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Author Topic: Simspeed UWD LSR Design Project  (Read 25474 times)

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Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #120 on: August 05, 2019, 09:56:14 PM »
I've worked up a skid stabilizer of sorts to help keep the car upright at slow speed.  The design is based on a double acting hydraulic cylinder where the ski shoes can pivot side to side at extension but sucks up to fit flush against a steel pocket welded to the chassis when retracted.  The height of the shoe bottom can be set wherever the builder chooses but is a fixed height once housing is welded in place.  The welded housing is 4" dia with likely 3.5" dia. extension tube.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #121 on: August 05, 2019, 09:56:48 PM »
Chassis view...

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #122 on: August 05, 2019, 10:04:27 PM »
I think this topic has come up before in your project. I mention it only because your initial premise for the car was the minimal frontal area and lowest possible Cd. Great goals. Most of the fast cars, not just the 'liners, have power in excess of traction and, within the rules struggle to improve aero in any meaningful way. Therefore ballast. Indeed accelerating the added mass is a problem and as you point out, the balance of power vs traction and at higher speeds the aero becomes the major factor. For cars like yours, there are no paved surfaces available, only salt or dirt and traction on those surfaces is variable foot by foot down the track so any attempt at calculating traction coefficients  really tough. Your traction control will go a long way to make things work but I think there is no way to really see what you need until you have an actual car and see what happens. Sure build it strong and it is going to "weigh  a ton" from the start. Maybe you don't need anything added but you have  the possibility of adding active aero  or ballast as needed and see what gives the best result.
I think you are absolutely correct Jacksoni...see what we've got once the build is complete and test to find where the sweet spot is for all factors.  Programming for power output and traction control with an active aero element won't be one and done.  A lot will go into optimizing this combination.  Thanks... Terry.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #123 on: August 05, 2019, 10:06:52 PM »
I fall in the 'no lift or downforce' aero camp (active aero is another story and too sophisticated for my skills) but I am only mid build so can't prove anything.

The airbrake discussion made me think of the SLR's when the disc brakes of Dunlop were giving the Jags a shorter stopping distance on the Mulsanne ....

Thanks Lemming...I'd never seen that photo.  Makes great sense to use it as they did right?  I'm wondering how structurally sound that cover was and did it last long under load.  Thanks... Terry.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #124 on: August 05, 2019, 10:09:39 PM »
I tried something like that once with my first road car but it was my hood that accidentally popped up. It did slow me down but caused a serious vision problem.

BTW, Sim, your car appears to be flat bottom with low ground clearance. That should provide a measurable amount of suction (downforce) with little if any drag.

John

Hi John,
I drew up a tunnel floor with bottom exhaust for my initial design but abandoned that due to the need for added room on the floor to run the power cables.  Like you say the flat bottom will likely offer a good balance  of room and downforce.  Thanks... Terry.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #125 on: August 05, 2019, 10:23:10 PM »
I like the exhaust.  I have never been able to really "prove" the results,  it would take a wind tunnel at full speed and the ability to put full load on the motor to really get accurate results.  On paper it makes sense.

Hi Eddie,
Glad you like my use of your design.  I think its a great idea pushing hot air down the side of the body to lessen skin layer friction.  From what I've been able to see in you photos you executed it nicely.  I wish I could apply it to both sides of this car but one side would have the exhaust dumping ahead of the intake and that wouldn't work.  Turning the two powerplants on end allowed use of your design and freed up room to place the motor controllers beside the IC/Gens by offsetting the engines a few centimeters toward the exhaust side of the chassis. 

I'm really happy with this current design as it gets the FA back to less than 4 sq.ft. as I first intended without crushing the driver into the cage which the first design did.  The more we work on this project the better the results with the input I've been getting from everyone.  We may not be there yet but I think it's getting really close.  I'm really interested in learning that FA and Cd other liners have for for comparison.  Any help from you guy would be appreciated.  Thanks... Terry

BTW...Good luck to everyone whose running Speed Week this year!!

