Griffon vs Merlin rotation.

[Landroger]

Just watched a Youtube vid on the Military forum, of the BBMF starting up and departing for the Royal wedding flypast.

Unless I am mistaken, the Merlins on the Hurricane and - the starboard engines certainly - the Lancaster rotate clockwise as seen from behind, while the Griffon in the PR Spitfire rotated ACW.

Two question arise, I suppose. Is that in fact the case and why? Followed by was the Merlin ever 'handed' for right and left side on multis?

I know the Griffon went back to the 'R' Type 36 Litres, so did it also inherit the 'R' Type rotation?

Roger.

[photofly]

From the Wikipedia page on the Griffon engine:
"Pilots who transitioned from the Merlin to the Griffon engine Spitfires soon discovered that, because the Griffon engine's propeller rotated in the opposite direction to that of the Merlin..."

I have that in another text too, which states that Griffon-engined spitfires handled very differently to the earlier marks, largely due to the opposite engine rotation.

[Brian Abraham]

The Merlins on the Hornet were handed - ie rotated in opposite directions.

The direction of rotation on the Griffon was the result of the Society of British Constructors deciding in the late 1930s to standardise the direction of rotation.

The R engine rotated clockwise as seen from the cockpit.

[27/09]

I have that in another text too, which states that Griffon-engined spitfires handled very differently to the earlier marks, largely due to the opposite engine rotation.
Certainly the rotation direction was a major difference, but from a basic handling point of view I think the comments probably related to the extra torque that had to be controlled by the same size tail feathers as the lower powered Merlins (at least until the very latest marks that had bigger tail surfaces) and the extra weight up front which affected the C of G.

It was generally recognised that the Griffon Spitty's were not as nice to fly as the Merlin ones. Though I have seen it written that the lastest marks (I think the Mark 24 and 47) were the nicest Griffon versions as they had the bigger tails.

[sycamore]

The Merlin was `handed` for the deH Hornet.

[Dan Winterland]

I heard an account of a delivery pilot collecting a MkXII Spitfire for the first time. She got a briefing off a company test pilot who mentioned everything about the new aircraft - except for the fact that the prop went the other way round. It made for a very excitng take off!

[diesel addict]

IIRC the Packard Merlins rotated the same way as the Griffon

I think this is why the Mk XVI had a different mark number to the otherwise identical Mk IX

(Old age and failing memory excepted )

[Landroger]

I love this forum - not only do you usually get the answer to the most obscure questions, but a whole lot of incidental information. :ok:

I'm not a pilot and thus didn't think the issue through automatically, but I am an engineer and I should have realised at once. Rotating the donk the other way, especially one as powerful as the Griffon, would really make your eyes water in the wrong circumstances. It would fly very differently. :eek:

Thanks again guys.:ok:

Roger.

[Brian Abraham]

IIRC the Packard Merlins rotated the same way as the GriffonSorry, not the case.

[27/09]

To illustrate the controlability issues of the Griffon engined Spitfires with the small tail surfaces.

From the Pilots Notes of the Mark XIV and XIX, Griffon 65 or 66 engines.

Para 49 (i)

"When ever possible open the throttle slowly up to +7lb/sq. in boost only. This is important as there is a strong tendency to swing to the right and to crab in the initial stages of the take off run. If much power is used tyre wear is severe. +12lb/sq. in boost may be used at heavy load and should in any case be used on becoming airborne to minimise the possibility of lead fouling of the sparking plugs, but +7lb/sq. in boost is suffficient for a normal take off"

[twochai]

Rotating the donk the other way, especially one as powerful as the Griffon, would really make your eyes water in the wrong circumstances. It would fly very differently.

50+ years ago, when I was a 17 year old sprog with a brand new PPL and 40 hours on the Fleet 80 'Canuck' (with clockwise rotation) a friend with access to a Chippy offered me a flight in it - which I accepted, of course - it was FREE.

Without much briefing he passed control to me as we lined up on the runway. As 'I' lifted off I got the impression he had taken control of it as the aircraft swung right, slightly nose down; I let him continue what he wanted to do - he was in command, wasn't he?

After going in between the hangars of Carp airport at 70' with nobody in real control, Steve said "Next time I fly it"!

We both learned about 27 lessons that lovely day and 'next time I fly it' wasn't one of them!

[diesel addict]

Brian Abraham -

Ooops !

