Author Topic: Frontal Area / Cd numbers  (Read 75068 times)

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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #90 on: April 30, 2019, 02:32:46 PM »
Gary Eaker (owns the Aerodyne and A2 wind tunnels in NC) ran a firebird  to 298 mph in 1989 with N2O blowing onto intercoolers for the turbos. Though running on gasoline, because of all the N2O floating around I think he was put in a Fuel class. So yes can and has been done. CO2 could also be used. There are some street setups that do this.

Thanks jacksoni...I knew I'd read something about that many years ago.  I like the idea for this application so I'll study up on the pros and cons and see if its something that can be used here.

Offline Dynoroom

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Re: Frontal Area / Cd numbers
« Reply #91 on: April 30, 2019, 02:55:20 PM »
Gary Eaker (owns the Aerodyne and A2 wind tunnels in NC) ran a firebird  to 298 mph in 1989 with N2O blowing onto intercoolers for the turbos. Though running on gasoline, because of all the N2O floating around I think he was put in a Fuel class. So yes can and has been done. CO2 could also be used. There are some street setups that do this.

The above is true. the missing link was the used four 20 lb. bottles a pass...
Michael LeFevers
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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #92 on: April 30, 2019, 03:17:09 PM »
I agree that the point of this exercise is being the fastest of the fast. Lets stop talking about recognized classes.

Being involved with a couple of cars using a front wheel set up similar to yours we discovered, actually Richie knew, you need Ackerman effect.

DW

Hi DW...as I understand it the ackerman effect deals with steering wheels that turn in two different radii.  Where the front wheel and tandem mounted rear wheel such as the Speed Demon and others, use two different axle hubs that pivot or turn on separate king pins, then the two steer wheels in those designs would indeed turn in two different radii likely requiring the Ackerman effect to be taken into consideration in the design.  

The design I've applied here uses a non-suspended walking beam type arrangement where both wheels are fixed positioned along the beam and turn as one from a single forward king pin.  Therefore both wheels follow a single turning radius based on whatever angle the beam itself takes from the rearward mounted steering mechanism.  I've used a dual lever steering mechanism because it was easy to fit and didn't take up much room.  The angular movement steering speed can be sped up or slowed down based on the intersecting angles of the two levers at their crossing point.  It would be better from a control standpoint to mount a horizontal steering damper at the real  of the beam to smooth the input to the driver.   Thanks...

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #93 on: April 30, 2019, 03:23:46 PM »
Gary Eaker (owns the Aerodyne and A2 wind tunnels in NC) ran a firebird  to 298 mph in 1989 with N2O blowing onto intercoolers for the turbos. Though running on gasoline, because of all the N2O floating around I think he was put in a Fuel class. So yes can and has been done. CO2 could also be used. There are some street setups that do this.

The above is true. the missing link was the used four 20 lb. bottles a pass...

Well that's not good is it.  Use of an expansion valve setup as with conventional A/C systems might help to reduce the need for so much liquid.  You don't get the full benefit and capacity of a nitros system unless you heat the bottle to raise the internal pressure.  I wonder how that would apply here?  I need to study the effects.  Thanks Dynoroom...

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #94 on: April 30, 2019, 03:47:51 PM »
At this stage, this appears to be a fantasy CAD exercise with an interesting powertrain.  No provision for necessary ancilliaries or a realistic or competent structure.  It is doubtful that any kind of a one-off powertrain control system has been worked out.  With a razor’s edge nose, no suspension, scary steering linkage, and 9.5” track it would probably fall over in the first 200 yards, if that far.

LOL...Well IO every wild idea starts out as a fantasy and evolves if it has merit, or peters out if if doesn't.  I think I've made provision so far for engine coolant, fuel, motor/gen coolant, IC oiling, driver padding, front and real wheel housings and containment, driver visibility, steering, turbos, intake, and exhaust.  What other ancillary systems besides electronics, fuel delivery, and parachutes do you believe are needed IO?  Please describe what there is about the structure (I assume you are referring to the tube chassis) that's unrealistic or incomplete?

No, I have not worked out the power train control system beyond the understanding that similar systems are in use today in the automotive world.  Ever heard of parallel hybrid drives IO?  I'm not knowledgeable or skilled in those systems but I don't have to be a know-it-all of all things that will ultimately be part of this design if it ever comes to light.  There are people with different skill sets that if an when appropriate will have to be sourced to make this project fly...I'd dare to say that's true of 90% of all the LSR cars running today.  Do you know of any major one man efforts in the LSR community IO?

You are likely correct that this design would be vertically challenged.  I have considered that condition and explored a couple of different approaches to keep the thing from falling over.  It amazes me that there are so many motorcycle streamliner LSR records on the books.  How in the world do they keep those things upright on just two wheels with zero track width beyond the width of each tire?

Ok, I've beat on you enought IO...stability as you've described is a major challenge that needs to be address.  I'd appreciate reading any recommendations you care to make.   Thanks...

