Spitfire Prop- Direction of rotation?

[redleader]

Sorry if this has been answered before, but I couldn't find anything when searching.

From the pilot's viewpoint, what was the direction of rotation of the prop of a Merlin III engined Spitfire Mk1a?

Ta

[Max Headroom]

Sitting in he cockpit the prop spins clockwise on all Merlin Spitfires. If it's a Griffon engined type, it's the other way.

Trevor

[redleader]

cheers Trevor

[NPL]

Sitting in he cockpit the prop spins clockwise on all Merlin Spitfires. If it's a Griffon engined type, it's the other way.

Trevor

Yes, it is well-known that the Merlin prop spins clockwise and the Griffon anti-clockwise, but is this as seen from the cockpit or from a standpoint before the prop? I guess that the impression you would get, if it spins clockwise when you stand in front of it, will look like anti-clockwise from the cockpit, alias behind the prop.

From a pilot's viewpoint is somehow a wrong question, as it has to do with his position when he sees the prop spinning.

[The James]

But surely he's only the pilot when he gets behind the controls, right?!

This thread reminds me of my last visit to Duxford. When walking around the maintenance and restoration hangar, I noticed a spitfire being worked on, the engine removed. Note the masking tape above the prop shaft. Made me giggle...

Edited April 15, 2015 by The James

[redleader]

Sorry for being unclear. From 'the pilot's viewpoint' was inferring someone piloting the aircraft, not observing it. Trevor was astute enough to supply the info 'viewing from the cockpit' You raised a good point tho' NPL, backed up by The James' photo - which viewpoint (if any) is the standard reference...

[Jon Kunac-Tabinor]

Going from memory theres a story of a WW2 RAF pilot who been flying Merlin spits before he was shot down and made a POW. He either escaped or returned post war to his squadron , which had converted to Griffon Spits.

He flatly refused to listen to any advice before climbing in for a flight, opened up the throttle for his take off run, kicking the rudder over as usual to counter the torque from the engine: Except the griffon rotates the other way..... Oops. Broken Spit. Humble Pilot.

Jonners - well it goes something like that anyway

[gingerbob]

I've heard the story, though I don't remember where I ran into it.

Another possible factor besides arrogance: I run two different boats during the "temporary thaw" here in Maine, and one has the engine controls low and on the right, the other has them high and on the left. The wheel is also of a very different size, and thus where one grabs it is different. If I drive "the other boat" for just one day, then the next time I'm on the usual boat I find myself reaching into mid-air looking for the wheel or the engine levers- that "muscle memory" will get you!

bob

[fingers]

Was there any reason for the rotation to change or was it just a whim of the Rolls Royce designers?

[Graham Boak]

It was the recommendation of the Royal Aircraft Establishment, that British piston-engines should rotate anti-clockwise. However, the Merlin was very much the "odd one out" among contemporary engines - whether that could be described as a whim of the RR designers I couldn't say.

[The James]

I've heard the story, though I don't remember where I ran into it.

Another possible factor besides arrogance: I run two different boats during the "temporary thaw" here in Maine, and one has the engine controls low and on the right, the other has them high and on the left. The wheel is also of a very different size, and thus where one grabs it is different. If I drive "the other boat" for just one day, then the next time I'm on the usual boat I find myself reaching into mid-air looking for the wheel or the engine levers- that "muscle memory" will get you!

bob

My wife drives a Mitsubishi that has the indicators on the 'wrong' side of the steering wheel. Whenever I get into her car, I remember this, but when I return to the trusty Citroen I turn my wipers on every time I reach a junction or roundabout! Weird...

[avro683]

I've heard that story too, can't remember where I read it but in that version it was an erk. Either way, it must have been a very red faced human being exiting the cockpit.

[Graham Boak]

I heard the ex-POW story about Bader, but I don't think it ended in a write-off. However, removing the POW element, I've seen a number of such accounts. I think that Clostermann tells of being taken by surprise by the Typhoon's veer on take-off, and that was without setting the trim wrongly.

