Howmet TX, Le Mans 24h 1968

[stevehnz]

A fascinating thread in every way, not lest the history behind these cars & the problem solving going on, really enjoyable. I'll drop back more often now.

Steve.

[PatW]

A fantastic car and kit. It looks amazing already!

[Malc2]

Cheering you on from the side lines and loving every new post!

 

M.

[Bengalensis]

On 01/08/2022 at 02:04, stevehnz said:

A fascinating thread in every way, not lest the history behind these cars & the problem solving going on, really enjoyable. I'll drop back more often now.

Steve.

Thanks a lot for the kind praise Steve!

I often find the history behind the model subject, the time travel and the research as fascinating as the build itself, if not more.

 

On 01/08/2022 at 08:55, PatW said:

A fantastic car and kit. It looks amazing already!

Thank you very much Pat, glad you like!

On 01/08/2022 at 18:03, Malc2 said:

Cheering you on from the side lines and loving every new post!

 

M.

Thanks a lot Malc! At some moments it feels I need all the cheers there is... 🙂

[Bengalensis]

Work on the rear end continues. There are photo etched parts supplied for the rear anti roll bar and links, but they give a much to flat appearance for my liking, and the bar itself is too short and the links too long for where I need to place it.

 

 

More scratch work. A new anti roll bar was bent from copper wire with drilled out Evergreen rod as mounts, and more Evergreen rod for the links. And yet more Evergreen rod used for suspension links and the bar up to cockpit wall. Strange as it is that bar was only present on the right side.

 

 

It's slowly getting there. Another dry fit of the major components. I still have to finish the exhaust pipes...

 

 

There are times when it's two steps forward and one and a half back... As I was trying the fit of the photo etched inner side panels for the engine room it dawned on me that the whole opening wasn't symmetric. The left side doesn't taper in as much towards the rear as the right side, and as far as I can tell they should be equal. It can be discussed which side is correct, if either, but my choice is to alter the left side.

 

 

I moved the two edges inwards about 1 mm by gluing Evergreen strips and then cut and sanded them back to zero at the front. A thin layer of filler was applied to restore the shape of the top of the body panel.

 

 

Then some more work to adjust the fit of the engine cover. Here the finished work with the filler sanded smooth. Now something more happened as well...

 

 

I have been quietly wondering how long it would be before this would have to happen. The answer came today. The five moulded in bars across the rear opening had to go. They were not symmetrically or correctly placed and provided more problems to fit the inner side panels of the engine room. With those gone the opening was adjusted and sanded smooth.

 

 

Here we are a little later with three different sizes of Evergreen rod fitted. The two thicker inner bars should really be positioned a bit further forward at the bottom, but it would create more problems with fitting them to the body shell only, as well as fitting the inner side panels, so this is the compromise it will be.

 

 

There is another photo etched part supplied to be folded and fitted to the top square bar across the rear opening, but it tapers in shape when it should be straight, so I'll be fabricating something on my own.

 

 

But now at last I could finally adjust the inner side panels and reach a good fit. They have here also been sanded 1200 grit to be painted with Alclad Aluminium later.

 

[klubman01]

Wow! Some good work there. Pity the errors occur in the first place.  Still, keep pushing on.  Looking better at every step.

Trevor

[Bengalensis]

6 minutes ago, klubman01 said:

Wow! Some good work there. Pity the errors occur in the first place.  Still, keep pushing on.  Looking better at every step.

Trevor

Thanks a lot Trevor!

I agree with you fully. Having said that it's not a bad kit, especially keeping in mind the low volume subject etc. But I get the feeling that the masters may have been rushed somewhat, as well as the last research details. The sign GC (known from some LMM masters) inside the two main parts tells me it's not Jean-Philippe's original creation and that some out sourcing or changing of hands is in the history. Still there's nothing that some proper work can't overcome 😎

[Malc2]

Great stuff.

