naphtha and paper towels,
was my best way out.
--
Jim in NC


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On 27 Oct 2004 17:43:27 -0700, (sidk) wrote:

Here is a link to a photo from last month's tuft-testing on my
Velocity with hopes that some clue would appear as to why my engine
cooling is worse than marginal. Tape was duct tape and some was on
for several months (waiting for weather, photographer, digital camera,
photoplane, etc...) and was a pain-in-the-butt to remove.
For the test, the left (pilot) side NACA has two VGs, the right side
none.

http://img35.exs.cx/img35/5182/HPIM0430.jpg

Sid Knox

Velocity N199RS

Sid, I hope that there are some other scoops somewhere besides the two
I see on top of the airplane. From what I've read over the years if
the two scoops I see are it for cooling, there are two really glaring
problems. 1. Naca scoops are really marginal for engine cooling
intakes, this is something that has been known for many years. 2.
Naca scoops do not work when placed in a low pressure region of the
fuselage. Your two scoops are on the downside of the rear of the
fuselage and for sure are in a low pressure area.

What works? Pitot type scoops placed in an area of positive pressure,
or out in the free air stream ala P-51 Mustang.

But if you have pitot type scoops on the belly of your airplane,
nevermind.

Corky Scott

Yes, I have some literature discussing the misapplication of these
submerged NACA inlets. Unfortunately, the previous owner/builder
installed them because the original scheme(s) were apparently worse.
I am willing to tradeoff a little extra drag for better cooling... I
am just not certain yet how best/easiest to do it.
I'll try the naptha.. thanks.

Sid


Interesting. I'm sure you have researched the data that shows NACA
submerged inlets are poor at cooling applications, where the pressure
required for good flow, are relatively high?

Wouldn't a scoop, ala upside-down P-51 scoop do much better, with low drag,
also?

Did you try naphtha, (lighter fluid)?

I made the mistake of leaving duct tape on a vehicle too long once, and I
commiserate. Slow steady progress with plenty of naphtha and paper towels,
was my best way out.

"sidk" wrote in message
om...
Yes, I have some literature discussing the misapplication of these
submerged NACA inlets. Unfortunately, the previous owner/builder
installed them because the original scheme(s) were apparently worse.
I am willing to tradeoff a little extra drag for better cooling... I
am just not certain yet how best/easiest to do it.
I'll try the naptha.. thanks.

You might give Goof-off http://www.valspar.com/val/resident/goof-off.jsp a
try.

I had to remove and replace an adhesive wing walk about 12" x 36" which had
been on the plane for three years. A little heat from a hair dryer allowed
the black stuff to peel off, but there was a thin film of adhesive
remaining.

Every solvent I tried either wouldn't touch the adhesive - or would dissolve
it for a moment until the solvent started to evaporate, then it would gel
again. The fumes from the various solvents (Alcohol, Mineral spirits,
Naphtha, Enamel reducer, Lacquer thinner, Xylol, & Acetone) weren't doing my
already-abused liver any favors, either!

The Goof-off didn't tend to evaporate and the citrus odor was a lot less
bothersome. It loosened the adhesive so I was able to remove it with a soft
plastic scraper. I used a whole roll of paper towels to wipe the resulting
"boogers" off the scraper!

A can of Goof-off is now standard equipment in the hangar.

Rich S.

Sid wrote:
Yes, I have some literature discussing the misapplication of these
submerged NACA inlets. Unfortunately, the previous owner/builder
installed them because the original scheme(s) were apparently worse.
I am willing to tradeoff a little extra drag for better cooling... I
am just not certain yet how best/easiest to do it.

OK, Jim Morgan's comment about submerged NACA ducts are "poor at cooling
applications" is perhaps overly broad. The NACA papers actually say they
are poor choices to feed air to heat exchangers, also known as radiators and
oil coolers. They are silent as to their application for cooling air to
traditional "air cooled" (I hat that term) engines.

But nonetheless, I'd like to add my speculation (it *is* Usenet y'know ;-)

The builder's choice of submerged NACA ducts seems to have several things
working against it in this case:

1. The photo seems to show submerged ducts, but they seem exceedingly narrow
and improperly proportioned compared to my recollection of the drawings of
the original submerged NACA ducts. How likely is it that the builder's
ducts are versions of actual tested NACA ducts and not some random ducts
that the builder preferred?

