RR Griffon and prop rotation
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RR Griffon and prop rotation
As an old time prop basher now retd I now have time to dig in the 'net for things I have always wondered about. Recently I found the Griff was specified by the Fleet Air Arm who required a left hand prop rotation. Now in my day the A/C yawed away from the downgoing blade...surely with a late Wave-Off an inadequately ruddered Seafire or such would then promptly impact the Island...or am I missing something entirely? Maybe airframes and sub-lieutenants were cheaper in those times!
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myth I think
I believe this to be myth. The Griffin preceded the Merlin in lineage going way back. I'll say that again... the Griff came first as a twinkle in the eye and the Merlin followed by which time the sense of rotation had been sorted. Later there was a requirement for more power and more cubic inches. So in the time honoured way old plans were dug out. In the tradition of second-best tomorrow as opposed to first-best next year the Griffin was re-born. After all there was a war on.
The eminent author and historian who wrote under the name "John Winton" describes how the early jet years forced the FAA to retain piston-power to get off the aircraft carrier. The short-comings of the Griffon 45 and 46 were many. But ship-borne aircraft and their engines had their place in the scheme of things and the answer meant that something had to give...let's face it, what do Admirals and submariners know any way... of course they got the prop rotation wrong. I told 'em but would the listen? Etc etc. The reality was wartime priority.
In essence we believe the Admiralty diktat story because it is funny and people believe the Griffin must have been a second stage of development from the Merlin. Not so.
Where is Brian Abraham? Mine's a horse's neck snid
[See also R-R Heritage site]
The eminent author and historian who wrote under the name "John Winton" describes how the early jet years forced the FAA to retain piston-power to get off the aircraft carrier. The short-comings of the Griffon 45 and 46 were many. But ship-borne aircraft and their engines had their place in the scheme of things and the answer meant that something had to give...let's face it, what do Admirals and submariners know any way... of course they got the prop rotation wrong. I told 'em but would the listen? Etc etc. The reality was wartime priority.
In essence we believe the Admiralty diktat story because it is funny and people believe the Griffin must have been a second stage of development from the Merlin. Not so.
Where is Brian Abraham? Mine's a horse's neck snid
[See also R-R Heritage site]
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On the road at the moment so library not to hand. The Griffon was developed after a standard had been agreed to by international authorities re prop rotation. Not sure which authorities were involved without the library.
Edited to add http://www.pprune.org/tech-log/45055...-rotation.html
Edited to add http://www.pprune.org/tech-log/45055...-rotation.html
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hail brian and snid
To clarify... it is the lineage that counts. The first thinking went on before the Merlin.
While the focus was on the Merlin there came about the need for more power and more cubic inches. But the factories and the ministries saw to pressing needs and the inspiration for the Griffin came from earlier ideas and tooling. If the Griffin is anything it is a prequel rather than a sequel, strange though it may seem. That is what I meant by saying the Griffin pre-dates the Merlin rather than being a lineal descendent.
Without diverting too much effort away from Merlin production jigs and tooling could be refined into an engine that among other thing "turned the other way". But it is not progress to change gears, firing order etc for no good reason except in the middle of a war it makes sense to put to good use what you have to hand. You make do. Second-best tomorrow rather than first-best next year as Watson-Watt had it.
Bill Prentice [also spelled Practice and Prattis] left me all his work from the 1930s until 1948. R-R chose for some reason to destroy almost all of this ostensibly to clear out useless files. Alas a spirit of revisionism seems to have motivated R-R also, almost malice you might say. It is as if someone "got his own back" and consigned records to the dustbin rather than posterity. Certain it is that much has been written out of history and great work destroyed for the pleasure it gives lesser souls. But... wait for it.
Bill never threw anything away! If the vaults at Derby are empty mine are still full. All 18 years worth.
While the focus was on the Merlin there came about the need for more power and more cubic inches. But the factories and the ministries saw to pressing needs and the inspiration for the Griffin came from earlier ideas and tooling. If the Griffin is anything it is a prequel rather than a sequel, strange though it may seem. That is what I meant by saying the Griffin pre-dates the Merlin rather than being a lineal descendent.
