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M5 Stuart Light Tank

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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thin armor and small 37mm gun became ineffective against more modern and more powerful opposition, the M5 Stuart was withdrawn from tank v tank operations and went on to serve as an excellent scout or reconnaissance vehicle.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


what is path for the air cooling?

 :ThumbsUp: :ThumbsUp: :ThumbsUp:  :praise2:



--- Quote from: tghs on January 15, 2021, 08:10:41 PM ---what is path for the air cooling?

--- End quote ---

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.


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.


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