11 replies to this topic

[Magoo]

As noted in this forum, radials are weird and wonderful engines. Here is a cutaway-in-motion video which does a good job of illustrating crank train motion and firing sequence etc. The animation by Manolis is awesome (It's in the VW radial thread, don't miss it) but probably beyond the reach of a general audience --- this video provides some straight, simple illumination.  

 

 

VIDEO: How a Radial Engine Works---An Amazing Cutaway in Motion | Mac's Motor City Garage.com 

 

 

 

 

 

 

[malbear]

The pistons seem to have an oil control ring below the plugged gudgeon . Is this for oil control ? especially for the bottom cylinders. . I can remember when fighting fires in the narkat reserve some radial powerd water bombers landing on the main road . when they started after loading with retardent they smoked from the lower cylinders but cleared later. 

[GreenMachine]

The pistons seem to have an oil control ring below the plugged gudgeon . Is this for oil control ? especially for the bottom cylinders. . I can remember when fighting fires in the narkat reserve some radial powerd water bombers landing on the main road . when they started after loading with retardent they smoked from the lower cylinders but cleared later.

A Temora I watched the Constellation start up, expecting lots of smoke. That I saw, but what surprised me was the length of time each engine smoked. I thought that it would clear quickly, like in a few revolutions, but no, the smoke continued for 5? 10? seconds.  This suggests to me that the oil is either not cleared in the first few cycles, or that it is replenished perhaps due to loose clearances allowing oil to be sucked past the rings of the lower cylinders, or down valve stems, until the clearances close up as the engine gets warmer.

[Lee Nicolle]

That is obviously a short coming in radial engines. No ring will ever totally seal. Turn the engine off and the oil leaks past the extra ring. Deonation then happens in that 10 sec or so until the excess oil clears. The 4th ring itself  is more drag too ofcourse and more wear to the bores too probably.

[bigleagueslider]

The pistons seem to have an oil control ring below the plugged gudgeon . Is this for oil control ? especially for the bottom cylinders. . I can remember when fighting fires in the narkat reserve some radial powerd water bombers landing on the main road . when they started after loading with retardent they smoked from the lower cylinders but cleared later. 

The OEM pistons in my old 356 Porsche air-cooled engine had the oil control rings below the wrist pin.

 

[Lee Nicolle]

The OEM pistons in my old 356 Porsche air-cooled engine had the oil control rings below the wrist pin.

 

A few older style engines did. As did some aftermarket pistons too. Some 4 rings. 

I once pulled apart a "Hot" grey Holden motor with 4 rings. Made no sense then and less now!

Those barrels are a bit flash,, go the Burt Munro way with [used]  water main with sleeves shrunk over them. And home made pistons.Then you can get the desired dome, squish and compression I presume he bought his rings though off the shelf though. Then maybe not!

[BlinkyMcSquinty]

A Temora I watched the Constellation start up, expecting lots of smoke. That I saw, but what surprised me was the length of time each engine smoked. I thought that it would clear quickly, like in a few revolutions, but no, the smoke continued for 5? 10? seconds.  This suggests to me that the oil is either not cleared in the first few cycles, or that it is replenished perhaps due to loose clearances allowing oil to be sucked past the rings of the lower cylinders, or down valve stems, until the clearances close up as the engine gets warmer.

The engine in the Connie was a compound supercharger, and that was the cause of so much smoke. I am assuming that once that part warmed up, the tolerances closed. I watched many engine startups for another aircraft using the same engine, and yes, wow, did they ever smoke.

 

[bigleagueslider]

Blinky-

 

The R-3350 used on the Super Connie was supercharged and turbo-compounded. The 3 exhaust turbines were coupled to the crankshaft by gear drives and fluid couplings. The intake supercharger was driven separately from the crankshaft. The smoke produced at startup was from lube oil that accumulated in the lower cylinders when the engine sat idle.

[JtP2]

Oil collection in the lower cylinders is the reason for walking the prop through before starting to avoid hydraulic lock.

[GreenMachine]

That vid was interesting.  The smoke went way longer than what I remember, and while it will certainly be some oil collected and burning off, there HAS to be more than just clearing pooled oil as surely it would not survive that long in an operating cylinder, unless it was getting topped up by more oil sucked past loose rings or valve guides. 

 

Interesting that there was no load on the engine, and no cooling fan either.

[gruntguru]

That engine has a problem - the smoke should clear sooner. Its not just from lower cylinders either.

 

This one https://www.youtube....h?v=wVmMd2BnbJ4 clears much more quickly, (white) smoke is mainly from the lowest turbine outlet. Engine start at 3:40.

Edited by gruntguru, 16 January 2015 - 02:15.

[BlinkyMcSquinty]

Blinky-

 

The R-3350 used on the Super Connie was supercharged and turbo-compounded. The 3 exhaust turbines were coupled to the crankshaft by gear drives and fluid couplings. The intake supercharger was driven separately from the crankshaft. The smoke produced at startup was from lube oil that accumulated in the lower cylinders when the engine sat idle.

 If it was just the oil from the lower cylinders then all radial engines would smoke like that. But in this startup of another radial engine, the smoke stopped within seconds.

 

 

The difference was that the one that smoked excessively had exhaust recovery turbines. They had loose tolerances when cold, and once warmed up, the seals closed and the smoking stopped.