Apologies for relying on memory -
I really do not know where that came from, one is fully aware of the L/H Merlin R/H Griffon ( excepting the Merlin 131 / 134 of course ) - brain fade, crossed wires .......

[Smilin_Ed]

The Allison engines in the P-38 Lightning were identical but were installed facing different directions to get the props to rotate in opposite directions. This was simpler than building the engines differently by using different valve camshafts and simplified the supply problem. Does anyone know if the Merlins and Griffons were capable of being installed "backwards"?

[diesel addict]

Smilin Ed -

The oipposite handed Merlins ( Mk 131 and 134 ) changed propellor rotation direction via an additional idler pinion in the reduction gearbox, the whole unit aft of the gearbox was unchanged - whether that is less simple than fitting the engine "backwards" is debatable ?

[barit1]

Smilin_Ed:The Allison engines in the P-38 Lightning were identical but were installed facing different directions to get the props to rotate in opposite directions.

Don't think so - it was the crankshaft that was reversible. (I had thought it was the camshafts that reversed, but was later advised differently)

[barit1]

Another aspect to Allisons reversing rotation: I believe they were designed, among other things, for dirigible use; and they could be shut down and reverse-started in flight for docking operations.

Not sure just how this was done, although it might have included reversible bevel gears on tower shafts driving the cams.

[NG_Kaptain]

Back in my earlier days when I had the chance to fly with many WWII vets there was a favourite captain I flew with who had lots of great stories, one of which how he used to fly Spitfires but made the mistake of volunteering for Asia duty after VE Day and was assigned Mustangs. Told me on his first Mustang take off in India he lost control of the aircraft and hit a house, killed a cow and was court-martialed, not for writing off the aircraft but for killing the cow.:)

[3holelover]

Gents.... Brits turn their motors backwards. The Yanks have them going the right way around....[;)] So, the "licence built" Merlins, built in the US of A, turn CW (from aft looking forward), and the Brit built Merlins and Griffons turn backwards, unless they to maintain the centre of thrust on multi's.

[27/09]

and the Brit built Merlins and Griffons turn backwards, unless they to maintain the centre of thrust on multi's.

Not so old chap.

The Packard Merlin variants turned the same way as the Britsh ones. It was the Griffon engine that turned the opposite direction.

[3holelover]

OK... izzatafact? I'll defer to your greater knowledge... Sorry mate, I shoulda said, I'm repeating what I've read, but it probably came from some Time/Life magazine or something... I'd kill to fly anything with a Griffon or a Merlin in it! [I've named two dogs after each] But I've never put myself airborne with anything beyond an O320...

I can well imagine the torque effect of a single 1500-2000 hp monster, swingin' a full paddle wheel of prop blades, would be quite the animal to tame... One would certainly like to know which foot to have ready...

[27/09]

I think it's to do with the heritage of each engine. While both were V12s built by Rolls Royce I don't think they have the same heritage. One of the two from memory can trace it's heritage back to a Curtis Wright V12, probably the Merlin since it turns the same way as other American types.

From an ownership persepctive the Parkard Merlins are better to own since they were mass produced using modern manufacturing techniques and therefore parts e.g. pistons, crankshafts etc will fit from one angine to another. The Rolls Royce engines were hand finished with each part being finished by hand to fit into the journals etc and therefore are not likely to fit another engine.

[GQ2]

From memory, the Packard Merlins were just the same as their U.K-built counterparts, except that they used U.S. sized nuts, bolts, threads etc. The engine designations were similar too. The Packard Merlin version of the RR Merlin 66 being a Packard Merlin 266, and so on. Otherwise, there were very few differences.

A MkIX Spit' produced at Castle Bromwich, but fitted with a Packard Merlin 266 simply became a Spit'XVI. Externally, the a/c looked the same. :hmm:

[howiehowie93]

I posted this on the Concorde Question thread:

I had to look it up on Wikipedia::ugh:

Quote:
Counter-rotation was achieved with the use of "handed" engines, which meant that the crankshaft of each engine turned in the opposite direction of its counterpart. The V-12 engines only required that the spark plug firing order be changed in order for the direction of the crank shaft to be reversed, according to the General Motors Allison V1710 Service School Handbook.
Lockheed P-38 Lightning - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/P38_Lightning)

Also I believe the Lancaster was retrofitted with spare ex-Shackleton Griffons as there were ample spares. Dowty also made five special gearboxes for them too. I'm ready to be corrected on this though.

regards
Howie

[rigpiggy]

hence the reason for the contra rotating props

[27/09]

rigpiggy

I'm not sure what you refer to with your comment

hence the reason for the contra rotating props

My understanding re the use of contra-rotating props was the need to be able to absorb the horsepower of the more power full engines. They were used on the Spifires and the Shakletons and other piston types as well no doubt. The Russians used contra-rotating props on some of their turbo-props.

