Van's Air Force
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I want to watch the air flow...
- Thread starter kentb
- Start date
Allen Barrett
Well Known Member
double cinch 
Kevin Horton
Well Known Member
The one time I was directly involved with tuft testing, we used high quality duct tape to hold the yarn on. Mind you, we planned to fly at over 400 kt, so we needed something pretty sticky.
The whole thing was a complete waste of time, as the additional roughness from the tape and yarn changed the airflow, and the problem we were trying to diagnose wasn't there when the tufts were on. It came back as soon as the tufts and tape were removed.
We maybe should have tried again with thinner tape to hold the tufts on - clear packing tape? Maybe the thinner tape wouldn't have tripped the boundary layer, and allowed us to confirm the vortex shedding we suspected was occurring.
The whole thing was a complete waste of time, as the additional roughness from the tape and yarn changed the airflow, and the problem we were trying to diagnose wasn't there when the tufts were on. It came back as soon as the tufts and tape were removed.
We maybe should have tried again with thinner tape to hold the tufts on - clear packing tape? Maybe the thinner tape wouldn't have tripped the boundary layer, and allowed us to confirm the vortex shedding we suspected was occurring.
flyeyes
Well Known Member
Kevin Horton said:The whole thing was a complete waste of time, as the additional roughness from the tape and yarn changed the airflow, and the problem we were trying to diagnose wasn't there when the tufts were on. It came back as soon as the tufts and tape were removed.
We maybe should have tried again with thinner tape to hold the tufts on - clear packing tape? Maybe the thinner tape wouldn't have tripped the boundary layer, and allowed us to confirm the vortex shedding we suspected was occurring.
I have seen a friend (retired Pratt and Whitney engine engineer) use magnetic tape from an old cassette in a wind tunnel rather than yarn. I would suspect regular clear "scotch" tape and a recycled old cassette might work.
I tufted one wing aft of the spar from fuselage to the wing tip. Instead of taping each tuft individually I just ran long pieices of masking tape the whole length of the wing holding down 4 inch pieces of yarn knoted at the tape end. Never came off.
Tuft all the way out to the very end of your wing tip, very interesting airflow going on out there. Removal was just the opposite, very easy. Don't worry about the tape coming off, its in the boundry layer. Just think of that dead bug stuck on your wing that never comes off till you wash it of.
have fun.
Tom
Tuft all the way out to the very end of your wing tip, very interesting airflow going on out there. Removal was just the opposite, very easy. Don't worry about the tape coming off, its in the boundry layer. Just think of that dead bug stuck on your wing that never comes off till you wash it of.
have fun.
Tom
George in Langley BC
Well Known Member
Airflow & Yarn
I have used small pieces of masking tape over the forward 1/4 inch of two or three inch long strips of knitting yarn. In areas that you cannot see, such as around gear fairings you can get some idea of turbulent airflow because yarn that is wildly flapping around in turbulent flow will soon unravel while yarn in smooth air will retain it's twist.
I was always amazed to see the tufts facing forward in reversed flow on my C-182 gear-leg wheel pant intersection.
I have used small pieces of masking tape over the forward 1/4 inch of two or three inch long strips of knitting yarn. In areas that you cannot see, such as around gear fairings you can get some idea of turbulent airflow because yarn that is wildly flapping around in turbulent flow will soon unravel while yarn in smooth air will retain it's twist.
I was always amazed to see the tufts facing forward in reversed flow on my C-182 gear-leg wheel pant intersection.
pierre smith
Well Known Member
Oil
You can use old, black, engine oil as well. I once dabbed a few drops on my intersection fairings on my old Cassutt to see if the flow was laminar....Yep, smooth streaks from the leading edges all the way back. It ain't too messy to clean up if you only use a drop here and a drop there and it'll be there when you land. I got the idea from watching the turbulent chemical patterns around fairings during days of heavy ag work and chemical accumulation on the leading edges, streaking rearward eventually.
Regards,
You can use old, black, engine oil as well. I once dabbed a few drops on my intersection fairings on my old Cassutt to see if the flow was laminar....Yep, smooth streaks from the leading edges all the way back. It ain't too messy to clean up if you only use a drop here and a drop there and it'll be there when you land. I got the idea from watching the turbulent chemical patterns around fairings during days of heavy ag work and chemical accumulation on the leading edges, streaking rearward eventually.
Regards,
