Spitfire engine question.
(a bear of little brain)
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Don't know about US/Europe etc. but about 40 years ago a bloke I knew modified his Ford Anglia by fitting a 2 litre Honda engine into it. And the was very surprised when it turned out to have 4 reverse gears and one forward. Turned out to be because the Japanese engines revolved the opposite way round to European engines.
And, from years ago, a quiz question:- 'Why do car (and, presumably, aero) engines always start the same way?'. Answer: 'Because the starter turns them that way'.
And, from years ago, a quiz question:- 'Why do car (and, presumably, aero) engines always start the same way?'. Answer: 'Because the starter turns them that way'.
Last edited by MadsDad; 2nd Apr 2013 at 15:51. Reason: spelling (although 'madified/ was not wrong in the circumstances)
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Torque rotation was very noticeable on acceleration on some older shaft-driven motorcycles. Big BMWs were a PITA to keep upright at times, in wet weather the back wheel would slip sideways on acceleration. Honda got round it (to a point) on the CX500 and (some) Goldwings by making the gearbox and shaft rotate in the opposite direction to the engine, with the gearbox weighted to act as a flywheel.
Is the same effect seen on aircraft? If the prop is geared to rotate in the opposite direction to the engine, is the torque rotation lessened?
I realise the airflow will still have a twist in it.
Is the same effect seen on aircraft? If the prop is geared to rotate in the opposite direction to the engine, is the torque rotation lessened?
I realise the airflow will still have a twist in it.
Most of the torque is in the propellor. There is some torque reaction from the crank shaft and the supercharger but it dows not count for much. The engine reaction depends a lot on size and weight; a small engine will not react much to throttle blipping but a dragster running on nitrous oxide will practically jump out of the engine bay.
Milo, the effect was greatest in the rotary engined beasts from the WW1 era. Because the entire engine rotated with the propellor (the crankshaft was fixed to the airframe), aircraft like the Sopwith Pup Camel etc would turn far faster one way than the other.
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For the OP, prior to the SBAC issuing the the standardisation edict in the late 30's it would seem that Rolls were the odd man out in the direction of rotation of their engines. A brief check shows that all I could find (even the humble Gypsy) had clockwise rotation (Bristol, Pobjoy, Cirrus, Napier) but Rolls tradition was for anti clockwise, until the Griffon.
The question on rotation direction of the Griffon crankshaft vs the Merlin is probably, at least partially, answered by the position of the camshaft drives. The Griffon cam drives were moved to the front of the cylinder blocks rather than at the rear on the Merlin, in order to minimise the length of the Griffon. The geometry of the new position required the crankshaft to run in the opposite direction if simple gearing and the same rotation direction of the camshafts, as the Merlin, was to be used. The direction of rotation of the camshafts is the same in the Griffon and the Merlin, clockwise viewed from the rear, although the crankshaft turns anti-clockwise on the Merlin and clockwise on the Griffon.
Packard Merlins mainly differed from Rolls-Royce Merlins in the type of supercharger drive and, earlier Packard Merlins used an American designed two-piece cylinderblock. Overall, great engines. Worth buying the RRHT books.
OAP
Packard Merlins mainly differed from Rolls-Royce Merlins in the type of supercharger drive and, earlier Packard Merlins used an American designed two-piece cylinderblock. Overall, great engines. Worth buying the RRHT books.
OAP
Last edited by Onceapilot; 3rd Apr 2013 at 17:15.
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...earlier Packard Merlins used an American designed two-piece cylinderblock.
A common fallacy is re-drawing (for Packard production) equates to re-designing. There are plenty of reasons to re-draw, including internal company standard use of first-order or third order projections, dimensions specified in inches and fractions vs. metric inches (inches and thousandths) etc. etc.
Yes I am sure and, I checked my info from RRHT sources.
There are many other differences and, many different marks or build standards of engine. Overall, they were the same engine with specific differences according to the mark you are comparing. Cheers
OAP
There are many other differences and, many different marks or build standards of engine. Overall, they were the same engine with specific differences according to the mark you are comparing. Cheers
OAP
As far as I know the Merlin always had a two piece engine block. The difference, some people believe , between the Royce and Packard versions were that the Packards were built to American automobile tolerences which were far closer so that component changes were just a 'pull out, slot in' job. British engines always required individual selection and fitting.
This was also apparant in the British car industry in the 40s and 50s. Cylinder block would have 0.20 or 0.10 stamped by the bores to indicate what oversize piston to fit; same with the crankshaft. You never had to worry about that on American engines.
This was also apparant in the British car industry in the 40s and 50s. Cylinder block would have 0.20 or 0.10 stamped by the bores to indicate what oversize piston to fit; same with the crankshaft. You never had to worry about that on American engines.
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I recall reading a contemporary account in an ancient aircraft magazine of the time that the Packard engineers were taken somewhat aback when presented with several tons of drawings for the Merlin that the dimensions lacked tolerance specifications - the RR machinists / fitters were expected to know such information when building the parts.
