Author Topic: M5 Stuart Light Tank  (Read 3024 times)

Offline Vixen

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M5 Stuart Light Tank
« on: January 15, 2021, 07:03:23 PM »
The M3 Stuart and it's improved derivative, the M5 Stuart Light Tank were the first production-line tanks to be built in the US factories. The Stuart light tanks were made available to the British and Commonwealth forces under the Lease-Lend agreement. They were later used by the US Army and all the allied forces in all theaters, until the end of the war.

When the relatively thin armor and small 37mm gun became ineffective against more modern and more powerful opposition, the M5 Stuart was withdrawn from tank v tank operations and went on to serve as an excellent scout or reconnaissance vehicle. The Stuart tanks were well liked by their crews. It acquired the affectionate nickname 'Honey' because it was a joy to drive, a real 'Honey', due to light weight, powerful aircraft radial engine and good reliability.

Many Stuarts were modified, in the field, by removing the turret and the inadequate 37 mm gun. The reduction in weight improved both the speed and maneuverability of this remarkably reliable vehicle. The only down side of the M5 Stuart Recon conversion was when it rained.

Here is a full size M5 Stuart Recon giving joy rides at a military vehicle show.




Part 1  The Hull
My journey into the realm of 1/6 scale model tanks began when found a huge, 1/6 scale, radio controlled plastic model (made by 21st Century Toys) listed on E-bay at an affordable price, under 'for spares or repair'. It turned out that the battery charger had the wrong pins for British wall sockets and the model was sold, virtually unused, when the battery ran flat.

I planned to fit a 40cc 5 cylinder air-cooled Siedel ST540 radial engine, being as close as I could get to the original 7-cylinder Continental W-670 air-cooled aircraft radial engine. Close enough for me. I would also need to build some sort of transmission and steering gearbox. Fortunately, the tracks and running gear and most of the model parts could be reused with little modification.

My first task was to completely dismantle the vehicle in order to convert it to IC engine power. All the internal bulkhead and floor were removed from the hull so that a 3mm thick sheet metal inner hull could be fitted. As you can see, I recycled a No Entry sign, found in a waste skip (dumpster?) The inner hull would be screwed and riveted together.







The Siedel radial engine was suspended off the 8mm thick rear bulkead. The removable intermediate bulkhead, both stiffened the inner hull box, and provided a mounting point for the engine cooling fan. The exhaust gas collector ring is connected to the copper plumbing on the rear bulkhead. Later large cooling holes were machined into the rear bulkhead to aid engine cooling






Here you can see the remains of the plastic hull slipped back over the new metal inner hull. The plastic hull parts now only serve decorative purposes as the engine, gearbox and running gear are all to be bolted directly to the metal inner hull.




Air cooling for the 5 cylinder radial engine was achieved, like the full size engine, by a large diameter fan attached to the flywheel and prop-shaft. As you can see, I recycled a large industrial equipment cooling fan. The big brass flywheel was made the same size as the discarded electric motor.




Here you can see the running gear and tracks have been assembled back onto the tank. Some of the plastic suspension arms needed to be reinforced with 3mm metal inserts, but as much as possible was used with out further modification.




A small aluminium cooking pan donated it's body parts to make a cooling shroud to go around the cylinders and the enclosure underneath the hull. Lots more rivets.




This final image shows the internal layout of the M5 Stuart model rather well. The radial engine is in the rear, the engine pull starter is in the centre, beneath the turret ring and the transmission and steering gear box is in the front of the hull. The sponsons over the tracks, make convenient storage space for the new radio control equipment and batteries.

In the next installment I will describe the design and construction of the transmission and steering gearbox





Stay in and stay safe

Mike

« Last Edit: July 29, 2021, 07:50:09 PM by Vixen »
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Online tghs

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Re: M5 Stuart Light Tank
« Reply #1 on: January 15, 2021, 08:10:41 PM »
what is path for the air cooling?
what the @#&% over

Offline propforward

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Re: M5 Stuart Light Tank
« Reply #2 on: January 15, 2021, 08:26:02 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp:  :praise2:

Excellent!
Stuart

Offline Vixen

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Re: M5 Stuart Light Tank
« Reply #3 on: January 15, 2021, 08:43:41 PM »
what is path for the air cooling?