I have come to realise that with each resin model I make there is nothing that can't be fixed with superglue, filler and time!

The only variation is the quantity of each required.

 

It will be alright in the end - and if its not alright, its not the end!

 

Malc.

[Bengalensis]

15 minutes ago, Malc2 said:

Great stuff.

I have come to realise that with each resin model I make there is nothing that can't be fixed with superglue, filler and time!

The only variation is the quantity of each required.

 

It will be alright in the end - and if its not alright, its not the end!

 

Malc.

It is exactly like that! Very well said.

[JeroenS]

Nice work. I was wondering when you were going to give in and replace those rear struts 🙂

[Bengalensis]

20 hours ago, JeroenS said:

Nice work. I was wondering when you were going to give in and replace those rear struts 🙂

Thanks a lot! Well, at least I managed to pretend it would work for a few days 😉

[Bengalensis]

The small tank that goes to the right of the turbine can be seen in some different versions. I cut down the supplied resin part to get something close to what I see at Le Mans.

 

 

Then I had to do the work inside the exhaust pipes, drilling, Dremel and sanding.

 

 

I made my own new "photo etched" replacement for the rear top bar from 0,2 mm aluminium cut and folded to shape with five rivet marks drilled.

 

 

And there I think all parts for the rear end internals at this stage are done. It will be good to move on to the other small parts for the interior and exterior for a change.

 

[Malc2]

Those opened up exhausts look so much better now - its such a feature of the real car!

M.

[Bengalensis]

17 minutes ago, Malc2 said:

Those opened up exhausts look so much better now - its such a feature of the real car!

M.

Thanks, they sure needed the work. I just hope I can give them a descent colour later on.

[Sabrejet]

Nice job! I love Profil24 kits, but they do need a bit of work. I hope my Howmet looks anywhere near as good as yours!

[Bengalensis]

On 03/08/2022 at 22:07, Sabrejet said:

Nice job! I love Profil24 kits, but they do need a bit of work. I hope my Howmet looks anywhere near as good as yours!

Thanks a lot! I'm sure you'll make great work of it.

P24 is one om my favorite 1/24 resin makers too. Some need less work some need a bit more, but I have always enjoyed them. But then I am a resin addict...

[Brandy]

I just found this thread and I've never heard of this car before. Very impressive detective work and corrections so far!

 

I'm intrigued. I assume the turbine drove the rear wheels through what would have been the accessory gearbox underneath the engine. An increase in N1 (turbine speed) would result in an increase in the rotation speed of the accessory gearbox driveshaft, which is basically what the mounting pin you added under the front end is. I can't see how else it would work, other than pure thrust to drive it and freely rotating wheels, but then it wouldn't need a gearbox!

 

Any engineers here who could elaborate?

 

Ian 

[Bengalensis]

2 hours ago, Brandy said:

I just found this thread and I've never heard of this car before. Very impressive detective work and corrections so far!

 

I'm intrigued. I assume the turbine drove the rear wheels through what would have been the accessory gearbox underneath the engine. An increase in N1 (turbine speed) would result in an increase in the rotation speed of the accessory gearbox driveshaft, which is basically what the mounting pin you added under the front end is. I can't see how else it would work, other than pure thrust to drive it and freely rotating wheels, but then it wouldn't need a gearbox!

 

Any engineers here who could elaborate?

 

Ian 

Thanks a lot for the kind praise Ian!

It's indeed mechanically wheel driven through the gearbox, no thrust, unlike modern LSR-cars. The resin parts are a compromise and doesn't fully replicate the real thing in this detail.

[Bengalensis]

The rest of the few resin interior parts were soon finished.

 

 

There are some quite nice race number lights supplied, but they are not the same type as I see on GTP1 #23 at Le Mans. Again the two cars differed in this detail.

 

 

The lights I see on GTP1 through the whole season looks very much like the drop shaped lights on the 1966 GT40 MkII's. So that's the source I use. I have cannibalized many of the Fujimi kits for parts before, and now I had to cut into another of those body shells. One light for each side number.

