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Author Topic: Australian Belly Tank  (Read 1854467 times)

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Offline Dr Goggles

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Re: Australian Belly Tank
« Reply #4125 on: December 13, 2013, 01:40:09 PM »
Ah,that was great, seems I collect. They're both right,well one's right and the other is left,if you follow. Shame is now I don't have an excuse to go back to the tyre place.....
Few understand what I'm trying to do but they vastly outnumber those who understand why...................

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Offline Dr Goggles

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Re: Australian Belly Tank
« Reply #4126 on: December 15, 2013, 06:25:17 PM »
Got the front axle on again. New height is 12mm lower than the old, estimated difference in ride height is 1mm lower.

Now I have to notch the radius rods so I can hide the tie rods behind the axle.
Few understand what I'm trying to do but they vastly outnumber those who understand why...................

http://thespiritofsunshine.blogspot.com/

Current Australian E/GL record holder at 215.041mph

THE LUCKIEST MAN IN SLOW BUSINESS.

Offline Reverend Hedgash

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Tailfin and streamliner update
« Reply #4127 on: December 18, 2013, 06:40:35 AM »
Good work Sunshine team, any photos of the new work?

I have finally finished a very hectic semester and can start to think about the car design again even for a moment.

Today I want to talk Tailfins and please everybody throw in their three pence worth or correct any glaring or minor errors.

The purpose of a tailfin is to keep the centre of pressure behind the centre of gravity so that it keeps the car in a straight line, just like a dart. Throw a dart backwards and it will turn around and end up forwards. Probably the best example of a late addition of a tailfin was on Donald Campbell's Bluebird after it crashed at Bonneville and ready for its run in Australia. (I am currently reading Gina Campbell's biography which highlights just how strange a family they were, and she suggests she thinks he crashed due to driver error and not undue instability.)

As readers will be aware we design under the mantra of Fast Safe Beautiful and so I am looking for a design of the tailfin that will be all three and for various reasons I have been attracted to angled tailfins such as in the Alfa Bat and the Joint Strike Force Fighter (see images below) as cool looking twin tailfins.

They fit the bill of interesting to look at (beautiful though?) but more importantly I wonder if they are appropriate for LSR. My reckoning is this: If they are on an angle of anything other than vertical they run the risk of causing lift which is an absolute no-no. If the car's nose were to lift and the tailfin were angled like the fighter then it would be an angled plane wanting to lift up it would seem. It sort of depends what angle the air is travelling at as there is a car body in the way and it gets more complicated in that if it is trying to lift the rear end up maybe it is doing so by trying to turn the nose back down and so maybe a help in this situation...?

Does anyone have any thoughts/experience on this? I am thinking of modelling this to see what the computer says as its answer so will be interesting to see.

I am also wondering if it is advantageous to have two tailfins or better to have a single central one. One seems economic but there will possibly be helpful properties on the rear diffuser with two in helping to draw out hte air in a controlled manner and then connecting it with the air on the side.

Dik


« Last Edit: December 18, 2013, 06:53:18 AM by Reverend Hedgash »

Offline tauruck

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Re: Australian Belly Tank
« Reply #4128 on: December 18, 2013, 07:16:04 AM »
Naca0006 profile is the best for the application.

It's symmetrical which is what you need. :wink:

Offline Ron Gibson

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Re: Australian Belly Tank
« Reply #4129 on: December 18, 2013, 09:22:35 AM »
Sum
I know about the tire directional mounting, my Dunlops are that way. I was asking about right and left "wheels". :-)

Ron
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Offline Milwaukee Midget

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Re: Australian Belly Tank
« Reply #4130 on: December 18, 2013, 10:52:09 AM »
Well, hmmm . . .  MG Anecdotes?

The MG EX 181 ran a tail fin in 1957, but Sterling Moss complained of cross winds.

When they came back in 1959, the fin was gone, and Phil Hill ran faster, but there were other improvements to the car.

Unofficially, Hill was on the team in 1957, and drove the car faster than Moss, but they wanted Moss for the press value.
"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  :roll:

We are NOT rebuilding . . . We are reloading.

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Offline Stainless1

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Re: Australian Belly Tank
« Reply #4131 on: December 19, 2013, 12:01:29 AM »
That airplane has 2 tails so the computer can steer their rudders independently to make it turn faster.  You do not want to turn faster...

single symmetrical and straight
Stainless
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Offline gidge348

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Tail Fin
« Reply #4132 on: December 19, 2013, 06:14:45 PM »
I think a single tail fin the same height as the canopy and angling off at the rear kind of like the ones on F1 air boxes but extended would suit the car.

One thing to bear in mind is that if it is "too tall" and you have a cross wind, this will have a "toppling over" effect by shifting weight from one side of the car to the other.

I feel 2 fins would just add drag and look "tacked on" any way that's my threepence worth...

You may want to make it a bolt/dzus on item in case you want to take it off?

Ian...
« Last Edit: December 19, 2013, 06:18:22 PM by gidge348 »

Offline Reverend Hedgash

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Re: Australian Belly Tank
« Reply #4133 on: December 20, 2013, 05:12:59 AM »
I should clarify that I am talking about the streamliner body for those that missed it...

Good thoughts about the tail, keep them coming and I'll have some images for discussion shortly.