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #95 on: April 30, 2019, 08:59:21 PM »
I've toyed with the idea of running a front splitter as shown in the attachment below for two purposes.  First to provide downforce at the nose of the car to offset any lift that may develop from frontal pressure along the lower concave face of the nose.  Second, as a prop to prevent rolling the car onto its side as I and others have given concern for because of the narrow wheel track and solid suspension.  The rounded skid pads on the bottom of the splitter ride above the ground at rest but may contact and skid along the surface if the body rolls in either direction.  Is a splitter legal under sanctioning rules?  Do you see and problems in its use?  Thanks...

Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #96 on: April 30, 2019, 09:35:08 PM »
Thanks for the compliment!
The question that too few ask.
How much further back does the cp have to be from the cg?
One of my hobbies is large model rockets. The basic rule of thumb is 1-2 calipers (body diameters).
Some say that is fine for rockets but this is cars. I contend that is one and the same. The road holding power that the tires have with the salt is just about next to nothing compared to the aero loads.
If you can get 1.0 calipers back, the car will be stable and cross winds will have negligible effect on weather vaneing.

Remember the textbook equation for calculating aero drag.
Stagnation drag + Separation drag + Wetted area drag = Total Aero Drag
Cross section or displacement is not part of drag equation.
Optimum finess ratio (length to diameter) for subsonic design is a little over 3:1. We ended up at over 9:1 because of the tire choices available. It’s a long story. Lol. Anyhow, our car looks faster as we designed it but it would be much better shorter and fatter.
I’m excited for you! This is the fun part!
I look forward to following this build!
Feel free to reach out to to answer any questions. Tom Burkland did this for me. He called me up and said that he didn’t want to see me make the same mistakes he made. His input was invaluable and I saved and printed all our correspondence.  I can’t say enough about Tom.

Rob Freyvogel
#496
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Thanks for you input and encouragement Rob.  Like others who have offered their advice and assistance I value and appreciate your and their openness and kindness.

the widest diameter cross section of this body is roughly 22".  So having the Cp location between 22" and 44" back of the theoretical Cg is considered ideal for a real world design?  I'm guesstimating its at 20" now so that's good to hear.

I understood that cross section (frontal area) did factor into aero drag along with the others you mentioned. Body displacement or volume, along with length factor into Cd based on what I've read on the subject and the formulas I found on fxSolver.  

In the car world they use frontal area x Cd. In the aircraft world drag is measured in flat plate equipment. I think we are actually in the aircraft world and are flying aircraft at zero elevation but we do need to factor in ground effect.
Btw, these are Tom Bs words, not mine and I have to agree with him.
IE frontal area on the Carbiliner is deceptive.  I can’t remember what the number is but it was pretty big. The fuselage is actually fairly small even at its thickest point but frontal area is based total shadow cast from front or back. The cross section of the car near the thickest part of the wing and wheel pants are a bit less than the thickest part of the fuselage. These two areas of the car are very different shapes but pass though the same section of air at different times.
It is not “Area Ruled” perfectly but it is not horrible either. We could have done better and I am trying to keep track of the changes for Mark II.

I like the idea of using nitrous as an intercooler. Just inject it right after the turbos. I would not spray it on an intercooler.
I would start off on Methanol as many guys don’t run any cooling system at all and get away with it when running meth. You just need to run it very rich and you will need a killer ignition system to light that wet mixture.

I have thought many times of getting rid of the heavy intercooler and running about 600 hp of nitrous right after the turbos (300 for each).
I would probably not use it until 4th and 5th gear.


Rob Freyvogel
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Offline SPARKY

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Re: Frontal Area / Cd numbers
« Reply #97 on: May 01, 2019, 11:34:42 AM »
its not a walking beam unless it "walks" from pivot pin between the wheels.  To gain the stability of tandem front wheels to be able to resist a "step out" it can't pivot on either end.. As Gary Allen found out on Higginbotham's first attempt.
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #98 on: May 01, 2019, 11:38:59 AM »
The Carbiliner has absolutely no Ackerman built into it. I did this on purpose.
When you are heading down the track and you have to steer, it is because your back wheels are sliding left or right. You’re not actually making a turn you are keeping the car going straight and you want the two front wheels to stay lined up right down the middle of the course and only countersteer not steer.
I’m very pleased at how our car steers even with aluminum front wheels with very little tread machine into them.


Rob Freyvogel
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Offline dw230

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Re: Frontal Area / Cd numbers
« Reply #99 on: May 01, 2019, 01:14:07 PM »
Rob,

How does the steering feel when turning off course to the return road?

DW
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Offline robfrey

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Re: Frontal Area / Cd numbers
« Reply #100 on: May 01, 2019, 01:23:25 PM »
Rob,

How does the steering feel when turning off course to the return road?

DW
Perfectly, you can watch the in car camera on YouTube.
There is nothing precise about driving on salt. Also, we do not run a spool which helps a lot.