2. Any air inlet, NACA or not, works best when the inlet is positioned in a
(relatively) high air pressure region, and works poorly or even in reverse
when placed in a (relatively) low air pressure region. I do not have a
pressure region map for the Velocity, but you as an owner/(re-)builder have
access to more information than I. See if you can locate a pressure map.
Just speculating, the site just aft of the point of greatest fuselage height
(where the ducts are now) seems like a local *low* pressure area.

3. Submerged NACA ducts work abysmally in areas of turbulent separation of
flow. The photo seems to indicate that turbulent separation is occuring at
the rear door seam. If you need air, and you're constrained to get it from
an area of turbulent separation, then there are only two choices: either the
thing that wants the air better be at substantially lower air pressure than
the turbulent area, or you use a scoop with a standoff to keep the turbulent
boundary layer out of the captured air.

4. The position of the existing ducts suggests that the engine uses
downdraft cooling, i.e. the cooling air is introduced on the top side of the
cylinders and pressures are used to force it out the bottom side of the
cylinders. Downdraft cooling is prone to problems at low airflow velocities
because of the tendency of heated air to rise. Low airflow velocities tend
to coincide, unfortunately, with situations that need the best possible
cooling, namely climbs (high power, low airspeed).

Regards,
Russell Kent

"sidk" wrote in message om...
Here is a link to a photo from last month's tuft-testing on my
Velocity with hopes that some clue would appear as to why my engine
cooling is worse than marginal. Tape was duct tape and some was on
for several months (waiting for weather, photographer, digital camera,
photoplane, etc...) and was a pain-in-the-butt to remove.
For the test, the left (pilot) side NACA has two VGs, the right side
none.

http://img35.exs.cx/img35/5182/HPIM0430.jpg

Sid Knox

Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ

http://img35.exs.cx/img35/5182/HPIM0430.jpg

"keepitrunning" wrote in message . com...
I was reading and saw a picture of a wing being tuft tested. I was
wondering, since I do not have a clue, how much difference the tape holding
the tufts would cause. In the picture it appears that 1/2 inch blue masking
tape was used and it was torn rather than cut. The tufts were spaced a
couple of inches apart and there were seven rows and eight columns. His
results were that the wing was not showing any separation. Just wondering
if there are accepted methods of doing this type of testing? How would you
determine where to test? Any discussion and comments would be appreciated.

Interesting to see the left side duct is pulling air forward and in around the center of the of the back lip of the
duct. Am I seeing that right? Are the two vortex generators causing it?

"Russell Kent" wrote in message 1. The photo seems to show submerged ducts, but they seem exceedingly narrow
and improperly proportioned compared to my recollection of the drawings of
the original submerged NACA ducts. How likely is it that the builder's
ducts are versions of actual tested NACA ducts and not some random ducts
that the builder preferred?

Kent, to the best of my knowledge, this duct mod is from the Velocity
factory and I believe all (most?) current Velocitys use it. The ducts
feed a pressure cowling (also factory designed/approved?). I have
added a photo of this to the free photo web hosting site.. see

http://img87.exs.cx/img87/4545/MVC-006F6.jpg

As you can see, the cowling is a very good fit.. no gaps for
leaks..sealed around edges with RTV Si.

There is more to the story... the right-hand duct is divided about
33/66 with the 33% going to the engine air induction via an air
filter. At full power take-off I see about 27.5 inches MAP (at 800 ft
msl and measuring/reading with a Vision Microsystems 800 display).
The left duct is divided about 33/66 with the 33 going to the oil
cooler (one of two coolers... the second is up front in the nose-gear
space).


2. Any air inlet, NACA or not, works best when the inlet is positioned in a
(relatively) high air pressure region, and works poorly or even in reverse
when placed in a (relatively) low air pressure region.
....
Just speculating, the site just aft of the point of greatest fuselage height
(where the ducts are now) seems like a local *low* pressure area.
....
3. Submerged NACA ducts work abysmally in areas of turbulent separation of
flow. The photo seems to indicate that turbulent separation is occuring at
the rear door seam.
....

4. The position of the existing ducts suggests that the engine uses
downdraft cooling, i.e. the cooling air is introduced on the top side of the
cylinders and pressures are used to force it out the bottom side of the
cylinders. Downdraft cooling is prone to problems at low airflow velocities
because of the tendency of heated air to rise. Low airflow velocities tend
to coincide, unfortunately, with situations that need the best possible
cooling, namely climbs (high power, low airspeed).

Yes, and the increased AOA during these conditions probably make the
situation even worse.

Sid

http://img87.exs.cx/img87/4545/MVC-006F6.jpg