[Landroger]

I think it's to do with the heritage of each engine. While both were V12s built by Rolls Royce I don't think they have the same heritage. One of the two from memory can trace it's heritage back to a Curtis Wright V12, probably the Merlin since it turns the same way as other American types.


As I understand it, the USA took part in the Schneider Trophy races in the early twenties - very successfully - with a seaplane powered by a Curtiss D12 'Wetsleeve Monoblock' V12 engine. The Air Ministry were very impressed by these engines and bought two of them for RR at Derby to look at.

In 1931 the S6B won the Trophy outright with an RR 'R' type 36 litre, supercharged engine, using much of the technology from the Curtiss D12. Very few years later and developed directly from the 'R' type, although shrunk down to 27 litres, the Merlin was produced. Of course it was supercharged, the major difference was aneroid control of the supercharger gearbox and boost.

As development went on and the Merlin got more and more powerful, it became obvious that there would be a limit on just how much. I believe this was the reason why RR went back to the original 36 litres, even though there was, I believe, another stage to the supercharger and another gear on an otherwise very similar engine? The difference was enough to call the engine Griffon, although it is difficult to see why RR decided to make the engine turn in the opposite direction?

Roger.

[Yamagata ken]

No-one can be trusted less than an American wrt to Merlin history. The Merlin was a successfull design (and build), so America takes the credit. Production: "112,000 in Britain and more than 37,000 under license in the U.S" Merlins were built in the USA to UK design and specification. Mustangs were ****e with US (Allison) engines until the RAF fitted them with UK built Merlins

[clunckdriver]

As one who has worked on both US and UK Merlins the main difference from a maintaining perspective is that the US models were a little easier to work on, if memory serves me right they cut down on the number of bolt sizes and as stated on a previous post the parts were more interchangable. As for the Allison P51 "Being a pile of ****e", the fact is the USAAC did not foresee that fighter combat was going to take place above 10,000ft, thus the engine/airframe was optimised for this, in fact it was a very good aircraft at low level {Just check on the scores of Polish/RCAF units in this role, also its record in the low level recon role} The instalation of the Merlin with its supercharger optimised for high level did of course make it into a superlative high level escort fighter. { When instructing on Harvards I had one of the "New Luftwaffe" re- treads who had been shot down four times by Mustangs!}

[barit1]

As has been discussed on other threads, the motivation to use contra-rotating prop (coaxial shafts) is to INCREASE PROPULSION EFFICIENCY. A conventional prop creates a rotating slipstream vortex, which represents a loss of useful energy. Adding the second prop assembly gives the opportunity to straighten out this vortex and recover that lost energy. (In a turbofan engine, the fan stator vanes serve the same function.)

And, in a single-engine type, it's that rotating vortex which acts against the vertical fin & rudder that requires the pilot apply a rudder input to keep the airplane straight on takeoff. It's called "torque", but that label is obfuscation. It's the prop vortex, and a contrarotating prop overcomes the situation. ;)

[Screenworx]

I think this is a very important factor. Handing the props helps in terms of equalling the torque effect but as you say its the slipstream vortex in reality. However this proved not to be as straightforward in practice as at first expected by Aerodynamicists. The process of evening out the slipstream vortex proved to cause all sorts of other less predictable aerodynamic problems mostly on take off and landing when airflow was slower as well as additional cooling problems. The Whirlwind with true handed Peregrines had serious rudder ineffectiveness while landing in particular, which delayed it and led to a bigger fin being fitted but landing speed was always high.

The Hornet with handed (via gear) Merlins tried to learn from this but had very similar problems in Mk 1 form which was never experienced with its predecessor the Mossie (not handed) until a long strake was fitted in front of the tail. Until that change it was never able to exploit its full power on take off without fishtailing.

