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Author Topic: Simspeed UWD LSR Design Project  (Read 25473 times)

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Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #285 on: October 24, 2019, 04:28:59 PM »
Here's my concept on an idea for sucker technology for LSR cars posed by Tortoise over on the Pan Skirts thread.  It involves use of a jet boat pump to suck air from under the body bounded by pan skirts for a vacuum seal.  It's designed to work much like the Chaparral sucker car back in the 60's to pull air out from under the skirted area.  The suction created by the pump would help to add downforce on the wheels for better traction.  Your thoughts...  Thanks, Terry.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #286 on: October 24, 2019, 04:29:34 PM »
More images...

Offline tortoise

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Re: Simspeed UWD LSR Design Project
« Reply #287 on: October 24, 2019, 05:32:29 PM »
It's driven off the crankshaft, right? Wouldn't you want something controllable? Enough downforce at low speed/rpm could create too much at high speed.

Offline Dynoroom

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Re: Simspeed UWD LSR Design Project
« Reply #288 on: October 24, 2019, 05:48:51 PM »
Salt is not pavement...
Michael LeFevers
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Offline dw230

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Re: Simspeed UWD LSR Design Project
« Reply #289 on: October 24, 2019, 06:47:28 PM »
Your alum drive wheels currently have 0 traction.

DW
White Goose Bar - Where LSR is a lifestyle
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Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #290 on: October 25, 2019, 05:04:22 AM »
It's driven off the crankshaft, right? Wouldn't you want something controllable? Enough downforce at low speed/rpm could create too much at high speed.
Hi Tortoise,
Yes, like a jet boat the pump is directly driven off the engine crankshaft...or in the case of a rotary engine the eccentric shaft.  If control of the downforce effect proved to be desirable then something as simple as a port or flap could be opened to reduce the vacuum load and lessen or eliminate the surface suction.  When we read about really fast cars where wheel speed at 400 to 500 mph exceeds ground speed by 100 mph or more, then I doubt this system would ever create too much downforce at high speed.  Achieving desirable levels of downforce at low speed would be more difficult given that vacuum efficiency at lower engine rpm would likely be less than optimum.  Thanks... Terry

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #291 on: October 25, 2019, 05:06:45 AM »
Salt is not pavement...
Hi Dynoroom,
Well that's a given I believe we can all agree on.  But do tell how you believe the differences would impact the effectiveness of a sucker system like this for LSR cars?  Thanks... Terry.

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #292 on: October 25, 2019, 05:11:55 AM »
Your alum drive wheels currently have 0 traction.

DW
Hi DW,
We have discussed this issue previously.  The solution I believe lies in SlipNot (tm) sputter coating that bonds molten aluminum spray onto the contact surface of the aluminum wheels.  The random pattern of the applied coating provides a .80 traction coefficient as stated by the mfg.  Whether such a coating for aluminum wheel/tires will work on the salt will have to be tested before development of this vehicle design would be pursued.  Thanks... Terry.

Offline RichFox

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Re: Simspeed UWD LSR Design Project
« Reply #293 on: October 25, 2019, 09:27:59 AM »
Salt is not pavement...
Hi Dynoroom,
Well that's a given I believe we can all agree on.  But do tell how you believe the differences would impact the effectiveness of a sucker system like this for LSR cars?  Thanks... Terry.
I think testing is warranted to find if this would suck the car down or the salt up. I think the salt is going to be the first to go. I liked it better with all the wheels.

Offline Dynoroom

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Re: Simspeed UWD LSR Design Project
« Reply #294 on: October 25, 2019, 09:39:17 AM »
Salt is not pavement...
Hi Dynoroom,
Well that's a given I believe we can all agree on.  But do tell how you believe the differences would impact the effectiveness of a sucker system like this for LSR cars?  Thanks... Terry.

Running by yourself no problem. The process will work in my view.
Running at an event, well, lets just say you better bring some pepper to go with the salt your spraying on everyone & everything.
You might also notice that the wheel wells on streamliners fill up with salt & need to be scraped off before the next run. Might be tricky in you jet pump.
Michael LeFevers
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Without Data You're Just Another Guy With An Opinion!

Racing is just a series of "Problem Solving" events that allow you to spend money & make noise...

Offline kiwi belly tank

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Re: Simspeed UWD LSR Design Project
« Reply #295 on: October 25, 2019, 11:40:07 AM »
Your alum drive wheels currently have 0 traction.

DW
& the big vacuum cleaner will suck salt, I hear course damage. It's not going to create much negative pressure when it's pulling the surface up.
  Sid.

Offline thefrenchowl

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Re: Simspeed UWD LSR Design Project
« Reply #296 on: October 26, 2019, 05:54:19 AM »
Hi Terry,

Looking at your pan without any skirts, the air displacement speed of the sucking device  will have to be higher than the speed of the streamliner to generate any vaccum...

By my quick calculations, a streamliner 10 m long x 1 m wide and sitting 5cm off the ground has 0.5 cubic meter of air underneath.

