World War Two Radial Engine functionality?

Okay, online flightsim question time.

Did the Curtiss or P&W Radial engines rotate on a mount and spin the propellor like their WWI predecessors or were they fixed and drove a propellor shaft?

I've seen WWI Era fighters with the engine exposed which and they spin, but all the WWII aircraft the engine is mostly enclosed in a cowl and not clearly visible if the cylinders are rotating as well.

Additionally, what effect if any would flying inverted for an extended period have on the engine.

The Radial engines were fixed to the mount; the crankshaft turned and thus drove the prop, either direct or thru reduction gear. The WW1 engine you describe is called a Rotary engine. They did not survive much past the end of the Great War, except as a curiosity. By the end of WW1 or shortly thereafter, the Radial engine was in production, although I don't believe any saw service in WW1.

Effects from inverted flight are a carburation issue, not engine type.

John

Before radial engine start-up, the carrier deck crewmen would turn the engine over by manually pulling the prop through a couple of rotations. I understood that this was necessary for an easy start-up, but I never understood why. Can someone enlighten me?

Army dudes did it too. It prevents/eliminates 'hydraulic lock', which can happen when oil drains down into the lower cylinders. If you just hit the starter and there is a significant amount of oil in the lower cylinders it can bend/break the connecting rod or pop the jug off the crankcase or other significant damage.

In addition to turning the engine over, the sparkplugs on the lower cylinders would be removed first in order to allow any accumulated oil to drain out. This was necessary because the oil, being incompressible, might have damaged the engine parts if not removed before working the engine. Once the cylinders had been cleared, the sparkplugs could be replaced.

Turning the prop may have also primed the engine before startup.

I believe the Rotaries were used on at least one French a'cft, but Brits used a radial on such as the Sopwith Camel and Pup in WW1. These radials were so low on power that there were, for practical purposes, only two throttle positions - on and off. Thus, for final approach on landings, power was controlled by turning the ignition switch on and off - repeatedly. Rotaries caused terribly strong gyroscopic reactions - therefore control problems, in any maneuver involving an attitude chance. These reactions had to be anticipated by pilots or they would never get the proper direction that they wanted. In any prop a'cft, especially a taildragger, when raising the tail at low speed for takeoff, we still have some 'P' factor and gyroscopic factor to contend with, which are greater and more important than torqe reaction, but nothing like the gyroscopic force from the heavy mass of an entire engine rotating, as with the WWI one rotary engines. believe the Rotaries were used on at least one French a'cft, but Brits used a radial on such as the Sopwith Camel and Pup in WW1. These radials were so low on power that there were, for practical purposes, only two throttle positions - on and off. Thus, for final approach on landings, power was controlled by turning the ignition switch on and off - repeatedly. Rotaries caused terribly strong gyroscopic reactions - therefore control problems, in any maneuver involving an attitude chance. These reactions had to be anticipated by pilots or they would never get the proper direction that they wanted. In any prop a'cft, especially a taildragger, when raising the tail at low speed for takeoff, we still have some 'P' factor and gyroscopic factor to contend with, which are greater and more important than torqe reaction, but nothing like the gyroscopic force from the heavy mass of an entire engine rotating, as with the WWI one rotary engines. [Some models of the 'Champion' were terrible, due to their wings' angle of incidence and resultant disturbed tail airflow

Rotaries were used extensively by the French, including the series of Nieuport pursuits and most of the Morane-Saulnier pursuits

Most of the Sopwith Camels were powered by 130 hp Clerget rotaries or 110 hp Le Rhone rotaries although a small number, mostly the naval Camel 2F.1 versions, used the Bentley 150 hp BR1 rotary engine.

All the Sopwith Pups used rotary engines - either 80 hp Le Rhones or 100 hp Gnome Monosoupapes.

SFAIK, there were no large scale uses of radial engines on WW1 aircraft (save the odd-ball Salmson water-cooled radials) though power plant designers could clearly see that rotaries were reaching the limits of their development potential and were devoting more and more effort to radials - as well as liquid cooled in-line and vee engine designs.

Cheers and all,

The Camel and Pup were both powered by rotary engines. So where the French Nieuport 11, 17, and 28 (and a host of other Nieuport types), the Hanriot HD.1, and the Fokker E.III and D.VIII.

These engines were fairly interchangeable in those days. The Pup was built with a Clerget, Le Rhone or Gnome, all of French origin; the Camel was built in substantial numbers with a 110 hp Le Rhone, 130 hp Clerget, 150 hp Bentley BR.1 or a 170 hp Le Rhone engine. The Germans often installed captured allied engines, considered to be of better quality, instead of their own Oberursel rotaries (which were copied Gnomes).

Radials were only perfected after WWI, with the exception of the French Salmon 9, which was a liquid-cooled radial. Towards the end of the war the RAF invested heavily in ABC Wasp and Dragonfly radial engines, but these turned out to be an engineering disaster. The Cosmos (later Bristol) Jupiter was the first successful radial, and it was too late for WWI. The big problem for the stationary radial was to find a cylinder head design that was strong enough yet offered adequate cooling; British research cracked the problem late in WWI and was later incorporated in radial engines world-wide.

The original Gnome had no throttle, nor did it have a carburettor; it only had a fuel valve. Switching the ignition was the only means to control power.

Big problems of rotaries, apart fromt the gyroscopic effect, where high fuel and oil consumption. Engine cowlings were installed, not for aerodynamic reasons, but to catch the oil that the engine splashed out as it rotated.

The diaphragm was in the fuel line, not in the float chamber. (How could a float carburettor work with such an obstruction in the chamber?) The major problem of the Merlin under negative g was not fuel starvation, but flooding of the carburettor by the powerful fuel pumps when the fuel in the chamber moved to the wrong side of the float. The diaphragm mitigated this by restricting fuel flow to no more than was necessary.

There are two reasons for this:

1) built up compression in the cylinders to make it easier to start. Same process to start a Tiger Moth, spin propeller 2 rotations backwards.

2) with a radial engine this is done to clear the oil from the lower cylinders, otherwise the conecting rods might bend from pressure in the cynder from oil when starting.

I know this proceedure is still followed with people who fly boeing Stearmans.

Cheers

Radial (aircraft) engine oil would drain down from the cylinder walls and other vital engine components following shut down. I'm not sure how long it would take for this to happen, let's assume hot oil would drain to the sump inside two hours, thus the need for a "pull through" of the propeller to lubricate the engine before start up, or the engine would be damaged and the aircraft would be unservicable for flight, and need an engine change.
During battle it was imperative to "keep 'em flying" thus the "pull through" for aircraft with radial engines.

Ron.