Author Topic: Frontal Area / Cd numbers  (Read 75073 times)

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Offline Jack Gifford

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Re: Frontal Area / Cd numbers
« Reply #225 on: May 28, 2019, 01:45:07 AM »
... the surface temperature is a lot warmer... what would happen on a blacktop surface. High speed LSR tires won't survive...
So now we are truly needing a billionaire- to include plumbing in the asphalt for liquid cooling. :roll:
M/T Pontiac hemi guru
F/BFL 1-mile Loring record 2020

Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #226 on: May 28, 2019, 08:31:32 AM »
Sim,
Your Solidworks skills are impressive!
I’m sending g you a PM.


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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #227 on: May 28, 2019, 08:38:52 AM »
I may have modeled that rocket car but it was designed by Eric (Blue).
It is a really design. I mean all tanks, engines, etc are in place and math is done. I believe it to be the most practical approach to 1000mph.


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Offline Eddieschopshop

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Re: Frontal Area / Cd numbers
« Reply #228 on: May 28, 2019, 01:09:22 PM »
More drawings


If you are going to go the way of carbonite just copy their design more closely.  Your flaps will not work the same in ground plane. Rob will argue with me about this,  but I feel there is drag penalty to the wheel pods being a separate entity even if by ruler there is no more cross section at a given point with the body being so much smaller at that point.   You have drawn big wheel pods without the requisite smaller cross section of body size to offset it in order to maintain frontal surface area.  What you have drawn is the worst of both worlds. 


I said it earlier in the thread.  All streamliners should have good aero,  the minor differences in drag are the least of the issues.  More important is driveability and traction/acceleration.  Now if you are talking about slower cars then its all about drag,  but if your still accelerating decent at the 5 then the numbers say that even a moderate aero reduction is not as significant as non fast guys think.

Offline tortoise

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Re: Frontal Area / Cd numbers
« Reply #229 on: May 28, 2019, 01:36:57 PM »
All streamliners should have good aero,  the minor differences in drag are the least of the issues.  More important is driveability and traction/acceleration. 
You went with 4wd with good result. Did you consider 2wd for better power/weight combined with aero downforce for traction?

Offline Eddieschopshop

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Re: Frontal Area / Cd numbers
« Reply #230 on: May 28, 2019, 01:43:23 PM »
All streamliners should have good aero,  the minor differences in drag are the least of the issues.  More important is driveability and traction/acceleration. 
You went with 4wd with good result. Did you consider 2wd for better power/weight combined with aero downforce for traction?


I did,  every way I ran the numbers the 4wd won out.  This was with the intent of more power than I am currently running though.  I am at the bare minimum hp to have the advantage swing towards 4wd.  Any less power then the added weight/complexity etc wouldn't pay for itself as proven by speed demon, Jack Costellas car etc.  But more power/less perfect salt and I think the 4wd wins.  With speed demon running a bigger motor this year than they have it will be interesting to see their numbers.  I don't see them picking up anything by the 2.25 so it will all be on the back end.  At 400 plus it is less than 8 seconds to go a mile,  it is a lot harder to make gains in less time. 

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #231 on: May 28, 2019, 02:32:42 PM »
More drawings

If you are going to go the way of carbonite just copy their design more closely.  Your flaps will not work the same in ground plane. Rob will argue with me about this,  but I feel there is drag penalty to the wheel pods being a separate entity even if by ruler there is no more cross section at a given point with the body being so much smaller at that point.   You have drawn big wheel pods without the requisite smaller cross section of body size to offset it in order to maintain frontal surface area.  What you have drawn is the worst of both worlds.  

I said it earlier in the thread.  All streamliners should have good aero,  the minor differences in drag are the least of the issues.  More important is driveability and traction/acceleration.  Now if you are talking about slower cars then its all about drag,  but if your still accelerating decent at the 5 then the numbers say that even a moderate aero reduction is not as significant as non fast guys think.

