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Author Topic: Australian Belly Tank  (Read 1289019 times)
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Rex Schimmer
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« Reply #15 on: December 20, 2005, 05:56:08 PM »

Dodge!!!! THAT IS A NICE LOOKING TANK!!!!!!


REX
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« Reply #16 on: December 20, 2005, 06:37:28 PM »

I love the tail on the blue one and the canopy on the yellow. cool stull and good luck
kr
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Sumner
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« Reply #17 on: December 20, 2005, 07:29:58 PM »

Quote from: Drewfus
Wayne's car was running a 'b' engine, but that died before it even left the test track which was a disappointment.



You say a 'b' motor.  Blown?  Is that a turbo on the side in the picture with a draw thru carb setup?

Thanks for all the pictures they are great  Cheesy .

BTW do any of you guys over there know Carps (Peter Carpenter)?

c ya, Sum
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Drewfus
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« Reply #18 on: December 20, 2005, 07:35:19 PM »

that engine was turbo'ed.

Carps (quote boy).....sure do, its a small world.

Cheers,

Drewfus Cheesy
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Sumner
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« Reply #19 on: December 20, 2005, 07:53:45 PM »

Quote from: Drewfus
that engine was turbo'ed.

Carps (quote boy).....sure do, its a small world.

Cheers,

Drewfus Cheesy


   

In the picture he is dreaming of driving this car  Cheesy .  He has driven my truck on the salt at b'ville (2001).  That was ok, but I did worry when we went to town if he would remember which side of the road he was suppose to be on  rolleyes .

He has been trying to get back for the past couple years, but health and job have kept him away.  He told me yesterday that there is a chance of him making a trip to the states this spring.

I'm envious of the guys from here going over there this spring.  I'll be over sometime in the future to meet as many of you guys as I can.

You probably also know Brootel.  He and Sue stayed at my house on their Honey Moon a couple years ago.

c ya sometime,  Sum
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« Reply #20 on: December 20, 2005, 08:32:29 PM »

Quote from: Sumner
He told me yesterday that there is a chance of him making a trip to the states this spring.


His health has caused him alot of heartach, as it has left him at times allowing him to achieve some of his goals, but he's getting there.

Quote from: Sumner
I'm envious of the guys from here going over there this spring.  I'll be over sometime in the future to meet as many of you guys as I can.


belive it or not we've met, talked to you guys at b'ville this year...I was the one with the forgettable face... Cheesy



Quote from: Sumner
You probably also know Brootel.  He and Sue stayed at my house on their Honey Moon a couple years ago.


Good friends with both Boris and Sue, they recently had a boy, and are moving back to Perth.

A shot from Boris, some Friends, and myself drove down to Melbourne..



Cheers,

Drewfus
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Sumner
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« Reply #21 on: December 20, 2005, 09:16:20 PM »

OK, I didn't put the name and the "forgetable face" together  embarassed .  I remember now talking to you guys.

It is funny, but when I'm there with Hooley vs. before as a spectator I seem to get wrapped up in things, have tunnel vision and miss a lot of things I use to do.  Like spend more time with others.

If you see Boris and Sue tell them hi.  Nice car!!

I'll be seeing you again  Cheesy,

Sum
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Reverend Hedgash
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« Reply #22 on: January 12, 2006, 03:42:11 AM »

Thanks for all the replies we received regarding our latest updates unfortunately lost due to the slacker hacker.

I shall repost some of our images to patch up the gap.

In short we have chopped the tank up and placed the pieces around the car and were very happy with the fit.

We checked our dimensions along the way using CAD an example of which is attached which lead to a very keen observation by Rex Schimmer which I shall answer next post.

Back on the Block.

Reverend H+


* cad side.jpg (26.73 KB, 600x202 - viewed 1280 times.)
« Last Edit: January 29, 2007, 10:44:11 PM by Reverend Hedgash » Logged
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« Reply #23 on: January 12, 2006, 05:18:34 AM »

Rex,

thankyou for your observation regarding our low ride height and potential drag.

I am writing this reply to you and to whoever else is interested or wish to chuck their two cents in.

Apologies for the usage of the high falutin metric system.

For those who missed it Rex pointed to a page in Goro Tamai's "The Leading Edge" discussing the manner by which drag quickly increases below a certain ride height and cited some figures which seem to threaten our design's efficiency.

I must admit that this area has had both the good Doctor Goggles and myself ponderous as to the correct direction to take so I went out and found a copy of the book. Below is a history as to how the bottom is as it is at present.

