Questions about AC piston engines that I've never dared to ask

[The Flying Pram]

O.K. - It was a long while ago!! As for Sleeve Valves these take the form of an extra liner between the cylinder and piston. They have slots cut out which line up with ports in the cylinder when the sleeve is rotated. I have read horror stories of the extremely complex drive mechanism and the difficulty of setting it all up... I assume the varying expansion rates causes the the high oil consumption, and start up smoke. Mind you all radials are prone to this. A local pilot bought an AN2 some years back and it was not a good idea to stand downwind when he fired the engine up!

[matt_hooks]

And another problem with the old rotary and radial engines was hydraulic lock after standing overnight,

Oil drains down, past leaky seals around pistons etc. to gather in the lowest cylinder(s).

Hence the hand turning that was necessary on most of these types. Attempt to start with a hydraulically locked head and all sorts of things could be bent/broken/damaged!

[Old Fella]

Sleeve valve engines

As the name implies, sleeve valve engines do not have conventional pushrod operated valves. The piston moves within a sleeve which has inlet and exhaust ports cut through the wall. The sleeve in turn moves within the cylinder outer casing, by means of a bell-crank to open and close the ports as required, i.e. opens to the inlet manifold to allow the flow of fuel/air mixture into the cylinder via the corresponding opening on the cylinder barrel and opens the exhaust port to the corresponding opening in the cylinder barrel to allow the combusted gas to flow to the exhaust stub. The cylinder head, known as the junk head, houses the spark plugs. So what you have is a piston moving within a sleeve which moves within the cylinder barrel. Sleeve valve engines are generally very reliable and deliver good power to weight ratios. They, like any radial engine, do emit copious clouds of oil smoke on start up. This is why ignition is not introduced until the oil is scavenged from the lower cylinders on start-up on radial engines and the sleeve-valve engine in particular used a good quantity of oil in normal operation due to the need for additional lubrication as compared to a conventional OHV engine, three to four gallons per hour not being uncommon, although they also usually leaked plenty too in my experience with them on Bristol Freighters.

[GotTheTshirt]

When I moved from P & W to sleeve valves ( I did the course at Bristol) like Flying Pram I thought this will never work and if it did not for long and the bellcrank mentioned looked like is was only strong enough for a lawn mower
I worked Hercules and Centaurus and they beat the P & W into a cocked hat
P&W 1830 had a an ARB TBO life of 1400 hours but the Centaurus we ran 2,200 hours
No routine maintenance on the sleeve part of the engine,and nothing to set up or adjust in service
P&W valve clearance adjustment and rocker check every 500 hours.
Rocker check took 3 guys 2-3 hours !
Changed 50 plus cylinders on P&W all failures ( Some spectacular.)
Changed 2 on the Centaurus one for a stripped plug thread Never heard of a sleeve failure

Centaurus had LT ignition much easier than Magnetos on 1830

[The Flying Pram]

When we visited Ken Wallis at Reymerston Hall many years ago he had a Centaurus in the back of his workshop. I don't know if he was intending to build a gyro around it....

[The Flying Pram]

When we visited Ken Wallis at Reymerston Hall many years ago he had a Centaurus in the back of his workshop. I don't know if he was intending to build a gyro around it....

[Basil]

IIRC, when increasing power on the Hercules, you increase boost then RPM contrary to poppet valve technique.

[WHBM]

Originally Posted by GotTheTshirt

Changed 50 plus cylinders on P&W all failures ( Some spectacular.)

What was that manufacturers logo on the side ? Something about "Pratt & Whitney" and .... um ... was it "Dependable Engines" ?

Mind you, if you'd had Wrights instead it would have been 100 plus cylinders. A story about B-29 Superfortress maintenance at Pacific bases in 1945 with Wright R-3350 powerplants described an enormous pile of failed engines, heaped up higher than a house, at the back of the maintenance base. And when it got put on the Connie and the DC7 there were similar stories. Broken valves were most common but other components took their turn as well.

[Old Fella]

Wright 3350 Engine

I guess Wright 3350's were little better or worse than P&W's or Bristol's however I do remember one event in early 1959 when a RAAF P2V5 Neptune, on a final test flight before departure on an overseas flight, was lost with all 10 persons on board perishing.

The cause of the crash, which happened near RAAF Base, Richmond, was the uncontained failure of a Power Recovery Turbine. When the turbine failed and broached the casing it severed fuel lines and initiated a fire which burnt through the wing spar before the aircraft could be recovered to Richmond.

The sight of the aftermath has stayed with me for almost fifty years. It would be unfair for me to accuse Wright's of building inferior engines because of this one event. I have also had to dis-mantle many P&W Twin Row Wasps with broken articulating rods, cracked cylinder heads, sheared cam pack gears etc and on one occasion had bits of a Bristol Hercules engine come through the cargo compartment wall of a Bristol Freighter when a sleeve valve actuating crank let go. Also had JT3's fail and RB-211's suffer turbine failures, let alone numerous Allison T56 engine and gearbox failures, so I guess any engine can have problems. At least these days the DFDR's can enable a look back over the history of the engine and sometimes find evidence of operating abuse as a contributory cause.

[411A]

Ahh, yes, PRT's.
Having flown 1649 Connies for awhile, I found that the average life of a PRT was 150 hours...200 tops.
However, when the 3350 turbocompound engine was running properly, is was very smooth indeed....almost turbine like.