Offline Eddieschopshop

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Re: Simspeed UWD LSR Design Project
« Reply #126 on: August 06, 2019, 10:20:53 AM »
My frontal area is  6-7' even things as little as this can be debated where and how it gets measured.  I have to guess what my cd is as I have never had any cfd or wind tunnel testing done.  I am probably the lowest budget car to ever hit 400.  My personal opinion is that people sweat the drag stuff a little too much.  Of course do the best job you can, but I can tell you from personal experience,  that when you talk about being the fastest wheel driven car, accelerating the weight is a much bigger penalty.  The people who say that ballast isn't as big of penalty as drag are wrong.  It maybe  true for a car that hits terminal velocity before going through the lights though.   

One thing I do is compile a lot of real world data on acceleration.  A 500 lb weight loss would make a bigger difference than a 30 percent drag reduction.  Think about that.  I dont think I could lose 30 percent in drag no matter how much money I spent.

Offline tortoise

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Re: Simspeed UWD LSR Design Project
« Reply #127 on: August 06, 2019, 12:56:17 PM »
A 500 lb weight loss would make a bigger difference than a 30 percent drag reduction.   
What are your speeds in gears and how soon can you use full throttle?

Offline kiwi belly tank

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Re: Simspeed UWD LSR Design Project
« Reply #128 on: August 06, 2019, 02:04:02 PM »
We played the wing & ballast game on the road to 400+ & ended up without the wing & changed the ballast to find the sweet-ish spot. We were 2WD.
  Sid.

Offline Eddieschopshop

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Re: Simspeed UWD LSR Design Project
« Reply #129 on: August 06, 2019, 02:08:07 PM »
My gearing is not ideal as my trans is put together from swap meet lencos.  That being said when I buy a new set of gears to get where I really want to be it will change those numbers.  I hold some of that info close.  I have only made three full passes in this car  352 385 403.  I have been creeping up on the power levels.  I will tell you that based on my possible hp I can give the car full throttle in fourth gear,  This should put nearly 50 mph on my best quarter mile speed to date.  I have been being conservative and whatever my top boost was for the run, I have been running 5 psi less in fourth.  This being said if things go well this years goal is to make a full power pass so I can say for sure what this engine package is capable of and then go on to a bigger engine. 

When developing this car a lot of decisions were made based on the engine I currently have and what I would run next.  The weight penalty of the 4 whd barely pays for itself at the power level I have run to date.  However my personal belief is that as I ramp in the power it will be the right choice.  On my car I have decided that any type of active aero doesn't gain me any appreciable speed.  As any additional downforce would only be desirable under 200 mph, above that it is extra drag with no benefit to my accel numbers

Offline Eddieschopshop

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Re: Simspeed UWD LSR Design Project
« Reply #130 on: August 06, 2019, 02:12:00 PM »
We played the wing & ballast game on the road to 400+ & ended up without the wing & changed the ballast to find the sweet-ish spot. We were 2WD.
  Sid.

Do you feel the weight helped in traction or just got the center of gravity in a different spot which made the car drive different allowing more throttle?  I know it is a weird distinction but an important one that I don't think most people really try to understand. 

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #131 on: August 06, 2019, 05:57:46 PM »
My frontal area is  6-7' even things as little as this can be debated where and how it gets measured.  I have to guess what my cd is as I have never had any cfd or wind tunnel testing done.  I am probably the lowest budget car to ever hit 400.  My personal opinion is that people sweat the drag stuff a little too much.  Of course do the best job you can, but I can tell you from personal experience,  that when you talk about being the fastest wheel driven car, accelerating the weight is a much bigger penalty.  The people who say that ballast isn't as big of penalty as drag are wrong.  It maybe  true for a car that hits terminal velocity before going through the lights though.   

One thing I do is compile a lot of real world data on acceleration.  A 500 lb weight loss would make a bigger difference than a 30 percent drag reduction.  Think about that.  I dont think I could lose 30 percent in drag no matter how much money I spent.