Rob Freyvogel
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carbinitelsr.com
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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #101 on: May 01, 2019, 01:28:17 PM »

In the car world they use frontal area x Cd. In the aircraft world drag is measured in flat plate equipment. I think we are actually in the aircraft world and are flying aircraft at zero elevation but we do need to factor in ground effect.
Btw, these are Tom Bs words, not mine and I have to agree with him.
IE frontal area on the Carbiliner is deceptive.  I can’t remember what the number is but it was pretty big. The fuselage is actually fairly small even at its thickest point but frontal area is based total shadow cast from front or back. The cross section of the car near the thickest part of the wing and wheel pants are a bit less than the thickest part of the fuselage. These two areas of the car are very different shapes but pass though the same section of air at different times.
It is not “Area Ruled” perfectly but it is not horrible either. We could have done better and I am trying to keep track of the changes for Mark II.

I like the idea of using nitrous as an intercooler. Just inject it right after the turbos. I would not spray it on an intercooler.
I would start off on Methanol as many guys don’t run any cooling system at all and get away with it when running meth. You just need to run it very rich and you will need a killer ignition system to light that wet mixture.

I have thought many times of getting rid of the heavy intercooler and running about 600 hp of nitrous right after the turbos (300 for each).
I would probably not use it until 4th and 5th gear.

Rob Freyvogel
#496
AA/BFS

All I know about aerodynamics is what I learn from reading and the experiences of others such as yourself Rob.  Based on my reading the objective for my LSR project is to reduce frontal area to the least possible number using the best Cd geometry I can come up with.  My wheel options are limited, and also limit the body geometry because I have to fit the elec. motors inside the wheel envelop, so thin cross section and profile aluminum wheels are all I see so far that will work.  I started with M/T 16" profiles which fit the car shape but didn't leave room to plumb the motor coolant.  The wheel profiles as currently drawn fit the car and give plenty of room for the elec. motors.  Vertical stability is another challenge.

I remember back when I was a kid on the farm we'd shoot a quick burst of butane gas from the tractor tank to chill our soda bottles for lunch (propane didn't come along until later).  Had to be really careful because the ice cold gas would freeze the Dr. Pepper and explode the glass bottles in a heartbeat.  We need something similar to cool the intake charge between the turbos and the engine intake.  

I spent the better part of yesterday researching the subject and I've come up with a plan to design just such a system using non-flammable refrigerant gas.  No compressor, no condenser, no dryer, just high pressure liquid refrigerant, digital thermostatic expansion valve(s) and expansion tank(s) where the compressed air passes between the turbo and engine and an accumulator tank.  

I'm looking to combine the methanol fuel tank with turbo-air routing in my currently design with finned refrigerant lines into an air-fuel-refrigerant intercooler to chill fuel, air, and extract heat through the refrigerant gas simultaneously.  The methanol would chill first from direct liquid contact with the refrigerant lines, then extract heat from intake tubing before being burned in the engine. The refrigerant lines would also be in welded contact with the intake charge lines to suck heat through thermal conduction.  The system would be programmed through the engine management controller to trigger refrigerant flow through the system based on thermal metering of the air intake and discharge ports at the intercooler tank.  

Hot refrigerant gas would exit the intercooler and fill an accumulator tank during the run.  Between runs the high pressure liquid refrigerant tank and the accumulator tanks would be recharged and/or drained ready for the next run.  The system wouldn't be super light but it would definitely be lighter, more effective, and dependable than carrying several hundred pounds of iced water on every run.  My design has limited room...I have to combine systems where possible to make everything fit.

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #102 on: May 01, 2019, 01:40:05 PM »
its not a walking beam unless it "walks" from pivot pin between the wheels.  To gain the stability of tandem front wheels to be able to resist a "step out" it can't pivot on either end.. As Gary Allen found out on Higginbotham's first attempt.

True enough Sparky...the beam doesn't walk in the conventional suspension sense but it does walk from side to side through an arc from the kingpin back to a slot in the chassis where the beam rests between and slides along two high density plastic pads directed by the steering levers.  I could use a rack and pinion instead of pivoting levers to control the steering motion but that may not be necessary given the simplicity and low cost of this method.  With reaction dampers I think this will track straight and work well.
« Last Edit: May 01, 2019, 06:37:41 PM by Simspeed »

Offline SPARKY

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Re: Frontal Area / Cd numbers
« Reply #103 on: May 02, 2019, 12:54:14 AM »
What is the mechanical advantage of your steering set up?
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #104 on: May 02, 2019, 02:06:05 AM »
What is the mechanical advantage of your steering set up?

For this design its a matter of getting everything to fit the body envelop Sparky.  The steering design evolved entirely from that aspect.  So narrow and so little room to work with as far as fit and resulting turning radius were concerned I just worked with the room given and this mechanical design is all I could come up with that would be structurally sound and doable.  Luckly, I think its a practical design and because it trails the kingpin it should be pretty stable with good lateral dampers.