Through the fan to the centre of the engine, than outward and rearward through and between the fins of the five cylinders. Through the cutouts in the rear bulkhead and eventually out through the vents at the rear and top deck of the tank. Much the same as the full size machine

Here is an additional photo showing the large airflow holes in the rear bulkhead which were added later.



Mike
« Last Edit: July 29, 2021, 07:50:52 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline petertha

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Re: M5 Stuart Light Tank
« Reply #4 on: January 16, 2021, 02:47:38 AM »
Fascinating project. I've always been curious - why were radials considered a match for these tanks? Air cooled vs liquid?. Power/space footprint? Reliability? Or maybe 'inventory' from that particular wartime period? Seems like different flavors of tanks used different engines by different countries at +/- the same time.
https://www.wikiwand.com/en/M3_Stuart#/US_variants

Offline steamer

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Re: M5 Stuart Light Tank
« Reply #5 on: January 16, 2021, 03:45:56 AM »
That is a sweet looking installation buddy!    Loving this!   Following along!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline AVTUR

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Re: M5 Stuart Light Tank
« Reply #6 on: January 16, 2021, 12:45:28 PM »
Petertha

I am sure that Mike will answer your question better than me, but here goes.

Obviously a tank needs a light, powerful and reliable engine. I think most tanks designed before the war used engines designed for them, In most cases the tank was under powered and not too reliable. The Germans and, I think, the Japanese and Russians continued with this practice. The British and, initially, the Americans turned to the aero-engine. Most American aero-engines were air cooled (OK, the big Allison engines were not) which probably gave installation problems. This, the need for engines for aircraft and spare capacity in the car industry led to them using large multi-banked car engines as on the Sherman. The British used the RR Meteor engine, an un-supercharged version of the Merlin. In 1942 Rolls-Royce swapped their Meteor manufacturing plant near Nottingham for Rover's jet engine factories in Lancashire.

I may not have got everything correct since it is a quick reply.

AVTUR

There is no such thing as a stupid question.

Online tghs

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Re: M5 Stuart Light Tank
« Reply #7 on: January 16, 2021, 03:06:47 PM »
much better view of the air path.. that plate wasn't swiss cheesed in the early photos..
as for use of an radial air-cooled engine, the weight to HP ratio is great,, no need for a complex liquid filled cooling system,, Sherman tanks produced in great numbers operated in northern Russia to North Africa (from one extreme to another that would test a liquid cooled vehicle)  watch some of the hedgehog sherman vids,, they had great performance.. the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..
what the @#&% over

Offline Vixen

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Re: M5 Stuart Light Tank
« Reply #8 on: January 16, 2021, 03:08:43 PM »
The choice of engines powerful enough to propel a tank, at the required speed over a variety of terrain conditions, was limited by availability rather than an esoteric choice between radial or inline engine.

The power requirement for an effective armored tank is between 15 to 20 HP per ton. The choice of big powerful engines was limited. Suitable aircraft engine were available but even the biggest truck engine was nowhere near powerful enough. Big watercooled in-line engines were eventually developed, but it took time

A Light tank like the M3 or M5 Stuart needed a 220HP engine. Initialy a Continental W670 (220HP) radial was installed. Later, two Cadillac V8's (210hp) were needed to replace the the radial engines when supplies ran short.

A Medium Tank is much more heavily armored and needs a significantly more powerful engine. The M3 Lee/Grant and the M4 Sherman all started life fitted with the 400 to 450 HP Continental R975 radial engine. These big radials were eventually replaced with watercooled  in-line V engines, but only after engines of this enormous power had been designed and put into mass production.

By comparison the V12 RR Meteor tank engine was a  non supercharged derivative of the famous RR Merlin aircraft engine. It produced around 600HP from it's 27 litre engine and went on to power the more heavily armored and heavier tanks of later years.

Aircraft engines were therefore an obvious first choice. The US aviation industry in the 1930's favored the air cooled radial over the water cooled in line engine. In UK the industry were evenly split between the two. Bristol's lead the way with powerful air-cooled radials, while Rolls Royce produced equally good water cooled V12 in-lines.

The air cooled radial engine was light and compact but had the disadvantage of a larger diameter. The larger diameter engine forced their tanks to be much taller than desirable and therefore presented much bigger targets for the enemy to fire at.

Well that's my understanding

Mike
« Last Edit: January 16, 2021, 06:18:44 PM by Vixen »
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Offline Vixen

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Re: M5 Stuart Light Tank
« Reply #9 on: January 16, 2021, 03:16:37 PM »
the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..