Our main Aerodynamics text to date has been  "Race Car Aerodynamics" by Joseph Katz, Ph.D which I can recommend for its readability and information.

The difference between the two texts is that Katz's book focuses on methods of maximising downforce due to aero effects whilst minimising drag whereas Tamai's focus is about eliminating downforce altogether.

Tomai's book is written primarily for  solar cars where energy conservation is a priority and traction issues marginal. As the title suggests Katz's focusses on racecars which have different criteria (eg cornering and acceleration issues).

Upon reading Katz and understanding the traction difficulties on salt,  we found ourselves considering all sorts of thoughts of ground effect devices but for a number of reasons were reticent to embrace them.

Firstly we did not wish to destroy the traditional style of the belly tank so we were reticent to go too far with a diffuser etc.

Secondly, we are building against the clock so we wish to keep it simple for its first years out then can tune the shape against a base model.

Finally it is a bit of a black science when you don't possess a wind tunnel and you could do a lot of work that makes the Dodge thing slower.

We were cheered up by the fact that the So-Cal Lakester belly tank wannabe (So-Called belly tank?) turned up sporting a similar method that we considered. Rex mentioned that it hasn't performed well yet but in its defence Bonneville has seemed to be pretty rough of late and not conducive to ground effect technology. Neither is several inches of water  so the jury is out for me on that one.

My understanding of how it works by looking at it is a splitter at the front to stop air creeping under and provide some downforce at the front, then has a difuser at the back to accelerate the air that is underneath so that a low pressure zone is acheived by the Benouli affect pulling it down. It doesn't seem to have skirts so I would imagine that it sucks more in from the side rather than the car down causing drag inducing vortices... correct me if I am wrong. (anyone GM?)

Anyway, for the above reasons we have decided to not have any ground effects for March and have addressed the issue of traction by making it HEAVY. (No replies please Propster).

Our intention was to get the car as low as possible for stability and to acheive the goal of having the axles on the centre line this put the diff in the widest point of the car and meant body panels could sit over each appendage minimising cutouts, oh yeah it looks cool too.

A number of cars at the salt are really low and perform well so we assumed that the drag due to ground proximity was minimal. For example one car we have enjoyed watching develop is John and Paul Brougham's belly tank which has put in multiple 200mph runs over the past couple of years at Gairdner and is very low (see image). Admittedly it is a little TOO low as it bottoms out a bit at the moment but larger Goodyear Eagles are on their way! Both John and Paul have been very helpful in providing us with much info along the way.

The Brougham tank does have a curved base though where we are proposing a flat base. Our favorite tank was the Hooper tank (the flat head killer) (see image) and part of its charm is the low flat base, as is Xydias' original SoCal and we made the decision early to go down this path.

So what height is the best height?

On page 118 of Tomai is a graph outlining the best ground clearance heights for certain shapes to ensure lack of drag due to ground effect.

Rex indicated the row entitled, ?torpedo shape with an oval width / height of 1.25 and length/height of 3.6. has a H/l of  0.3 min. to 0.05 ; that is a minimum ground clearance of 126mm to 210mm for ours (our car being 4.2m metres long.)

Currently we are around 40mm so that looks way under.

But our w/h is 0.88 / 0.81 = 0.92 and l/h is 4.2 / 0.884 =4.75 and extremely tapered. Tomai's calcs are predominantly to be used for a solar car of width of 2metres and 400 to 700mm thick and of fairly uniform shape for the length.

A better zone of the graph therefore to look at is:

?Torpedo with flat bottom with various cambers and width=height? which is worked out as a ratio of height to breadth at a Hmin ratio of 0.15.

For our car that makes 121.5mm (a whole 3.5mm lower!!!!) but at least it confirms that we are at the lower end of the scale.

The fact the whole shape is tapering I assume will lower the impact as well....?

The mention of "Camber" refers to the amount the centreline axis of the shape is above the chord from tip to toe expressed as a percentage. (Bloody ?camber,? couldn?t the nerds have used a term not already in the automotive lexicon???)

The curve of the centerline of our car caused by the extra tank on top and chopped bottom  helps counter the drag caused by proximity to the ground  by increasing the distance traveled over the top of the car and hence similarly accelerating it helping equalize pressure.

The book says the ideal amount is between 3% and 6%. I worked out ours to be 4.7% (yay). Apparently the best shape to have is a slight ?S? shape in this camber. Ours is that slight S shape so that seems helpful.


Drag versus downforce?

It would seem to me though if we are running a car with more horses than we are putting to ground through traction issues on salt then ground effects are the way to go. The racecar book says that the downforce via diffusers et al is a cheap payoff, and we can overcome the extra drag by the extra efficiency of getting power to ground.