Hi Eddie... Yes I agree there will be a definite aero drag penalty with the wheel pods.  I'm considering using them anyway for several reasons, added traction as I've stated being one, but more importantly my power train design allows very narrow body geometry which is inherently difficult to stabilize with inboard wheels.  Center to center track width for the drive wheels is only 9".  As Rob Freyvogel and others noted pencil rolling a car such as my inboard wheel design has deadly consequences.  The outboard wheel pods should help greatly to minimize the danger.  

The flaps are not designed to work the same as one might expect on an airplane wing.  Here the point is to add downforce to the wing to place added weight onto the  inboard and outboard drive wheels; the weight load being transferred through the surrounding structure. As Rob's design has shown added drag due to the raised flaps directly translates into added weight on the rear section of the chassis which is reduced at higher speeds as the flaps are lowered.  I'm not concerned about airflow below the flap across the bottom of the wing as there will be an edge seal to prevent much of the air from going under the wing and body sections.  Downward pressure on the wing itself is another component of the design where the leading edge is tapered down for air to deflect over the top creating downward pressure at speed with what is yet an unknown drag penalty.  We'll see how much when I submit the final model for CFD analysis.  Thanks for your input...
« Last Edit: May 28, 2019, 02:37:42 PM by Simspeed »

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #232 on: May 28, 2019, 02:44:49 PM »
I'd really like to learn more about the cars and LSR history/experience of forum members.  If you have personal LSR information and pictures somewhere on the internet please share links where we can find and study your cars and hopefully learn from your experiences.  Thanks... Terry

Offline Eddieschopshop

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Re: Frontal Area / Cd numbers
« Reply #233 on: May 28, 2019, 03:30:19 PM »
More tires does not equal more traction.  Its all about the percentage of vehicle weight that is on the drive tires regardless if its 2 or 4 tires.  If you have a 5 wheel vehicle and one coaster is carrying 30% of the vehicle weight the 70% being used for traction will not care how many tires it is sitting on.  I could even argue that with the compound used on land speed tires, having too much of a contact patch could reduce traction.... 

The new Zealand teams new car has had a 4 front wheel drive system proposed in the past with either one or two coasters in the rear.  Their tires seemed to be in tandem which creates other problems as well having a drive tire running in the rut 2 feet behind another drive tire..  It will be interesting to see if this is the design they come out with.  I can't see the point, but there are a lot of people smarter than me.  I know I am not done learning and will be the first to admit I am not a real doctor I just play one on tv. 

Long story short,  I spent a lot of years thinking through various designs and trying to get "fancy".  In the end I went with what maybe a more traditional approach but on limited budget and talent it seemed to be the best approach for me.  I am happy with the result so far, with more potential still I think.  I think I am on par with the best for dollar per mph. 

The lack of large incremental increases in speeds was mentioned earlier in the thread.  I look at it this way.  The physics hasn't changed so why would we be able to continue to make leaps and bounds in speed?  The low hanging fruit is all gone,  its going to be harder to make small increments as time goes on.  Does that make the Summers brothers geniuses? or us stupid?  No,  While technology has opened a lot of doors as a small racer, I now have to be an expert in several more fields including EFI computers etc.  Through technology I have gone faster with less resources than most but I have made a significant investment in my own education to make me a better "racer" and my opinions and theories are constantly evolving.   

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #234 on: May 28, 2019, 04:46:20 PM »
More tires does not equal more traction.  Its all about the percentage of vehicle weight that is on the drive tires regardless if its 2 or 4 tires.  If you have a 5 wheel vehicle and one coaster is carrying 30% of the vehicle weight the 70% being used for traction will not care how many tires it is sitting on.  I could even argue that with the compound used on land speed tires, having too much of a contact patch could reduce traction.... 