[RadioSaigon]

IIRC it was this very "opposite rotation" of the Merlin/Griffon engines that bought Sir Tim Wallis of the NZ Alpine Fighter Collection so nearly fatally undone at NZWF around 1999-2000...

He had not long got out of the Merlin powered variant into the Griffon powered aircraft and inadvertently set the rudder trim appropriately for the Merlin -forgetting he was behind the Griffon- only to have the torque/trim couple screw him off the runway upside-down.

He was lucky to survive.

Others with better memories will be able to provide more complete information, no doubt.

[Davaar]

It would fly very differently.


Would that not "torque the same, but in the other direction"?

[Davaar]

and a contrarotating prop overcomes the situation.

Except in a single-engined aircraft. I did not fly them myself, but as I recall tha Wyvern had a truly mighty turbo-prop engine (Python) that drove two contra-rotating five-bladed (could that be?) props on the one "spindle" as it were. Throttle back too much on finals or landing and you had the dreaded "discing", a solid wall of propeller up-front that cut off airflow from the control surface aft. I was told that this could be disconcerting.

[Landroger]

From an ownership persepctive the Parkard Merlins are better to own since they were mass produced using modern manufacturing techniques and therefore parts e.g. pistons, crankshafts etc will fit from one angine to another. The Rolls Royce engines were hand finished with each part being finished by hand to fit into the journals etc and therefore are not likely to fit another engine.

From 'Not much of an engineer' it seems that it was when the Ford Motor Company began producing Merlin engines, that the 'hand builtedness' of RR engines was swept away. Intuitively the RR factory would be working to the closest tolerances, but it seems the opposite was true. While Ford were tooling up for the Merlin, some redesign was necessary to adapt it to the closer tolerances of Ford production methods.

It is possible that Packard started making Merlins to Ford Motor Co. specs, straight out of the box. They were primarily a motor company after all.

Roger.

[Landroger]

Smilin Ed.

The Allison engines in the P-38 Lightning were identical but were installed facing different directions to get the props to rotate in opposite directions. This was simpler than building the engines differently by using different valve camshafts and simplified the supply problem. Does anyone know if the Merlins and Griffons were capable of being installed "backwards"?

Probably not. The Allison engines in the P38 were turbocharged, the Merlin and Griffon were supercharged ie; the supercharger was driven through a two or three speed gearbox from the aft end of the crankshaft. A glance at either engine shows the entire rear end is full of supercharger, gear boxe and the carburetor/aneroid assembly.

27/09

My understanding re the use of contra-rotating props was the need to be able to absorb the horsepower of the more power full engines. They were used on the Spifires and the Shakletons and other piston types as well no doubt. The Russians used contra-rotating props on some of their turbo-props.

Absolutely. The Spitfire had quite short legs and even after the mighty Dowty three blade prop was fitted, the Merlin power output just kept on going up. If you remember, the Griffon Spits had five blade props and the contra rotating prop was mostly needed for the Seafires, because they tended to 'peck' with even the five blade prop.

Look at the F4U Corsair. 4000hp available and it had whacking great long legs to clear that windmill of a four blade prop. Apparently they were called 'widow makers', because of their tendency to 'torque flip' on short finals, if an incautious driver was tempted to 'give her a little nudge' to slow the sink rate.

Roger.

[DozyWannabe]

Enough of the transatlantic willy-waving already!*

As I understood it the Griffon and Merlin designs were nothing more nor less than the result of RR having two different design teams working on separate concepts in the late '30s, with the Air Ministry simply trying to make the best of the resources at its disposal at any given time.

From Wikipedia (http://en.wikipedia.org/wiki/Rolls-Royce_Griffon):

Unlike the Merlin, the Griffon was designed from the outset to use a single-stage supercharger driven by a two-speed, hydraulically operated gearbox; the production versions, the Griffon II, III, IV and VI series, were designed to give their maximum power at low altitudes and were mainly used by the Fleet Air Arm. The Griffon 60, 70 and 80 series featured two-stage supercharging and achieved their maximum power at low to medium altitudes.

[* - Because, let's face it, advances in engine development from about 1936 onwards in the UK were driven by necessity, even if few would mention it aloud.]

[Lightning Mate]

....with its predecessor the Mossie (not handed)

If you care to get a copy of "633 Squadron" you will clearly see that the Mossie had counter-rotating props.

[FERetd]

Lightning Mate Quote:-"If you care to get a copy of "633 Squadron" you will clearly see that the Mossie had counter-rotating props."

