Gurney Flap Study
03-14-2011, 04:03 PM
#61
Rennlist Member
Sorry to interfere in those highly academical matters, I can admit I know nothing about any flaps. It is just not my field of expertize. Nevetheless I opened up that PDF in the mid of the thread and it states:
It was found that Gurney flaps produce an upward shift in the lift coefficient that
is approximately proportional to the flap height. At angles below
stall, the drag increase to the Gurney flap with a height less than the
trailing edge boundary-layer is less than 20%. For flaps of larger
height, or for an aerofoil that has stalled, the drag increase can typically
become up to twice that of the plain aerofoil. The maximum lift
to drag ratio occurs when the flap height is about 90% that of the
trailing edge boundary-layer thickness. This leads to an optimum
height equation that enables the efficient optimisation of any
constant-chord aerofoil. The experiments have shown that as long as
the height remains less than the thickness of the boundary-layer at
the trailing edge, the additional drag will be negligible, which is
coherent with other data available in the technical literature for high
Reynolds number flows.
Is that stuff in bold essentially all what this thread was about? Or was it, well, that the accuracy of paper statements getting debated?
It was found that Gurney flaps produce an upward shift in the lift coefficient that
is approximately proportional to the flap height. At angles below
stall, the drag increase to the Gurney flap with a height less than the
trailing edge boundary-layer is less than 20%. For flaps of larger
height, or for an aerofoil that has stalled, the drag increase can typically
become up to twice that of the plain aerofoil. The maximum lift
to drag ratio occurs when the flap height is about 90% that of the
trailing edge boundary-layer thickness. This leads to an optimum
height equation that enables the efficient optimisation of any
constant-chord aerofoil. The experiments have shown that as long as
the height remains less than the thickness of the boundary-layer at
the trailing edge, the additional drag will be negligible, which is
coherent with other data available in the technical literature for high
Reynolds number flows.
Is that stuff in bold essentially all what this thread was about? Or was it, well, that the accuracy of paper statements getting debated?
03-14-2011, 04:34 PM
#64
Rennlist Member
Utkinpol, No this is not what the thread is about. Its about the range of use that provides an advantage. we all agree that a 1/8" gurney flap (one so small, i havent seen one, have you? plus its already part of a stock cup car wing) provides benefits with very little cost to drag (but, based on the graphs, the drag is greater,even as small as it is, than a clean wing)
What the thread is about, is whether the GF makes the wing more efficient over all. based on the facts and experiment data, it doesnt.
Ive said it 100 times so far and it is clearly stated in the Cal Poly paper. for that wing tested, at Cl greater than 1.4, the GF will give better lift to drag ratios (more efficient) and we know that by adding a GF of near any sized discussed (less than 1% to 5%) it increases lift. HOWEVER , at Cl below that certain level, if you can achieve the lift without the GF, you can save near 40% of the drag due to the increased lift.
real world. the wing with GF that TrackCar posted. If that set up puts out the down force that cannot be achieved by pure wing angle change, then he is doing things right. however, if not, he could be suffering a 40% increase in drag. This is very hard to know, as the downforce can remail relatively constant at or near or even after stall. (even though it does drop significantly after stall) BUT, the drag will continue to skyrocket. So, there is nothing wrong with putting on a GF if you suspect to be at these higher limits . But, if you are not, and have plenty of downforce with your wing set at 5-7 degrees, putting on a GF and backing the wing down to 0 (for the same net Downforce) would cost more drag in the end.
Im doing nothing more than repeating what is found on the charts, consistant with all 3 studies. where i have a problem is when J Richard, will make bold statements that GFs increase wings efficiency when all they really do is increase downforce, AND efficiency beyond high levels of lift for a given wing.
There is no debate on the studies, however, it is J richard that thinks that the first one was skewed to combine the experiments with the "t strips" and GF's. in those two studies, the exact same graphs were generated.
Its the interpretation of those graphs and the verbage that is under review.
herd mentalities.......
its not that amazing. many are not seeing the trade offs using the GF and misinterpreted the verbage from the three studies presented.
What the thread is about, is whether the GF makes the wing more efficient over all. based on the facts and experiment data, it doesnt.