Without diverting too much effort away from Merlin production jigs and tooling could be refined into an engine that among other thing "turned the other way". But it is not progress to change gears, firing order etc for no good reason except in the middle of a war it makes sense to put to good use what you have to hand. You make do. Second-best tomorrow rather than first-best next year as Watson-Watt had it.
Bill Prentice [also spelled Practice and Prattis] left me all his work from the 1930s until 1948. R-R chose for some reason to destroy almost all of this ostensibly to clear out useless files. Alas a spirit of revisionism seems to have motivated R-R also, almost malice you might say. It is as if someone "got his own back" and consigned records to the dustbin rather than posterity. Certain it is that much has been written out of history and great work destroyed for the pleasure it gives lesser souls. But... wait for it.
Bill never threw anything away! If the vaults at Derby are empty mine are still full. All 18 years worth.
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Props
Ahah, all becomes clear(er). I recall an unkle of mine, ex FAA, telling me how the late Seafires with contra props would go straight enough when you opened the taps, but the had a tendency to crack the fuselage just ahead of the cockpit when they did...Sounds a bit too exciting for me.
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I had always thought that opposite rotation of props was achieved by changes to the propeller reduction gear rather than the engine itself?
Of course, the effect achieved would depend on whether the torque effect comes from the prop or the engine internals and I don't really know enough to determine whether one or the other is dominant.
It does seem silly to re-engineer the entire engine to rotate in the opposite direction necessitating two sets of spare parts if the same effect could be achieved in the reduction gear?
Of course, the effect achieved would depend on whether the torque effect comes from the prop or the engine internals and I don't really know enough to determine whether one or the other is dominant.
It does seem silly to re-engineer the entire engine to rotate in the opposite direction necessitating two sets of spare parts if the same effect could be achieved in the reduction gear?
Ulric:
Merlin opposite rotation was done by an extra gear in the reduction 'box - quite simple and sensible, c.f. Allison who built engines with opposite rotation thus adding complexity and doubling the spares inventory as you say. Never clever, but particularly not in wartime.
Griffon, being a different design, rotated the other way for reasons not connected with this point. Later they had contra-props so, as said above, no torque problems.
The sense of the torque reaction depends on the sense of what is being reacted to - in this case the propellors. i.e. it doesn't matter which way the motor turns to achieve that.
There is a case to be made for the gyroscopic effect of the motor's rotating assembly and I assume the Allison designers believed it was important. Having known well a man who was a test pilot on the de Havilland Hornet (Merlins with lh and rh props) I'm sure he never mentioned the gyroscopic effect but he did say how much more controllable it was than the Mosquito (unhanded Merlins) which did swing on take-off.
Merlin opposite rotation was done by an extra gear in the reduction 'box - quite simple and sensible, c.f. Allison who built engines with opposite rotation thus adding complexity and doubling the spares inventory as you say. Never clever, but particularly not in wartime.
Griffon, being a different design, rotated the other way for reasons not connected with this point. Later they had contra-props so, as said above, no torque problems.
The sense of the torque reaction depends on the sense of what is being reacted to - in this case the propellors. i.e. it doesn't matter which way the motor turns to achieve that.
There is a case to be made for the gyroscopic effect of the motor's rotating assembly and I assume the Allison designers believed it was important. Having known well a man who was a test pilot on the de Havilland Hornet (Merlins with lh and rh props) I'm sure he never mentioned the gyroscopic effect but he did say how much more controllable it was than the Mosquito (unhanded Merlins) which did swing on take-off.
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Thank you. I knew I'd read that somewhere.
I know the Spaniards had some problems using a Hispano engine in the Me109 airframe because it rotated in the opposite direction to the DB601.
I also know that the P38 had a pair of Allison engines so I'm off to research whether they were handed now.....
I know the Spaniards had some problems using a Hispano engine in the Me109 airframe because it rotated in the opposite direction to the DB601.
I also know that the P38 had a pair of Allison engines so I'm off to research whether they were handed now.....
I also know that the P38 had a pair of Allison engines so I'm off to research whether they were handed now.....
It doesn't mention the P38 at all.
Allison who built engines with opposite rotation thus adding complexity
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Having read up about this now, I have found out some interesting things about the Allison engine. It seems that the counter rotation was achieved by engineering the parts so that the crank/cams could be swapped end over end. After that, it was a matter of wiring the spark plugs to change the firing order to change the direction of rotation of the engine. For me, that is quite an interesting solution and alleviates much of the problem associated with keeping two sets of parts.
