What defines a landing gear bogie? (Wikipedia) A Boeing 737 main landing gear arrangement.



What defines a landing gear bogie (truck)?

In its airframe maintenance handbook, the FAA defines it as:


  When more than two wheels are attached to a landing gear strut, the attaching mechanism is known as a bogie.


But, they go on and describe the Boeing 777 main landing gear (MLG) as:


  A triple bogie main landing gear assembly.


That means each lateral pair of wheels is a bogie, which is what the undercarriage arrangements Wikipedia article calls a 2-wheel nose landing gear.

For me, a bogie is when a strut holds a longitudinal arrangement of wheels (like trains). For example, the MLG of a Sukhoi Su-34 (shown below) would be a bogie, but not a Boeing 737 MLG, despite both having two-wheels each.

Are there technical terms to distinguish the two images shown in this post?

(Wikimedia Commons)
The term bogie initially meant (atleast in Britain) an assembly of wheels forming a pivoted support at either end of a railway coach, which provided flexibility on curves.

So, the term bogie refers to the set of wheels, rotating about the (landing gear) axis, while their arrangement- lateral or longitudinal doesn't matter.

An old patent for Bogie undercarriages for aircraft notes:


  ... a bogie having multiple wheel assemblies mounted on transverse rotational axes spaced one behind the other ...


The issue is that the term has been in use for a long time an has come to mean a number of things (even in railways, the entire carriage can be called a bogie)- so while the correct term is to call it a four (or six) wheel bogie rather than double or triple bogie, it is used quite often. Also, as I already noted, whether it is lateral or longitudinal doesn't matter as long as they are attached to the same (nose or main) gear.