aero questions

[oldschooleco]

Hey y'all
I'm confused on two things and they both have to do with the length/placement of certain mods inside the teardrop template. one is a roof extension, i understand it should be in the template curving with the roof, but i want to see out my rear window and still use my trunk (its a notch back sedan). does it have to be a certain length to be affective? and another question on a flat trunk spoiler, does it work with the roof extension? is its purpose to reattach flow? what is the optimum length on that? thank you!

[freebeard]

The Template, she is a harsh mistress.

Anything that's not a half-body of revolution, IOW a half circle from the front or back, will not satisfy The Template.

Search instead for K-form, Kamm-back or Jaray body styles.

[aerohead]

Originally Posted by oldschooleco

Hey y'all
I'm confused on two things and they both have to do with the length/placement of certain mods inside the teardrop template. one is a roof extension, i understand it should be in the template curving with the roof, but i want to see out my rear window and still use my trunk (its a notch back sedan). does it have to be a certain length to be affective? and another question on a flat trunk spoiler, does it work with the roof extension? is its purpose to reattach flow? what is the optimum length on that? thank you!

*The 'Template' would require converting the notchback into a Kamm-back,if at normal car length.To be most effective,it would need to be as long as the rear of the trunk.
*You would lose conventional use of the trunk unless you articulated the roof extension as other members have,allowing the addition to swing up and away,allowing access to the trunk.
*Otherwise,you'd lose the trunklid and covert to a rear hatch.
*Your rear vision would be with a new passenger side side window,and rear vertical backlight.
------------------------------------------------------------------------
*If you do the 'Template' extension,a spoiler would be unnecessary,as the template generates zero rear lift and has full flow attachment.
*Spoilers must be designed according to :
---- Percentage of roof compared to vehicle length
---- Whether the roof has camber or not
---- Design of the C-pillars
---- Whether the quarter panels are boat-tailed or not
---- The length of the trunk
---- The height of the trunk
---- The angle of the backlight
There is a high probability that what the factory has done is already optimized for all the parameters listed above.

[oldschooleco]

Originally Posted by aerohead

*The 'Template' would require converting the notchback into a Kamm-back,if at normal car length.To be most effective,it would need to be as long as the rear of the trunk.
*You would lose conventional use of the trunk unless you articulated the roof extension as other members have,allowing the addition to swing up and away,allowing access to the trunk.
*Otherwise,you'd lose the trunklid and covert to a rear hatch.
*Your rear vision would be with a new passenger side side window,and rear vertical backlight.
------------------------------------------------------------------------
*If you do the 'Template' extension,a spoiler would be unnecessary,as the template generates zero rear lift and has full flow attachment.
*Spoilers must be designed according to :
---- Percentage of roof compared to vehicle length
---- Whether the roof has camber or not
---- Design of the C-pillars
---- Whether the quarter panels are boat-tailed or not
---- The length of the trunk
---- The height of the trunk
---- The angle of the backlight
There is a high probability that what the factory has done is already optimized for all the parameters listed above.

So if i even extended the roof 8in to a foot, would it help any? or should i just go with the flat spoiler how would i know it would be affective?- ps i hate to burst your bubble but its a 1965 dodge dart 4 door, i doubt they optimized the parameters above

[freebeard]

Peter DeFazio (D-OR) drives a mid-60s Dodge Dart, so they can't all be bad. (Politicians that is, not Dodge Darts)

So if i even extended the roof 8in to a foot, would it help any? or should i just go with the flat spoiler how would i know it would be affective?

You get 40% of the drag from the front and top, 40% from the wheelwell, underside and rear and 20% internal (for engine cooling). Grille blocks, fender skirts and bellypans may be called for.

A modest kamback might make a modest improvement. A flat 'Bonneville' spoiler would be the one to use. It allows air falling off the roofline to re-attach.

[oldschooleco]

Originally Posted by freebeard

Peter DeFazio (D-OR) drives a mid-60s Dodge Dart, so they can't all be bad. (Politicians that is, not Dodge Darts)



You get 40% of the drag from the front and top, 40% from the wheelwell, underside and rear and 20% internal (for engine cooling). Grille blocks, fender skirts and bellypans may be called for.

A modest kamback might make a modest improvement. A flat 'Bonneville' spoiler would be the one to use. It allows air falling off the roofline to re-attach.

ok cool, how do i know how long will be optimal? thank you!

[freebeard]

Short answer: when it's short enough you don't back into things with it.

Long answer:


This is for a full boattail, but the curve for your result would be similar.

[aerohead]

Originally Posted by oldschooleco

So if i even extended the roof 8in to a foot, would it help any? or should i just go with the flat spoiler how would i know it would be affective?- ps i hate to burst your bubble but its a 1965 dodge dart 4 door, i doubt they optimized the parameters above

Chrysler was heavy into aerodynamic drag reduction by the 1920s.
There is a chance that they actually tested models of the Dart.Don't know.
If you arbitrarily did just a partial roof extension,it might cause the air to overshoot the trunklid.Don't know.Kamm did full extension out to the rear of the trunklid.Nothing 'halfway.'
I'm gonna give you the stuff on the Cd 0.28 Dodge Daytona.You should also check out George Poteet's Cd 0.20 1969 Baracuda 'Blowfish',Bonneville land speed record attempt car's roofline and serving tray spoiler.

Here is Chrysler's Cd 0.244 DeSoto Airflow test mule of 1934

Here is the 1967 Lotus Europa,Cd 0.29.It has a high boot,and the tail extends out into 'Template' territory,with good reattachment and small locked-vortex.

[freebeard]