Thank you, Ulric, for your summary of your internet reading. Can I remind you that anyone can put things online as true, whether it is or not and whether they have any qualifications so to do.
I too have seen the claims that "all that was necessary" was to turn the crankshaft and camshafts end-for-end (etc.) without explaining how and why that could have the desired effect.
Here's the crankshaft (albeit the early version) and you can see it's a normal six-throw job with the throws paired symmetrically about the centre main bearing:
Elsewhere I have seen it stated "The V-12 engines required changing only the spark plug firing order in order for the direction of the crankshaft to be reversed" which is quite impossible. (e.g. consider valve events: if it worked you'd have it drawing in charge through the exhaust and exhausting through the intake).
ETA Stanwell's post arrived whilst I was looking for that photo and he's right about that - and much much more!!
I too have seen the claims that "all that was necessary" was to turn the crankshaft and camshafts end-for-end (etc.) without explaining how and why that could have the desired effect.
Here's the crankshaft (albeit the early version) and you can see it's a normal six-throw job with the throws paired symmetrically about the centre main bearing:
Elsewhere I have seen it stated "The V-12 engines required changing only the spark plug firing order in order for the direction of the crankshaft to be reversed" which is quite impossible. (e.g. consider valve events: if it worked you'd have it drawing in charge through the exhaust and exhausting through the intake).
ETA Stanwell's post arrived whilst I was looking for that photo and he's right about that - and much much more!!
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This is turning out to be quite a puzzle. Helical cut gears would be a problem of course but the pinions on the components we see are straight cut. This is as one would expect if they were designed to be reversible.
Thinking about this a bit more, what would need to be achieved is that the driving pinion on the end of the crank would need to be at the opposite end of the block. The changes at the top end would be easy if the heads (rather than just cams) were made such that they could be swapped left to right. I'm not sure how the cams were driven but I assume gears not chains.
I know someone who does pylon racing - I'm sure there is someone in that community who has good familiarity with these engines.
Thinking about this a bit more, what would need to be achieved is that the driving pinion on the end of the crank would need to be at the opposite end of the block. The changes at the top end would be easy if the heads (rather than just cams) were made such that they could be swapped left to right. I'm not sure how the cams were driven but I assume gears not chains.
I know someone who does pylon racing - I'm sure there is someone in that community who has good familiarity with these engines.
I too have seen the claims that "all that was necessary" was to turn the crankshaft and camshafts end-for-end (etc.) without explaining how and why that could have the desired effect.
Allison V-1710 Gear Train for Right-Hand Rotating Engines
Allison V-1710 Gear Train for Left-Hand Rotating Engines
AFAIK, engaging the extra idler gear on the LH rotating engine reversed the camshaft rotation (no need to flip it), though obviously the crankshaft had to be reversed and the magneto wiring changed as previously mentioned.
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Dave, you beat me to it re illustrations, but I'll post anyway so folks can see them side by side.
A piece from the people who overhaul Allisons. Yancey Allisons
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
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.
left hand rotating
right hand rotating
A piece from the people who overhaul Allisons. Yancey Allisons
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
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.
left hand rotating
right hand rotating
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P38
Okay now I'm even more confused; looking at pics of the P38 the unfortunate pilot seems to be faced with TWO critical engines as each are outward turning. Maybe something to do with the twin fin configuration? As I grow older and dimmer the world makes less and less sense.
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This is great information! Mystery solved. All down to the little gears labelled H & K in the drawings then?
http://miravim.org/avimlibrary/Manua...01,%201943.pdf
I also discovered the P38 is not the only aircraft to have used twin counter rotating Allisons - the F82 used them too.
North American F-82 Twin Mustang - Wikipedia, the free encyclopedia
http://miravim.org/avimlibrary/Manua...01,%201943.pdf
I also discovered the P38 is not the only aircraft to have used twin counter rotating Allisons - the F82 used them too.
North American F-82 Twin Mustang - Wikipedia, the free encyclopedia
Last edited by Ulric; 29th Jul 2014 at 17:23.
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Picture I have done.
