Author Topic: Frontal Area / Cd numbers  (Read 75071 times)

0 Members and 1 Guest are viewing this topic.

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #165 on: May 23, 2019, 03:11:28 PM »
I might be mistaken but I don't think the camera idea would ever fly with SCTA/BNI.  Now I realize you aren't going to set an international record at their meets but you might need all the time you can get on the salt to prep for an international record.  George has sure used those meets to his advantage.  I'd at least consider an alternative that would meet SCTA requirements even if it slowed the car at those meets,

Sumner

Well that's a excellent point Sumner.  I figured the SCTA wouldn't allow it but didn't consider the practical need to use their events to get track time for the car and driver. Creating removable top section for the body that allowed use of a conventional canopy for SCTA events would solve that problem.  I'll design a SCTA version of the body and use CFD to compare the two configurations.  Thanks...

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #166 on: May 23, 2019, 03:19:46 PM »
Ah,  new and better technology (good cameras and video) causing trouble again. I am pretty sure SCTA had outlawed periscopes. A TV screen instead of a canopy to see out is likely not far behind. I agree with Sumner. The practice time etc could be invaluable. See all the issues all the fast cars have keeping things together before the big numbers happen (Target 550 and even George seem to wring stuff off pretty regularly)

What happens when the lights go out...….

Agreed jacksoni... As with any critical system, using proven componentry and back up circuitry helps protect against unintended consequences.  It's safe to say the run would be aborted and parachutes deployed to bring the car to a safe stop. Anything can go wrong of course but that true regardless the circumstances or systems used.  Given a proper design I wouldn't be afraid of the technology in this application.  Thanks...

Offline tortoise

  • Sr. Member
  • ****
  • Posts: 685
Re: Frontal Area / Cd numbers
« Reply #167 on: May 23, 2019, 05:50:41 PM »
Facing backwards, wow...that's interesting.
You inspired me to refresh my memory on this. The backwards HPV is the invention of Damjan Zabovnik, and he actually does not use a camera, but a mirror. You can google him.

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #168 on: May 23, 2019, 06:40:03 PM »
Facing backwards, wow...that's interesting.
You inspired me to refresh my memory on this. The backwards HPV is the invention of Damjan Zabovnik, and he actually does not use a camera, but a mirror. You can google him.

I looked him up...that's pretty amazing.  Real innovation!!  Thanks for sharing tortoise.

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #169 on: May 23, 2019, 06:58:42 PM »
Ok, so I did a quick body section to change the top panels and canopy to more conventional geometry to run SCTA events for testing.   The frontal area will remain the same as before but the Cd will obviously change somewhat.  It'll be interesting to see how much difference in Cd there is between the two geometries.  If the difference is inconsequential then no sense going to the time and expense to build both configurations.  Any guesses on the two Cds before we run the numbers?  I've added a rear view to show how the skirts run the full length of the body.  The intent is to apply downforce for traction which I think will be need more than the added drag will penalize.
« Last Edit: May 24, 2019, 05:08:27 AM by Simspeed »

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #170 on: May 23, 2019, 08:37:27 PM »
Here is a scaled size comparison between Simspeed 4.4 and the Challenger 2 and Turbonator II.  All three cars are scaled in inches based on info on respective websites.  The standing man model next to D. Thompson is scaled to 6'2 which looks correct compared to the Challenger II crew members.  All 3 cars are set equally at ground height.  The biggest difference (frontal area) would be most noticeable from and head on view but I couldn't find correct perspective photos of the other cars to make that comparison.  I didn't find any dimension info on the Speed Demon in order to scale that car for comparison so i left it out.

Offline manta22

  • Hero Member
  • *****
  • Posts: 4137
  • What, me worry?
Re: Frontal Area / Cd numbers
« Reply #171 on: May 23, 2019, 10:17:15 PM »
The trick is to get everything within that envelope.

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline dw230

  • Hero Member
  • *****
  • Posts: 3165
Re: Frontal Area / Cd numbers
« Reply #172 on: May 23, 2019, 11:47:26 PM »
This car is beginning to look more and more conventional.

DW
White Goose Bar - Where LSR is a lifestyle
Alcohol - because no good story starts with a salad.

Don't be Karen, be Beth

Offline RaceEngineer

  • Full Member
  • ***
  • Posts: 56
Re: Frontal Area / Cd numbers
« Reply #173 on: May 24, 2019, 01:10:51 AM »
Yes it is,  but the "conventional" vehicles it is being compared with took many years to get "conventional" as well.  Design without experience is dangerous.  There still may be some packaging advantages that will allow some improvement in cd.  As you know the faster you go the more important that becomes with limited traction.  The CFD drag predictions will be interesting. Hopefully reduced surface area (skin drag) and shape will show some improvement.  If the front skirts are effective at creating some down force the drag will be higher than the skirtless design but final weight distribution and rear drive only may make the shirts unnecessary.