[Work In Progress]

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 http://www.enginehistory.org/Piston/Rolls-Royce/RHM/RHM.shtml

Edited April 15, 2015 by Work In Progress

[Max Headroom]

It was the recommendation of the Royal Aircraft Establishment, that British piston-engines should rotate anti-clockwise. However, the Merlin was very much the "odd one out" among contemporary engines - whether that could be described as a whim of the RR designers I couldn't say.

It's with hesitation that I disagree!

The DB601, and Allison V1710(?) all had props rotating the same way. No idea about the French or Russian engines of the period though!

Trevor

[Work In Progress]

Griffon style rotation was very commonly seen in European and Russian designed engines, and Merlin style rotation was the norm for US engines.

The Allison was extensively manufactured in both rotations, for the P-38.

And unlike the Hornet's Merlins, the P-38's Allisons were genuinely handed engines, the crankshafts rotated in opposite directions. The Hornet's reverse-rotation engine was a modified standard rotation engine with an additional idler gear on the front, which is why Hornet cowlings are about three quarters of an inch longer on one side than on the other.

Edited April 15, 2015 by Work In Progress

[Graham Boak]

The David Birch quote (#14) may have been clearer in context, but appears to be confusing two matters. The first is the "power egg" principle for rapid engine replacement (and standardisation). This certainly was adopted in wartime by RR for the Merlin and later engines, and also by other companies, Bristol at least. The recent "Rolls Royce and the Halifax" book castigates HP for not taking RR's advice on this matter, but this criticism seems to have problems with timing. I don't think the power egg arguments had been accepted before the Halifax design was finalised, but the main problem with the Halifax's Merlin installation was that it was mounted too high. The ideal (lower) position of engines relative to the wing came from RAE's wind tunnel work too late for the Halifax but before the Lancaster.

The second is the interchangeability of engines in design/production, and this again did happen, as on the Beaufighter and Wellington with their Hercules and Merlin variants. However, nowhere was it seriously suggested that a Beaufighter would fly with a Merlin on one wing and a Hercules on the other...

There may be a third factor, affecting trim on single-engine failure, in that having odd rotations might have guaranteed that it was the wrong one that failed.

Quite what the propeller on the dead engine had to do with anything is unclear, as the two different engines would have two different propellers anyway.

Edited April 16, 2015 by Graham Boak

[noelh]

I didn't know the merlin rotated opposite to most British engines. The my 'learn something new every day' quota taken care of.

I have some sympathy with the 'arrogant' ex POW who used the wrong foot in a Griffon Spit. I'd blame muscle memory or at least I did when I went from my usual 300 hp ride down to an little 100 hp Cessna 150 for my biennial check flight. Frightened the life out of the Instructor when I put the boot in and veered off to the right on take off. Oops!

[Work In Progress]

However, nowhere was it seriously suggested that a Beaufighter would fly with a Merlin on one wing and a Hercules on the other...

Well, it appears on the face of it that is the sort of possibility which may have been suggested by the pre-war committee. A high powered twin with a a high proportion of its total weight represented by the engine weight would be the toughest design case to accommodate so I imagine they may have considered it more appropriate for singles, for trimotors or for four-engined (or more-engined) types, though that is mere speculation on my part.

However, unless we have the committee papers (I don't) it would seem peremptory to gainsay what RRHT (which does have the papers) reports the committee suggested.

I think the points about props is that the original pre-war committee did indeed envisage that if rotation direction were standardised you would be able to specify a common prop for all engines intended to be available for a given type of airframe, thus simplifying at least that aspect of the supply chain (though probaby at the expense of complicating the array of reduction gearing ratios required on various versions of the engines).

In referring to the 'dead engine" he is not using the phrase referring to the asymmetric power problem, in the way that we refer to it in multi-engine flying training, but simply to an engine which requires replacement. Substitute "the engine requiring replacement" if you prefer.