The new Zealand teams new car has had a 4 front wheel drive system proposed in the past with either one or two coasters in the rear.  Their tires seemed to be in tandem which creates other problems as well having a drive tire running in the rut 2 feet behind another drive tire..  It will be interesting to see if this is the design they come out with.  I can't see the point, but there are a lot of people smarter than me.  I know I am not done learning and will be the first to admit I am not a real doctor I just play one on tv. 

Great post Eddie...although I agree with your outlook on life and experiences I'm not sure I agree or even fully understand your comments on traction.  Traction is a function of contact patch and distributed weight in my estimation.  The greater the contact patch (one tire vs. multiple tires) the greater traction potential there is for a given amount of weight distributed evenly across all drive tires.  Power should be looked at as a constant force that turns the wheel(s) to the limit of available traction without exceeding the friction coefficient where slippage is incurred.  Application of power beyond that point is detrimental to reaching maximum speed.

Certainly there is a weight/contact patch limit where maximum traction is limited given fixed parameters of total weight, power, and available traction coefficient.  My view is that spreading the weight across multiple drive tires of equal contact patch increases traction potential for a given weight.  What has the better chance of greater traction and higher speed given equal surface conditions (traction coefficient)...one drive wheel/tire carrying 70% of total weight, or 4 tires of equal contact patch carrying 25% of the 70% each?  2 wheel drive vs 4 wheel drive...why is 4 wheel drive better given that using your theory weight per tire is decreased proportionally thereby reducing traction per tire? 

I'd like to learn more about you track experiences Eddie...and links you can share? Thanks for commenting... Terry.

Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #235 on: May 28, 2019, 05:03:45 PM »
Yes,
Good comments Eddie!

Btw, does anybody know how much distance the Summers Bros used to run the 425mph speed?
I bought the book but skimming through it, I did not see that info.
Have not read it cover to cover yet.


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Offline Eddieschopshop

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Re: Frontal Area / Cd numbers
« Reply #236 on: May 28, 2019, 05:43:00 PM »
4wd is better in the sense that no matter what all your weight is available to be used for acceleration/traction. Any weight resting on a coasting wheel is pure penalty without any benefit.  Weight bias is key for stability so a rear wheel drive car is always fighting this relationship of stability vs traction.  A front wheel drive car will always be fighting its own weight transfer under hard acceleration.    People don't talk about weight transfer much but it is still a factor. 

Until this sport gets developed to the nth degree we will continue seeing a wide range of designs (which keeps it fun).


I don't have any facts readily explainable to back up my thoughts on multiple tires vs less given the same weight on said tires.  Call it racers intuition.  Again maybe I am wrong.  Maybe its as simple as the nature of the surface, Bville racers have long said a narrow tire is better than a wide one.  There is something to be said for a tire being planted and biting vs floating on the marbles. 


If you are on facebook, you can look me up at Ed Umland or Eddie's chop shop.  I don't really post too much technical specifics but am happy to answer most questions.  I don't have a long storied history, just a low buck racer doing what I can.  I have run several classes being what I consider successful in all of them.  Since getting into LSR my goal was always to go as fast as I could on my own budget and talent so I ran a little in other classes to gain experience before building my streamliner.  I left a lot of potential on the table in the other classes though since I didn't spend Years chasing either of them.   

Rob brings up another good point about Summers distance used.  This years speedweek saw the highest speeds ever and in less distance.  Again physics,  this would definitely qualify as big jump in accomplishment if you ask me. 

Offline superleggera

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Re: Frontal Area / Cd numbers
« Reply #237 on: May 28, 2019, 06:43:26 PM »
Given the proposed hybrid-of-sorts propulsion system discussed in this thread, maybe one should look at what the big electric streamliners are doing for traction (and traction control), driveline motors (or wheel hubs), speeds obtained, vehicle weight and aerodynamics for some historical reference. 

