Draughting Pens

For anyone not familiar with the 'twisty' concept , its a single or double acting engine that has an extended piston with ports in its sides, the drive to the flywheel is some sort of universal joint so as it lifts and lowers the piston it also covers and uncovers the ports.

With care its possible to make an engine with only two moving parts (piston and flywheel/shaft). The downside is the lack of adjustment.

Twisty was an example described in ME as a new idea, but in fact a similar model had been descrivbed many years before, and clearly this engine is even older.

Nihil sub sole novum

Neil

Just had a look at that Twisty in ME and you could well be right, just ned to work out why it has such a thick piston rod or is that a tube full of steam

I think the engine is definitely a reciprocating type.

I assume the crank pin engages with the lump attached to the piston rod and it slides in the upper tail rod support. There is probably an oil well in the lozenge shaped bit which is bolted to the piston rod, you can see the cross bolt in the diagram. That would be enough to keep the crank pin and piston rod lubricated.

The governor is driven by the belt pulleys (belt not shown in diagram) and there must be a pair of bevel gears inside the casting. The governor operates the steam regulator. The mystery is - where is the valve gear? Possibly it is contained within the piston casting and as with most stationary engines it only rotates in one direction, so a simple piston or slide valve would do the necessary.

I have seen similar steam engines in old books but never one like this one.

There appears to be a sort of name or logo cast into the main support but it is too indistinct to decipher.

Indeed I have pondered it over the years. I can sort of see how the crank may be articulated, although it seems rather complicated. Neil may well be right about it being a twisty. It seems to show steam entering on one side with the exhaust in line on the other. I'm afraid I have no clue about the origins of the engine, or whether it ever existed in full size. Here are some closer shots of the elevations:

Andrew

Edited By Andrew Johnston on 24/05/2016 22:54:50

Some background - my grandfather was born in 1888 and came south from Edinburgh in 1904 looking for work. So he would have been about 20 when the drawing was done. That seems a little late for an apprentice piece? My mum thought it might have been a demonstration drawing (like an artists portfolio) when looking for work. If that is the case it may well be that the engine never existed, and wouldn't work as drawn. However, that seems odd. Remember that in the good old, bad old, days the draughtmen often did a lot of the detail design and calculations, so not good if the engine design was wrong?

I know that my grandfather was working at the Royal Aircraft Factory at Farnborough in 1912, as there is an entry in Geoffrey de Havillands flying logbook in that year stating "took Mr Johnston for a ride". In the early 1920s he was working on high voltage switch gear at BTH in London. In 1925, a few months after my father was born, he moved to Yeovil to join Westlands as chief draughtman. As an aside my father had his first trip in an aeroplane at Westlands. Aged 10 he cycled out to the airfield, spoke to the test pilot, Harald Penrose, and was given a trip in the back of an aeroplane about to be test flown. Can't imagine that happening today!

In the late 1930s my grandfather moved to Airspeed as chief draughtsman, working with Tiltman and Neville Shute Norway. He lived in Portsmouth during the war, where they had an indoor Morrison shelter, rather than the more common Anderson shelter. When Airspeed was taken over by de Havilland my grandfather transfered across and became their design office manager at Christchurch. He retired from de Havilland in 1960, and promptly joined a local engineering company in charge of the stores.

Andrew

Andrew, thanks for the extra photos and family history.

J

PS could you provide one dimension so an idea of size could be worked out, say flywheel diameter

Edited By JasonB on 25/05/2016 07:27:45

Gee Andrew

Those drawings are wonderful. He must have used CAD LOL

I hope they are framed and hanging on the wall (Not near Sun). Too good to be locked away.

Regards
John

Andrew - that's quite a respectable aviation engineering family history. There definitely seems to be a genetic component to what makes us tick. In my case, it seems to be agricultural engineers and carpenters, also from the Scottish Borders - not quite in the same league perhaps! My dad came South for work with his PhD and found ICI (remember them), while his cousin (and now his son, my second cousin?) took the other route and stayed to run the farms.

From what I can now surmise, it's pretty much complete as shown. The "Twisty" concept sounds right, whereby the piston is also a rotary valve, being both raised and lowered as well as rotated back and forth by the connection to the end of the crank.In the process, it opens (uncovers) the inlet and exhaust ports, a little bit like a sleeve valve engine (without a sleeve as such). Can't see the detail of the connection between the governor and the steam valve but that's not critical.

Murray

In it's simplest for the joint between piston rod and crank could be something like this. A second top plate would support the top of the rotating bearing.

It does seen a very small piston area with such a thick rod?

The governor link is visible, that "ring" between the flange from the cylinder and the regulator flange would have a butterfly valve or similar. A lever from the governor to the rocker shaft and then a second lever from the shaft to the butterfly valve complets the linkage. It is there if you blow things up.

Edited By JasonB on 25/05/2016 08:38:38

Edited By JasonB on 25/05/2016 08:42:50

It could be a type of sleeve valve engine. The sleeve is connected to the piston rod and moves to open and close the ports. As the exhaust seems to be directly opposite the inlet steam pipe that could work. But the piston must have been quite a small diameter compared to the cylinder outer diameter?

I expect the port timing would be controlled by suitable holes in the piston skirts, so no need for sleeve valves as such. The piston could be not much smaller than the outer wall.

Although there is no need for a conventional conrod, one of the main downsides of this concept must be the greater stresses on the piston rod. It is subject to significant bending stresses, as most of the thrust is generated when the connecting pin at its greatest off-axis distance. This probably explains the hefty piston rod - possibly hollow but still quite sturdy. And although the piston motion is linear, there will be significant friction generated in the sliding piston rod bearings by the crank / connecting pin.

Murray

Jason: Flywheel diameter measures as 7.5". Thanks for the excellent 3D CAD models. It seems that it may well be a viable engine? With your workrate I expect that you'll have knocked one out by the end of the coming Bank holiday weekend.

Andrew

Yes, all three of my pictures are framed, and hanging in the hall or corridor away from direct sunlight.

Andrew

Quite so, although I had no choice about being an engineer as I'm darn all use at anything else.

Andrew

Andrew's drawings have a subtle quality and warmth that a cold CAD program could but hope to reproduce.

Maybe not technically perfect but quite usable and easy on the eye.

It's quite difficult to explain why, but I like them as a work of engineering art.

* Danny M *

And if you want scale, I suspect those brown rectangles at the bottom will scale to just under 9" long and 3" high - allowing for mortar

Bit blurred but there's a scale in the lower right hand corner of the drawing. I think it says 1 1/2 inches to the foot which makes 7.5" mean the engine has a 5 foot flywheel.

And makes the bricks 8.5" long, looks like they left the mortar out

Hiatus maxime deflendus!

Neil, being in the construction industry I know all to well the variation in old imperial bricks so they can only be taken as a rough guide.

Thanks Andrew for confirming a known item looks like 2" scale or 1/6th would be a nice size to model it in and a 10" flywheel will fit nicely on the lathe, though it's not quite such a nice scale to get to suit nominal sizes, the original 1/8 of the drawing is better for that.

Also good to know that all that macheneryu and tooling in the house is doing a good job blocking out the daylight