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#1
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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. |
#2
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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 |
#3
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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. |
#4
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"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 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.782 / Virus Database: 528 - Release Date: 10/22/2004 |
#6
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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. |
#7
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"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. |
#8
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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 |
#9
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"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? |
#10
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"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 |
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