Thanks for sharing that Eddie.  I'm measuring FA as a cross section of the exposed body and appendages from nose to tail.  I haven't included the wheels as I expect the nose skirt will largely cover those.  Its pretty easy to do with the drawings as I can make multiple section cuts and then blend those to show the overall outline of exposed FA.  The program calculates the area within the outline in whatever increments I choose.

Comparing your average 6.5' to this car at a rounded 4' shows a 38.5% reduction in FA and an identical number in body drag force shown by the HP-Lakester weight needed spreadsheet I found here on the forum.  That's using the same 0.09 Cd number and 4000 total weight just for comparison purposed.  I'm using 0.09 Cd for analysis because that's the published number for the Buckeye Bullet III car arrived at through wind tunnel and CFD analysis.  Your body geometry and theirs appears to be very similar with yours probably slightly better because its somewhat shorter.  I think the Simspeed car is probably better still because it just looks slicker...if looks alone is any way of judging such a thing.  I certainly don't think it's worse.

The horsepower calculated for a given speed in this spreadsheet is bogus in my opinion as it shows you'd only need 410 hp to go 400 mph, and 1071 hp for 600 mph.  Where mine are 316 hp (23% less) and 755 (29.5% less) respectively.  I doubt anyone would agree with those numbers.

The hp calculator I found at https://www.rbracing-rsr.com/aerohpcalc.html shows 688 hp @ 400 mph for you and 577 hp (16% less) for me; with 2,494 hp @ 600 mph for you and 2117 hp (15% less) for me.  Given that aero drag is said to increase as the cube of speed, the 38.5% difference in FA between your car and my design would indicate a much greater difference in hp needed for these speeds all else being equal. 

JL222 commented he calculated the Summer bros needed 2400 hp to go 425 mph based on available input data using a program that he owned.  Unfortunately, he hasn't responded back what was needed for the Simspeed design based on the input data I posted for him. For $79 I guess I should just buy that program to see for myself.  Thanks for contributing Eddie...great help!
« Last Edit: August 06, 2019, 09:51:37 PM by Simspeed »

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #132 on: August 06, 2019, 06:03:07 PM »
On my car I have decided that any type of active aero doesn't gain me any appreciable speed.  As any additional downforce would only be desirable under 200 mph, above that it is extra drag with no benefit to my accel numbers
That's the reason I decided to go with the flush plate active aero (AA) rather than the wing because the flush plate has no drag penalty once retracted.  The wing FA sticks out there even at zero angle of attack.  Thanks... Terry

Offline kiwi belly tank

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Re: Simspeed UWD LSR Design Project
« Reply #133 on: August 06, 2019, 07:06:47 PM »
We played the wing & ballast game on the road to 400+ & ended up without the wing & changed the ballast to find the sweet-ish spot. We were 2WD.
  Sid.

Do you feel the weight helped in traction or just got the center of gravity in a different spot which made the car drive different allowing more throttle?  I know it is a weird distinction but an important one that I don't think most people really try to understand.
You are correct Eddie, it is an important point. We added equal amounts of weight to both ends to not change the characteristics of the car. The only thing the wing seemed to change was the top end speed. Adding weight picked up the bottom end speed where you spend more time & that related to a better top end. The wing just took top end away.
  Sid. 

Offline jl222

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Re: Simspeed UWD LSR Design Project
« Reply #134 on: August 06, 2019, 10:52:18 PM »
 Simspeed .. My bville pro is not responding to streamliner data? Says inputs out of parameters?

 I have a Bville book with all the info on Summers Bros. Goldenrod but have been to busy with the 222 Camaro to look for it, From what I remember weight and hp were about the same as yours and I don't
remember the CD or frontal area but I know it was pretty good.

 i need to buy another program too as it's not transferable to my newer laptop.

    JL222
« Last Edit: August 06, 2019, 10:56:43 PM by jl222 »