How number of cylininder affects engine reliability.
I mean more cylinders, less vibration and less fatigue,
but on the other side more moving parts.
Is six cylinder engine more reliable then four cylinder engine in terms of total power loss.
As far as I know 80% of total power failures are due to engine missmanagment, not fatigue.
So, what would be more reliable in terms MTBF?
Partial failures are more likely with more cylinders, but also less severe.
Wright Aeronautical had an R-2160 with 42 cylinders (6 banks of 7 cyls.) that was used on some experimental aircraft during WWII; mainly the Republic XP-69 (mid-engine tractor type)and Northrop XP-56 flying wing (mid-engine pusher. Also it was water-cooled, not air-cooled.
Presumably the lower frontal area was one advantage they were shooting for, at the expense of complexity. I don't know what else it may have been used in or what happened to that engine.
Most cylinders for a production aircraft engine: Pratt & Whitney R-4360, with 28 (4 rows of 7).
Most cylinders for a US-built aircraft engine: Curtiss Wright R-2160 "Tornado," which had 42 (6 rows of 7). A 70-cylinder version was planned.
As has already been pointed out, the R-2160 was intended to power several aircraft, including the Hughes D-2, Lockheed XP-58, Vultee XP-68 (a variant of the XP-54), and Republic XP-69.
Work on the engine was never completed and it never flew. Only seven were built. Curtiss Wright needed all its managament and engineering talent for aircraft engine production requirements of World War II, resulting in the cancellation of many experimental projects like the R-2160. The single remaining example of the R-2160 is on display at the Aviation Hall of Fame and Museum of New Jersey in Teterboro, NJ.
“In the case of the R-4360, the cylinder arrangement required a crankshaft set at a 120- degree angle. It was a bit of a nightmare to balance out.”
Please forgive me for arguing, but in the interest of accuracy, I thought it might be useful to explore the construction of the R-4360 a bit further.
Several features of the R-4360 were revolutionary. Its design is well documented in the patent literature (most notably US Patent 2,426,879). Of particular interest is the fact that adjacent cylinder rows are indexed 12 6/7 degrees clockwise from the one behind it. Similarly, each crankshaft throw is indexed 192 6/7 degree clockwise from the one behind it. This arrangement results in even firing for all 28 cylinders.
In terms of balance, R-4360 development was relatively trouble-free, especially when compared to the P&W R-2800, or even worse, the Curtiss Wright R-3350.
The R-4360 did suffer from crankshaft breakage during development. P&W called in MIT vibration consultant J.P. Den Hartog, who ordered metal removed from strategic crankshaft locations, thereby changing the resonant frequency of the crank and solving the problem of breakage.
Kimble D. McCutcheon
President
Aircraft Engine Historical Society
"What is the largest number of cylinders ever incorporated into one engine?..."
Someone recently reported seeing a 56-cylinder diesel in a German aviation museum. Further investigation revealed it was probably of Russian design, intended for very large bombers. It may have found a more modern application as a marine power plant. In its largest configuration, two of them are geared together to form a 112-cylinder engine. Please see
