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Why don't wings have dimples?
Hi all,
I always wanted to build my own airplane but the time and money has eluded me. So I've decided to design and build my own recumbent trike, with farings. This brings me to my question, if golf balls have dimples, to help them sail further, why don't wings -- especially for STOL aircraft? Would putting dimples in my faring reduce my wind resistance? Just curious. Chris |
#2
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Why don't wings have dimples?
"Dancing Fingers" wrote in message
ups.com... Hi all, I always wanted to build my own airplane but the time and money has eluded me. So I've decided to design and build my own recumbent trike, with farings. This brings me to my question, if golf balls have dimples, to help them sail further, why don't wings -- especially for STOL aircraft? Would putting dimples in my faring reduce my wind resistance? Just curious. Chris Dimples work on round things under a relativly narrow range of reynolds numbers (a function of speed, size and properties of air) by helping keep the boundry layer attached. Golf balls happen to fit into that range and have the right shape. Gliders sometimes use "turbulator" tape to trip a laminar boundry layer and make it turbulant so it will stay attached longer - but the placement is critical (and only works if you have a very laminar wing to begin with). So, if you are having boundry layer seperation problems due to the shape of your fairing aft of the maximum "thickness", then dimples or other boundry layer devices may or may not help but most likely they will not. -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#3
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Why don't wings have dimples?
Capt. Geoffrey Thorpe wrote: ... Dimples work on round things under a relativly narrow range of reynolds numbers (a function of speed, size and properties of air) by helping keep the boundry layer attached. Golf balls happen to fit into that range and have the right shape. Gliders sometimes use "turbulator" tape to trip a laminar boundry layer and make it turbulant so it will stay attached longer - but the placement is critical (and only works if you have a very laminar wing to begin with). So, if you are having boundry layer seperation problems due to the shape of your fairing aft of the maximum "thickness", then dimples or other boundry layer devices may or may not help but most likely they will not. So maybe you could use dimples on fairings, fuselage or struts, especially if the struts are circular tubing, eh? -- FF Lots of aviation stuff for sale cheap: http://groups.google.com/group/rec.a...e=source&hl=en |
#4
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Why don't wings have dimples?
wrote in message ups.com... Capt. Geoffrey Thorpe wrote: ... So maybe you could use dimples on fairings, fuselage or struts, especially if the struts are circular tubing, eh? -- FF Could be. Somewhere or another I saw some wind tunnel data on golf balls that nicely showed how the flow remained attached further around the back side (no spin was involved - just a reduction in the wake). But you would have to find out what the range of Reynolds number this works for... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#5
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Why don't wings have dimples?
Thanks everyone for the great answers vto my silly question.
Capt. Geoffrey Thorpe wrote: wrote in message ups.com... Capt. Geoffrey Thorpe wrote: ... So maybe you could use dimples on fairings, fuselage or struts, especially if the struts are circular tubing, eh? -- FF Could be. Somewhere or another I saw some wind tunnel data on golf balls that nicely showed how the flow remained attached further around the back side (no spin was involved - just a reduction in the wake). But you would have to find out what the range of Reynolds number this works for... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#6
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Why don't wings have dimples?
Does anyone know of a good simulation program where you could play with
dimples on a large hot dog shape, just to see what happens. Just more curious. Chris Dancing Fingers wrote: Thanks everyone for the great answers vto my silly question. Capt. Geoffrey Thorpe wrote: wrote in message ups.com... Capt. Geoffrey Thorpe wrote: ... So maybe you could use dimples on fairings, fuselage or struts, especially if the struts are circular tubing, eh? -- FF Could be. Somewhere or another I saw some wind tunnel data on golf balls that nicely showed how the flow remained attached further around the back side (no spin was involved - just a reduction in the wake). But you would have to find out what the range of Reynolds number this works for... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#7
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Why don't wings have dimples?
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
... wrote in message ups.com... Capt. Geoffrey Thorpe wrote: ... So maybe you could use dimples on fairings, fuselage or struts, especially if the struts are circular tubing, eh? -- FF Could be. Somewhere or another I saw some wind tunnel data on golf balls that nicely showed how the flow remained attached further around the back side (no spin was involved - just a reduction in the wake). But you would have to find out what the range of Reynolds number this works for... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. I've seen a video of that, but don't recall where. However, I believe that you have it backward--the flow detaches earlier (from the non-spinning golf ball) and reduces the drag. I am not quite sure how that might relate to wings and propellers; but I suspect that they (wings and props) are two radically different, and possibly opposite, phenomena. Peter |
#8
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Why don't wings have dimples?
"Peter Dohm" wrote in message
... I've seen a video of that, but don't recall where. However, I believe that you have it backward--the flow detaches earlier (from the non-spinning golf ball) and reduces the drag. I am not quite sure how that might relate to wings and propellers; but I suspect that they (wings and props) are two radically different, and possibly opposite, phenomena. Peter Ok, now you've done it. You are going to make me look this up... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... http://www.aerospaceweb.org/question...cs/q0215.shtml with a little math and some graphs http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html plots drag as a function of Reynolds number for a golf ball and a smooth sphere - a good starting pont if you want to dimple your nosegear strut to reduce drag - just figure you your own Reynolds number... That's enough. Didn't find the picture I was looking for. But I see references to both the reduction in wake and Magnus effect that converts the spin into lift. Apparently both contribute to the increase in range. (and the drawings I've seen show the boundry layer staying attached longer as I thought.) -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#9
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Why don't wings have dimples?
"Dancing Fingers" wrote in message ups.com... Hi all, I always wanted to build my own airplane but the time and money has eluded me. So I've decided to design and build my own recumbent trike, with farings. This brings me to my question, if golf balls have dimples, to help them sail further, why don't wings -- especially for STOL aircraft? Would putting dimples in my faring reduce my wind resistance? Just curious. Chris You may hear stories of the "Golf Ball Effect" improving performance of aircraft - usually from those trying to sell hail damaged aircraft. bildan |
#10
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Why don't wings have dimples?
When air moves past a rotating sphere or cylinder the surface friction can induce a rotational component into the airflow. This shifts the pressure distribution and causes a net lift. The lift allows a golf ball to achieve a longer flight. The dimples 'dirty' the surface and increase this rotational effect. Lift on a wing can be considered in different and equivalent ways. Some of the ways to look at lift from a wing a -Deflection of the ambient air is a mass pushed down which results in a force up on the aircraft. -Faster airflow on the upper surface and slower airflow on the lower surface create a pressure difference and lift. -The wing induces a circulation in the ambient air which can be directly related to lift. It is interesting to note that a vortex in free air must be closed. Just like a common smoke ring. But the wing is finite. The vortex peels off the wing in an approximately elliptical distribution across the span and is left behind both wing tips as the aircraft flys away. Aside from friction eventually stopping the circulation a few minutes after the aircraft is passed, theoretically the vortex continues back behind the flight path all the way to the runway where the plane took off where the first inch of movement of the wing began a very small vortex and very small lift. A baseball pitcher gets a similar effect when the spinning ball does not sink as fast as it should thus fooling the batter. On the other hand a knuckle ball appears to stagger like it was drunk and makes the batter queasy. eww! James Dancing Fingers wrote: Hi all, I always wanted to build my own airplane but the time and money has eluded me. So I've decided to design and build my own recumbent trike, with farings. This brings me to my question, if golf balls have dimples, to help them sail further, why don't wings -- especially for STOL aircraft? Would putting dimples in my faring reduce my wind resistance? Just curious. Chris |
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