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Griffon vs Merlin rotation.

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Griffon vs Merlin rotation.

Old 6th May 2011, 00:21
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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.
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Old 6th May 2011, 02:04
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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.

Last edited by GQ2; 6th May 2011 at 02:15.
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Old 6th May 2011, 14:51
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I posted this on the Concorde Question thread:

I had to look it up on Wikipedia:

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
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Old 8th May 2011, 04:31
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hence the reason for the contra rotating props
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Old 8th May 2011, 07:56
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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.
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Old 8th May 2011, 13:03
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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.
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.
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Old 8th May 2011, 14:04
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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 shite with US (Allison) engines until the RAF fitted them with UK built Merlins
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Old 8th May 2011, 14:44
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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 Shite", 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!}
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Old 8th May 2011, 16:22
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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.
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Old 25th Sep 2012, 14:56
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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.

Last edited by Screenworx; 25th Sep 2012 at 14:57. Reason: typo
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Old 26th Sep 2012, 01:03
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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.
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Old 26th Sep 2012, 01:36
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It would fly very differently.
Would that not "torque the same, but in the other direction"?
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Old 26th Sep 2012, 01:43
  #33 (permalink)  
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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.
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Old 26th Sep 2012, 23:43
  #34 (permalink)  
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27/09

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.
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Old 27th Sep 2012, 00:03
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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.
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Old 27th Sep 2012, 01:09
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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:

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.]

Last edited by DozyWannabe; 27th Sep 2012 at 01:21.
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Old 28th Sep 2012, 10:33
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....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.
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Old 28th Sep 2012, 11:32
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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?feature=player_embedded&v=HgxTD1DULKU

.
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Old 28th Sep 2012, 12:47
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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.
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Old 28th Sep 2012, 14:01
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The Mosquito does not have `handed` engine/props..the Hornet does/did..
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