Dik

Offline Jon

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Re: Australian Belly Tank
« Reply #4134 on: December 20, 2013, 11:43:57 AM »
Bit of a conundrum the tail.
One will let you attach it to main frame so that any energy it develops goes to the frame rather than the body.
One will also force you to redo your chute system.

If you add tail/s I'd be tempted to add two running back from the rear wheel bulges for a few reasons.
Main one is to help stop the rear of the car wanting to create lift if it gets crossed up.
Second is so you don't have to redo the chutes.
Third is I think you'll get more correction by adding surface area to the relatively slab sides than a single tail sitting on a sheltered section of the car.

Just my opinion
jon
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Offline Dr Goggles

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Re: Australian Belly Tank
« Reply #4135 on: December 21, 2013, 03:29:50 PM »
Sum
I know about the tire directional mounting, my Dunlops are that way. I was asking about right and left "wheels". :-)

Ron

Ron,it was about offering an enticing bet.....heads I win,tails you lose......
Few understand what I'm trying to do but they vastly outnumber those who understand why...................

http://thespiritofsunshine.blogspot.com/

Current Australian E/GL record holder at 215.041mph

THE LUCKIEST MAN IN SLOW BUSINESS.

Offline SaltPeter

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Re: Australian Belly Tank
« Reply #4136 on: December 21, 2013, 04:17:20 PM »
Doc and Rev

Thinking out loud here... :?

Given Sunshine is Aero rather than Power dependent to get the speeds it does, and therefore Drag will have a proportionally greater effect.

Does the new body style actually need a Tail for Stability, at the speed you're working towards? or will it add more Drag?

Does adding weight assist stability or just Traction or is more power needed to get gains here?

I don't know the answers but they are the questions that come to mind, as my Bike is also Aero rather than power dependent for max speed.

Pete  :cheers:
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Offline Reverend Hedgash

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Re: Australian Belly Tank
« Reply #4137 on: December 22, 2013, 03:46:53 AM »
Doc and Rev

Thinking out loud here... :?

Given Sunshine is Aero rather than Power dependent to get the speeds it does, and therefore Drag will have a proportionally greater effect.

Does the new body style actually need a Tail for Stability, at the speed you're working towards? or will it add more Drag?

Does adding weight assist stability or just Traction or is more power needed to get gains here?

I don't know the answers but they are the questions that come to mind, as my Bike is also Aero rather than power dependent for max speed.

Pete  :cheers:

Some good questions here, thanks Pete.

The tail is primarily for safety and not for speed although remaining stable for longer will mean being able to go faster. If there is some penalty for it and I presume there is then the payoff of safety should be worth it. Is it worthwhile for the speed that we wish to go? Well the streamliner records are typically faster than the bellytank ones so we will be targeting faster speeds (I don't want to intentionally design something that cannot achieve the record speed safely).

Adding more weight does affect traction positively but it also affects the centre of gravity. Again like a dart having the weiht up the front is best for stability but given we are rear whell drive the weight would be better at the back for improving traction so it is not a simple solution. Putting more weight over the rear wheels will increases the requirement for a tail behind the rear wheels.

Dik

Offline Reverend Hedgash

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Re: Australian Belly Tank
« Reply #4138 on: December 22, 2013, 03:55:57 AM »
Bit of a conundrum the tail.
One will let you attach it to main frame so that any energy it develops goes to the frame rather than the body.
One will also force you to redo your chute system.

If you add tail/s I'd be tempted to add two running back from the rear wheel bulges for a few reasons.
Main one is to help stop the rear of the car wanting to create lift if it gets crossed up.
Second is so you don't have to redo the chutes.
Third is I think you'll get more correction by adding surface area to the relatively slab sides than a single tail sitting on a sheltered section of the car.

Just my opinion
jon

Thanks Jon, I hadn't though about the chute... I shall consider accordingly.
Your thoughts about structure make sense too as there would be a lot of force on it when sideways and it needs to remain on to work and turn the car not just the body if it is to do its job.

I am still intrigued by the double fin behind the wheels as you say. If it is built out of carbon fibre we should be able to cater for the load. Having played with the carbon fibre A piller of the Aston Martin Vantage I am left in no doubt about the strength of the stuff, it will be about transmitting the force appropriately to the chassis which will be a line of force exercise.

Dik
« Last Edit: December 22, 2013, 04:02:41 AM by Reverend Hedgash »

Offline Sumner

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Re: Australian Belly Tank
« Reply #4139 on: December 22, 2013, 08:33:48 AM »
....I am still intrigued by the double fin behind the wheels as you say....

The only advantage I'd see with two vertical stabilizers would be if there was a wing between them for your added downforce.  Otherwise there is more aero penalty to be accrued with no real gain in center of pressure with two over one.  A vertical stabilizer is going to have more effect on CP than a canted one.  Then again you would need two along with their added drag.  Saying that properly designed verticals and a wing for downforce don't necessarily need to add a lot of drag.  They both can have Cd's down under .1 and very little frontal area.

On Hooley's Stude we have added no weight behind the axle and considerable weight ahead of it but then also more weight further ahead to keep the CG forward.  So you end up with a lot of weight that is doing nothing for traction but still needed for safety.

I guess I missed it but are you converting the tank to a streamliner or is this a whole new car?  Also you coming this way at all?  We'd love to see you.  Ruth said to say hi to you guys, me to  :-),

Sum