Spitfire fin and engine mount off-set

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10 years 7 months

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Looking at the video that DaZ put up made me wonder whether the off set of the fin and engine mounts were altered on the Spitfire when the Griffon was fitted to compensate for the opposite rotation of the engine. I appreciate it was a different type of engine mount and that larger rudders were fitted with the Griffon ,but what about the geometry of things? I am hoping someone on the forum will know as I had heard that the Buchon was not altered when the Merlin was fitted but don’t know if this is fact or just rumour. Thank you in advance for any replies.
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Profile picture for user Bradburger

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19 years 9 months

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Sopwith, The Griffon powered Spitfires never had any fin offset. The engine however was set up with 2 degrees of downthrust. I believe the issue with the Buchon fin was that the airfoil shape was reversed on the earlier Hispano-Suiza powered versions to suit the opposite prop rotation. Those airframes that where then converted to Merlin power kept the same arrangement, whilst the Buchon's that were built new had the correct profile for right hand prop rotation. Cheers Paul

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11 years 8 months

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I'm not a Spitfire expert (there are plenty of knowledgeable ones on this Forum) but I understood that the late Griffon Spits had a permanent fin tab offset to counteract the engine's torque? Glad to be corrected. Anon.

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4 years 4 months

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Why was the Griffon designed to rotate the other way? Anyone know? I've heard it said that the navy wanted a high performance engine that wouldn't torque-roll an aircraft into a carrier island, so it was factored into R-R design from the start. Is this true? Doubt it though, there were plenty of Merlin Seafires weren't they.

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10 years 7 months

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Thanks for the replies Paul and Anon.

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10 years 10 months

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The Merlin was the odd-one out as far as rotation was concerned. Better to ask why in that case, I'd have thought. I suspect that no-one cared too much at the time, but the RAE were to recommend that all British engines rotated the same way i.e. not like the Merlin. However, back to the initial point. At least two writers (David Brown and Peter Caygill) have covered the problems of the late model Seafires in some detail. The basic problem was that the inner wing leading edges were set at differing angles to cope with wave-off case, the naval need for maximum power at very slow speeds. Unfortunately the required amount of differential incidence resulted in an uncontrollable roll in high speed dives. The solution was the contra-prop. I suggest this implies that earlier Spitfires also had differential wing-root incidences to cope with the propeller downwash, but the power and speed range required didn't result in uncontrollable forces in the extreme cases.

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Thank you Graham didn’t realise about the leading edges, very interesting.

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The merlin was originally developed as a Private Venture (hence PV12) by Rolls Royce for the American market, but there was no interest. Hence why it swings in the conventional direction for American engines and opposite to the British engines. The Griffon was a development of Rolls’ earlier engines hence why it swung in the conventional British direction. FB

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10 years 10 months

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I can't confirm that the earlier Spitfires did have differential wing roots, but as they didn't have asymmetric fins nor engine mountings (nor differing spans, as on the Macchi fighters) then what did they use to counter asymmetries due to thrust? Perhaps there's evidence in the Monforton plans book?

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10 years 7 months

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Perhaps Mark12, might know more about it as I haven’t got a copy of the Monforton book, which I understand covers the MkIX.

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4 years 7 months

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Surely the Merlin would rotate in the same direction as all it's predecessors, having been designed under Henry Royce ? Looking at pictures of Merlin Spitfire and Falcon engined Bristol F.2B, they look to have the same rotation ?

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12 years 7 months

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Not the case, I’ll refer back to my previous comment. the Kestrel engines were being used quite widely by the military - it was thought that the R engine was most likely to be developed into something later on too so what was to become the Merlin was developed as a Private Venture for the American market. By adapting a spur gear reduction box in the PV rather than the epicyclic of the Kestrel, the direction of propeller rotation was reversed. FB
Profile picture for user Vintage

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1 year 1 month

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FB. Of course, the Kestrel was spur gear RH tractor, Peregrine, Buzzard, R and Merlin. You have to go back to earlier Rolls-Royce aero engines for LH tractor. The later LH tractor engines were the Vulture and the Griffon. Although I believe that there were some "Ministry" type of directives, I strongly suspect that the engine designers had to make some layout related choices to suit their engine rotations. For instance, the Griffon emerged with it's camshaft drives at the front and, the Vulture was,...complex. In amongst all those engines, there were also some "funnies", The single reverse rotation R engine- I think for a record attempt boat, the Merlins with reversed prop drive( 131etc) for the handed engined Hornet and the contra-prop Merlins and Griffons. Cheers V

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10 years 10 months

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As I understand it, the "Ministry ruling" came after the Merlin appeared rather than existing earlier but being ignored. It has the air of being an austerity/simplifying ruling rather than anything based on deep aerodynamic reasons. I admit that the carrier take-off/wave-off case appears sound, but hardly a major driver given the small size of the market. Given the wide variety of aircraft types for which engines were used, designing them to suit aircraft layouts seems very unlikely. Aircraft were usually designed to fit the engines available, rather than the other way round. The Kestrel cannot have had RH rotation with a spur gear and LH rotation with an epicyclic. The Peregrine and Vulture were Kestrel developments, so presumably at least the Peregrine went round the same way?
Profile picture for user Vintage

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1 year 1 month

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Graham. The Kestrel is spur gear RH tractor, no epicyclic production versions. The info I wrote is correct. Yes, it does seem strange that the Vulture is LH tractor and it is basically two Peregrine RH tractor but, the photo's of all these back-up that data. Cheers V

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Why was the Griffon designed to rotate the other way? Anyone know? I've heard it said that the navy wanted a high performance engine that wouldn't torque-roll an aircraft into a carrier island, so it was factored into R-R design from the start. Is this true? Doubt it though, there were plenty of Merlin Seafires weren't they.
I saw a TV-program about Ark Royal and Bismark. I noticed that the island is on the starboard side. Aircraft with a Griffon engine driving a single propeller which rotates anti clock-wise seen from behind, will induce a torque-roll which is clock-wise, towards the starboard side of the carrier. The slipstream will yaw the aircraft towards the starboard side of the carrier. Was there a design change on which side the island was located? If not, the Merlin will induce the opposite torque-roll and yaw compared to the Griffon, away from the island. Am I missing something? If not, my vote is for "not true"!