Frontal Area / Cd numbers

[John Burk]

The streamliner design I personally like is front wheel drive with a high front weight bias and reasonably low weight . The traction of a ballasted streamliner with the acceleration of a light one and the safety of directional stability .

[Simspeed]

Interesting concept John.  Are there many front wheel drive only liners?

[Simspeed]

Weight is an issue for certain cars.  Speed demon 2.0 went on a big diet from the first version.  Weight is a factor on any car that is still accelerating at the 5. If your speed flattens out before that than aero is the biggest problem.  If you are still accelerating at the 5 (read fast streamliner) than weight is a big factor in how hard you are accelerating to that point.

Has the team benefited substantially from the weigh reduction? Seems like they're trapped in the 450/460 mph range at best.  What do you think is the aero limit for their current combination?

[Eddieschopshop]

Yes speed demon is benefiting from the diet.  Ask Steve Watt.  I don't have the numbers to back it up, but I am certain of the facts.  More Weight will never make a streamliner accelerate harder, (weight bias may)  it may make it easier to drive and less prone to spin the tires though.  Pour throttle control makes the car spin tires easy which slows down the car,  it isn't too light.  This is based on zero aero lift which should be the case for a liner,  now a roadster would be a different discussion.  Variable aero drag can work and does work for higher hp cars.  I fall into a gray area with moderate hp.  Being lightweight and four wheel drive is my choice at the moment although their is some mutual exclusivity here...  Being low on hp I don't want any extra aero drag.  I have ran the numbers forward and backwards on this,  including my own real world experience.  Now blown nitro hemi power levels are not in my experience..

[Eddieschopshop]

Weight is a factor on any car that is still accelerating at the 5. If your speed flattens out before that than aero is the biggest problem.  If you are still accelerating at the 5 (read fast streamliner) than weight is a big factor in how hard you are accelerating to that point.

If you have the power to get to big speeds, then you probably have enough power at lower speeds so that the limiting factor in acceleration is wheelspin, not power to weight. You need aero downforce for that.  Variable aero downforce, ideally.

So far none of the "fastest" cars have varying downforce.  Now that may change in the future, but Danny, Vesco, speed demon.... only built in aero, some and none for a few... I tried to build in a certain amount of downforce into the body shape that I could do without sacrificing any additional drag and relied on the 4x4,  again fastest 1/4 speeds are 4x cars.  Flashpoint was hitting some numbers last year though.

[Eddieschopshop]

The streamliner design I personally like is front wheel drive with a high front weight bias and reasonably low weight . The traction of a ballasted streamliner with the acceleration of a light one and the safety of directional stability .

This was my original plan,  I think it is still good up to a certain power and speed level.  But people don't factor enough for weight transfer though.  Once you start talking 400 plus it really is a long drag race.  All the math changes when you talk about acceleration vs terminal aero drag etc..

[Simspeed]

My design has no built in aero drag.  I'm shooting for the smallest frontal area and lowest Cd number for the overall shape.  I have considered a front lip for down force to keep the nose planted with skid pods on either side but that's just an idea for discussion.

[Simspeed]

Weird what I have to do to add attachments. Post without attachments and then modify the post to add the attachments otherwise I get error message.  Oh well...here is my basic design with no aero drag built in and the front lip to add downforce.

[Simspeed]

Here are more views of the chassis, running gear and odds & ends.  To refresh...this concept uses dual 4 rotor Mazda based engines to turn 4 electric generator.  The electric power is fed to 4 wheel motors to power the car.  Generators and motors I've resourced for this configuration can generate and drive the wheels with kW equal to 2100 hp.  The two turbo 4 rotors can produce close to 2800 hp for this application.  Even considering the energy loss of this power coupling system the car should be competitive all else being equal. At least that's my theory...

BTW...the engines are turned nose to nose for packaging of the 2 turbos and 1 shared intake for both engines with separate throttle bodies.  That way output can be programmed to use one or both engines together as needed depending on available traction to the 4 wheels.

[jacksoni]

Prefacing this question with "I know nothing" but: Generally speaking generators to convert 2100hp into KW's and then electric motors to take those KW's and make them into motive force (motors for the wheels) usually are rather sizeable. I'd be interested in some information about those parts which I am sure you have figured out.

[Simspeed]

Here's the steering system I've concocted for the extremely narrow front end.  The orange steering frame is hinged at the front and supported in a framed slot at the rear where the steering column attaches with a double pinon lever arrangement.  Total movement through the inline wheel steering is 6 degrees lock to lock.  The front electric motors bolt directly to the steering frame and the wheels bolt to the motor rotors through a hub/axle arrangement. Power for each wheel is independent of the rest but the motor controller will coordinate all motors simultaneously with wheel slippage metered for each wheel for controlled application of power.

[Simspeed]

Prefacing this question with "I know nothing" but: Generally speaking generators to convert 2100hp into KW's and then electric motors to take those KW's and make them into motive force (motors for the wheels) usually are rather sizeable. I'd be interested in some information about those parts which I am sure you have figured out.

Hi Jacksoni...there are several manufactures of suitable axial flux coreless motors and generators to my knowledge.  The motors shown in my drawings are scaled to dimension for Yasa PD400 series motors which can be wired to generate peak 200 kW max each for high rpm use.  Each wheel in this design uses 2 of those motors stacked together with a common axle/hub through the coreless middle.  Similarly, motors of that type can be use as generators with the same output based on whatever power supply is chosen to turn them.  In this case the design uses 4 rotor Mazdas because of the small cross section to power potential.

[tortoise]

I keep looking at Simspeed 3 and 4, and the long bit of structure on the front, which appears to do nothing but support the bodywork comprising this Sears Haack profile. This nosepiece appears to be a bit concave on the sides.  Tell me why this long, tall, concave-sided nose doesn't massively move the center of pressure forward.

[manta22]

I would also worry about the effect of side winds.

Regards, Neil Tucson, AZ

[Simspeed]

I've attached a profile view of the body with all the geometric lines that make up the arcs and curves of the body shape.  This helps to visualize the "flow" of the aerodynamic shape.  At the undercut of the "bow" we go from an sharp point and leading edge to the widest point at the middle of the length. the body eventually narrows and tapers to another point and sharp lower edge at the back. You can see the transition point from the spherical upper body to the tapered slab sides of the lower body along the sweeping arch from front to back.  Realize that Simspeed 1 shows the relative sides of the car to a 6' 2" man standing along side.