Direction of Plane Engine Rotation

[Martin-123]

TL;DR Summary

Is it the same on both sides of the aircraft?

Hi All,
Do the left side and right side engines of a plane rotate in the same or opposite directions?
Is the angular momentum (gyroscopic effect) of the engine shaft, blades, etc., sufficient to affect the flight path of a plane with large engines?
In military fighters, such an effect could be advantageous in tight turns.
Thank you for any responses.

 

[FactChecker]

I think this is a good article on the subject: https://simpleflying.com/aircraft-propellers-typical-rotation-direction/

 

[Flyboy]

It depends on the aircraft. In most cases, they turn the same direction due to simplicity, as then you only need one model of engine.

But there are definitely some notable cases where they turn opposite directions. Most of them are smaller propeller-driven planes where there is a noticeable increase in safety in doing so. I’m still waiting for morning coffee to finish hitting, so I’ll be doing a follow-up on this with more info in a bit when I’m more coherent.

 

[Bystander]

https://en.wikipedia.org/wiki/Lockheed_P-38_Lightning

 

[Lnewqban]

Is the angular momentum (gyroscopic effect) of the engine shaft, blades, etc., sufficient to affect the flight path of a plane with large engines?

Please, see:
https://en.m.wikipedia.org/wiki/P-factor

https://fly8ma.com/topic/left-turning-tendencies/

https://www.kitplanes.com/torque-and-p-factor/

https://en.m.wikipedia.org/wiki/Vought_F4U_Corsair#Technical_issues

WW2 warplanes with huge propellers, high maneuverability, and high torque engines, had some control issues.

I believe that airliners, with their slow changes of directions and smaller diameter rotating mass inside their jet engines, suffer less of that phenomenon.

 

[FactChecker]

In military fighters, such an effect could be advantageous in tight turns.

Modern fighters have jet engines. Jet engines have a lot of smaller compressor blades and less gyroscopic effect. If they need to, they can make some turn in opposite directions. I don't remember ever considering jet engine rotations in fighter simulation equations of motion. (The effects of firing a gun was considered and compensated for in the flight controls.)
In any case, the engine rotation is not a big player in a fighter's turning capability. Banking a fighter can generate very large turning forces.

 

[Flyboy]

In military fighters, such an effect could be advantageous in tight turns.

When the ratio of rotating mass to total aircraft mass is sufficiently high, yeah, it does. Look at the WWI fighters with rotary engines, as typified by the Sopwith Camel. It turned noticeably harder in one direction than the other due to that massive gyroscope that the rotary engine turned into.

Modern aircraft try to minimize the amount of spinning mass, so it’s far less noticeable at any point other than low and slow, like during an engine failure during takeoff.

Most cases today where they have “handed” engines are to provide added safety in those situations. If they both turn the same direction, the effects of losing an engine during the climb out after takeoff (the worst time to suffer an engine failure) are not the same for each engine. I don’t recall which engine is the “critical” engine off the top of my head, but the TL;DR is that if your critical engine dies, your minimum controllable airspeed (Vmc) goes up significantly, to the tune of 10 knots or more in some designs, and if you turn into that engine, there is a very good chance that you will depart controlled flight due to the asymmetrical thrust and drag, the torque and P-factor, and the rudder input needed to coordinate your turn.

Having handed engines on the correct sides eliminates all these issues, allowing for not only simplified handling in an engine out scenario, but across the board. The complexity just gets passed over to the maintainers, who now have to keep two different engine models, along with accompanying accessories, in stock. The engine case will be the same, but things like camshafts, vacuum pumps, propellers, prop governors, tachometers, reduction gearboxes, oil pumps, starters… all of those are “handed” as well and will need to be kept in duplicate, one for each side. And the “opposite” engine, usually the left-handed rotation engine, is much less common, so spares for it are going to be more expensive.

That issue largely disappears when you deal with jet engines, as the torque effects are negligible and there’s no P-factor, only the asymmetry of thrust and drag after a failure, so everything turns the same way. Most, but not all, turboprops are the same way, with a notable exception being the Airbus A400M Atlas, which has a left- and right-hand engine on each wing.

https://en.wikipedia.org/wiki/Lockheed_P-38_Lightning

A more approachable example: the humble Piper Aztec.

 

[Martin-123]

Thank you Flyboy, and all others, for these excellent replies.

 

[Astronuc]

https://en.wikipedia.org/wiki/Lockheed_P-38_Lightning

I was thinking of that aircraft and the DeHavilland Mosquito, and more recently, I watched a video on the F82, Twin Mustang.

The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with an additional gear in the propeller reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control. This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work, North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved.

https://en.wikipedia.org/wiki/North_American_F-82_Twin_Mustang#Design_and_development

DeHavilland Mosquito
https://www.nationalmuseum.af.mil/V...y/Article/196281/de-havilland-dh-98-mosquito/
https://www.rnz.co.nz/national/prog.../2018839138/world-war-ii-mosquito-flies-again

The engines rotate in the same direction, clockwise if looking forward from behind the propeller, or counterclockwise looking from the front toward the propellers. Note propellers blades have the same pitch on both engines.


Left engine starts at 5:15, right engine at 5:36 in the following video. Same rotation on both sides.

 

[berkeman]

This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work, North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area.

Oops!

 

[Martin-123]

Thank you Astronuc.