Not sure about that, but will need to look at "633 Squadron" again.

But have a look at these clips. The new build Mosquito flew for the first time a few days ago in New Zealand. Several years ago I saw the fuselage being fitted out - a work of art. At that time the jigs for the wings were still being made.

But have a look at these clips. The new build Mosquito flew for the first time a few days ago in New Zealand. I offer these clips not as any arguement, but for your enjoyment

http://www.youtube.com/watch?v=YEyDlgJYIF8&sns=fb


http://www.youtube.com/watch?feature=player_embedded&v=HgxTD1DULKU (http://www.youtube.com/watch?feature=player_embedded&v=HgxTD1DULKU)

.

[Lightning Mate]

l..u..v..e..r..l..y

The sequence in 633 is the one taken at low level from a camera ship in front of the Mossie.

Because of the camera frame rate and the Mossies' rpm, the props may be clearly seen rotating in opposite directions.

Reduced assymmetric blade effect on one.

[sycamore]

The Mosquito does not have `handed` engine/props..the Hornet does/did..

[DaveReidUK]

If you care to get a copy of "633 Squadron" you will clearly see that the Mossie had counter-rotating props.

Hmmmm.

http://upload.wikimedia.org/wikipedia/commons/7/7d/Mosquito_bomber_%28P03823-001%29.jpg

[enicalyth]

The current and last few issues of the Rolls-Royce Heritage mag available on the web are instructive. Not only which way to turn but subtle mods to superchargers, turbochargers as a consequence of the handing. Its not just firing order.

Errors, myths, clangers etc would be avoided if only it dawned on folks that the FACTS are available through the Heritage society and even R-R itself rather than perpetuating some nonsense.

The Heritage soc is a separate body to R-R proper and includes Allison and Packard sections. The missives from the Derby and Hucknall branch are notable for their first-hand knowledge and technical authority.

Rather than recycle tired and wrong info why not sign up?

[Yamagata ken]

Excellent. Thank you sycamore, DaveReidUK and enicalyth. Merlins aren't Etruscan vases. They still exist, still work, and the people who built them and maintained them are still alive. And yet, there is an amazing amount of total borrox spouted by those who should know better, and those who have nothing but an opinion.

[MarkerInbound]

Look at the F4U Corsair. 4000hp available and it had whacking great long legs to clear that windmill of a four blade prop.


To be pedantic, the F4U-5 got about 3200 horse out of a R2800. Even the F2G only got 3000 horse out of an early R4360.

[Brian Abraham]

Errors, myths, clangers etc would be avoided if only it dawned on folks that the FACTS are available through the Heritage society and even R-R itself rather than perpetuating some nonsense.Agreed enicalyth. To put to bed a couple here Packard Merlins were just the same as their U.K-built counterparts, except that they used U.S. sized nuts, bolts, threads etcThe American engines used the very same British thread system. Packard had to produce all the taps and dies themselves, something they were not set up to do, and delayed actual engine manufacture for some period of time.

Lightning Mate, the Mossie props rotated in the same direction, irrespective of Mark. Your observation would be down to film frame rate as you say. You see the same effect in a film of a car wheel, at some point it will appear to be rotating in the reverse direction compared to its actual rotation. The clip you saw must have been on the very point where this effect takes effect, to coin a phrase. Slight difference in actual prop RPM would give the appearance of reverse rotation. Instructors used to use this strobe effect to determine if students had the RPM set correctly by flying astern and looking through their own prop disc at the students, and determining which direction the students prop appeared to be turning.

[Yamagata ken]

Thank you very much Brian Abraham. That is a nugget I have been looking for for a long time. I have been led to believe that within the development cycle, parts were essentially interchangeable between UK and US built merlins, but have found nothing authorititive. To have built different versions with either BSW/BSF or SAE threads would have been an incredible procurement SNAFU and led to a logistical and practical nightmare.

[porch monkey]

Very little internally would interchange, due to the differing production methods described earlier. The hand fitting that took place in UK built engines put paid to that.

[Yamagata ken]

Are you sure, absolutely certain that UK Merlins were all individually hand built by skilled fitters?