Ive said it 100 times so far and it is clearly stated in the Cal Poly paper. for that wing tested, at Cl greater than 1.4, the GF will give better lift to drag ratios (more efficient) and we know that by adding a GF of near any sized discussed (less than 1% to 5%) it increases lift. HOWEVER , at Cl below that certain level, if you can achieve the lift without the GF, you can save near 40% of the drag due to the increased lift.
real world. the wing with GF that TrackCar posted. If that set up puts out the down force that cannot be achieved by pure wing angle change, then he is doing things right. however, if not, he could be suffering a 40% increase in drag. This is very hard to know, as the downforce can remail relatively constant at or near or even after stall. (even though it does drop significantly after stall) BUT, the drag will continue to skyrocket. So, there is nothing wrong with putting on a GF if you suspect to be at these higher limits . But, if you are not, and have plenty of downforce with your wing set at 5-7 degrees, putting on a GF and backing the wing down to 0 (for the same net Downforce) would cost more drag in the end.
Im doing nothing more than repeating what is found on the charts, consistant with all 3 studies. where i have a problem is when J Richard, will make bold statements that GFs increase wings efficiency when all they really do is increase downforce, AND efficiency beyond high levels of lift for a given wing.
There is no debate on the studies, however, it is J richard that thinks that the first one was skewed to combine the experiments with the "t strips" and GF's. in those two studies, the exact same graphs were generated.
Its the interpretation of those graphs and the verbage that is under review.
Sorry to interfere in those highly academical matters, I can admit I know nothing about any flaps. It is just not my field of expertize. Nevetheless I opened up that PDF in the mid of the thread and it states:
It was found that Gurney flaps produce an upward shift in the lift coefficient that
is approximately proportional to the flap height. At angles below
stall, the drag increase to the Gurney flap with a height less than the
trailing edge boundary-layer is less than 20%. For flaps of larger
height, or for an aerofoil that has stalled, the drag increase can typically
become up to twice that of the plain aerofoil. The maximum lift
to drag ratio occurs when the flap height is about 90% that of the
trailing edge boundary-layer thickness. This leads to an optimum
height equation that enables the efficient optimisation of any
constant-chord aerofoil. The experiments have shown that as long as
the height remains less than the thickness of the boundary-layer at
the trailing edge, the additional drag will be negligible, which is
coherent with other data available in the technical literature for high
Reynolds number flows.
Is that stuff in bold essentially all what this thread was about? Or was it, well, that the accuracy of paper statements getting debated?
It was found that Gurney flaps produce an upward shift in the lift coefficient that
is approximately proportional to the flap height. At angles below
stall, the drag increase to the Gurney flap with a height less than the
trailing edge boundary-layer is less than 20%. For flaps of larger
height, or for an aerofoil that has stalled, the drag increase can typically
become up to twice that of the plain aerofoil. The maximum lift
to drag ratio occurs when the flap height is about 90% that of the
trailing edge boundary-layer thickness. This leads to an optimum
height equation that enables the efficient optimisation of any
constant-chord aerofoil. The experiments have shown that as long as
the height remains less than the thickness of the boundary-layer at
the trailing edge, the additional drag will be negligible, which is
coherent with other data available in the technical literature for high
Reynolds number flows.
Is that stuff in bold essentially all what this thread was about? Or was it, well, that the accuracy of paper statements getting debated?
its not that amazing. many are not seeing the trade offs using the GF and misinterpreted the verbage from the three studies presented.
03-14-2011, 04:53 PM
#66
Rennlist Member
sorry, I'lll try
BTW,
Here are the two graphs that are consistant and very clear as to the effects on lift, drag based on angle of attack. Make your own conclusions but it seems to be pretty clear. the only graph that is missing is a L/D curve, but that can be plotted out pretty easily.
For example. at 1.2 Cl. which is the max lift for the wing, it jumps to 1.8Cl for a use of a 2% gurney flap. drag goes up by 150% to .25Cd from .1Cd, lift goes up 50% and this is useful, because the clean wing has no ability to create 1.8Cl. This is the net net of the gurney flap use.
However, if you are operating at 1.0Cl, and then want to keep this level of downforce (near 90% of its max capabilites), it does so with 15% less drag than that same downfoce with use of a GF.
With a 5% GF, this figure goes up to 40% reduction in drag by using a plain wing at a higer AOA (5degrees vs 12 degrees) . that would be like a .5" tall GF. This looks to be as high as the GF shown by TRACKCAR
does anyone see flaws in this analysis?
