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Brabham BT46B 'fan-car'

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82K views 159 replies 66 participants last post by  c-vroom  
#1 · (Edited by Moderator)
So as those following my stalled Vanwall build will already know I'm off on another project without of course finishing the first......

I got to thinking after another of those frustrating race nights (with folk who actually buy modern competition cars and practice (for hours and hours) as drivers) where I always seem to come last.........

What I need to do is build a car (an F1 of course as that's my thing) which will have a clearly unfair advantage so I can go faster!

So I thought well there was that car that was deemed legal just for that one Swedish GP - the Brabham BT46B. As most will know there was a big fan in the back and a skirt around the bottom so it literally sucked down onto the road.

like this....

it just happened that I finally got one of the Spanish Scalextric BT46's and I found some drawings and hey, with some thining and lowering its not bad.

so I did some drawings.......

and then I started building........



The real problem seems to be that with slot cars there's, ...... well, a SLOT, so I'm never gonna get the suck I really need. I had ideas about making two skirted zones one under each side pod, hoping that provided the car didn't slide too far (it shouldn't as it'll be sucking!) adhesion should be better.

Then I thought, heck the speed, power and aerodynamics at 1/32 just aren't like the real thing so maybe the fan will overcome the slot problem.

So I'm just going to build it and see what heppens. This is where I am now....

Question - anyone know where I can get a 14mm diameter fan / propeller / axial impeller from???????????

I'll update as it evolves (and it'll be quicker than the vanwall which I WILL finish afterwards)!

Andi
 

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#4 ·
You had just better hope that while it works like the real thing, real life is not emulated by the event officials and your creation of imagination and art becomes a shelf queen within 24 hours of a wheel turning.

Great work so far of course!
 
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G
#5 ·
Nice ! Also curious as to how this works out as (also) in my distracting-me-from-what-i-should-be-finishing project stack is a usefully wide 1/24th Chaparral 2J that's just begging for working fans. More or less decided on an anglewinder with a crown mounted on the "clear" end of the back axle to run the fan, or fans if I can get them to fit.

Didn't look for actual fans or propellers but think you'll get what you need out of a piece of thin aluminum sheet - scribe out a circle, cut it and drill a hole dead center, cut the blades and twist them to the appropriate angle, and then secure it on a piece of threaded rod with nuts maybe ? Good to be able to tweak the angle of those blades...

Re suction around the slot; thinking it a good idea to cover the slot as much as possible a (ie with a thin strip of lexan) and drawing from around it but maybe hooking something up to the guide that maintains it's position over the slot while the car drifts is possible also ? Skirting would be good...

Hmmm...

Keep posting updates ! That looks excellent and pretty sure it'll work...

And if it works well enough to get banned you can put a bag on the back and rent it out as a track cleaner instead !

Cheers,
S.
 
#7 ·
OK - let's play a game - it's called "Fun With Numbers"

Air pressure at sea level is roughly 1000g/cm2

Assuming the body of the car is about 3cm wide at the rear, 13 cm long and tapers to a point at the front, the area is (3 X 13)/2 or 19.5 cm2 - let's call it 20 cm2

If we could pull a perfect vacuum under the car, the down force would be 20cm2 X 1000g/cm2 - 20 Kilos! (that would bend a few axles!)

Obviously we neither need nor want that much force - how much do we want? How about the equivalent of the down-force provided by a moderate magnet - say 200g.

So how much vacuum is that? 200/20,000 = 1/100 = 0.01 or 1% of 1 atmosphere or 7.6mm of mercury.

Now mercury is a nasty, toxic substance (that we used to play with when I was in school) so let's convert it to something else. 1 Atmosphere = 34' of water = 1036 cm. We need to be able to lift a column of water 1036/100 = 10.4 cm

This is 1/10 or less than the vacuum pulled by the average vacuum cleaner.

