Leaf springs for engine valves

Since seeing the plate springs for the valves in ‘Rammerc’s’ mystery outboard, I’ve been looking out for something similar.

This is a 1915 Beardmore aero engine at London’s Science Museum. Presumably this was an Austro-Daimler feature? (Beardmore had some sort of licence agreement with A-D). One rocker arm operated both inlet and exhaust valve (Porsche patent).

Asquith

Great picture.I have found leaf springs mentioned in several publications but rarely have I found any pictures. One book comes to mind, Aviation Engines by Lieut.Victor W Page ( 1917 )Now I will have to try to locate it and look back through it.

I also turned up a book that mentioned a 1906 Woseley auto that used leaf springs. When I emailed the museum in the UK where it supposedly was displayed they said they no longer had the car. I never followed up on that one.

Thanks for the posting, I will print it and add it to my file.

Rick

Asquith,

Thanks for the photo - I knew I'd seen a picture of another engine with laminated valve springs somewhere, but couldn't remember where. The 120 HP Beardmore had a couple of other interesting features besides the single rocker arm and the laminated valve springs according to the 1917 Air Board Technical Notes.

It was fitted with a starting magneto. These were mentioned in a couple of times in your Clockwork Starter thread. The way these worked on the Beardmore was fairly complex and the description takes up about half a page of the notes.

The main magnetos were not driven at half engine speed as is common with stationary engines, but made three revolutions to two of the engine.

The water jackets on the cylinders of the 120 HP Beardmores were electrically deposited copper.

The center line of the cylinders is offset from the center line of the crankshaft.

Some Beardmores survived the war and entered civilian service. Four of Qantas' first eight aircraft were fitted with the slightly bigger 160 HP Beardmores.

franco.

[ 06-14-2006, 12:44 AM: Message edited by: franco ]

Rick,
I have a booklet "The Horizontal-engined Wolseleys, 1900-1905". Herbert Austin was the man who designed these cars, and they began to go into production after Vickers bought the motor car side of Wolseley in 1901. The two cylinder 10hp model became the most popular, there was nothing great about it, but it earned a name for reliability at a time when most were not...

The 10hp engine used atmospheric inlet valves with normal coil springs and exhaust valves with laminated leaf springs.

The horizontal Wolseleys that interest me are the racing versions, in particular the Beetles. These were good looking cars for their day, low slung (with their horizontal engines) and some were quite powerful four cylinder horizontally opposed - 72 and 96 hp versions being made. Not sure about the valves on these engines, I would suspect the atmospheric inlet was done away with?

Why leaf springs? There is considerable friction in them and the operating frequency is high.

On the face of it the application would seem to contra indicate the use of any kind of flat springs, let alone a flat spring pack.

Jim

I wish I was more knowledgeable about the subject. In past conversations about my engine the subject of heat treating of coil springs came up. I guess they had trouble back then with valve float because of the springs where flat material may not have posed the same problem. Someone also mentioned he thought the friction caused by the stacking of the springs would dampen the Harmonics ??? Vague memories from the past that may have been BS.

Rick

Since they did not have the vast knowledge base to draw on that is available now, leaf springs seemed to be a good idea.
Progress is sometimes a process of elimanation; ("OOPS, THAT did not work!!")

Someone commented when asked why so many goofy aircraft designs in the early years: " Because no one knew what an airplane SHOULD look like"

One of the joys of studying old technology is that it takes you back to first principles and makes you appreciate the difficulties to old designers faced. Ken’s quotation " ….. no one knew what an airplane SHOULD look like" is very appropriate.

Nowadays we are accustomed to seeing refinement rather than revolution in design. It may be difficult now to understand why designers went down so many blind alleys to get to where we are today. Without knowing the barriers they faced, it’s hard to know what they were up against. In some cases available materials imposed a limit. Patent avoidance was another strong influence, then there was conservatism, lack of technology, knowledge, plain madness, etc., etc.

