Converting 3 Tamiya Brabham BT50 into BT49 versions

[JM]

As I very much like the Brabhams of the late seventies and early eighties, the BT49 can not be missing in my collection. And because the BT50 was basically the same car adapted to the BMW engine, converting Tamiya’s BT50 into a BT49 is not too difficult. There is also an AMD transkit consisting mainly of resine body, PE-parts and decals that needs the suspension, wheels and the rear of a Tamiya BT50 to complete it. This one I will build parallel to the conversions into the 1981 Las Vegas BT49C Nelson Piquet version. The 3 conversions will be the 1980 Long Beach BT49B and 1982 Brazil BT49D Nelson Piquet cars and the 1982 Monte Carlo BT49D Riccardo Patrese version.

From doing the BT51 conversion a few weeks ago I kept some templates I used to cut the cowling and making the new insert parts. The insert parts are made from polystyrol sheets with various thicknesses.

Marking the cut out areas:

Cut out cowling and new inserts:

Cowlings complete with new inserts, puttied and sanded. The upper sidepod radiator outlet openings have been shortened by about 5mm through inserting small polystyrol sheets. The upper cowling in the picture is for the 1980 BT49B version; the lower one with the extended “dovetail” rear end is for one of the 1982 BT49D versions:

The next step is to modify the tank which is lower than for the BT50 but wider at the top. So after cutting off the tank’s top two slits are made at the front to be able to spread the side walls.

Then a 20mm wide plate is inserted as new top while the gaps at the front are closed by inserting two wedge shaped parts:

At the undertray the panelling has to be extended to the end of the engine so to build a kind of engine bay. Unfortunately I have not got a definite reference picture to show how far back the undercover reaches. At Gurneyflap there is a very good feature of the BT49D (http://www.gurneyflap.com/brabhambt49.html) where it looks like that at least for that version even the gearbox is covered. Anyway, as I will not detail the engine area I will go for a cover to the engine’s end i.e. the gearbox’s beginning. This way it is done at the AMD transkit:



Now for the engine. As it will be covered anyway I did not bother with replacing the BMW engine with a Cosworth. I will just do a kind of Cosworth fake at the top (where the air intake trumpets will be partly visible trough the cover mesh). Therefore the BMW engine’s top (Tamiya parts A7, A8 and A17) has to be cut off as shown:



As the tank shape is slightly changed by widening it’s top the tank’s back part (C43) is cut off at the panel line above the third hole for inserting the engine mount. The upper part of the tank’s back is made from plasticard:



On top of the BMW engine I glued the Cosworth fake where later the air intake funnels will be insertet:



That’s how far I have come so far. Next steps will be priming, correcting surface defects and then painting the chassis/tank/engine assembly and cowling.

[Tormentor]

Great start !

[JamesB]

Fantastic, but it's a shame to dismantle three BMW engines...
You might use resin DFV replicas

[roly01]

That's a great project!!!

Looks very good prepared aswell.
But do the bodies fit ofer the wider chaccis?
I had quit some problems when I did basicly the same thing with my BT48 conversion.
My body doesn;t really fit very well anymore. I had to make some brackets, on the sidepods, where I could put a screw in to hold the body down.

But your work looks veery good sofar.
Will follow this thread closely.

[Emersonsquirrel]

Really interesting thread!

I have the AMD transkit as well and was planning on making mine into the '79 car. I'd had thoughts about converting a BT50 as well, but hadn't worked out the details of how I was going to do it. This thread will be a great help when I get round to it

One question - while the nose of the BT49D and BT50 are pretty similar, I feel that the 1980 car version is slightly flatter at the front - does your research agree with this, or do you think they are basically the same?

Looking forward to the next update!

ES

[smirkoff]

Great project, great start, I'm looking forward for the next updates!!

ES, the BT49D and the BT50 indeed share the same bodywork from cockpit onwards, while the other BT49 cars had a flatter nose. The 1980 "B" car was in fact the experimental one with the Weissman transverse gearbox, tested by Piquet but raced only by Rebaque (and Zunino, I think). There's a very good history of the car in the www.gurneyflap.com site (FOCUS section).

It's good to notice too that the 79 and 80 versions (until Zandvoort) had a shorter wheelbase, because the of different front suspension geometry.

[JM]

JamesB wote:
Fantastic, but it's a shame to dismantle three BMW engines
You might use resin DFV replicas

It's too late now What's more - I wouldn't know where to get some. Looking for some time for some resin replicas of gearboxes, suspensions and wheels to complete some Tyrrell kits without cannibalising Williams kits - but no success so far
But honestly I think the BT49s will be fine with the chopped BMW's. Cannot see where to use them anyway. And there will be a complete one left from the 1981 BT49C which I will build from the AMD transkit (that needs only the rear from the gearbox onwards).

Emersonsquirrel wote:
One question - while the nose of the BT49D and BT50 are pretty similar, I feel that the 1980 car version is slightly flatter at the front - does your research agree with this, or do you think they are basically the same?

