Going wingless?
Instructor
Joined: Oct 2015
Posts: 116
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Rennlist Member
Joined: Jun 2009
Posts: 769
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A Rennlist search provided the formula below I believe on a GT2. I'll let you guys decide if that's significant.
Another said the turbo has 9 kilos (20mph) of downforce at 190 MPH. So not apples to apples with a 996 but directionally says the spoiler is for looks. Y'all can find some more data so our discussion can be based on facts.
L = 1/2 p V^2 S Cl, we can make a rough calculation;
where L = Lift, what we want to find
p = density of air 1.225 Kg/M^2
V = velocity say 33 m/s (around 119kmph or 74mph)
S = Plan surface area say .15m^2 (around 1m by .15m)
Cl = lift coefficient say 1.5 which is a good high value for this size and speed
the equation looks like
.5*1.225*33^2*(1*.15) which yields 61 newtons or 6.2 kg's (13.2 lbs) of downforce at 75mph.
This comports well with Paul Frere's statement in the 911 story (excellent book by the way) where he states about the GT2:
“Porsche claims that a front down force of 2.2 kg and a rear down force of 7.5 kg at 200 kph (124 mph) are produced. Corresponding forces at 300 kph (186 mph) would be 5 and 17 kg respectively”.
Since our spoiler is smaller than a GT2 then the numbers are pretty close. Most pilots also know that you cannot have lift without drag so a better way to make downforce is to create suction with a smooth underbody and thus take advantage of Bertonian and Newtonian effects.
Another said the turbo has 9 kilos (20mph) of downforce at 190 MPH. So not apples to apples with a 996 but directionally says the spoiler is for looks. Y'all can find some more data so our discussion can be based on facts.
L = 1/2 p V^2 S Cl, we can make a rough calculation;
where L = Lift, what we want to find
p = density of air 1.225 Kg/M^2
V = velocity say 33 m/s (around 119kmph or 74mph)
S = Plan surface area say .15m^2 (around 1m by .15m)
Cl = lift coefficient say 1.5 which is a good high value for this size and speed
the equation looks like
.5*1.225*33^2*(1*.15) which yields 61 newtons or 6.2 kg's (13.2 lbs) of downforce at 75mph.
This comports well with Paul Frere's statement in the 911 story (excellent book by the way) where he states about the GT2:
“Porsche claims that a front down force of 2.2 kg and a rear down force of 7.5 kg at 200 kph (124 mph) are produced. Corresponding forces at 300 kph (186 mph) would be 5 and 17 kg respectively”.
Since our spoiler is smaller than a GT2 then the numbers are pretty close. Most pilots also know that you cannot have lift without drag so a better way to make downforce is to create suction with a smooth underbody and thus take advantage of Bertonian and Newtonian effects.