The experiment is simple:

Build a body mock-up and install fan

Attach a flexible tube to the body (air tight seal) and attach the other end of the tube to one leg of a U-tube containing water (beginning to sound like a high school physics class?)

Support the body mock-up in typical operating position

Turn on fan

Measure rise in column of water in leg attached to tube.

Results to be written up in standard form and turned in next Thursday

EM
 
#8 ·
You what?
Image


Andy had a chance to belt this thing round Walter's track last night and I have to say it's already pretty quick, even without the body and front axle, etc. It's going to be fun timing laps with and without the fan working. He seems convinced that this is going to be a race winner!

By the way Andy, it's my Dremel you need to cut the axle down not my bloody hacksaw. Bring it over and we'll grind the end flat too.
 
G
#9 · (Edited by Moderator)
Some years ago I built a slot car with a fan to suck it down to the road.
Getting the fan sucking up the air was no problem, and it was quite quick round the track. Quite quick but an otherwise similar conventional car was slightly quicker.

That was without skirts, so the next move was to fit some skirts.
Static pressure tests were quite encouraging, but trying it for real, didn't produce a performance improvement.
I tried lots of different ways to make the skirts work and ended up with either
Enough load on the skits to stop them leaking too much which reduced the load on the wheels and produced drag
Or
Reduced the drag and put nearly all the weight on the wheels which resulted in too much leakage to achieve much of a pressure differance.

Even with skirts it worked well enough to be quite quick round the track but an otherwise similar conventional car was still slightly quicker.
After a while I gave up on fans & skirts and decided I'd be better off building conventional cars. Maybe somebody else will find a way of making it work better????

Best of luck with the Brabham, I reckon there's every chance you'll get a model that looks great and goes pretty well. Quick enough to beat all the conventional cars? That's a huge challenge.
 
#10 ·
I think it was E.S. Young who wrote this engineers prerogative: "The first concept of superior principle will always be beaten by by a proven example of established practice."

I say press on and go for all maximum of downforce!
 
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#14 ·
Screwneck's observation present just another small challenge; the volume of air that can enter through the slot must be mitigated by the volume of air that the fan can suck. Add a vane or two. You could create a skirted tunnel where there is no suction too. There is always a solution. I think you should keep going.
 
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#16 · (Edited by Moderator)
very creative, good luck with it!

I'm tipping the guide would do some work sealing the front of the car? I understand it won't be a seal as such however the volume of air escaping that way will be a lot less than the rear.

should you build a twin chamber vacuum under the car imagine when it gets sideways!!! actually it's not that hard to imagine, it'll be the same as a sideways mag car..

I'll be following this one with interest,

Chris
 
#17 · (Edited by Moderator)
Get a few of those whistles like the ones in Marc's link and figure out how to cut one apart and fit it so it turns easily... they turn very easily in the whistles... I have had one. Let the speed of the air flowing under the car make it turn.

Let it be for show only... it is simply not feasible to get it to actually make the car go faster than a well-built and carefully set up conventional car.

Reread what Gone Racin wrote and really, really think about it. Putting down working skirting and expecting the motor to overcome the extra friction is asking too much.

Magnets, anyone?
Image
 
#18 · (Edited by Moderator)
I built a chassis for a, then popular, 1:24 thingie wedge many years ago. They didn't come much more wedge like than this particular shell. As part of the build I put clear lexan sidewalls on the body, as high and long as was allowed then.

The chassis, being 1:24 was wide so I wanted to keep the weight down. In order to do that I cut a big rectangular hole in the centre of the chassis. The car went like a proverbial rocket! What I didn't realise was that the shell sucked the air through this hole and out the back, a huge empty space. Remember this was in the days before F1 cars had skirts and things. The sidewalls helped to keep the displaced air on top of the body as well as acting like the vanes on a dart in corners, stopping the car sliding too much. I'm amazed that this principle has only just been adopted in F1, behind the airbox.

The point is that this project of Andy's could well work but other considerations such as additional gear friction, weight, and aerodynamics also need to be included, and I'm sure Andy will be doing that, knowing him.

