Is it a 'thing' that Airbus produce helicopter rotor systems that rotate differently?
Not quite true though. Early 80s the major operators got together to look at an upgrade package: Helikopter Service, BAH, Bristow, Greenlandair ++. Bristow eventually pulled the plug as they'd done a deal to buy 332Ls instead.
Confirming the Merlin and Griffon cranks rotated in opposite directions. The de Havilland Hornet had handed Merlins which was achieved by an idler gear in the prop reduction gear casing, done to reduce torque effects.
On the P-38 the engineering was some what different.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 because 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 because you must be able to get to the gear case 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 build up 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 gear cases 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.
The reason for the prop rotation, and they tried all directions and combinations, was to reduce the pitching moment (trim change) power on/off so as to make a steadier gun platform.
On the P-38 the engineering was some what different.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 because 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 because you must be able to get to the gear case 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 build up 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 gear cases 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.
The reason for the prop rotation, and they tried all directions and combinations, was to reduce the pitching moment (trim change) power on/off so as to make a steadier gun platform.
Sycamore - TH late 60s, Whirlwind (10, of course), discovered when rotor start went nasty. Quick shut down and, thereafter, pre-flt check that lower t/r blade matched tail pylon aerodynamics. Memory says George Kelson 'made the discovery', but memory frequently false nowadays!
Below the Glidepath - not correcting
Not forgetting the Airbus A400 Atlas has "handed" props that rotate in different directions on each wing to minimize torque effect. Airbus realized that "handed" engines would be a problem from a logistics viewpoint, so one engine on each side has a reversing gearbox between the engine and the prop to produce a clockwise and counter-clockwise prop on each wing. All very clever.
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A very wise and long-time Bell employee once told me that main rotor blades advance "ideologically", Soviet helicopters on the left, American helicopters on the right and Europeans can't make their minds up.
Avoid imitations
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Sycamore - TH late 60s, Whirlwind (10, of course), discovered when rotor start went nasty. Quick shut down and, thereafter, pre-flt check that lower t/r blade matched tail pylon aerodynamics. Memory says George Kelson 'made the discovery', but memory frequently false nowadays!
Shy - Oddly, taking a lunchtime stroll in Crawley during my Virgin days, a bloke passing me sparked an instant GK recognition flash, but , by the time it had properly registered, he had disappeared. ... just realised, that was nearly 20 years ago!!
212, You were very nearly correct regarding the AH (Previously Eurocopter) brand of Helicopters. Eurocopter was born out of an amalgamation of the German Manufacturer Messershmit Bolkow Blohm and the French Company Aerospatial. So AS not SA. Otherwise quite correct.
The EC (Now H) 135 was initially a derivative of the Military MB 105, the 108, later to become the EC135 Aimed at the Para Military market. Built in Donauworth Germany.
Aerospatial also built Military Aircraft, but tended to specialise in Civilian Helicopters like the AS350 and AS355. Mainly built in Marignan France.
TF
The EC (Now H) 135 was initially a derivative of the Military MB 105, the 108, later to become the EC135 Aimed at the Para Military market. Built in Donauworth Germany.
Aerospatial also built Military Aircraft, but tended to specialise in Civilian Helicopters like the AS350 and AS355. Mainly built in Marignan France.
TF
212, You were very nearly correct regarding the AH (Previously Eurocopter) brand of Helicopters. Eurocopter was born out of an amalgamation of the German Manufacturer Messershmit Bolkow Blohm and the French Company Aerospatial. So AS not SA. Otherwise quite correct.
The EC (Now H) 135 was initially a derivative of the Military MB 105, the 108, later to become the EC135 Aimed at the Para Military market. Built in Donauworth Germany.
Aerospatial also built Military Aircraft, but tended to specialise in Civilian Helicopters like the AS350 and AS355. Mainly built in Marignan France.
TF
The EC (Now H) 135 was initially a derivative of the Military MB 105, the 108, later to become the EC135 Aimed at the Para Military market. Built in Donauworth Germany.
Aerospatial also built Military Aircraft, but tended to specialise in Civilian Helicopters like the AS350 and AS355. Mainly built in Marignan France.
TF
and the French Company Aerospatial
Pumas and Gazelles before 1970 would have had the prefix SA.
Sud Aviation of course came from the amalgamation of Sud Est and Sud Ouest hence the early Alouettes are SE3130 and the Djinn SO 1221.
