Need aerodynamic help for a tank

[SPARKY]

smallest posible

[kiwi belly tank]

Small will have the least aerodynamic drag but the least traction & now you need to come up with gearing to spin the little suckers which will probably mean some kind of overdrive to your underdrive (ring & pinion) & all that sucks HP.
Best range for off the shelf gears is the "2 series" 7-1/2 10 bolt, the highest ratio is 2.14 down through 2.29 2.41 2.56 2.73 & 3.08 the lowest. With a 30" Mickey, 7k rpm, direct drive in the trans & a 2.56 gear will give you 244mph. That'll give you ratio options with no other changes all the way up to 290-ish with the 2.14 if you are making HP to pull it.
Besides, a little tire on a 38" tank is going to make it look like a pregnant roller skate.
  Sid. 

[salt27]

Sid, What would be your tire recommendations for the front of a tank?

  Don

[oj]

Thanks for the tire/gearing explanation, which brings up the next question: I'd thought about using a champ style quickchange, is that a nono due to powerloss?  I think the most efficient might be the 9" ford case with a Strange Engnr'g 12bolt 'drop out' 3rd member, is that the one I need?  I'd prefer the QC. 
Anybody use a transaxle?

[Ron Gibson]

A GM 10 bolt is more efficient than a 9" Ford due to pinion location. If you're down on power = flathead, efficiency might make a difference in speed.

Ron

[RichFox]

I keep looking at Audi, maybe an A4, trans axles

[Sumner]

What size tire & wheel should I use. the speed will have to be 240ish.

I have some spreadsheets that could help you here...

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

You can plug all your data in them and the speed ones also show rpm drop at any shift point.  There are others there that might help,  like ....

HP needed for a certain speed and Air Inlet Size recommendations.

Good luck,

Sumner

[Sumner]

Thanks for the tire/gearing explanation, which brings up the next question: I'd thought about using a champ style quickchange, is that a nono due to powerloss?  I think the most efficient might be the 9" ford case with a Strange Engnr'g 12bolt 'drop out' 3rd member, is that the one I need?  I'd prefer the QC. 
Anybody use a transaxle?

With the Champ QC you can start looking at some pretty high pinion speeds, especially if you start running faster.  The highest ratio with the Ford 9 inch is going to be 2.47.  I'd take the advice you've been given on the 7.5 GM,

Sumner

[kiwi belly tank]

Sid, What would be your tire recommendations for the front of a tank?

  Don

You can't get any more aerodynamic than a pair of dragster spindle mounts with inner & outer discs & run them with C3 ball bearings with a center spacer not tapered roller bearings.
  Sid. 

[salt27]

Sid, What would be your tire recommendations for the front of a tank?

  Don

You can't get any more aerodynamic than a pair of dragster spindle mounts with inner & outer discs & run them with C3 ball bearings with a center spacer not tapered roller bearings.
  Sid. 

Thanks

[Stan Back]

The Flathead Fuel Lakester record at Bonneville is 207.  Gearing for 240 will definitely get you in the 40s -- the 140s.

[SPARKY]

ROTFLMAO

[salt27]

oj mentioned a 250ci non-vintage engine.

E-G/L, 2016 rule book has the record at 236.431 if it didn't get bumped this year.

  Don

[Stan Back]

My bad!

I got cornfused.  Thought somebody mentioned those underhead-valve V-8s.

[Rex Schimmer]

OJ,
Sounds to me like you may be considering building the actual tank your self. If this is your plan then you need to be looking at some of the NACA 66000 wing sections for dimensions. My preference is the 66018 section in revolution which also happens to be the section that the number 496 AAgas supercharged streamliner of Rob Freyvogl and Branden Barnard. Check out their build at http://www.landracing.com/forum/index.php/topic,8665.0.html . You can see their great design of a car that is very similar to a tank. As Nathan Stewart said, tanks are a difficult build bit it is a challenge that many people take just for the sake of doing it. Also look closely at the CFD picture that Woody has provided, it does not address the wheels and their affect on the cars total aerodynamics but if you look at the rear of the car you can see where the air flow separates from the body both on the top and also the bottom. The top is due to the specific aero shape of the body but the bottom shows what happens when you run the car to low. The "perfect" shape would have the air flow be attached to the body for its complete length to minimize pressure drag. The most important part of a lakesters aero are the wheels/tires, how they are connected to the body and their relationship to the body and how their areo may affect the bodies aero.

Sounds like a great project and keep us up to date with your progress.

Rex