Push back trucks (dt. Schlepper)

   Those trucks are used to push and pull
aircrafts, whenever it is desired to
relocate them without its engine power.
Aircrafts are pushed back from nose-in
positions, simultaneously the aircrafts
engines are started, when the area behind
is clear of apron facilities that might
suffer from the jet blast. (Small prop
planes are sometimes allowed to move
backwards by own power, this is called
power back.) For repositioning the 
aircraft is normally towed.
   There are two kinds of trucks. Both have
to be flat to fit below aircraft noses. So
usually it is necessary to hydraulically
lift the small cockpit for driving backwards.
Some have cockpits on both sides!
   The old ones have a tow bar connected
to the airplanes nose gear. The airplanes
steering hydraulic is turned off therefore, 
so the aircraft is steered through the
tow bar. This is easy when pulling, but
pushing is very difficult, because the
driver has to steer in the wrong direction
initially to make the airplanes nose
gear turn into the right direction. For
this the truck needs good steering and
-of course- a lot of power and mass that
brings the power on the ground. A big truck
can weight 60 tons (a heavy B747 can
have almost 400 tons).
	My 8-knob-wide red truck contains
0.3kg brass, sawed in bars of approx. 7x7mm, 
that fit with some simple cardboard casings
into the knob-wide spaces around the engine
and gear. At its total weight of 0.5kg it does
pull a 1.5kg-airplane. The tires are cut from
medium size technic tires.
  The six-knob-wide yellow truck is not 
motorized. The 4-knob-wide steering of the
aft axis contains a technic brick with cut
knobs. Its cockpit can be lifted and lowered.
   Both trucks can connect the towbar at
the front or at the aft. The towbar has small
releasable wheels, to pull it for transportation.
During push-back the truck and the aircraft
is accompanied by a walking ground personel,
who communicates with the pilots through
a headset. This is important during engine
start. Besides, disconnecting the tow-bar is
done manually. This is very dangerous. We had a
fatal accident in FRA this year at night.
   The new trucks are called tow-bar-less
push back trucks. They are U-shaped, the 
mechanic inside can lift and hold the airplanes 
nose gear which makes steering much easier. 
Additionally the trucks must not be heavy, 
because they carry the nose of the aircraft. 
Some of these trucks can lift and rotate
its cockpit by 360 degrees!
   Building a tow-bar-less motorized truck
in LEGO is a very big challenge, because LEGO
technic axes are not designed to carry such
forces assymetrically... and especially the wheels
at the thighs of the U-shape have to be motor
driven. Possibly the problem can be worked-around
by adjusting the aircrafts center of gravity to
the aft. The tow-bar-push-backs require a lot of
forward c.g., as the nose gear needs some weight 
to transport the steering forces.





Hello
   My name is Uli Meyer, about 36 years old.
I live in Friedberg, Germany.
   The whole model shows a section through 
an airport, cut along the gate finger

                         position A35.

The section is 96 knobs wide and 320 long.

For pilots:
   One medium type aircraft can park nose-in 
and pushback. There is complete ground support:
docking system, electric, fuelling, baggage handling, 
toilet service and maintenance. 
   A bridge connects the terminal building with
either the jetty or a ground level bus station.

For passengers:
   The terminal has three levels.
   Upper level: road, departure hall, check in 
counters, security, gate, waiting lounge, 
bridge.
   Ground level: bus station, baggage claim,
lost and found, customs, arrival hall, road,
car park.
   Basement: Underground train station,
S-Bahn.

All pictures (C)opyright 2001, Uli Meyer, Germany
contact ulimy@freenet.de