What does a spoiler do?
12-30-2003 | 07:23 PM
#151
Guest
Posts: n/a
Re: What does a spoiler do?
> Ah, but don't forget - the coefficient of drag also increases as a square of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
12-30-2003 | 07:23 PM
#152
Guest
Posts: n/a
Re: What does a spoiler do?
> Ah, but don't forget - the coefficient of drag also increases as a square of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
12-30-2003 | 07:23 PM
#153
Guest
Posts: n/a
Re: What does a spoiler do?
> Ah, but don't forget - the coefficient of drag also increases as a square of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.
12-30-2003 | 09:24 PM
#154
Guest
Posts: n/a
Re: What does a spoiler do?
Ah...yes Drag....There is a trade off between lift and drag but the drag
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
12-30-2003 | 09:24 PM
#155
Guest
Posts: n/a
Re: What does a spoiler do?
Ah...yes Drag....There is a trade off between lift and drag but the drag
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
12-30-2003 | 09:24 PM
#156
Guest
Posts: n/a
Re: What does a spoiler do?
Ah...yes Drag....There is a trade off between lift and drag but the drag
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
12-30-2003 | 09:24 PM
#157
Guest
Posts: n/a
Re: What does a spoiler do?
Ah...yes Drag....There is a trade off between lift and drag but the drag
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.
The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.
Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span
Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area
So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.
The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.
On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.
I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.
Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:
http://www.bmwworld.com/models/m3_ltw.htm
Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.
Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.
Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.
That's my position on this subject.
"Scott MacLean" <scottNO@SPAMnerosoft.com> wrote in message
news:m5oIb.6271$Vl6.1550128@news20.bellglobal.com. ..
> > For those who have studied aerodynamic you'll recognize this formula:
> >
> > L=1/2pV^2SCl
> >
> > L=lift
> > p=density
> > S=surface area
> > Cl=Coefficient of lift
> >
> > Noticed that velocity is squared. Yes you'll get expotentially more
lift
> at
> > 100 MPH than 50 MPH but as long as you have airflow going through the
> > airfoil you will get lift. It has been 8 years since I was last in an
> > aerodynamic class so please don't quiz me on it. Notice that if you
have
> > more surface area, you get more lift. This is why you see those AM SCCA
> > cars with double or triple decker spoilers that is sometime bigger than
> the
> > vehicles, it must work because they sure produce really fast time around
> the
> > track.
>
> Ah, but don't forget - the coefficient of drag also increases as a square
of
> velocity - so the faster you go, the more drag that wing is creating. The
> more lift created by that wing, the slower your top speed.
>
>
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