"Ford's factory, which was completed in May 1941, was built in two distinct sections to limit potential bomb damage.[nb 10] (http://en.wikipedia.org/wiki/Rolls-Royce_Merlin#cite_note-76) At first, the factory had difficulty in attracting suitable labour, such that large numbers of women, youths and untrained men had to be taken on. Despite this the first Merlin engine came off the production line one month after the factory's completion, and the production rate was 200 Merlins per week by 1943.[27] (http://en.wikipedia.org/wiki/Rolls-Royce_Merlin#cite_note-Lumsden_p._201-28)[67] (http://en.wikipedia.org/wiki/Rolls-Royce_Merlin#cite_note-Nicholls103-75)[nb 11] (http://en.wikipedia.org/wiki/Rolls-Royce_Merlin#cite_note-77) Ford's investment in machinery and the redesign resulted in the 10,000 man-hours needed to produce a Merlin dropping to 2,727 man-hours three years later, while unit cost fell from £6,540 in June 1941 to £1,180 by the war's end. In his autobiography Not much of an Engineer, Sir Stanley Hooker states: "... once the great Ford factory at Manchester started production, Merlins came out like shelling peas. The percentage of engines rejected by the Air Ministry was zero. Not one engine of the 30,400 produced was rejected ...""

Rolls-Royce Merlin - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Rolls-Royce_Merlin)

[Lancman]

There was film made of flight refuelling trials with a Belfast attempting to fuel from a Victor; not very successfully. As the Belfast throttled back in order to make a fresh stab at the basket one very senior officer in the audience was heard to say that he hadn't realised that the engines could be reversed in flight in order to slow down.

[porch monkey]

Sorry Ken, my point was meant to be relevant to rolls production, not Ford. You are quite right about engines built by Ford. Very little actual fitting required. Pretty much just assembly necessary!

[Yamagata ken]

Thanks for the clarification :ok:

[barit1]

one very senior officer in the audience was heard to say that he hadn't realised that the engines could be reversed in flight in order to slow down.

"I thought so little, they rewarded me
by making me the ruler of the Queen's naveee!"
- Sir William Schwenck Gilbert

[Peter-RB]

No one has yet mentioned the Griffon with the Contra Prop fitted to Spits, these must have been a dream to fly, all that grunt and no descernable torque effect on t/o or landing, just a lot of willing horses trying to pull all the rivets out..!

Peter R-B

[kkiwi]

The Allison engines in the P38 were turbocharged, the Merlin and Griffon were supercharged

Of course supercharging can be mechanical or via a turbo (turbocharged) ;)

[megan]

The Allison engines in the P38 were turbocharged, the Merlin and Griffon were superchargedThe Allison in the P-38 was both supercharged and turbocharged. Only the "B" model used in airships was unsupercharged.

[Tom Griffith]

The Allison engines in the P-38 Lightning were identical but were installed facing different directions to get the props to rotate in opposite directions. This was simpler than building the engines differently by using different valve camshafts and simplified the supply problem. Does anyone know if the Merlins and Griffons were capable of being installed "backwards"?

The above is a very OLD post, so maybe someone has clarified it, but Allisons (and, as far as I know, no OTHER aircraft engiine) could be installed "backwards" to effect a prop rotation direction that was opposite the standard rotation direction.

Allisons were built with left and right-rotating crankshaft versions. They could fairly be changed-over to the OTHER direction by replacing a few bits and bobs.

(All references to direction of rotation are as viewed from behind the engine)

Note...the Allisons with right-handed (Clock-Wise or "CW") props had crankshafts that were left-handed (Counter-Clock-Wise or "CCW" or Anti-Clock-Wise in the UK "ACW"), and the prop reduction gear assembly gave a prop that turned opposite in direction from the engine's crankshaft. The ones with left-handed/CW props, the reverse was true.

That said, ALLLLLL Merlins had left-handed crankshafts, and a prop reduction gear assembly similar to that of the Allison - two gears in the assy, so the prop turned to the RIGHT. The Merlins with left-handed props had a THREE gear assembly and therefore, their props turned to the LEFT. This setup was seen on the Merlin-powered P/F-82 Twin Mustangs and the Hornet/Sea Hornets. There were several Marks of Merlins where an engine with a right-handed prop had a "mirror-image mate" - with a different Mark.

Isn't this a LOT of fun!

[megan]

Conversion of the Allison for different prop rotation as given by an overhaul shop..

