[QUOTE=Bicycle Bob;119013]
Quote:
Originally Posted by aerohead
---- The template respects streamline flow with an economy of structure and literally guarantees attached flow,at least if you don't cheat the minimums.----------- YOU CAN make the body with higher fineness ratio,I just want everyone to understand that there will be a small penalty to extra skin friction.
I agree that it is good to avoid extra skin friction, but when only one study suggests that flow can stay attached to a shape at 2.5 : 1, and hundreds of tests at a more suitable Reynold's number disagree, I want to see some tuft tests. In the NASA tests for streamlining trucks, you can see a tailcone extension eliminating a Kammback, while increasing the angle a bit, and the tell-tales show separation there, at an angle that is still less than this "ideal."
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Bob,sorry for the lapse in response.
With respect to the 2.5:1 streamlined body of revolution,at Cd 0.04,it's the lowest Cd free-body who's boat-tail is as steep as Mair's 22-degree maximum,but no shorter.
If it's shorter,it will be like an NFL regulation football ( Cd 0.055 )with no way for the air to remain attached.
If it's longer,the flow isn't any better attached,it uses more material,it's heavier.Not as good of engineering.
The 2.5:1 produces a body of Cd 0.08.When wheels are added the drag goes up to Cd 0.13.If wheel fairings are installed the Cd comes back down.
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If the constant velocity portion of Mair's wind tunnel model is removed it creates a 'template' of about 2.5:1.
In Hucho's 2nd Edition,p.199,Fig.4.117,3rd image down is a 'template' derived from a Cd 0.05 streamline body of revolution which produces Cd 0.15.
In Fig.4.188 below it depicts the 'Template.'
In Fig.4.199,the lowest Cd for ellipsoids.@ above critical Reynolds number falls at 2.5:1 l/d.
In Hoerner's Fig.5.13,Cd min occurs at just above 2:1 but this violates Mair's 22-degree aft-body slope maximum so we can't go that steep.
On pg. 210,Hucho discusses the 1982 Cd 0.15 ARVW .The fineness ratio of the ARVW is l/h= 5.53 which according to Fig.4.118 corresponds to an effective free air fineness ratio of 2.27 "This approaches the drag mimimum recognizable."
On pg. 324,Fig.8.46,Cd vs L/D for geometric shapes,the body#4 ( ellipsoid ) demonstrates the lowest Cd of all bodies depicted.When ground clearance is factored into the dimensions,the drag minimum occurs at L/D= 2.478
On pg.141-142,when discussing the boat-tail on the Mercedes-Benz C-111 III he observes "Qualitatively,the effect of the (Boat-tail) length upon the aerodynamic drag is similar to that of the body of rotation..."
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As an airship,the 2.5 l/d body would be extremley low drag,separation free,although the crew would suffer motion sickness.
Hucho says "...low drag can only be achieved when the separation at the rear is eliminated." pg 16
"Optimum shapes are 'streamline' bodies having a very slender rear part." pg 61
"Lower drag can only be achieved by extending the length of the vehicle's body." pg 201
"...drag coefficient ....may be plotted against vehicle length,...if the (drag) evaluation is limited to vehicles...developed for the lowest possible drag coefficient,this expected trend is in fact confirmed." pg. 202
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Hucho cites Dornier's 1920 truncated wing research to justify not boat-tailing.
Dornier's work is shown in Fachsenfeld's book.It is the Deutsch Reichs Patent 394 184 depicting a cambered wing profile with 24% of its aft-section cut away.There are no quanta listed.
For a DVL or Gottingen section of 20.5% thickness,with 24% of the aft-section removed,the drag increases 223% ( 2.23X).
For a 12% d/l DVL smooth fuselage,cutting 50% of the tail away as recommended by Kamm results in a drag increase of 59%.
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Jaray's 1921 pumpkin seed is "Template" out to 32% aft-body,then goes hypo with an exit slope of 26-degrees for Cd 0.13
Lay's pumpkin seed is at "template" and registered Cd 0.12.
Fachsenfeld's Omnibus with inflated boat-tail is very close to the 'Template'.
Other vehicles considered for 'Template' comparisons:
1957 MG EX 181
1957 Grumman E-1 ( WF-2 ) Tracer (radome)
1963 Alfa Romeo TZ
1965 Ford Mk IV
1967 Lotus Europa
1967 Ferrari 330 P4
1967 Chaparral 2F
1968 Mickey Thompson LSR Mustang fastback
1970 Porsche 917 long -tail (D)
1974 VW Golf/Rabbit
1980 Medusa,Ital Design
1981 Flow body,VW Cd 0.15
1981 Drop Shape,VW,Cd 0.16
1981 Blunt Body,VW Cd 0.15
1984 Ferrari Testarossa
1984 Maya,Ital Design
1984 Imperator 108i,Isdera
1987 Express,Chevrolet Cd 0.195
1987 Vesta II,Renault,Cd 0.19
1987 Sunraycer,AeroVironment/GM,Cd 0.089-0.12
1988 Lamborghini Countach 5000
1988 Lotus Esprit Turbo
1991 HX3,GM,Cd 0.258
1991 Ferrari F40
1994 Viper Defender,Dodge
1994 Bugatti EB 110
1994 Saleen S-351 Mustang
1995 Ferrari F355 Berlinetta
2004 Team Corvette C50R
2005 AeroCivic,Cd 0.17
2008 Boxfish (Bionic),Mercedes-Benz,Cd 0.19
2009 Koenigsegg CCXR
2009 1-Liter concept,Volkswagen Cd 0.195
2010 Murcelago,Lamborghini
2010 CTS Wagon,Cadillac
2010 Ford GT
2010 Ferrari 458 Italia
2010 Honda Type R
2010 Ferrari 599XX