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Author Topic: Reducing front aero down force:  (Read 4222 times)
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Rex Schimmer
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« on: November 24, 2014, 11:01:44 AM »

This is a quote from John Burk "One recent idea to work out is something to eliminate the ground effect suction under the nose . My thought is a 36" 66-021 plan view perimeter skirt under the middle of the nose with an opening in front to create just enough pressure to offset the low pressure there . The question is what size should the skirt be and how big the opening in front and should it be aluminum or rubber ."

John is building a front wheel drive A class streamliner and has a BBC hanging in front off the front axle so he has lots of body and weight at the front of his liner. He estimates that he may have 90% of the car static weight on the front wheels so additional aero down force is not really needed.  Any good thoughts as to how John could eliminate or reduce his un-needed front aero down force?

Check out John's build site for some pics the car. It is very neat!!

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.motorsportsinnovations.com%2FBvile-pics%2Fbonneville.htm&ei=gixyVMLvGtPksASovYCACg&usg=AFQjCNHaLihrMPnJ

Rex
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« Reply #1 on: November 24, 2014, 04:01:11 PM »

You are really trying to solve an undesirable situation with a fix. That much weight & body forward of the front wheels is probably going to be a handling nightmare. The weight will have a pendulum effect on the front of the car & the body will act as a sail panel & likely exaggerate the situation. A whole lot of rear weight & a huge tail will compensate for some of it but it's really going to want to wag it's tail.
I am a streamliner guy & have helped a lot of people around the world with advice on their builds. A while back one of those people asked my opinion on a similar design & I advised against it but I believe they went ahead with it anyway. My advice is just that, take it or leave it. I have never told anybody how to build their car, I only try to steer them clear of what I think is a mistake.
A bunch of years ago there was a two engined liner done this way with one in the back as well & that was apparently a disaster. Anyone have info on that?
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Elmo Rodge
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« Reply #2 on: November 24, 2014, 04:20:54 PM »

Was that the Rhinoceros? Wayno
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Glen
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« Reply #3 on: November 24, 2014, 04:59:10 PM »

Elmo I think so, don't recall of another with that design.
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Glen
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« Reply #4 on: November 24, 2014, 06:15:06 PM »

Looks like the Danny Boy team is going that route too, so we shall see.


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Michael LeFevers
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« Reply #5 on: November 24, 2014, 07:20:56 PM »

Was that the Rhinoceros? Wayno

http://www.landracing.com/gallery/displayimage.php?album=208&pid=9065#top_display_media

Motion 1, crashed in 1970 [my first trip to the salt] and killed the driver, Noel Black.
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« Reply #6 on: November 24, 2014, 08:54:33 PM »



Do you have any idea if the turbo is going to stay in that location or rotated 90 degrees CCW so the intake is point ahead and the exhaust rearward?

Thanks for the pictures,

Sumner
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John Burk
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« Reply #7 on: November 24, 2014, 11:20:32 PM »

As I see it the best moderate hp (800 honest Bonneville hp) streamliner design is maximum traction under 150 hp , light as practical , minimum drag and the CG behind the AC . The engine in front gives good traction at lower speed and directional stability and tilting the engine minimized the frontal area . I wasn't worried about 90/10 weight distribution because my dragster handled fine with 5/95 and the front pulling is more stable than the back pushing . There is more sq ft of belly behind the front wheels than ahead so I wasn't worried about problems with low pressure but smart people told me otherwise . I added the rear canard wings which will give 300# of down force but that may not be enough and something to cancel low pressure sounds like a good idea . A test with a model and blow gun verified where the CP is . The frontal area is 5 sq ft except for the area around the windshield and the weight is about 2700 with the driver . Calculating speed gained in 25 mph increments convinced me of the value of getting the power down early . 10 mph gained early adds about that much to the 5th mile speed for low drag medium power cars . High drag high hp cars gain from being heavy . Rick Yacoucci going 360 with 700 hp because of 1500# and low drag points to weight not helping streamliners . Another advantage of the engine being in front is picking up ram air pressure at the very front that's there in every gear .
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Rex Schimmer
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« Reply #8 on: November 25, 2014, 10:45:28 AM »

As I remember the cause of Nolan Whites streamliner crash was not because of the weight forward design. Also this car did set the top time of the meet, around 325 as I remember.

One of the basic ideas for John's design is of course the basic keeping center of pressure behind  the center of gravity and the example is of course the dart. Try throwing a dart with the weight on the back. It will not go straight.

Rex

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« Reply #9 on: November 25, 2014, 11:01:17 AM »

Noel Black's crash was caused by a broken axle,Nolan White's crash was all 3 chutes came off the car at 400 mph and when he tried to turn it was in soft salt and flipped.
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« Reply #10 on: November 25, 2014, 12:07:46 PM »

Rex on the subject weight verse aero, something I have given some thought to is to throw an empty water bottle as compared to a full one or a empty water bottle crashed into a ball. It seems to me weight and or mass over comes aero. Doesn't seem correct but that's the way it works with a bottle.
I think a dart has some balance to it.

Just my thought
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« Reply #11 on: November 25, 2014, 12:51:07 PM »

For traction limited cars adding weight reduces aero drag becomes a smaller percentage  . For power limited cars weight just reduces acceleration .
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Rex Schimmer
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« Reply #12 on: November 25, 2014, 02:05:57 PM »

Thanks Glenn!! I got my Blacks and Whites mixed up. I figured you probably knew the reason for Black's car crashing.

Rex
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« Reply #13 on: November 25, 2014, 04:32:39 PM »

As in the 911 Roadster Glen
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« Reply #14 on: December 06, 2014, 01:25:08 PM »

Looks like the Danny Boy team is going that route too, so we shall see.
The Danny Boy liner has a whole lot more car behind the front axle & a lot less mass in front of it. I would expect the weight bias will be pretty good when it's done plus they have room behind the axle for the "other" evil engine too. They also have a history of running huge tail fins since their big crash.
Rationalising the dart theory, as the speed increases the length needs to increase with it. A dart is a short range low speed projectile & an arrow is a long range high speed one. This isn't an opinion, physics denotes why they work best where they do. Reverse the role of these two & see what you get.
The higher the speed is the smaller the correcting input needs to be.
This is also relevant to steering. I've seen many LSR vehicles with handling problems attributed to the steering being too fast & resulting in the driver unknowingly overcompensating. I helped some guys with a door car a few years ago with this issue. They weren't convinced I knew what the hell I was talking about but were so frustrated they were willing to try anything. Redrilling the Pitman arm reduced the ratio & solved the problem.
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