Author Topic: Frontal Area / Cd numbers  (Read 13840 times)

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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #300 on: July 01, 2019, 07:51:17 AM »
How will the wing affect your bailout procedure? In an emergency I'm sure there would be no hesitation to step onto the wing but how will you do during tech?

Keep going, I'm enjoying the evolution.

Pete

Hey Pete...I think the wing structure will be strong enough to handle driver ingress and egress given the need to engineer it for high aero loading.  Thanks... Terry.

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #301 on: July 01, 2019, 07:59:43 AM »
Pete,

Valid question.  The final position of the wind (within the wheelbase) needs to be adjusted based on detailed aero work.  When I said "it is in the right place I meant generally (ie: behind the rear wheels won't work).  Final position may likely be more forward to balance downforce on front vs. rear wheels (for stability).  Which is the linear ratio of position. The weight of the driver is a low load relative to the aero loads so the wing could be built robust enough to have a "step plate" area.  Thanks for highlighting this detail.  Lots of design considerations to balance. 

Don

Yes, I agree Don.  For V.4.8 I've placed the wing as close to the traction wheels as practical for maximum effect.  For V.5.0 I'm splitting the drive wheels fore and aft in a conventional 4 wheel drive configuration so the wing/fins would likely be more centrally placed for equal weight distribution.  I'm designing V.5.0 as an experiment based on input I received from Tom Burkland.  Hopefully we'll get a good discussion going on that design and how it compares to V.4.8.  Thanks... Terry.

Offline RaceEngineer

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Re: Frontal Area / Cd numbers
« Reply #302 on: July 01, 2019, 10:34:13 AM »
Terry,

I have never had the privilege of meeting or talking with Tom Burkland only know him by reputation (and advice he has given others on the forum).  IMHO, your talking to an excellent resource. 
So the V.5.0 will have drive wheels inline? (still 3?)   Hopefully this will allow narrower cross section (smoother taper) at the rear.
My guess on wing placement would be 20% to 30% of w.b. ahead of the effective center line of the rear (drive) wheels, but the analysis will fine tune that. I would think, it not be 50/50 balanced, but biased to the drive wheels for "traction" with enough downforce on the front wheels for stability.  A multi element wing, in the horizontal section, should increase the downforce and may be of net benefit (drag racers claim 6000 lbs downforce at ~300 mph with multi-element wings, but CFD should help refine).  The body and the "vertical" wing section should act as spill plates making the inverted wing(s) more effective.  The initial wing placement looks to be coincident with a reduced body cross section this is good and may be important if speeds above .80 mach are achieved (in deference to the area rule).
Looking forward to V.5.0.   
Regards,  Don

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #303 on: July 06, 2019, 03:05:27 PM »
Attached are screenshots of the new V.5.0 design.  This is a conventional 4x4 wheel drive layout with a sprung front suspension and solid mounted rear axle.  The steering geometry pivots at the center of the wheel contact patch as suggested by Tom B.  The body geometry began as a tear drop but ended up as shown in order to fit the drive system in place.  Your thoughts are appreciated. Thanks... Terry

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #304 on: July 06, 2019, 03:09:35 PM »
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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #305 on: July 06, 2019, 03:10:02 PM »
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Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #306 on: July 06, 2019, 03:12:47 PM »
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Offline Jack Gifford

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Re: Frontal Area / Cd numbers
« Reply #307 on: July 06, 2019, 11:29:57 PM »
Motorcycle streamliner? It appears that you'd need to counter-steer to maintain balance, as with a motorcycle.

I'm not criticizing- just my knee-jerk reaction to the pictures.
« Last Edit: July 06, 2019, 11:32:35 PM by Jack Gifford »
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline Eddieschopshop

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Re: Frontal Area / Cd numbers
« Reply #308 on: July 07, 2019, 01:39:27 PM »
I see a few problems with this design.  Structurally take a look at your lower tube of the rear half of the chassis where it turns up and intersects the cage portion of the chassis.  This will flex that cage tube and create a major flex point in the chassis.  Just run that tube straight along the bottom of the car.  People like to get too fancy with the bends most of the time just creating problems.

Stability wise I see some potential problems.  Not knowing where the cg is for sure,  it appears to be far behind the center of pressure.  This thing will be twitchy.  It may or may not straighten itself out.  For this type of shape to work the cg has to be really far forward.  Even then a tail fin will probably still be required.  I had a similar plan with my car and while the aero would self straighten it had to get a certain amount of yaw before creating enough drag to straighten.   This shape will have a similar problem. 

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #309 on: July 14, 2019, 09:18:34 PM »
New Wing
« Last Edit: July 14, 2019, 09:22:50 PM by Simspeed »

Offline Rex Schimmer

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Re: Frontal Area / Cd numbers
« Reply #310 on: July 15, 2019, 12:20:10 PM »
If this car, as illustrated, even gets the slightest amount side ways it will redefine the expression "pencil roll"!

Nice CAD work though.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline Peter Jack

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Re: Frontal Area / Cd numbers
« Reply #311 on: July 15, 2019, 01:06:05 PM »
It appears to me that with the flat side design of the car the power units could be moved to the inside of the wheels instead of the outside. While your steering would be limited, this is normal for most streamliners and the lateral stability would be much improved.

Pete

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #312 on: July 15, 2019, 10:49:41 PM »
If this car, as illustrated, even gets the slightest amount side ways it will redefine the expression "pencil roll"!

Nice CAD work though.

Rex

Quote
It appears to me that with the flat side design of the car the power units could be moved to the inside of the wheels instead of the outside. While your steering would be limited, this is normal for most streamliners and the lateral stability would be much improved.

Pete

Thanks for your comments Rex and Pete.  I didn't think I could fit the wheels in the body work if I ran the power units on the inside, but I've checked and it appears I can make everything fit for the front wheels and still keep 12 degrees lock to lock steering.  The rears have to stay as mounted because the body tapers so much toward the back.  I'll redraw for that configuration.  Thanks... Terry

Offline Bratfink

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Re: Frontal Area / Cd numbers
« Reply #313 on: July 21, 2019, 04:15:07 AM »
From an aero drag perspective you don?t want a rounded rear section. You want a sharp trailing edge to separate the flow cleanly.

Offline Simspeed

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Re: Frontal Area / Cd numbers
« Reply #314 on: July 22, 2019, 11:48:54 PM »
Hi Everyone... I'm moving this topic to a new thread in the Build Diaries forum here http://www.landracing.com/forum/index.php?topic=17792.0.  I won't be updating this thread any more so come see the latest update V.5.2 in the Simspeed UWD design project diary and help critique the project toward an optimum design.  Thanks for contributing...