Also excuse the off-topic subject query:  With rotary engines spinning axial permanent magnet generators -- are the rotary engines to be throttle actuated or set at a fixed RPM for maximum output?  Will the electric wheel hubs be driven by the driver actuated throttle input and pulling "juice" as needed via a software (traction) control system -- or controlled by how?  No black box (power management system) necessary between said both to make it work?
- me: Mark - home: Dry Heat, AZ USA - build: motorcycle streamliner

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #238 on: May 28, 2019, 08:49:11 PM »
4wd is better in the sense that no matter what all your weight is available to be used for acceleration/traction. Any weight resting on a coasting wheel is pure penalty without any benefit.  Weight bias is key for stability so a rear wheel drive car is always fighting this relationship of stability vs traction.  A front wheel drive car will always be fighting its own weight transfer under hard acceleration.    People don't talk about weight transfer much but it is still a factor. 

Until this sport gets developed to the nth degree we will continue seeing a wide range of designs (which keeps it fun).


I don't have any facts readily explainable to back up my thoughts on multiple tires vs less given the same weight on said tires.  Call it racers intuition.  Again maybe I am wrong.  Maybe its as simple as the nature of the surface, Bville racers have long said a narrow tire is better than a wide one.  There is something to be said for a tire being planted and biting vs floating on the marbles. 


If you are on facebook, you can look me up at Ed Umland or Eddie's chop shop.  I don't really post too much technical specifics but am happy to answer most questions.  I don't have a long storied history, just a low buck racer doing what I can.  I have run several classes being what I consider successful in all of them.  Since getting into LSR my goal was always to go as fast as I could on my own budget and talent so I ran a little in other classes to gain experience before building my streamliner.  I left a lot of potential on the table in the other classes though since I didn't spend Years chasing either of them.   

Rob brings up another good point about Summers distance used.  This years speedweek saw the highest speeds ever and in less distance.  Again physics,  this would definitely qualify as big jump in accomplishment if you ask me. 

Thanks for the links Eddie...great stuff.  Look forward to following you adventures.  :cheers:

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #239 on: May 28, 2019, 09:02:28 PM »
Given the proposed hybrid-of-sorts propulsion system discussed in this thread, maybe one should look at what the big electric streamliners are doing for traction (and traction control), driveline motors (or wheel hubs), speeds obtained, vehicle weight and aerodynamics for some historical reference. 

Also excuse the off-topic subject query:  With rotary engines spinning axial permanent magnet generators -- are the rotary engines to be throttle actuated or set at a fixed RPM for maximum output?  Will the electric wheel hubs be driven by the driver actuated throttle input and pulling "juice" as needed via a software (traction) control system -- or controlled by how?  No black box (power management system) necessary between said both to make it work?

Hi SuperL...Traction control for this design should be easy to achieve.  As I envision it, wheel speed sensors will allow the motor controllers to see which wheels are spinning relative to each other and automatically adjust power to each wheel as needed to maximize acceleration given available traction.  We won't use a foot throttle because that too susceptible to driver nervousness.  A hand throttle lever (like a boat) will allow the driver to feed in IC power to the generators at a fixed rate which will in turn supply high voltage current to the motor controllers.  The controllers will direct current to the wheel motors based on programming fed by real time wheel sensor data.  The controllers will attempt to maximize motor acceleration to whatever limit electrical current is being received from the generators.  If for example the driver had the IC engines at full throttle wheel speed would ramp up progressively based on available traction to each wheel.  There would be no need to try and throttle the IC engines up and down during a run as controller programming will compensate for wheel spin effectively acting as the acceleration throttle.  Wouldn't want the IC engines to run at max output constantly, the driver's job is to push the IC throttle forward in tune with forward thrust and increase in speed.  The driver would most likely use a bump and run approach to advancing IC power letting the car build speed progressively as traction allows.  Pulling the hand throttle back would automatically kill power and slow the car when needed for whatever reason.  The whole scenario could be programmed to maximize acceleration but that's something that will need to be evaluated with testing.  Thanks...Terry