Gasoline was always the fuel of choice, everything, including the cookhouse stoves ran on it. It was a question of logistics, one fuel ran all. Supplying more than one type of fuel to the forward troops was out of the question.

As to the vulnerability of gasoline v Diesel. It did not matter much. One good hit would usually set off a ton of high explosive ammunition first.

Mike
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline AVTUR

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Re: M5 Stuart Light Tank
« Reply #10 on: January 16, 2021, 03:34:12 PM »
the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..

Gasoline was always the fuel of choice, everything, including the cookhouse stoves ran on it. It was a question of logistics, one fuel ran all. Supplying more than one type of fuel to the forward troops was out of the question.

As to the vulnerability of gasoline v Diesel. It did not matter much. One good hit would usually set off a ton of high explosive ammunition first.

Mike

The German army ran on hay all the way through the War. They had to. The only thing I do not understand is why they, the military, did not just give up.

There was a piece of amateur movie film shot by a Frenchman in the summer of 1944 near Falaise. The morning filming, done secretly, shows Germans retreating with big artillery pieces being drawn by horses. The afternoon filiming is of the arriving allies, completely mechanised.

On second thoughts, there is a lot I do not understand about WW2.
There is no such thing as a stupid question.

Offline petertha

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Re: M5 Stuart Light Tank
« Reply #11 on: January 16, 2021, 05:04:22 PM »
Sorry for some more tangent questions Mike. Pertains to a similar radial I'm building.
- I'm assuming the ignition module shown a Seidel original part? I cant seem to find much info on it, but maybe you know. After startup, does it continue to drive the glow plugs on high, or switch off, or revert to reduced current?
- was the ring exhaust assembly stock & modified or you made yourself?

If I have the story straight, Seidel's were actually pretty good RC engines. Eventually went out of production. Then my scent gets cold - picked up by a Swiss company & no more? I've also found links to HobbyKing (Chinese copy or maybe just distribution).

Interesting link of Seidel mods FWIW. I wish the web pics could expand, there are some good internal details throughout.
https://www.heilemann-sternmotoren.de/en/modification-seidel
https://www.heilemann-sternmotoren.de/en/ring-of-muffler

Offline Vixen

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Re: M5 Stuart Light Tank
« Reply #12 on: January 16, 2021, 05:48:45 PM »
Hello Peter,

You are as impatient as ATUR, getting ahead and asking questions about things I have not yet come to.

But to answer your questions. The glow plug driver module provides full voltage during start up, it can be reduced or switched off, when the engine has warmed up. In the Stuart tank installation, the engine never reaches high revs (unlike in an aircraft) so I always ran at the reduced voltage setting. Five glow plugs consume something like 10 amps from the battery at the full setting, deducing to about half that at the reduced setting. It all meant the glow plug battery needed to be big and heavy and carried on-board the model tank.

The exhaust ring was home made from domestic 15mm copper tube bent into two half circles and joined. The five compression fittings, with fat rubber glands, were soldered to the exhaust ring. I used soft lead free solder, not silver solder. Methanol fuel burns at a much lower temperature than gasoline. The soft soldered joints lasted well, provided I ran a rich mixture; until one day when I had a very  'lean burn'. Silver solder or TIG would be much better....... If only.

The five compression glands were made from recycled BNC co-axial video signal connectors. I soft soldered a standard 15 mm copper compression gland (olive)  to join the two halves of the collector ring

Not realy sure what went wrong for Siedel, Last I heard, they were now being manufactured in India.

Thanks for the two links. I am going to enjoy studying them.

Go safe

Mike

To quote from one of your links "Why some parts have obvious hammer marks probably only the Indian precision mechanic knows."  :hammerbash:
« Last Edit: January 27, 2021, 01:25:36 PM by Vixen »
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Offline petertha

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Re: M5 Stuart Light Tank
« Reply #13 on: January 16, 2021, 06:07:44 PM »
Thanks for the details. I'll throttle my enthusiasm & lay low now so you post without (too many  :D) distractions. You obviously did some detailed work on the powerplant side which I'm really looking forward to see as the story unfolds. Very interesting project!