There was also considerable flow of information back to RR about improvements and metalogy. For instance, it was said that RR decided to electroplate the head studs to prevent corrosion but found that this increased the occurence of the studs fracturing significantly. They had not known about hydrogen embrittlement until then.
Packard also encountered oil loss because of foaming at high altitude (25000+ft) and had to devise an oil seperator on the crankcase vents (why RR had not encountered that was not explained)
Surprising what picked up as a teenager gets retained after this time...
There was also considerable flow of information back to RR about improvements and metalogy. For instance, it was said that RR decided to electroplate the head studs to prevent corrosion but found that this increased the occurence of the studs fracturing significantly. They had not known about hydrogen embrittlement until then.
Packard also encountered oil loss because of foaming at high altitude (25000+ft) and had to devise an oil seperator on the crankcase vents (why RR had not encountered that was not explained)
Surprising what picked up as a teenager gets retained after this time...
Fareastdriver, in actual fact, the Merlin I did have a two piece cylinder block, with a "ramp head". This was unsatisfactory due to cracking and failure of the head at less than 100 hours. This engine had unfortunately been committed to production and the 172 built were primarily used in early Fairey Battle light bombers. Rolls-Royce worked tirelessly to re-design the cylinder and head assembly as a one piece unit and a prototype Merlin with one piece blocks was test flown for 100 flying hours in six and a half days at Hucknall during the summer of 1937. This block assembly was satisfactory and allowed the Merlin II and Merlin III to be released to production. These engines, with one piece blocks, powered almost all RAF fighters in 1940 and won the Battle of Britain.
The early Packard Merlins used a two piece block of Packard's own design and the Rolls-Royce designed two piece block came into production after the introduction of the two speed supercharger.
OAP
The early Packard Merlins used a two piece block of Packard's own design and the Rolls-Royce designed two piece block came into production after the introduction of the two speed supercharger.
OAP
Last edited by Onceapilot; 4th Apr 2013 at 12:50.
It may be worth explaining that the decision to design a one piece block, to replace the troublesome ramp head on the Merlin I, was made because Rolls-Royce had a good understanding of the one piece block design on the Kestrel. This was essentially scaled up and improved for the Merlin, even though it had some known weaknesses they were not as bad as the ramp head and, the redesign work could be achieved in a relatively short timescale. The brave decision to go for the simpler but faster fix of the one piece block in 1937 meant that enough Merlin II and Merlin III engines were there in time for the RAF to be able to win the Battle of Britain in 1940.
Ultimately, the two piece cylinder and head assembly allowed good reliability at very high powers. The Packard designed two piece block was used on their early versions although, they also reverted to the later Rolls-Royce designed two piece block after its introduction later in the war.
OAP
Ultimately, the two piece cylinder and head assembly allowed good reliability at very high powers. The Packard designed two piece block was used on their early versions although, they also reverted to the later Rolls-Royce designed two piece block after its introduction later in the war.
OAP
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Quoting myself:
We now have five posts confirming the two-piece cylinder block story. The "highly technical" people posting their technical expertise on Merlins seem unable to discriminate between a cylinder block and a cylinder head
And thus the "authoritative" sources continue to disseminate their disinformation.
QED
I've seen enough misinformation about Packard to be very sceptical of these sorts of claims.
And thus the "authoritative" sources continue to disseminate their disinformation.
QED
Thanks for raising the issue Yamagata ken. British piston aero-engines sometimes have component names that differ from automotive terms and certainly, from other languages. The part that contains the crankshaft is called the crankcase. In automotive use this is often termed "the block" and usually includes the cylinder liners. This is not generally the case in British inline aero-engines.
In later Rolls Royce V12 aero-engines, the cylinders are grouped in two banks of six. Because the cylinder liners were fitted into a one piece casting called a cylinder skirt, rather than being individual cylinders, this was termed monobloc construction.
Where the cylinder heads are cast with the cylinder monobloc as one piece, this is termed a one piece block. Where the cylinder skirt is cast separately from the cylinder heads, this is termed a two piece block. Hope that helps
OAP
In later Rolls Royce V12 aero-engines, the cylinders are grouped in two banks of six. Because the cylinder liners were fitted into a one piece casting called a cylinder skirt, rather than being individual cylinders, this was termed monobloc construction.
Where the cylinder heads are cast with the cylinder monobloc as one piece, this is termed a one piece block. Where the cylinder skirt is cast separately from the cylinder heads, this is termed a two piece block. Hope that helps
OAP
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Which way round ?
Going back to the very dark ages, and in the days of pre-war (and many post-war) automobiles, engines had to run clockwise (viewed from the front) for that was where you put in the bit of bent wire and wound it up.
Left-handers ? - Hard luck !.....D.
Left-handers ? - Hard luck !.....D.