Whether or not any of this made a lot of sense as official policy doesn't really matter. Official committees in British aviation have a long and honourable tradition of deciding fairly daft things (Brabazon, anyone? R101?), and this one's recommendations were clearly never applied with any great zeal, which may suggests that more conservative counsel may have protected the industry and the world from some of this particular committee's wilder notions.

Edited April 15, 2015 by Work In Progress

[PFlint]

...off the top of my head.....

Soviet engines of the period...

V-12 inline engines seem to have props that rotate clock-wise when viewed from the front. (backwards)

radial engines (5,7 & 14 cylinder) could have props that rotated clock-wise or COUNTER-clockwise depending on the make and model.

confusing , huh ???

[Graham Boak]

The thought of having to design all engines/reduction gears to fit a common prop would seem to be putting the cart before the horse. Better to optimise the design first and then cope with the changes in propeller design. After all, the propeller designs were changed on a much shorter timescale than engine production could keep up with - and retrofitting different props to the same reduction gear is much simpler than working the other way around.

I agree about the use of "dead" engine in the excerpt, but the asymmetric case would also have to be considered.

Official committees in British Aviation also have a long tradition of getting things right. Cherry picking those that didn't may be giving a false impression. After all, predicting the future doesn't have any great record in any endeavour.

[gingerbob]

The idea of interchangeability wasn't "to slap on any available engine" as necessary, but rather so that if, say, there was a sudden supply or other problem with Hercules engines, production of airframes could be switched to (for example) Merlins with the minimum of disruption to the production line.

When the Griffon Spitfire was being developed, the question was asked whether use of the "power egg" should be specified. Fortunately, it was realized that it was a little late to be trying to integrate the power egg with the Spitfire airframe! Who will be first to do a Whif using a Firefly cowling?

bob

[Graham Boak]

Or a Spitfire Mk.V with a Lancaster cowling? The problem, as discovered on the Mosquito, is that trying to fit a unit designed for one aircraft will not necessarily give an optimum result on another. It rather depends upon whether high performance is a bigger driver than servicing convenience and production. Arguably the one aircraft that scores high on both was the Martin Baker MB5, which did not have a "power egg" - though the claimed performance of this type was never confirmed it was probably pretty good. The Hornet didn't have a power egg, with a tightly tailored form offering low frontal area, but serviceability suffered badly. Performance was brilliant.

It is worth remembering that one reason why RR and Bristol were arguing for power eggs is that it places more business, and hence money, into the engine companies. Whereas when positioning and fit of accessories such as cooling are in the hands of the airframe designers, business and money go their way.

[gingerbob]

Well, and if I were an engine manufacturer I'd get rather annoyed being blamed for all of the problems caused by an airframe designer's poor installation.

bob

p.s. I always thought the Miles M.20 looked pretty good, but they were able to integrate the engine "pod" into the airframe.

Edited April 16, 2015 by gingerbob

[Graham Boak]

The argument between engine and airframe designers never went away, we had it on the Tornado ADV.

There's no doubt that the Halifax would have been better with the Morris radiators in the RR power egg, and the Mk.IV was designed to take just that. This was irrelevant to the design of the Halifax because it wasn't available, or the Manchester would have had it too, and the engine would still have been placed too high which was the major flaw. The power egg as fitted to the Beaufighter and Lancaster had the radiator beneficially positioned under the nose (as on the Typhoon) rather than under the belly as on earlier designs, but the non-p.e. installation was superior (lower drag) on the Mosquito and the Spitfire, thanks to the use of the Meredith effect for cooling. Putting a chin radiator on the Mustang also proved less than ideal.

You suggest a Firefly cowling on the Griffon Spitfire. It's a bit wide... but the Seafire MK.47 shows the same extended chin intake as the Firefly. This was pushed by the RAE because they were so impressed by the Mustang, but Quill (again) thought the classic intake superior. How much this was a matter of "not invented here" we'll never know, I suspect.

Sadly, I'm drifting too far from the direction of rotation.