Regards, Don


   

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #174 on: May 24, 2019, 04:41:43 AM »
The trick is to get everything within that envelope.

Regards, Neil  Tucson, AZ

Hi Neil...yes that's true.  I believe I've been able to scale all the major systems within the envelop.  The wiring and plumbing I've taken into consideration and space is allocated for that routing.  The power cables running from the generators to the controllers runs between the raised tubing in the chassis floor and the flat floor pan running the length of the chassis. The short run of cables from the controllers to the wheel motors snakes within the tubing entering the motors behind the wheels.  Oil, methanol, glycerin, and dielectic fluid to cool the controllers are contained in the combo tank/intercoolers.  Dry sump components for the IC engines are mounted adjacent to the generators and central oil tank/intercooler.  The fuel system will be fed by a Waterman pump running off the nose of the forward 4 rotor.  The engine control modules will ride in the flat space above the drivers foot well.  There are no radiators or mechanical brakes.  Cooling is via the chilled fuel and oil, and braking is via the chutes and measured reversal of the electromagnetic field driving the wheel motors.  Thanks Neil...

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #175 on: May 24, 2019, 04:53:01 AM »
This car is beginning to look more and more conventional.

DW

Hi DW...The look is a function of the application using feedback I've received from forum members.  This latest version is designed to meet SCTA rules so that testing can be done at their events as Sumner and jacksoni wisely suggested.  We may learn that "conventional" body geometry is sufficient to achieve record speed with the power train as designed so the added costs of the encapsulated driver and video system may not be needed for the first effort should we get that far.  The Cd results should tell us if that's true or not.  Thanks...

Offline Simspeed

  • Sr. Member
  • ****
  • Posts: 317
Re: Frontal Area / Cd numbers
« Reply #176 on: May 24, 2019, 04:59:33 AM »
Yes it is,  but the "conventional" vehicles it is being compared with took many years to get "conventional" as well.  Design without experience is dangerous.  There still may be some packaging advantages that will allow some improvement in cd.  As you know the faster you go the more important that becomes with limited traction.  The CFD drag predictions will be interesting. Hopefully reduced surface area (skin drag) and shape will show some improvement.  If the front skirts are effective at creating some down force the drag will be higher than the skirtless design but final weight distribution and rear drive only may make the shirts unnecessary.

Regards, Don    

Hi Don...valid points, thanks for stating them.  The skirts are just a design exercise for CFD analysis to see if there is any potential benefit to be had.  Cd, Cp, and Cg will all factor into those results.  Thanks again Don for your research on the light refraction issue and aluminum wheel design.  I very much appreciate your input. :cheers:

Offline robfrey

  • Hero Member
  • *****
  • Posts: 1206
    • carbinitelsr
Re: Frontal Area / Cd numbers
« Reply #177 on: May 24, 2019, 09:19:37 AM »
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.
Also, why settle for eight rotors when you can have 12.



Rob Freyvogel
#496
AA/BFS
496 BGS
carbinitelsr.com
carbiniteracing.com
carbinite.com

Offline revolutionary

  • Sr. Member
  • ****
  • Posts: 565
Re: Frontal Area / Cd numbers
« Reply #178 on: May 24, 2019, 01:10:13 PM »
Yes it is,  but the "conventional" vehicles it is being compared with took many years to get "conventional" as well.  Design without experience is dangerous.  There still may be some packaging advantages that will allow some improvement in cd.  As you know the faster you go the more important that becomes with limited traction.  The CFD drag predictions will be interesting. Hopefully reduced surface area (skin drag) and shape will show some improvement.  If the front skirts are effective at creating some down force the drag will be higher than the skirtless design but final weight distribution and rear drive only may make the shirts unnecessary.

Regards, Don    

Hi Don...valid points, thanks for stating them.  The skirts are just a design exercise for CFD analysis to see if there is any potential benefit to be had.  Cd, Cp, and Cg will all factor into those results.  Thanks again Don for your research on the light refraction issue and aluminum wheel design.  I very much appreciate your input. :cheers:

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.
Breaking Wind #9614
  ECTA Record AA/BGALT 214.8
  SCTA Bonneville PB AA/BGALT 237.4
Breaking Wind "Spirit of Effluvium" #451
  SCTA Bonneville Record SC/BF100 48.931

Offline JR529

  • Full Member
  • ***
  • Posts: 191
Re: Frontal Area / Cd numbers
« Reply #179 on: May 24, 2019, 01:52:29 PM »
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?