To make a left hand engine from a right hand engine, you have to reverse the crankshaft, replace a regular gear with an "H" gear (this is a gear that skips over a gear that was used), and add a standard gear to reverse the prop rotation after you skip with the "H" gear. Every Allison engine has the ability to be reversed if you have an "H" gear and the added gear.The right hand bank as viewed from the distributor end (rear of the engine) must have several spark plug leads interchanged becasue the cam lobes are backwards. It works out the same for the left-hand bank, somehow ... no left bank changes to the firing order

Firing order RH rotation 1L-2R-5L-4R-3L-1R-6L-5R-2L-3R-4L-6R
Firing order LH rotation 1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R You can see the firing order of the left bank is unaltered

Basically, to make a left from a right, the engine must be almost disassembled becasue you must be able to get to the gearcase in front and must split the case and disconnect all the rods to reverse the crankshaft.

However, if you are BUILDING a left or right from parts, the difference in buildup is trivial, assuming you have an "H" gear, the new gear, and you know the plugs to interchange (this means rewiring the ignition harness on one side ... so it is MUCH easier to simply build a left or right wiring harness than it is to change one that is already wired).

The "H" gear:

A Standard gear is just a gear with a keyed center. An "H" gear looks like two standard gears joined by a small cylinder in the middle to skip over the gear that was formerly meshed by the standard gear. The new gear you add is to turn the skipped gear in the other direction. All gearcases have the ability to turn either way ... the gear bosses are in all of them, internally.

For both left and right engines, the cams turn the same direction and the crankshaft is reversed and turns backwards.

There is no other engine I know of from WWII that as so easy to make turn in either direction when being built up ... two gears, turn the crankshaft around, and change the right bank firing order ... that's it.

You need a starter that turns the other way, and you need an idler type gear to reverse the direction of the cam towers.


https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1200x975/allisonv_fa81dbafe5f35f90dcf29a8ffd5532b784212bbb.jpg
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1200x951/allisonv1_85469d86b604bcd8b9ba1c9a7f899d3ca23cf2d0.jpg

[stilton]

I read somewhere that for some reason P38’s delivered to the RAF were not equipped with contra rotating props as was standard on all other versions

[megan]

stilton, because the Brits wanted the engines to be the same as fitted to the P-40. The Brits only received three examples, which were returned to the US after they realized it was not fit for purpose, and the order was canceled. Most of the order ended up being used in the US as trainers. The Brits were responsible for giving it the name "Lightning", Lockheed had wanted to call it the "Atalanta" after the Greek mythological virgin huntress, unwilling to marry, and loved by the hero Meleager.

[Jhieminga]

Also I believe the Lancaster was retrofitted with spare ex-Shackleton Griffons as there were ample spares. Dowty also made five special gearboxes for them too. I'm ready to be corrected on this though.
While we're on the subject of correcting things.... AFAIK no Lancaster was re-engined with Griffons. This may relate to a batch of ex-Shackleton Griffon 57 engines that were converted to drive a single prop for use in Spitfires. That did involve a different gearbox, and the idle setup became a bit of a compromise between the rather high idle setting of the Griffon 57 and the much lower setting that the original Spitfire Griffons had. I know that the Rolls-Royce operated Spitfire XIX used one of these engines, don't know if that is still the case.

[megan]

The Griffon was developed at the request of the Fleet Air Arm.

War time aircraft that used the engine were various marks of the Naval Firefly and various marks of Spitfire, Seafire, Spiteful, Seafang, and sole MB.5. The Griffon Spitfire was the result of needing an aircraft to combat the appearance of the FW 190. Highest rated engine was the 101/121/130 version with two stage three speed supercharger installed in the Spiteful and Seafang, 2420 HP, 101 was single prop, the others contrarotating.

Rolls Royce had a project called the FTB (Flying Test Bed) which was built up primarily of P-51 components with the Griffon mounted behind the pilot as with the P-39. Mock up only built as the war ended and jets were seen as the way forward..

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/800x617/ftb_mustang_eb345571d7be19dce3a1d47ac885490b8423d823.jpg

[nonsense]

https://en.wikipedia.org/wiki/Rolls-Royce_Mustang_Mk.X#Advanced_developments

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/2000x680/rr_ftb_mustang_bd59413bb3efb1c81bf1b372ba3f9dacdb96e6c8.jpg

[blue up]

IIRC it was built up from one Mustang that got the tail chewed off and another that was dropped whilst being offloaded from a ship in Liverpool Docks. Eric Clutton wrote about it.