Emersonsquirrel I think you are right there. I have looked at countless reference pict and it seems that for the 1980/81 versions there is a bigger kink between the windshield front and the cowling which goes a bit more horizontal for a while before it drops further down at the snout. At the BT50 (and the 1982 BT49D) there is just a smaller kink (i.e. its nearly straight with an angle of almost 180 degrees) between windshield and cowling which drops continually from there. But how big the difference is is difficult to tell. What is clearly to see is that the cowling's bottom edge of the 1980/81 cars runs horizontally from the front upper suspension mounting and drops only at the snout at an 30 degrees angle and then vertically. At the BT50 and 1982 BT49D the bottom edge drops immediately forward of the front upper suspension mounting. But see for yourself:

I'm currently in the process to modify one of the kits at that area (only necessary for the 1980 version). Furthermore the snout has to be more rounded than at the BT50 where it is very sharp pointed.
As soon as I have finished the modifications I will point the differences out with pictures of the kit.

roly01wote:
But do the bodies fit ofer the wider chaccis?
I had quit some problems when I did basicly the same thing with my BT48 conversion.

While testfitting I did not have problems with it. But it is very tight around the widened tank. I made sure it does not jam there, filing all excessive material (and maybe a bit more). So lateral fit should be alright. But I found with the BT51 that the longitudinal fit is difficult, i.e. when you hook up the snout at the front the cowling tends to stick up at the car's rear. I glued some brackets in there and might do so again with the Brabhams as I will not make the cowling removable because I do not use the correct engine anyway.

smirkoff wote:
It's good to notice too that the 79 and 80 versions (until Zandvoort) had a shorter wheelbase, because the of different front suspension geometry.

Yes the Gurneyflap site is a great help. But I cannot really see where and why the slightly different front suspension lead to a shorter/longer chassis. The mentioned 76mm translate into 3,8mm for the kit. But as I do not know where to cut them out I think I will get away without shortening the 1980 chassis. I know it's not perfect but you would realise the difference only when putting both versions directly side by side.

[roly01]

[quote="JM

Emersonsquirrel wote:
One question - while the nose of the BT49D and BT50 are pretty similar, I feel that the 1980 car version is slightly flatter at the front - does your research agree with this, or do you think they are basically the same?

Emersonsquirrel I think you are right there. I have looked at countless reference pict and it seems that for the 1980/81 versions there is a bigger kink between the windshield front and the cowling which goes a bit more horizontal for a while before it drops further down at the snout. At the BT50 (and the 1982 BT49D) there is just a smaller kink (i.e. its nearly straight with an angle of almost 180 degrees) between windshield and cowling which drops continually from there. But how big the difference is is difficult to tell. What is clearly to see is that the cowling's bottom edge of the 1980/81 cars runs horizontally from the front upper suspension mounting and drops only at the snout at an 30 degrees angle and then vertically. At the BT50 and 1982 BT49D the bottom edge drops immediately forward of the front upper suspension mounting. But see for yourself:


I'm currently in the process to modify one of the kits at that area (only necessary for the 1980 version). Furthermore the snout has to be more rounded than at the BT50 where it is very sharp pointed.
As soon as I have finished the modifications I will point the differences out with pictures of the kit.[/quote]

Maybe these 2 pictures make it more cleare what the diffirence is between the 2 chaccis.
Look at the rectangular part that goes fromt the nose.
On the BT49 the side of the chaccis is connected to this rectangle.
On the BT49d and BT50 the side of the chaccis goes fron the front suspension to the very front of the chaccis in one line.

[JM]

After the discussion about the differences between the 1980/81 and 1982 versions I changed my mind about the 1980 chassis. That means I shortened it which I did not want to do in the first place. Furthermore modifying the 1980's front end of chassis and cowling took some time. Pics will follow.
Then two questions came up. First, what is placed on top of the tank at the different versions i.e. what is under/between the anti roll bar behind the drivers head? The pics I've got don't tell exactly. And second, at my parallel built of the BT50 BMW GP Canada version I'm becoming more and more unsecure about the flip-up covers on top of the cowling. During 1982 there are versions with (upper pic) and without them (lower pic)

Watching the video of the race I somehow got the impression that in Montreal 1982 the flipup is only on the right side but not on the left side. Can someone enlighten me with a picture of the car in the 1982 Montreal race showing the relevant parts?

[JM]

Progress has been really slow lately. Reality did not permit a lot of time to escape to the 1/20 scale world. Spent a lot of time to modify the BT49B Long Beach version’s front according to the differences discussed lately at this thread. Have a look how it worked out.

Not the best picture but it shows the difference between cowlings. The upper one is the modified cowling for the 1980 BT49B the lower one is the one for 1982 BT49D (unmodified from the Tamiya kit):

Here are the cowlings fitted to the chassis. From top to bottom you see the BT49B, BT49C and BT549D. The BT49C is the AMD transkit with wings attached (to become the Las Vegas version).

Here from left to right: BT49B, 49C, 49D with wings (Brazil version) and 49D without wings (Monaco version):

Another look at the front ends. From front to back: 49D with wings, 49D without wings and BT49B

What I did as well was shortening the BT49B chassis which I did not want to do originally (the 49B was 75mm shorter than the 49D and 50 which would be exactly 3,75mm in scale 1/20). I took about 4mm off at the rear cowling area i.e. I divided the cowling into two segments and shortened them accordingly at the cutting line shown here:

Then I shortened the undertray at the rear where it’s bending upwards. To achieve a shortened wheel base I shortened the oil tank which is placed between engine and gearbox. Might not be really exact but at least the BT49 chassis is shorter now.

As can be seen from the last picture I have now assembled chassis, cowling and roll over hoop. Of course I placed the radiators in the sidepods before (without modifications). Furthermore I covered the engine air funnel area with mesh and placed the funnels at the Cosworth fakes.

Currently the kits are partly decaled. I still have to do the odd little thing such as finishing the decals, completing the drivers’ helmets etc. I hope I will finish all four kits within the next week.