If we find that we are only just pulling top gear (or heaven forbid worse!!!) then reducing drag to the utmost becomes paramount and then up she goes!

This will be one of the many possible learning things in March should all go well.

 
Sorry for the lengthy post Rex (trying to get those points) but I wanted to answer your query with a complete reply and to prompt some discussion on this and maybe even assist someone else...

Also I missed the forum!!

Reverend H+
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Rex Schimmer
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« Reply #24 on: January 12, 2006, 01:10:14 PM »

Reverend,
Thanks for the great reply! I certainly understand the pressures of trying to get something ready for the race, it seems that they will start the race if you are there or not! So you bust Acura to make it happen. As far as ground affects go, I did talk to the young aero engineer that claims responsibility for the new So Cal tank and he claims that the ground affects on that car have no effect on the drag. Well, he was claiming to be an "aerodynamicist" and I am just an old engineer that likes to "diddle" in the aero stuff BUT nothing is free! If you generate any kind of aero lift, up or down, then you have a coefficient of lift which means that you have to supply some kind of HP to make it happen. Yes maybe the So Cal car has a small Cl but it does have one and it does take power to overcome and with HP limited cars that can be the difference between just going fast and going fast enough to have the record. The one think about the "sun cars" discussed in the "Leading Edge" is that they are all very restricted on HPs and so they really do alot to make sure that they have everything low drag and very low lift. It makes a big difference as to the aero detail you need to look at if you have a 2000 HP Hemi in the back.

My favorite tank lakester is Seth Hammonds old car, look at the ground clearance, lots of it! and that car holds more records in more classes with more drivers, than just about any car.

Good luck on making the March meet and let us know how you do!!!!!

Rex
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« Reply #25 on: January 12, 2006, 06:17:07 PM »

Yes the Seth Hammond Lakester is a beautiful Car and obviously fast too.

I particularly like the front end, its nostril and flared axle housing. The rear driving position is particularly groovy too. It has a particular Syd Mead look to it.

We actually modified an image of his car as a mock up to explore which direction we wanted to take.

I hope I am not infringing copywrite by showing it here but it was an internal design exercise and consider it homage!

Rev. H+


* jarmanstewart01.jpg (40.22 KB, 900x180 - viewed 1137 times.)
« Last Edit: January 29, 2007, 10:40:21 PM by Reverend Hedgash » Logged
Sumner
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« Reply #26 on: January 13, 2006, 10:10:08 AM »

I look at the height issue from two different angles.  

If you aren't running suspension or very little the put it on the ground and maybe put some skirts on it, like Flatfire, and keep the air from under the car.

If you have a couple inches of suspension travel and putting it on the ground isn't an option then raise it like Tamai talks about in THE LEADING EDGE.  I'm in the second mode, so I have about 6 inches of clearance at the lowest point of what will be my rounded bottom body.  I have 7 to the bottom frame/cage members now.  I had read his book a year or so and made note of the part that says as the body gets close to the ground the drag goes up.

One note though on that thought is on page 128 right before section 3.4 he talks about a Yakel body, which looks somewhat like a lakester to me and he mentioned that type body on a b'ville type car (I couldn't find a picture) that went 248 mph on about 160 hp (I'd like to know which car this was).  Anyway the body had a drag of about 0.17 at a ground clearance of 10.2 cm (4 in).  The drag decreased about 6% when the body was lowered to a ground clearance of 7.6 cm (3 in.).  This seems to contradict what he says elsewhere in the book.

I'm trying to get my body into a shape somewhat similar to the Northern Essex Comm. Coll. car shown on page 15 and the back cover. Of course all cars are going to be compromises somewhere and no matter how hard you try to make an aero body right you are going to have to give up something somewhere just to make the car work.

How about some of you guys that are already running lakesters, have you tried your car at different ride heights?

c ya, Sum
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John Burk
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« Reply #27 on: January 13, 2006, 03:00:00 PM »

Reverend
Thank you for your interesting posts . The trouble with down force , there's little of it when it's needed and when it's strongest and adding drag it's not needed .
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dwarner
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« Reply #28 on: January 14, 2006, 01:10:33 PM »

The Lynn Yakel designed car mentioned is the Larson and Cummins streamliner.

DW
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Sumner
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« Reply #29 on: January 14, 2006, 03:32:16 PM »

Quote from: dwarner
The Lynn Yakel designed car mentioned is the Larson and Cummins streamliner.

DW


Thanks Dan, I think I have pictures somewhere of it.

Sum
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