Griffon vs Merlin rotation.
 

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.

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.

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.

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.

The Merlin was `handed` for the deH Hornet.

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!

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 )

Thanks guys.
 

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.

Sorry, not the case.

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"

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!

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 .......

Reversible Engines
 

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"?

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 ?

Smilin_Ed: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)

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.

Cows are more valuable
 

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.:)

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.

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.

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...

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.

Packard Merlins.
 

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:

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

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

hence the reason for the contra rotating props

rigpiggy

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

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.

27/09
 

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.

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

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!}

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. ;)

Rotation
 

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.

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.

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

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.

27/09
 

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.

Smilin Ed.

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

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.

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:

[* - 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.]

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

New build Mosquito in NZ.
 

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" target="_blank">http://www.youtube.com/watch?v=YEyDlgJYIF8&sns=fb

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

.

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.

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