 

 

With the knock offs, fuel caps and mirrors also done all the ordinary resin parts have past my work. Over to the other remaining things like lights and vac forms before primer.

 

[klubman01]

3 hours ago, Brandy said:

I just found this thread and I've never heard of this car before. Very impressive detective work and corrections so far!

 

I'm intrigued. I assume the turbine drove the rear wheels through what would have been the accessory gearbox underneath the engine. An increase in N1 (turbine speed) would result in an increase in the rotation speed of the accessory gearbox driveshaft, which is basically what the mounting pin you added under the front end is. I can't see how else it would work, other than pure thrust to drive it and freely rotating wheels, but then it wouldn't need a gearbox!

 

Any engineers here who could elaborate?

 

Ian 

The car is driven via a "free turbine", i.e. a turbine in the main unit's exhaust duct which is linked to the drive mechanism by an output shaft, and thence to the wheels.  The big advantage is that the main unit can be run at its most efficient RPM (typically very high) all the time.  As there is no physical connection between the main unit and the output shaft, it is possible to bring the car to a halt on the brakes without stalling the gas turbine engine. 

 

In the above diagram, the free turbine is on the right connected to the red output shaft.  The main unit, sometimes referred to as the "gas generator" is on the left, with all the components rotating on the blue shaft.

The whole thing is called a turbo-shaft engine.  Typically used in helicopters, etc.

Trevor

[Brandy]

Thanks. Similar principal to the PT6, but slightly different set up.

 

Ian

[Sabrejet]

On 04/08/2022 at 09:26, Bengalensis said:

But then I am a resin addict...

 

And I thought I was alone in my affliction...👍

[Bengalensis]

43 minutes ago, Sabrejet said:

 

And I thought I was alone in my affliction...👍

You're definitely not alone. The best resin kits comes with a lovely scent, especially when opening the new box for first inspection, that goes very well with a glass of good Shiraz, and possibly some good cheese. 😎

[Bengalensis]

20 hours ago, klubman01 said:

The car is driven via a "free turbine", i.e. a turbine in the main unit's exhaust duct which is linked to the drive mechanism by an output shaft, and thence to the wheels.  The big advantage is that the main unit can be run at its most efficient RPM (typically very high) all the time.  As there is no physical connection between the main unit and the output shaft, it is possible to bring the car to a halt on the brakes without stalling the gas turbine engine. 

 

In the above diagram, the free turbine is on the right connected to the red output shaft.  The main unit, sometimes referred to as the "gas generator" is on the left, with all the components rotating on the blue shaft.

The whole thing is called a turbo-shaft engine.  Typically used in helicopters, etc.

Trevor

 

To add further to Trevor's excellent explanation, here's a diagram that explains the waste-gate system on the Howmet TX that regulates the amount of hot gas passing the power turbine by bleeding some of it off with variable vanes to reduce power. That's the smaller exhaust pipe to the left on the car. This was important in making the car much more driveable, and when failing led to the car going off in corners, think stuck throttle. The car shown in the article linked below is restored and has a more modern turbine with a different exhaust layout compared to 1968.

 

 

www.autoconcept-reviews.com

 

 

 

 

[klubman01]

5 minutes ago, Bengalensis said:

 

To add further to Trevor's excellent explanation, here's a diagram that explains the waste-gate system on the Howmet TX that regulates the amount of hot gas passing the power turbine by bleeding some of it off with variable vanes to reduce power. That's the smaller exhaust pipe to the left on the car. This was important in making the car much more driveable, and when failing led to the car going off in corners, think stuck throttle. The car shown in the article linked below is restored and has a more modern turbine with a different exhaust layout compared to 1968.

 

 

www.autoconcept-reviews.com

 

 

 

 

Thanks very much for the additional information.  The waste gate is not dissimilar then to that on a turbo-charged piston engine.

Trevor