Hats off time, this is a great project by a great guy!
 
#19 ·
Throughout history there have been madmen thinking they can do what other
people keep telling them that there "thing" will not work it seems like we have
one of these guys in Andy.
His thinking reminds me of of other nutters of the past, two guy spring to mind,
they had these strange idea,s also,, one of which made many people chuckle,
they foolishly thought they could leave the surface of the planet !!! the idiots
where called Wright, i think they lived somewhere near a place called Kittyhawk.
in the US of A, i could be wrong ?
Mac P
 
#20 ·
Guys,I sort of get the feeling that Andi, is building a Brabham Fan car in 1/32 and he wants the fan out back turning in order to look good going around without actually creating suction. As far as the rest of it goes , I think he's having a bit of a wind up!
Sounds like he's got a few bites.
Image


Although I might be completely wrong and the guy will turn out to be a genius.
Image
 
#22 ·
well this turned out to rock lots of people's boat didn't it?

first, thanks to everyone who have spent time replying and trying to help.

second, i'm deadly serious - i've seen what other guys achieve in terms of scale builds and I really don't think I could match it with the sort of time I have available. I'm much more interested in the physics experiment end of it all!

To answer some points people have made:

- the simple thing to do is surely to make a simple mock up with the fan to test the concept first. The problem here is i'm always too excited to start the project when I haven't got all the bits and the one bit i'm missing is the fan!!!!

- love the calculations about atmospheric pressure - very special. My own calculations went around the concept that if a car travels 10m in 1 second and the slot is 2mmx8mm then how much air do I need to suck before I even overcome the slot problem. My rudimentary calc's showed positive signs on this one.....

- the microfan idea (comupter cooling etc.) was also my first thought. Then I decided that since I know mechanics better than eletronics I didn't want to use something that would draw too much current. I found one at 15mm diameter which would fit perfectly and I might still resort to this if the direct drive fan wont work. See http://uk.rs-online.com/web/search/searchB...t&R=0191856 or for something more special http://uk.rs-online.com/web/search/searchB...t&R=0580506.
these are a bit big but somewhere I found smaller still.....

- it also occured to me to make the fan from a circle cut from sheet - I would use brass so I can solder it direct tot the axle. I'm worried about vibration through lack of accuracy though and inefficiency and bent flat is not the best shape......... What I came up with is this http://www.cornwallmodelboats.co.uk/acatalog/R148-M2.html I reckon if I could turn the outer edge down to 14mm i'd be rocking. Actually i've order a plastic one for now to try before taking the plunge with this expensive item.

- now to the real problem. I agree with everone who said that it is unlikely to make any difference due to the fact that a well sorted production car is more likely to be better. I think that's totally true sadly. Despite Graham's optimism my 'plank' prototype is already 1 sec. (10%) a lap slower than a production class 'C' although most of that is about weight distribution so i'm not being too optimistic but just enjoying the challenge.

- finally skirts. I have my ideas about this to avoid too much friction and where to put them etc. but you'll just have to wait until I get there folks...........

thanks to everyone who answered and yes I know i'm totally bonkers

Andi
 
#23 · (Edited by Moderator)
oh and by the way sadly the siren whistle wont work. I found a picture of one and the axial fan part is just the far outer edge - wont give sufficient volume flow I don't think........

more ideas welcome..........
 
W
#26 ·
I have yet to add to the discussion here or anywhere else on the forum but since I want to post some photos of stuff I've built, Im not sure but I think I have to post a certain amount first. So let me start by saying what a great build, although the van wall is more my style. But I believe I have the same affliction, not being able so finish one project before I start a new one. Oh well, more to finish when I retire. BUT, seeing as this is the holy Grail of slot cars,(cars with suspension) I have to say keep up the posting and if there are others out there with some shocking ideas they too should add to this one. Maybe this could be a topic for the scratch building area.
Wbb1978
 
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