O/T? Twin crank engine

"John" wrote
100% primary balance - a certain Mr Lanchester had the same idea some years ago!
Nick H

It may have perfect balance, but the con-rod angle means next to no skirt on the piston, which would worry me a little. I suppose they are short of space otherwise they could have gone for a rhombic drive - but that appears to need more space under the crankshafts for the bottom part of the rhombus when the piston is at TDC.
Steve

But it doesn't need much skirt due to having *two* gudgon pins.

S> It may have perfect balance, but the con-rod angle means next to no S> skirt on the piston, which would worry me a little. I suppose they are S> short of space otherwise they could have gone for a rhombic drive - but S> that appears to need more space under the crankshafts for the bottom S> part of the rhombus when the piston is at TDC.
S> Rhombic_drive
S> Steve
Only ahieves primary balance - piston motion is still non-sinusoidal so there are higher order vibes to contend with. Also doesn't need much in the way of piston skirt as the side thrust from the two con rods cancels out. The type of rhombic drive illustrated in the link, with co-axial piston rods, is pretty much specific to Stirling engines. The Lanchester engine (ISTR 1903 or so) had a similar arrangement of four con rods but with pairedcylinders in a horizontally opposed arrangement. I'm not sure, but I think this may sort out some of the remaining, higher order, imbalance of the single cylinder arrangement.
nickh=== Posted with Qusnetsoft NewsReader 2.2.0.8

(snip) n> The Lanchester n> engine (ISTR 1903 or so) had a similar arrangement of four con rods but n> with pairedcylinders in a horizontally opposed arrangement.
Just pulled Jeff Daniels' "Driving Force" off the shelf (recommended reading) Lanchester twin crank engine - 1896. The good doctor later eschewed the complication of this layout and invented balance shafts!
nickh=== Posted with Qusnetsoft NewsReader 2.2.0.8

Lookinfg in the Patents, F W Lanchester has a number of patents in the period, but there seems to be an error in the index, as 22946 of 1894 is not there. Others include 15045 and 18908 in 1895, 5814, 7603, 18829, 22935 and 24805 in 1896.
The earlier books are a bit fragile so I won't go through and look now, some of the pages are literally crumbling away.
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

Righto - my instincts about piston skirts obviously stem from conventional engines, hadn't thought about the fact that having two gudgeon pins and balanced side thrust both eliminate the tendency for the piston to rotate. One downside of a skirtless piston would surely be less surface area contact between the piston and the bore which might mean it gets a little hotter.
Bet it doesn't have a kick start !
Steve