Author Topic: Scaled down LSR  (Read 10384 times)

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Offline fredvance

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Re: Scaled down LSR
« Reply #30 on: January 06, 2010, 09:54:34 PM »
Didn't Teagues liner have staggered front wheels??
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Offline bbarn

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Re: Scaled down LSR
« Reply #31 on: January 06, 2010, 10:35:05 PM »
better recheck that number    my  guess would be 6 sq ft                                                willie buchta

Actually a "better", really rough number is 10.7 ft2. I scaled the body right before Christmas to fit the height of the front wheels to prevent damaging the lines with wheel humps. I forgot how much I had to scale to get it them to fit, as a benefit, I picked up sufficient space to squeeze in all the internals and shortened the overall length at the same time. I think I can squeeze a bit more of the length out to further reduce the wetted area, I just need to work out a couple of more details first.

The calc is rough because the fuselage is not round, using the max radius of 18" for the fuselage and the wheel pants of 12X22 I came up the 10.7. Because I didn't add in the radius on top of the wheel pants and the axle fairings, the extra dims in the fuselage probably balance out. Once I get closer to a finalized design, I run off some official numbers and see what they are.

I think this thread is sufficiently hijacked, this should probably be moved to our build thread.
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Offline willieworld

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Re: Scaled down LSR
« Reply #32 on: January 06, 2010, 10:51:26 PM »
i think it will be better than that----sorry if i helped hi-jack the thread----i like your car although i wouldnt run the 2 wheels as outriggers---i run a sidecar bike and there is lots of drag on the sidecar and you are going to have 2 ---if you move the thread to the build diaries you will be better off---good luck with your build ---------------------------------willie buchta
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Offline bbarn

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Re: Scaled down LSR
« Reply #33 on: January 06, 2010, 10:53:47 PM »
Didn't Teagues liner have staggered front wheels??

At the risk of being hoisted on my own petard...I have no idea.

When Rob and I started to talk about building a liner, we went at it from two different approaches. He was more familiar with LSR and the other players than I am. He is taking ideas, concepts and designing based on what has worked and been done by other designers. I came at it from the idea of what are the most aerodynamic shapes and most efficient ways of keeping high laminar flow and turbulence to a minimum. I also started with the idea to build the "ideal" car, i.e. design the CG where I want it, put the CP where it belongs, then fit everything within that envelope, no "band-aide" fixes post build. added - Our main premise was that we would not order a single part or weld anything together until we had completely built the cars in the virtual world and tested them thoroughly as well. This should help cut down the post production fixes that tend to occur and reduce the cost...we hope!

Once we are done with our models, we want to take them to the wind tunnel and/or CFD them against each other to see what we have. Hopefully, we will be able to take the best of both and combine them into an awesome liner!

To the point, I have avoided getting "caught up" in who drives what and which design(s) have been where (in any kind of detail). I have really been looking at it from an aviation/aero standpoint and what works in the GA/low speed (less than Mach .8) designs. I know, ground effect, rolling road.... that all plays a part and there are differences in the surroundings of airplanes and cars, but that's why I think it is important to test several designs.
« Last Edit: January 06, 2010, 11:09:29 PM by bbarn »
I almost never wake up cranky, I usually just let her sleep in.

Offline bbarn

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Re: Scaled down LSR
« Reply #34 on: January 06, 2010, 11:03:42 PM »
i think it will be better than that----sorry if i helped hi-jack the thread----i like your car although i wouldnt run the 2 wheels as outriggers---i run a sidecar bike and there is lots of drag on the sidecar and you are going to have 2 ---if you move the thread to the build diaries you will be better off---good luck with your build ---------------------------------willie buchta

No problem, it is Rob's thread...

I think what is missing in the pictures that I posted are that there are actually two axles in the rear (4wd). The reason for the outriggers is twofold, first, we have a 15.8 ft2 wing in the axle fairing. At 400 mph we should be able to make up to about 9,000# (~12.5k#@500mph) of down-force with it. The second, note that there is no tail fin, granted the wetted area of the two wheel fairings is more than a single vertical stabilizer, but the trade off of half-ing the torque load on a single dif, wider stance (NO PENCIL ROLL - I hope!) and the massive downforce we can make...well it just seemed like a reasonable trade-off.

I really hope that the testing reveals what are good ideas and what isn't. That brings us back to the thread, we need to figure out the best way to test these models/concepts against each other to know we are headed in the right direction. (there, thread no longer hijacked!)
I almost never wake up cranky, I usually just let her sleep in.

Blue

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Re: Scaled down LSR
« Reply #35 on: January 07, 2010, 12:14:55 PM »
Bbarn, why not put the front wheels one behind the other? That would narrow up the frontal area.

Pete
An interesting challenge.  I am working on a two-front-wheels-on-one-steering-frame design for several applications.  Staggering them is a bad idea, since this creates an aerodynamic rudder set at an angle to the direction of travel.

Remember that "frontal area" is only a conceptual reference to separation drag.  When separation is eliminated (as on Bbarn's design) any use of frontal area is inaccurate.  Figure out the laminar percentages and Reynolds numbers of the various components, multiply the resulting section drag coefficients by the wetted area of the components, then add them all together.  Then, and ONLY then, add the stagnation and separation drag from any blunt areas and intersections.  That's called a "drag build up".

Offline panic

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Re: Scaled down LSR
« Reply #36 on: January 10, 2010, 07:21:12 PM »
Idle thought:
Not practical, but would a 1/12th miniature test in a chamber pumped down to 1/12th atmospheric density be closer?

Offline Rex Schimmer

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Re: Scaled down LSR
« Reply #37 on: January 11, 2010, 02:20:44 PM »
Panic,
It would not be a matter of "pumping down" the air pressure to adjust the air density it would be increasing the pressure and also cooling the air both which increase air density which helps the Reynolds numbers calculations.

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Offline bbarn

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Re: Scaled down LSR
« Reply #38 on: January 11, 2010, 02:28:35 PM »
You can also increase the velocity of the air to more than 1/12 scale to compensate for the Reynolds number or use something other than air that is more dense for simulation purposes.
I almost never wake up cranky, I usually just let her sleep in.

Blue

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Re: Scaled down LSR
« Reply #39 on: January 12, 2010, 12:43:42 PM »
See post in the Steering and Suspension forum for a web site describing the focusing link.