Re: O'Hare -> Hong Kong Non-Stop

From:         libove@libove.mindspring.com (Jay Vassos-Libove)
Organization: MindSpring Enterprises
Date:         22 Jul 96 01:53:10 
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Delta Airlines also has some of these new tugs, and at a recent
Delta family function, one of the tugs was on display, attended
by the engineering manager of the program handling the new tugs.
I spent a while looking at the tug and talking with the engineer.

In article <airliners.1996.1359@ohare.chicago.com>,
	kls@ohare.Chicago.COM (Karl Swartz) writes:
>>   How much does that add to the block time?  I'd think that taxi time
>>   would be significantly longer with a tug than on engine power.
>>Why would it take longer?
> Obviously because I'd expect the top speed for the tug to be slower
> than the best taxi speeds.

The tugs can move airplanes much faster than conventional tugs
because they are hydraulically driven and because of the method
of (non-)attachment to the aircraft.  The hydraulic transmission
has no gear shifting, so as the tug accelerates, there is no jerk
as the tugs shifts gears (as does a conventional tug).  Similarly,
since there is no towbar attached to a point on the nose gear strut,
but instead the whole wheel is picked up, there is less jostling of
the gear, again allowing for higher speed.

Whether the new tug can tow as fast as the plane can taxi is still
doubtful, but it sure makes for better time than the conventional
tugs.

>>Unlike a convential tug, which uses a drawbar connected to the front
>>wheels, this new tug has a wide slot in the back, going to the center
>>of the tug. It backs up until the front wheels are in the middle of the
>>tug, and then somehow grabs the front wheels and LIFTS them off the
>>ground.
>
> United has at least one at SFO as well.  It does seem to move at a
> pretty good clip, but I'd still be surprised if taxiing wasn't at
> least potentially faster.
>
> I'd also wonder about a tug that lifts the nose with a fully loaded
> aircraft, as opposed to an empty aircraft.  Weight might be all that
> much different, since most of the weight is on the mains, but the
> balance might be enough different to make the practice questionable.

The engineer made no indication of weight or balance being of concern.

The new tugs are very expensive (on the order of three to five times
the cost of the conventional ones), but he said that the fuel savings
(and presumably engine wear as well) would result in the entire purchase
price of each new tug being recovered in less than a year of operations.

--
Jay Vassos-Libove			libove@libove.MindSpring.com
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