Offline Vixen

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Re: M5 Stuart Light Tank
« Reply #14 on: January 17, 2021, 02:33:36 PM »
Part 2   Steering systems

As we all know, a tracked vehicle is steered by reducing the speed of one track. When this happens, both tracks are forced to skid sideways over the ground. This action produces massive (sometimes destructive) forces on the track links, wheels and running gear and especially the transmission system. The steering loads require maximum power from the engine. The magnitude of the steering forces are very dependent on ground conditions. Smooth hard paved surfaces are much kinder than soft or rocky ground. For a model tank, even long grass can can provide difficult conditions.

Most model tanks have two powerful electric motors, their speed being varied independently by radio control. I did not want to follow this route. I wished my model Stuart tank is to be mechanically powered so I needed to devise a mechanical steering system. In full size tanks and tracked vehicles, there are a number of ways to do this, some are quite basic and some more sophisticated. Among the possibilities are:

1  Clutch/ Brake steering.  Here the drive is removed from one track and a powerful brake is applied. The disadvantage is a jerky uneven ride as the vehicles forward speed is suddenly reduced by half during the turn.

2 Braked Differential steering    A powerful brake is applied to one side of a differential to slow that track, the track on the opposite side increases speed and the vehicle turns very quickly. Such a high rate of turn is uncomfortable and undesirable, so this system is usually only used on very light tracked vehicles such as the Bren Carrier.

3 Controlled Differential steering    A more sophisticated system which produces fixed radius turns. It was widely used on the early US tanks.

4 Double Differential steering   A more complex system where an external, variable speed, steering shaft is applied to two differentials. One track speeds up and the other slows. This system can provide infinitely variable turn rates and steering not unlike a wheeled motor vehicle.


For my model Stuart tank I decided to build a CT1 steering gearbox based on a design by Iliya Cerjak, a brilliant young Dutch engineer who works in Amsterdam's University. The central drive shaft from the engine supplies power to two sets of multi-plate clutches, one for each set of tracks. The multi-plate clutches are operated by servos via a wishbone arm, fitted with roller bearings. The clutches engage the engine power and turn the intermediate shaft in either direction. The intermediate shaft turns the worm wheel in the final reduction dive in either direction. The worm and pinon arrangement was chosen for the final drive reduction (30:1) because a worm and pinion can effectively lock (brake) the tracks when neither clutch is engaged (centre position).

The CT1 gearbox allows each track to move forward , backwards or lock.






Here you can see the components of one set of multi-plate clutches. The friction plates were made from laminated printed circuit board (with the copper foil removed). Their serrated outer edge are a sliding fit in the aluminium clutch spider. The driven plates are made from steel sheet 




The centre of the clutch spider was broached with a hexagonal hole and is a sliding fit over a short length of hex bar attached to the input shaft. It's a poor mans splined shaft. The steel drive plates also have the broached hexagon hole and they fit over the hex extending from the output gears. The multi-plate clutches operate at engine speed and therfore see lower torque than if they were at the output shaft end, so can be comparatively small in diameter




The servo controlled wishbone arm fits between the two multi-plate clutch sections. The use of nylon for the gears was not a good choice and they were soon replaced with stronger steel gears.




Here you can see the CT1 steering gearbox installed in the front of the model Stuart tank. The linkage between the servos and the clutch control arms have not yet been fitted. The clear poly-carbonate top cover for the gearbox was useful for seeing what was happening inside. Gear lubrication was by grease (applied with a stiff paintbrush). Only a small amount of grease was applied, for fear of lubricating the friction plates of the clutches.




The movement of the two servos had to be carefully adjusted to ensure the clutches were fully engaged at the end of the servo's travel. There was always a risk of the servos stalling (and burning out) if they could not reach the end of their travel, so I fitted two adjustable coil springs in each control rod to prevent this overload situation from happening.

My Futaba radio control set allows electronic mixing of the control channels. I set the right hand joystick to control the steering gearbox. Stick forward; engaged both forward motion clutches, rearward stick motion would put the tank into reverse. Side motion of the joystick would disengage the appropriate clutch and the model tank would turn. I used the left hand joystick for the engine throttle servo




I was now in a position to fill the fuel tank, switch on and start the engine for the first time. Then began the fun time of seeing what worked, what  didn't, what needed modification. I always enjoy the development phase.

Did I ever tell you that I like engines and mechanisms? :noidea:

Mike


« Last Edit: January 17, 2021, 04:07:22 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.