Frontal Area / Cd numbers

[robfrey]

This car is area ruled for Mach 1.5 and is a bit different than sub Mach.



Note, shapes on everything are way different than sub Mach designing.
We would be fighting wave drag much more that aero drag at these speeds.


Rob Freyvogel
#496
AA/BFS

[Stainless1]

As much as we all love the idea of long paved track we all know there is no way it can happen... and 60 feet would be scary at speed.... I think the SCTA uses 80-100... the FIA / FIM track in Bolivia was 130 if I remember that right... and still a sign got clipped. 

Thick salt does have better traction than thin salt... because it doesn't crumble as easily... there is mud under the salt... and when the salt it is as thin as it is now, racing surface is determined more on how the mud dried than how the salt dried. 

[kiwi belly tank]

Those of us who were around back in the good salt days will remember how the salt was always cool to the touch even on the hottest days. This is a big factor to the design & survivability of LSR tires that have minimal rubber thickness in the traction area. With the salt being so thin now the surface temperature is a lot warmer creating higher tire temps but nothing compared to what would happen on a blacktop surface. High speed LSR tires won't survive there.
  Sid. 

[robfrey]

You always have someone that can't stay on course no matter how wide they make it.
With a stable car and better traction, the course could be half the width.
A better question would be what would the run off surface be? Grass?


Rob Freyvogel
#496
AA/BFS

[jacksoni]

Did you say Grass? Maybe these would work -need up the speed rating by a factor of 10 but the engineers can do anything.....   8-)

https://www.msn.com/en-us/autos/news/meet-the-tweel-the-tire-that-never-goes-flat/ar-AABWhoz?ocid=spartandhp


Doh- sorry it's not Friday is it?

[robfrey]

I was thinking about running on a frozen lake. We could build spiked tires. No rubber.
Unlimited ice for intercooler and lower ambient temps to keep overheating issues in check.
Would it still be considered "land racing"? Hmmm?


Rob Freyvogel
#496
AA/BFS

[Peter Jack]

I was thinking about running on a frozen lake. We could build spiked tires. No rubber.
Unlimited ice for intercooler and lower ambient temps to keep overheating issues in check.
Would it still be considered "land racing"? Hmmm?


Rob Freyvogel
#496
AA/BFS

Sucking cold dense air into that engine ought to make more horsepower too!!! 

Pete

[JR529]

I was thinking about running on a frozen lake. We could build spiked tires. No rubber.Unlimited ice for intercooler and lower ambient temps to keep overheating issues in check.

Yeah, but Imagine the poor guy who has to drive the Zamboni back and forth after each run.

[Seldom Seen Slim]

Ah, he reminds me of my fantasy of building a Zamboni to work on the salt.  Wouldn't that be the ticket?  Kinda hard to keep enough supplies (water and salt to dispense) on board for a multi-mile course, though. . .

[kiwi belly tank]

You wouldn't actually need to cut a perfect course on a frozen lake. Just blade a berm around it, pump lake water into it & let it freeze. It could even be refreshed every night. Lets go ice racing, I think Utah Lake freezes!
  Sid.

[SPARKY]

it is amazing how much salt sticks to the tires at speed  when conditions are rightalso how fast it can

[Simspeed]

Sim,
Are you familiar with "area ruling"?
Where you pick up the wings and out riggers, the fuselage needs thinned.
If you take and cut up the car into 4" thick slices cross wise, then measure those cross sections and graph them, the graph should be smooth. This is important. We could have done a better job with this on the Carbiliner.
Flat sides are always bad even if it adds to frontal area.
You will always be more slippery if shape is changed gradually. IE your wheel pants should be shaped like airfoils.
Eric "Blue" was right when he steered us to the NACA 66 series airfoil. It is extremely efficient in terms of volume vs drag.
The wetted area of car that is laminar flow is only 1/3 of the drag of the wetted area not in laminar flow.
Believe it or not, if you would swell the sides of the car and shorten it, the drag should go down even though frontal area is increased.
You should also be able to lose the supports for the wheel pants by increasing cross section of the wing.
Those supports will be extremely draggy.
With the downforce in the rear, you will not need rear suspension. At least that has been my experience.

Rob Freyvogel
#496
AA/BFS

My original body based on the Sears Haack profile was a perfect spherical arch from nose to tail.  The length of the design currently is largely dictated by the power train and component systems.  Your point about the bracing is well taken and gave me an idea how to eliminate them all together as seen in the drawings below.

By moving the wheel motors outboard with the wheels we can eliminate the need for axles between the chassis and the wheels.  The wheel pods and flat wing structure would be a one piece molded carbon composite that saddles across the chassis just like the wing on a sport plane.  Access to the wheels would be through removable covers (not shown) on the outboard side of the pods.  The wheel motors would bolt to the pod from the backside above the wing (black circle) with the wheels bolted conventionally to the motor faces.

The flaps would work the same as before but here they're mounted down on the deck.  I think they would be just as effective for generating downforce in this position.  Cp would be well back of center line and my guess is that Cd would be much lower as well even with the added frontal area.  I have no doubt the structural integrity of the the design would be maintained using this outboard wheel/motor arrangement.

[Simspeed]

More drawings

[Simspeed]

This car is area ruled for Mach 1.5 and is a bit different than sub Mach.



Note, shapes on everything are way different than sub Mach designing.
We would be fighting wave drag much more that aero drag at these speeds.

Rob Freyvogel
#496
AA/BFS

Pretty wild design Rob...

[Jack Gifford]

... I was thinking about running on a frozen lake...

Henry Ford did that on Lake Michigan to set a speed record (93 MPH) with a stripped-down Ford model K (circa 1908?). They spread ashes for traction. There was no concern then for whether it would be labelled "land speed" or not. He was almost sideways a number of times during the run.