Sidevalve single

[Art K]

Hi, ownthesky2010,
I caught your last post and was reminded of a portion of Herschel Smith's book "A History of Aircraft Piston Engines", and yes I read the whole book. Chapter ten is about the opposed engine. He talks of a 1917 Lawrance C-2, "It set at naught the basic advantage of the opposed engine by using a single throw crank." He also used Mickey Mouses name in vain and mentioned Newtons first law. The gist of this was that both pistons going back and forth shook the airplane apart. I would suggest a two throw crank, although not as simple to make, the pistons going back and forth cancels each others movement out, making the engine fairly well balanced.
Art

 

[mu38&Bg#]

Saito produces single throw opposed twins. People say they run smoothly. I did run one maybe eight years ago and didn't remember any unusual vibration. The crank just needs enough counter balance mass. It balances just like a single cylinder. I can say that the opposed boxer twins OS makes run very smoothly. I have an FT-160 on an aircraft now.

Greg

 

[Niels Abildgaard]

Hello Richard
A hanging V2 will be much smoother and fit the nose of ME 109 models.
It is not difficult to design the counterweigths.
Bring relevant parts in these two positions and remove or add mass to counterweigths so that center of gravity is the same.

 

[Hopper]

Hi Ownthesky2010 -- Your engine sounds beautiful, that distinctive flathead noise. Very nice work.
Sounds like you got the right compromise between compression and flow. At the end of the day, all that counts is the actual pressure in the cylinder at the end of the compression stroke -- whether achieved by small combustion chamber or by cramming more charge into the cylinder before compression begins. Seems the latter is the way to go for flatties.

Looking forward to seeing your flat twin. Seems like the small mass of model engines allows makers to get away with single throw crankshafts. I know that all flat-twin motorcycle engines (BMW, Zundapp etc) use double throw cranks so both pistons travel in opposite directions, aka "boxer" like two fists pumping in and out alternately.

Might be the secret to single throw crank is getting the right balance factor? Makes may head hurt just to think about it. Like balancing a single, but then you have the weight of the other rod big end rotating and piston reciprocating in the same direction as the first piston. So balance weight might need to be double the weight of what you would use for a single??

Any how, have fun with it and keep us posted.

 

[ownthesky2010]

Thanks for the encouragement guys.
I think I just have my own funny little ways.
As long as I meet a minimum standard of performance/efficiency I don't think that more makes a better engine.
What really interests me is character and presence.
I chose the single throw crank because I'm hoping for a nice lopsided/offbeat exhaust note that will sound good in a model plane.
I'm thinking of it as a 180 degree v twin or 2 cylinder radial
These engines are a compromise in every way.
Maybe by getting it all wrong in all the sensible ways it will end up just right in the way of character.
Niels thanks for the v twin info. Its on my todo list too, although with another 10 cylinders.
As far as balancing goes, it does have me a little worried.
I think I just balanced the rotating mass + half the reciprocating mass with the single so I might try that again.
I will probably need to insert something heavier than steel as the crank web is not very thick.
Maybe tungsten carbide, my local Tesco doesn't sell depleted uranium.
At least a crankshaft is fairly easy to remake/modify.
If you turn it from an 8.8 bolt its halfway to the right shape already.

 

[Hopper]

Hi OwnTheSky
Yeah, I reckon you should get away with the single throw crank in a small engine.
What you are doing is essentially the same as what goes on inside parallel twins having a 360 degree crank: two pistons and rods travelling in the same direction at all times. I know from vertical 360-degree twin motorcycles (Triumph, BSA, Norton etc) that the 350cc and 500cc models were sweet running bikes. But the 750s were vibrating monsters and the 850 Norton necessitated a rubber mounted engine!
So such an unbalanced set up can work in small engines better than large.

Yes, I would think balancing like a single - all the rotating plus half the reciprocating mass -- would work ok. Just remember that the reciprocating weight now includes two pistons and the proportion of two rods. So it will need a counterweight twice the weight of the single.

Another advantage of the side valve is that its low compression causes less vibration than a higher compressed engine of the same layout. So that should help you get a smooth runner.

Have fun doing everyting the "wrong" way and making it work.

 

[Niels Abildgaard]

Can we see a drawing?
My fingers itch to make it into something just as outmoded, but never tried before.Two stroke with cam on crank and one side mounted exhaust valve.

I dreamt up a two stroke with sidevalve exhaust many years ago and have the pleasure of seeing it considered as future car engine.
Try reading session five papers from a conference 2020
Future two stroke

 

[Niels Abildgaard]

Can we see a drawing?
My fingers itch to make it into something just as outmoded, but never tried before.Two stroke with cam on crank and one side mounted exhaust valve.

This is first mentioning of my two stroke sidevalve idea I think 23 dec 2014.

It has been taken serious

Better late than never

 

[Niels Abildgaard]

A recent phantasy with thumbleweed compustion space and exhaust as a very good fourstroke and much less NOx
An old 40 times 40mm and the new 34mm bore 48mm stroke compared sizewise

 

[Niels Abildgaard]

This is first mentioning of my two stroke sidevalve idea I think 23 dec 2014.

It has been taken serious

Better late than never

There was a picture of a wet sump ,sidevalved two-stroke twin since removed.
Clean twin,two-stroke