BTW these graphs are consistant with all three studies.
BTW,
Here are the two graphs that are consistant and very clear as to the effects on lift, drag based on angle of attack. Make your own conclusions but it seems to be pretty clear. the only graph that is missing is a L/D curve, but that can be plotted out pretty easily.
For example. at 1.2 Cl. which is the max lift for the wing, it jumps to 1.8Cl for a use of a 2% gurney flap. drag goes up by 150% to .25Cd from .1Cd, lift goes up 50% and this is useful, because the clean wing has no ability to create 1.8Cl. This is the net net of the gurney flap use.
However, if you are operating at 1.0Cl, and then want to keep this level of downforce (near 90% of its max capabilites), it does so with 15% less drag than that same downfoce with use of a GF.
With a 5% GF, this figure goes up to 40% reduction in drag by using a plain wing at a higer AOA (5degrees vs 12 degrees) . that would be like a .5" tall GF. This looks to be as high as the GF shown by TRACKCAR
does anyone see flaws in this analysis?
BTW these graphs are consistant with all three studies.
Last edited by mark kibort; 03-14-2011 at 05:23 PM.
03-14-2011, 05:11 PM
#67
Rennlist Member
Utkinpol, No this is not what the thread is about. Its about the range of use that provides an advantage. we all agree that a 1/8" gurney flap (one so small, i havent seen one, have you? plus its already part of a stock cup car wing) provides benefits with very little cost to drag (but, based on the graphs, the drag is greater,even as small as it is, than a clean wing)
What the thread is about, is whether the GF makes the wing more efficient over all. based on the facts and experiment data, it doesnt.
What the thread is about, is whether the GF makes the wing more efficient over all. based on the facts and experiment data, it doesnt.
Here I am not going to argue with anybody or take sides in your local battles guys, I just was curious what all this fuss was about.can i ask one only thing about this - do Formula 1 cars have those 'flaps' or don`t they?
03-14-2011, 05:25 PM
#68
Rennlist Member
03-14-2011, 05:30 PM
#69
Still plays with cars.
Lifetime Rennlist
Member
Seems to me that Dan Gurney first used the flaps on his single seat race cars - American Eagles I think.
03-14-2011, 05:34 PM
#70
Rennlist Member
ps. the more one studies - less one really understands - like more you study corpuscular physics and field theory postulates less you understand how this stupid electricity can even be possible. should not exist at all if all science about it is supposedly right.
probably same applies to those flaps as well.
03-14-2011, 05:44 PM
#71
Rennlist Member
http://www.allamericanracers.com/gurney_flap.html
so, was that flap just a trick in a fixed setup where angle of the wing was forbidden to be adjusted by rules? why could they not simply increase angle of attack for this wing to increase downforce instead of messing with adding up flaps (essentially messing up with wing`s geometry)?
03-14-2011, 07:26 PM
#72
Addict
Rennlist Member
Rennlist Member
Discussion on use on the very lowest of downforce track: Monza
http://www.f1technical.net/forum/vie...php?f=3&t=4704
03-16-2011, 03:22 PM
#73
Still plays with cars.
Lifetime Rennlist
Member
The horse is dead. Thread closed.
03-29-2011, 01:31 PM
#75
Rennlist Member
Its an interesting topic with some good information here. I even got my dad (x-pilot who flew Dc10s) interested in that one part of the study, reading up on it. Glad the thread was revived.
The net net of it all was, that a GF as we would be using, would be around .5". (most cases near 5%) . Dont use it if you cant get more wing angle to provide the downforce you need, because you will incure 40% more drag. It only makes the wing more efficient, or doesnt change efficiency at near 2% GF size. coincidentially, that is already installed on the cup car wings, in the form of a 1/8", 2%, DTE (divergent trailing edge, which does the same thing as a GF).
The net net of it all was, that a GF as we would be using, would be around .5". (most cases near 5%) . Dont use it if you cant get more wing angle to provide the downforce you need, because you will incure 40% more drag. It only makes the wing more efficient, or doesnt change efficiency at near 2% GF size. coincidentially, that is already installed on the cup car wings, in the form of a 1/8", 2%, DTE (divergent trailing edge, which does the same thing as a GF).