This streamliner needs to move 10 meters to replace completely that volume of air.
So say it travels at 10 meters per second, 22.37mph, so in 1mn it will displace 18.65 cubic meters of air.
WE can then derive a ratio of air to speed ratio: 0.83.
Speed x ratio tells you how much air you have to displace 1st before generating any vacuum:

600mph * 0.83 = 500 cubic meters per mn

I know just enough about entropy to know air will be also gushing from the sides to replace the air displaced, but don't know if max air speed will be enough to totally replace the air moved and keep ATM under the car.

A vacuum might be created just by the speed of the car and the inability of the surrounding air to refill the space underneath the car above an unknown "balance" speed.

Has anyone fitted pressure or vacuum sensors underneath their streamliner to collect data?

Patrick
« Last Edit: October 26, 2019, 05:58:33 AM by thefrenchowl »
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Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #297 on: October 26, 2019, 08:44:37 AM »
Running by yourself no problem. The process will work in my view.
Running at an event, well, lets just say you better bring some pepper to go with the salt your spraying on everyone & everything.
You might also notice that the wheel wells on streamliners fill up with salt & need to be scraped off before the next run. Might be tricky in you jet pump.
Salt build up in the impeller could be a problem for sure.  For a project of this type I don't think running on anything but ideal track conditions is feasible.  This wouldn't be a club car that runs annually regardless of track conditions.  The high salt flats in Bolivia would likely be the only place to run in anger.  Low speed runs at Bonneville for systems tests would be the most likely scenario in the US.  Thanks... Terry

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #298 on: October 26, 2019, 08:48:30 AM »
Your alum drive wheels currently have 0 traction.

DW
& the big vacuum cleaner will suck salt, I hear course damage. It's not going to create much negative pressure when it's pulling the surface up.
  Sid.
Hi Sid,
Yes if it pulls up the salt in chunks then its no good in this form.  So long as the skirt seal was adequate pulling the salt up wouldn't it of itself negate the creation of negative pressure given that there's always something underneath to pull against if it's solid.  Thanks... Terry

Offline Simspeed

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Re: Simspeed UWD LSR Design Project
« Reply #299 on: October 26, 2019, 09:48:04 AM »
Hi Terry,

Looking at your pan without any skirts, the air displacement speed of the sucking device  will have to be higher than the speed of the streamliner to generate any vaccum...

By my quick calculations, a streamliner 10 m long x 1 m wide and sitting 5cm off the ground has 0.5 cubic meter of air underneath.

This streamliner needs to move 10 meters to replace completely that volume of air.
So say it travels at 10 meters per second, 22.37mph, so in 1mn it will displace 18.65 cubic meters of air.
WE can then derive a ratio of air to speed ratio: 0.83.
Speed x ratio tells you how much air you have to displace 1st before generating any vacuum:

600mph * 0.83 = 500 cubic meters per mn

I know just enough about entropy to know air will be also gushing from the sides to replace the air displaced, but don't know if max air speed will be enough to totally replace the air moved and keep ATM under the car.

A vacuum might be created just by the speed of the car and the inability of the surrounding air to refill the space underneath the car above an unknown "balance" speed.

Patrick
Hi Patrick, thanks for the detailed comments.

JimL over at the Pan Skirts thread commented that he added skirts all around but left the rear open.  Above 175 mph the natural vacuum created under the car sucked the belly pan off the car down to the salt surface.  They had to tie it back up and eventually mount it rigidly to stay in place.  So that lends credence to the idea that speed alone does indeed cause a vacuum to form where pan skirts are set in place.

If that's true then mechanical suction to further evacuate the air space bounded by the skirts should increase negative pressure up to the efficiency level of the skirt sealing.  So the total volume of air being displaced by the pump second by second of car movement should equal whatever volume of air is passed through the skirts beyond the balance speed further enhanced by the amount of total negative pressure mechanically and aerodynamically created.

This design is based on a 30' L x 24" W body shell.  I'm also allowing roughly 1" clearance between the belly pan and salt surface.  The skirted area ends approximately 18' from the nose so all tolled we're looking at a static enclosed area of 3 cu.ft. or .085 cu.m.  That's 5.1 cm/mn which at 12.27 mph is a 0.41 ratio.  So I believe the more relevant number would be...600 * .041 = 246 cm/mn.  But that's assuming no negative pressure is aerodynamically occurring which JimL has shown there is above some balance speed dictated by design factors. 

I tend to believe static negative pressure will exist above a certain speed such that vacuum pump efficiency isn't tied to a volumetric speed ratio, but rather is a volumetric constant depending on the level of aerodynamic negative pressure within the suction zone.  All theory of course that will have to be physically tested with appropriate sensors. 

BTW... the big F-3X-140 Procharger draws 4500 cfm through a 6" inlet producing 60 lbs of boost at 72,000 rpm.  So here we have a 6" discharge port drawing through a roughly 9" opening.  Without gearing the impeller is turning between 8 to 10K but there's no appreciable inline back pressure to constrict cfm flow. This system would probably only work as designed if my assumptions about cfm flow as noted above are true.  Interesting stuff... Thanks, Terry.