[Winemaker]

RE post #57 with the gear drive drawings, reversing the direction of rotation with the same camshafts would imply that the cam ramps were symmetrical on lift and return. Is this the case?

[nonsense]

RE post #57 with the gear drive drawings, reversing the direction of rotation with the same camshafts would imply that the cam ramps were symmetrical on lift and return. Is this the case?

The gearing between crankshaft and camshafts reverses, not to reverse the direction of rotation of the camshafts, but to preserve the direction of rotation of the camshafts while reversing the crankshaft rotation. The camshafts turn the same direction regardless of the direction the prop turns.

[DaveReidUK]

Rolls Royce had a project called the FTB (Flying Test Bed) which was built up primarily of P-51 components with the Griffon mounted behind the pilot as with the P-39. Mock up only built as the war ended and jets were seen as the way forward..

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/267x189/index_bd10485b83e7bfef01fbee638675b602514b457a.jpg

[megan]

The mockup was built up from components of AL960, AM148, and AM245. The first flight prototype was planned to have the tail surfaces of the Tempest. Remedial effort effort for the destabilisation effects of the additional power?


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/500x375/123772_6a8c0b5580e3cfaa56d94d17ea11bdc0_725cb7ae4f3eb18cce3e b6b53a4422751441035d.jpg

[stilton]

I just saw a documentary about the P38 confirming the three aircraft delivered to the RAF lacked superchargers and the contra rotating props of the American aircraft


Consequently their performance suffered greatly and they were rejected

[sycamore]

stilton ,the P-38 had counter-rotating props,not contra-rotating,which applies to props from one engine,ie Griffon.

[Winemaker]

Re the FTB P-51; wouldn't moving the engine back like that cause major c.g. problems? That's a huge hunk of iron to move back eight feet or so.

[pettinger93]

From memory, Eric 'Winkle' Brown has said in one of his books that the later marks of Mosquito DID have the two props rotating in opposite directions from each other, but that this was achieved by different gearing, rather than different engine rotations. This, he said, made the Mosquito one of his favourite wartime aircraft.

[DaveReidUK]

From memory, Eric 'Winkle' Brown has said in one of his books that the later marks of Mosquito DID have the two props rotating in opposite directions from each other, but that this was achieved by different gearing, rather than different engine rotations. This, he said, made the Mosquito one of his favourite wartime aircraft.

I think there's confusion by him (or possibly you) between the Mosquito, which didn't have C/R props in any marks and the Hornet/Sea Hornet, which did.

[pettinger93]

I think there's confusion by him (or possibly you) between the Mosquito, which didn't have C/R props in any marks and the Hornet/Sea Hornet, which did.

By 'C/R' do you mean 2 contra rotating props ? As far as I understood it, Eric Brown meant the single prop on one side went clockwise, and the other went counter-clockwise, thus eliminating swing. It was not a matter of maximising the power through the prop, just enhancing the behaviour of the aircraft. Am trying to find the book in which he said this, but it may takes some time. But of course, my memory may be faulty.

[pettinger93]

DaveReid: further : a quick search of wikipedia shows that Mosquito marks 32 and 34 PR models were powered by a Merlin 113 on one side and a 114 on the other. By searching for 'merlin 113 / 114' found a photo on another site that showed a photo of a mosquito with props with opposite pitch. But this is all very pedantic!

[pettinger93]

Unless Mr Brown was referring to the Hornet by mistake? (or my memory is failing even more than I thought) But I will shut up now.

[DaveReidUK]

DaveReid: further : a quick search of wikipedia shows that Mosquito marks 32 and 34 PR models were powered by a Merlin 113 on one side and a 114 on the other.

That's correct. But AFAIK, the difference between the Merlin 113 and 114 wasn't the prop rotation, but the fact that the 114 (of which nearly twice as many were produced, compared to the 113: 1200 vs 650) had an additional supercharger for cabin pressurisation.

By searching for 'merlin 113 / 114' found a photo on another site that showed a photo of a mosquito with props with opposite pitch. But this is all very pedantic!

I'd be very interested to see that. There's a pretty conclusive photo and a lot of technical detail on the PR.34 here: This Day in Aviation: De Havilland DH.98 Mosquito PR.34 (https://www.thisdayinaviation.com/tag/de-havilland-dh-98-mosquito-pr-34/)