Sherman Start Up

Originally posted by Hanno Spoelstra
I would not dare - but please don't keep us in suspense any longer!

H.

Seems daft doesn't it? First I could not believe it, but its true and involved an interesting journey to see my pals at the AFV Wing RCMS Shrivenham. They have a T 34 engine but regrettably with no rods or pistons, however, the crank had small diameter pins but very long and the bores are all in the same plane. The use of a big pair of vernier calipers confirmed the stroke difference from the piston ring witness marks in the bores.

How it occurs will become obvious, why I can only deduce from the aero heritage where a squat engine offering low frontal area (drag) is preferable. At this point you may well consider this unimportant having seen huge radials, but when this Hispano was designed, the art of cowling and the Townend Ring to negate the drag effect of a big radial was not well known.

The diesel Hispano unusually employs the radial technique of con-rod arrangement with a master rod and a slave rod, this is not normal in a V form engine as you have the option of making large diameter but slim big-ends to run on a common crank pin, but with the disadvantage of staggering the bores and making the block longer; or, like a Merlin and others, of having a forked rod with another plain rod inside; this has a tricky bearing shell which is clamped by the forked rod but has the plain rod running on its outer face. The bores are of course on the same axis block to block.

If you look at a typical radial layout with all the bores on a common line, you'll note that very long con-rods and slave rods are needed to clear the cylinder mouths and just taking two cylinders would make a very undesirably tall V form engine.
see:http://www.aviation-history.com/engines/radial.htm and http://travel.howstuffworks.com/radial-engine2.htm

Now to make it squat Hispano reduced the length of the rods but had to fiddle with the angular displacement of the slave rod bearing to get a miss on the cylinder mouths. The engine is a 60º V but the angular displacement of the slave rod "big-end" from the master rod is 67º and so the stroke this side is lessened as TDC occurs therefore 7º before the crank pin is on the cylinder centre-line.

Looking at the attached section drawing of a V-2-34 it is conveniently drawn with the centres and centre-lines shown, it is easy to join the slave rod bearing centre with the crank centre and then using the old school protractor the included angle is seen to be 67º; also it is obvious the extended centre-line of this crank/slave rod bearing is not parallel to the bore.

I think someone very clever worked this out ages ago when the original petrol Hispano 12Y aero engine was first produced around 1932 since you cannot fiddle the angles or dimensions without compromise or a foul situation. In its aero form the engine went on to make some 1100hp but generally rated at 820hp from 36 litres. The V-2-34 is some 38 litres and in original T34 form made some 500hp as a diesel which is quite mundane from 38 litres being just a tad over 13hp/litre; now in a huge leap of assumption I wonder if the Russians actually partly re-designed and down-rated the Hispano 12Y as a diesel, I have found this:

"In the mid-1930s, Russian engineer Vladimir Klimov was sent to France to obtain a license for local production of the 12Y. A series of design changes were added to cope with cold weather operation, and the engine entered production in 1935 as the M-100 with about 750 hp (560 kW). However a series of continual upgrades increased the allowable rpm from the 12Y's fairly low 2,400 to 2,700, thereby increasing power to 1,100 hp (820 kW). The resulting design, the M-105, became one of the major Soviet engine designs during the war. In 1941 designers were allowed to attach their own names to their designs, and the engine became the VK-105."

So what does it matter that the engine is 3% different down one bank to the other? I suggest bugger all.

One bank makes 257.3hp and the other 242.5hp or 2.5hp between nominal 41hp cylinders. Likely manifold casting imperfections, injection calibration and gas flows account for more variation than this; probably just our brains don't like the idea of an otherwise symmetrical V engine being a tiny bit asymetrical inside.

R.

Originally posted by FV623
Looking at the attached section drawing of a V-2-34

Which of course I entirely forgot so here it is.

R.

[Nigel Watson]

It was a simple question my learned friends. All I wanted to know was which way to turn the key!!!!!


Thanks for all your info which has been passed on to my overseas buddy and so far no load bangs so perhaps it was the other way! Will keep you posted as to the move with pics if I get any! Feel free to continue with your de-liberators!!

Nigel

[Hanno Spoelstra]

Originally posted by FV623
Now to make it squat Hispano reduced the length of the rods but had to fiddle with the angular displacement of the slave rod bearing to get a miss on the cylinder mouths. The engine is a 60º V but the angular displacement of the slave rod "big-end" from the master rod is 67º and so the stroke this side is lessened as TDC occurs therefore 7º before the crank pin is on the cylinder centre-line.

Amazing stuff - mechanical engineering at its pinnacle. And all this with merely a pencil and slide rule!

H.

Originally posted by Hanno Spoelstra
Amazing stuff - mechanical engineering at its pinnacle. And all this with merely a pencil and slide rule!

H.

Quite so, I used to rush home as a child with the latest gem of cutting-edge engineering technology to impress my C.Eng father only to be shown where it had been invented years before but usually failed owing to metallurgy.

The only mistake I recall was the chapter in his 1920's university text book by H.E. Wimperis on IC engines that dealt with the gas turbine as just an interesting lab experiment but that could never be an economic or viable power source. . . . . . . . . . .

However, I was fascinated by the discourse on the Humphrey Pump - a liquid piston engine and I see the Aussies have one still working; not bad for a 1901 design.
http://www.fortunecity.com/greenfield/bp/16/hump.htm

R.