Schnerle scavenging

The typical Cox Babe Bee and TD's have "radial porting", while Schnürle porting was used in the Cox Conquest engine.

An article about porting and scavenging of two stroke model engines in American Aircraft Modeler magazine by Glenn Lee:

Cox porting is most correctly described as 'reverse flow' scavenging-its not 360, nor is it cross flow, nor is it loop...though by a bit of stretch you might argue there is something of a loop effect when only a single transfer is used....and it certainly isn't schneurle [with the sole exception of the Cox Special 15 Mk II.]  I'm discounting the conquest as that IS unmistakeably a schneurle motor-and the original post refers to a Babe Bee.

If we take Cox porting in its 'general' form as having two diametrically opposed exhausts and one or two diametrically opposed transfer flutes-with symmetrical opening when there are two transfers, then the process involves an inbound jet of mixture (or two with twin transfers), directed upwards towards the centre of the head, combustion, and two exhaust jet flows, again simultaneous. (though this does match the original schneurle in Levent's diagram.*Whilst we might call it 'Cox' porting, a number of other manufacturers-most notably European manufacturers-also used the same setup-especially the 'fore and after transfers with two opposite sided exhausts-such as Cipolla, Barbini, FOK, and Davies Charlton to name but a few....

ChrisM
'ffkiwi'

* but this is not what we commonly refer to as schneurle in model engines these days-which can be minimally defined as " a single exhaust port(which may be divided by pillars), and at least two angled transfers generally opposite (but not necessarily directly in line with the exhaust) angled in two directions to direct mixture upwards towards the centre of the head, both incoming streams impinging together, and away from the exhaust, with an option third or boost port located between the two main transfers, generally-but not always, of smaller area-and normally timed to open either earlier-or sometimes later-than the two main transfers.   These days of course we can have 3, 5, or more ports, with additional tailoring of the shape to improve efficiency or minimise 'stagnant' areas in the upper cylinder.

Thanks Levent for the informative article clips and Chris for your detailed explanation.

Considering manufacturing costs versus performance, one thing that has amazed me about Cox engines is the simplicity of the engines. Schneurle cutting costs more, and the standard porting of the Cox engines were optimized to produce the best results given the technology of the time.

Bill Netzeband took it through further honing on the Testors engines and came up with the Testors 8000 reed valve engine and derivatives loving called the Pipe Bomb engines for the Testor RTF's, to the extent the 8000 outperformed the Black Widow.

Even though hotter engines like the Norvel out do the Coxes, these engines still are powerful enough to haul the goods with half-A models.

Like anything, matching the engine's power to the proper model proportions is key to good performance.

Although the standard cross scavenge engines with piston fence are considered less powerful, their advantages are their fuel economy and some can swing wider blade / greater diameter props easier, so they have their place with aircraft of greater fuselage cross sections and draggier planes.

An underpowered aircraft more or less sucks.

So far here in CEF, we have seen a very broad range of aircraft being modelled. I enjoy watching and reading about those.

The later, thick wall TD and Venom cylinders have only 1 instead of 2 booster ports in each transfer port and as such, add a tangential spin to the jet, like the Schnürle porting..

Does anyone have a reference for the "original Schnuerle" fig. D porting? I've only ever seen the patented Schnuerle design as per "F" above. Perhaps it was his early work. Schnuerle didn't even invent the boost port as seen in what we commonly call "Schnuerle".

Some modern engines are not Schuerle ported. The Profi 0.8 and 1cc with the 90° offset intake look more like the early Super Tigre patent with two symmetrical transfer ports opposite the exhaust.

Fox patent 4638770 refers to the Cox type as Villers (which I think should be Villiers). I couldn't find patents (non were referenced by Fox), but around 1930 Villiers did produce motorcycle engines using this porting.