In the case of the leaf springs, who knows? A point to consider is this: you’re up in the sky, in a single engined plane with new-fangled overhead valves. If a spring breaks, the big valve drops. With a highly-stressed helical valve spring, a single defect can quickly grow to cause failure. A multi-leaf spring of that era may be less likely to fail, and can have more redundancy built in. Of course, with helical springs, an extra one could be nested in to provide assurance.

It also strikes me that the use of coil springs in the Beardmore would have made the engine taller, usually a bad thing in aircraft. (Taller because the valve stems would need to be longer, and also because the cylinder head would have to be beefier where the spring sits).

Rick is quite right about the damping effect of friction in leaf springs (presumably one reason why they persisted in use for car suspension?), but I don’t know whether valve bounce would have been a problem at these speeds.

I’ve just looked at Bill Gunston’s ‘The Devlopment of Piston Aero Engines’, and this has a very nice picture of this engine, but labels it as a 1912 Austro-Daimler. In fact the brass plate soldered to the copper jacket says ‘Beardmore’.

Racing-car engines have used leaf springs on occasion; a long time ago, though.

I think it must have been for the damping properties of the multi-leaf spring; a property analogous to the friction damper used on old cars.

The multi-leaf spring was used at the rear of cars partly (at least) because the lever-arm friction and the later hydraulic dampers of the day were inadequate; the inter-leaf friction of the multi-leaf spring (which often had rubber/plastic/whatever elements between the metal leaves) supplemented the damper (the "shock absorber").

Coil springs can set up destructive undamped oscillations between the ends; play with one of those Slinky things and you will see something of this.

"Broken valve spring" was a common cause of retirement from motor races until c.1960 or so. It wasn't the spring breakage per se which caused the retirement; it was the disaster which followed the collision of the descending valve with the rising piston

I imagine that the metallurgy/mathematics of helical springs was not fully-understood a century ago and that the leaf springs in aero and car engines were, at least, a known quantity.

Another disadvantage of the coil spring when used on an air cooled engine that the leaf(s) could improve on engine is spring collapse from heat picked up from contact with the cylinder head.Note all the pre 60's racing motorcycle engines with exposed(for cooling) and maybe hairpin instead of coil for this reason(Norton,AJS,Parilla,Ducati.Also any oil thrown off halped to keep the dust down.I think this was one reason Phil Vincent put the spring above the operating lever(rocker arm)to increase distance from the heat source.

Enginenut,

I think you have lots of company. I emailed Peter a drawing from the book I mentioned above showing desmodromic valves being uilized in an engine from the teens. It also had four valves per cylinder. The book also mentioned dual coil springs being used in the same time period for safety purposes. I did a quick search Abe books, two copies are available cheap for other gear heads with the same interests.

I also mentioned to Peter that I owned a Norton international and a Manx back in the 60s. Loved those hairpin valve springs expose to the open air with a mist of oil around them when running.
Had we only been smart enough to have kept our toys from the past ---

Rick

Rammerc, Thanks for the tip on Page's book.I missed my bid on one on Ebay recently and it is on my want list.I have another by Page:"The Modern Gasoline Automobile" cw 1918 and it is a prize to me.Page certainly had a taste for the unusual and sought to find and publicize the variations.I have never seen so many different engineering approaches to the engine design as he pictures.Several 2 stroke with stepped piston size for enhancing the charge(supercharge),Ring valve, sleeve valve,disc valve,rotary valves of several flavors.He shows 2 desmodromic valve actions 1 by Michaux and 1 by De Lage.Engineering was not stagnant in the auto industries in those days.Wouldn't we like to see some of these ideas persued with modern materials and "cures" for the ills that killed them then?But I guess not on my nickel or I'd be doing it and starving.Just not dedicated--or at least my wife isn't.Mechanic/old car nut I worked with says a man has a wife to act like a governor on an engine--keep us from running to the point of destruction.In the back is listed under"catalogue of good,practical books" at least 20 books listing him as author.Page must have been a "nut"--too bad we didn't have more.