# Rolls Royce Griffon versus Merlin engines.



## windhund116 (Mar 29, 2021)

Is there a reason why the Griffon spun counter-clockwise (looking from the cockpit, forward). While the Merlin (and most single engine airplanes) spun clockwise?

Thanks! 

Spitfire with Griffon engine.

Spitfire with Merlin engine.


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## pbehn (Mar 29, 2021)

I found this.


Spitfire Prop- Direction of rotation?

The reason that almost all Merlins have prop rotation the 'wrong' way for most British designed types is as follows, quoted from correspondence from David Birch of the Rolls Royce Heritage Trust:

_" ...why did the Merlin rotate opposite to other engines: The early Rolls-Royce engines had epicyclic propeller reduction gears, so the propellers rotated the same way as the crankshaft. The original Kestrel had a direct drive but when they fitted a reduction gear they chose a spur-type making the prop rotate opposite to the crank. This design feature was incorporated into the Merlin. "_

As to why they then reverted to normal prop rotation for the Griffon was simply standardisation

_"In the late 1930s the Society of British Aircraft Constructors formed a committee (among others) to standardise aero-engine powerplants. One of the Committee's aims was to allow engines of a similar power to be installed on the same bulkhead. So, for instance, if a Hercules-engined aircraft needed an engine change and a spare was not available, then a Griffon could be substituted. The Griffon ready-to-be-bolted-on powerplant would be self-contained with radiators, etc, installed, the mounting pick-up points were the same as were the fuel supply and control lines connections and cowling diameters. Unfortunately this did not work for the Merlin because the propeller from the dead engine was not suitable. So, from the Griffon onward all new Rolls-Royce piston aero engines (Crecy, Eagle and Pennine) rotated the opposite way to the Merlin, and the same way as everyone else’s engines. This strategy was stifled by the outbreak of World War Two, and post-war the idea was dropped, even though Rolls-Royce produced many Universal Power Plants for the Lincoln and Shackleton. _"

And some info suitable for a pub quiz one day, though I assume it may apply only to the production before the 'handed rotation' Hornet engines:

_"Merlin engines were only allocated ODD serial numbers by Rolls-Royce. This practice apparently stemmed from manufacture of the Eagle in WW1, where the Company was required to supply some engines with right-turning propellers and some with left hand airscrew rotation. Odd and even numbers helped to identify the differently set-up engines. Merlin engines had right-hand tractor propellers; therefore, odd serial numbers. (Griffon engines mostly had left-hand tractor props; therefore, even serial numbers.)"_

That last is from Ramp Head Merlin
*Edited April 15, 2015 by Work In Progress*

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## windhund116 (Mar 29, 2021)

Thanks! Must have been a bit confusing for those pilots flying both clock- and counter-clockwise airplanes, at the time. Torque reaction must be different.


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## pbehn (Mar 29, 2021)

windhund116 said:


> Thanks! Must have been a bit confusing for those pilots flying both clock- and counter-clockwise airplanes, at the time. Torque reaction must be different.


Maybe one of those things that even when you are told about still takes time to get used to, the other thing with the Griffon was the torque wasn't just in the other direction, there was more of it.

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## gumbyk (Mar 29, 2021)

windhund116 said:


> Thanks! Must have been a bit confusing for those pilots flying both clock- and counter-clockwise airplanes, at the time. Torque reaction must be different.


It almost killed Sir Tim Wallis, flying both the MkIX and MkXIV. Pre-takeoff checks are to use full rudder trim for take-off, and if you wind it the wrong way, you can't over-power it to keep the aircraft straight.
Incident Supermarine Spitfire FR14 ZK-XIV, 02 Jan 1996 (aviation-safety.net)

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## fastmongrel (Mar 29, 2021)

The Griffon engined Seafires caught a few pilots out. The carrier's island is a hard thing to run into.

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