Date: 26 Dec 97 03:28:54 From: Joshua Turner <firstname.lastname@example.org> Organization: University of Michigan ITD News Server References: 1
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email@example.com wrote: > I flew on a BAe Jetstream 4100 aircraft the other day, and I noticed that the > two propellors turned in opposite directions. > > It was the first time I saw this on any aircraft. I presume the opposing > rotation is to cancel the moment on the body of the aircraft caused by the > turning engines. But I suppose then separate sets of spare engines - both > "clockwise" and "anti-clockwise" have to be kept in store since the engines > can not be inter-changed. The American P-38s had props set up this way, and while it might be theoretically possible to acheive with gearboxes, you are correct, at least as far the P-38 goes--each engine rotated in the opposite direction. On the original XP-38, the props both rotated inward. This caused buffeting problems, so later production -38s had both props rotating outward. The logistic headaches that this entailed were apparently considerable. Indeed, the P-322 (-38s built for England) had this feature eliminated, at the insistence of the British gov't. At the time (1939 or so), this was fairly uncommon, but I don't know what the situation is now. The exlanations I've seen for this was that it was supposed to eliminate the 'critical engine' that all twin wngine aircraft have. See Fork-Tailed Devil: The P-38, by Martin Caidin, at 24. Unfortuneately, the explantion in that book is rather spotty, and not being an engineer, I can't flesh it out very well. For a more in-depth discussion of this question, you can search Deja-News in rec.aviation.military, where there was a substantial back-and-forth over it within the past couple of weeks.