Frontal Area / Cd numbers

[robfrey]

I think Sim Speed is thinking more on the lines of Bolivia where there is this unlimited run up distance.
We know that Bonneville is good training for Bolivia but he will probably not set the world on fire at bonneville as far as numbers go.
Then again, he may surprise us!!!!!!
I think we should discuss whether a flat bottom car is more efficient than getting the car up away from the running surface and minimizing ground effect downforce.
Flat bottom car will make some down force at higher speeds but then again do you need that downforce at higher speeds and what price are you paying for that downforce.
Cfd does not do a good job of modeling this drag as far as I have witnessed so far.
What Woody and I have concluded is that if I were to build another car, it would be further from the ground.
That being said-
Flat bottom cars are way easier to build and maintain.


Rob Freyvogel
#496
AA/BFS

[Simspeed]

I might have missed it if you covered before, but rather than adding skirts, have you looked more into ground effect under the vehicle for downforce? Lots of benefits there.

My first design effort included a tunnel floor with IC exhaust dumping into the space to speed airflow exiting at the rear.  I soon realized we'd need that space to run power cables from the generators to the controllers.  So in an effort to add downforce to the nose and drive wheels I added the skirts for CFD testing.  I'm hoping we won't need them but it will be good to know to what theoretical degree they may help or hurt.  Thanks...

[7800ebs]

Are the current unlimited wheel driven vehicles more traction-limited at lower speeds or more aero-limited at higher speeds?

To put down a monster number at the 5 mile you have to put down a monster number at the 2 and a quarter mile as well. Which is the tougher nut to crack right now?



You need to be going between 370 to 400 at the 2 1/4 to go 500... 4wd is the probably the best way to get there. .. So a monster 2 is the 1st "Nut".

bob

[Simspeed]

Sim Speed,
I highly recommend that you get a hold of Bruce Carmichael’s book “personal aircraft drag reduction”.
This will no doubt of fully influence design.
Let’s not forget this is rocket science not rocket art.

Rob Freyvogel
#496
AA/BFS

Hi Rob...others also recommended Carmichael's book but I was unable to find a copy to purchase.  If anyone has a PDF copy to share I'd appreciate it.  Thanks...

[Simspeed]

I think we should discuss whether a flat bottom car is more efficient than getting the car up away from the running surface and minimizing ground effect downforce.
Flat bottom car will make some down force at higher speeds but then again do you need that downforce at higher speeds and what price are you paying for that downforce.
Cfd does not do a good job of modeling this drag as far as I have witnessed so far.
What Woody and I have concluded is that if I were to build another car, it would be further from the ground.
That being said-
Flat bottom cars are way easier to build and maintain.


Rob Freyvogel
#496
AA/BFS

Motorcycle streamliners appear to be good examples of geometry that minimizes ground effect downforce.  Your design of the Carbinite LSR car minics that approach in an innovative way that I've appreciated since I first viewed it Rob.  The active aero you employed to add downforce then transition to minimal drag at high speed is a nice feature of your design.  It would be interesting to combine your approach with mine and split off a pair of the drive wheels to outriggers such as yours so that each of the four drive wheels are running in their own track on the salt.  Without the need to provide mechanical linkage to power the wheels it would appear to be relatively easy to configure that layout and take advantage of the active aero flaps you designed.  I'm wondering what the drag penalty would be for outriggers such as yours. What are your thoughts Rob?

[Simspeed]

You need to be going between 370 to 400 at the 2 1/4 to go 500... 4wd is the probably the best way to get there. .. So a monster 2 is the 1st "Nut".

bob

Thanks for that info Bob.  Getting power to the ground early is apparently more important than one might assume. 

[interested bystander]

Been watchin this topic as it has transpired. Many credible and knowledgeable people have been giving you solid advice.

Finally someone posted IMHOP the most important thing.

Looking at all the + 400 mph  cars and how speed was approached  -obsolete and current generations of dragster type motors and Reher and Morrison pro stock style, WW 1 aircraft engines, high tech, high turbo boosted mills, Gas turbines, etc, shapes from the sublime to the ridiculous, all needed  TRACTION!

 Hope you turn theory into reality. GOOD LUCK                                   

[robfrey]

Summers brothers went 425 mph 50 years years ago. We’re all pikers.
We have made little progress with all our technology.


Rob Freyvogel
#496
AA/BFS

[robfrey]

I mention the Summers brothers and our lack of progress just to indicate that if you use conventional technology and do it everybody else is doing you’re pretty much get what everybody else has.
For some that’s enough, for me and Sim speed it is not.

[jacksoni]

I mention the Summers brothers and our lack of progress just to indicate that if you use conventional technology and do it everybody else is doing you’re pretty much get what everybody else has.
For some that’s enough, for me and Sim speed it is not.

I live by this as well (engine wise anyway). march on guys.

[Simspeed]

Been watchin this topic as it has transpired. Many credible and knowledgeable people have been giving you solid advice.

Finally someone posted IMHOP the most important thing.

Looking at all the + 400 mph  cars and how speed was approached  -obsolete and current generations of dragster type motors and Reher and Morrison pro stock style, WW 1 aircraft engines, high tech, high turbo boosted mills, Gas turbines, etc, shapes from the sublime to the ridiculous, all needed  TRACTION!

 Hope you turn theory into reality. GOOD LUCK                                   

Thanks IB...I hope so too.

[Simspeed]

Summers brothers went 425 mph 50 years years ago. We’re all pikers.
We have made little progress with all our technology.

Rob Freyvogel
#496
AA/BFS

It's amazing isn't it.  50 years and the 500 mph has just been broken.  As IB said traction is the common denominator and we've made virtually zero progress in that area. I don't know what it will take more than anyone else but there has to be new ground broken in how to put power to the salt.  Several people are working on aluminum traction wheels and I for one believe that's the most promising opportunity on the horizon.

[Simspeed]

I mention the Summers brothers and our lack of progress just to indicate that if you use conventional technology and do it everybody else is doing you’re pretty much get what everybody else has.
For some that’s enough, for me and Sim speed it is not.

Looking back at the Summers brother what did they have that gave them the record and put them ahead of the field for so long?  It wasn't HP; we can make more today with one engine than they did with four.  Tires...not really; we're using virtually the same tire technology today.  Aerodynamics...most likely that was their advantage because their body geometry is probably still as good as most everything running today.  They put a package together that optimized the technology they had then and put it to the ground on salt that is most likely much better than what we have today according to many veteran Bonneville racers. 

To get higher speeds increased traction and better aerodynamic body design is the key in my rookie opinion.  I like Rob's use of active aero to increase downforce where traction is most needed, that's something I may well incorporate in my design.  Smaller frontal area with clean geometry will allow higher speeds all else being equal, and that becomes exponentially more important as speeds increase.  I believe my current design offers the best opportunity to reach record speeds because we can put competitive HP in what may be the smallest profile body of any that's come before.  Like everyone else we need traction to reach the full potential of our design and that's going to take innovative ideas and borrowing the best of what's been proven to work.  I'll be pitching ideas and asking those who are interested to help sort out the best design possible.  Thanks for everyone's continued input and guidance...  Terry

[SPARKY]

you just might be dealing with salt to salt traction

[Jack Gifford]

... there has to be new ground broken in how to put power to the salt...

By whose decree "the salt"? If no satisfactory stretch of pavement can be found, lay some asphalt- doesn't need to be durable (as highways are). On flat/level/desolate/cheap land, safely wide (60'?), whatever length (10 mile? 13 mile?). Other 'Unlimited' landspeed competitors will gladly share the costs.