From: firstname.lastname@example.org (Matthew J O Scott) Organization: Yale University Date: 30 Oct 94 21:29:40 References: 1 Followups: 1
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Bill Simpson <email@example.com> wrote: : I saw a paper that had been given at an SAE A6 meeting on the use of : hydraulic motors to apply torque though gearboxes to landing gear wheels : and thus move the airplane on the ground. This would allow maneuvering : the airplane on the ground with only its APU operating to drive a : hydraulic pump. Have high torque low speed wheel hub or direct drive : motors been considered? These are widely used for off-the-road vehicles, : etc. The motors would have to freewheel or be mechanically disconnected : during takeoff and landing. Very high torque low speed motors would be : required to move a 747 size airplane. The motors would have to be built : to aerospace standards of light weight and high strength. I don't see how or why this idea would fly. (Excuse me) 1. The weight penalty would be exceesive for a feature that has no clear and immediate benefit. (Aircraft have done fine without directly driven wheels for the entire history of aviation. The Wright Brothers of course, had a ground drive system of sorts, but we understand why it was necessary for them) 2. Airlines are interested in fuel savings. Yes, a hydraulic torque pump running on APU juice would consume less fuel than all four fires on a jumbo, but as it is, almost every airline only runs essential engines while taxiing after landing (Jumbos shut down the two outboard ones, commuter twin-turboprops shut down the port engine next to the door) after landing. Most big jets get pushbacks from their gates (unless they are able to taxi straight forward from the gate) that save fuel. Frankfurt Airport at one point in the late eighties (someone help me out, tell me if they still do it) practiced a policy of towing all the widebodies right out to the holding point to save fuel (and cut down incredibly on jet fuel - hundreds of tons a year). I have a hard time seeing how even lightweight, high strength direct-drive motors designed for ground handling would take off (excuse me again). A simple system to spin up landing gear wheels just prior to touchdown might reduce wear and tear on tires, but it is hard to see designers embrace the weight penalty involved across the board. __________________________________________________________________________ Matthew Scott "I'm an Englishman in New York." Sting Yale University "I'm a Canuck in Connecticut, eh!" M.S.