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enter image description here
(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?

enter image description here
(Wikimedia Commons)

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    $\begingroup$ I believe “triple bogie” should be read as “bogie that is a triple” (i.e. has three axles) rather than as “three bogies”. $\endgroup$
    – Jan Hudec
    Jul 26, 2017 at 17:24
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    $\begingroup$ A triple bogie is three over par. :P $\endgroup$
    – TomMcW
    Jul 26, 2017 at 18:15
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    $\begingroup$ @TomMcW +3 for you. $\endgroup$
    – user14897
    Jul 26, 2017 at 18:20
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    $\begingroup$ This is known as a birdie. Good thing it wasn't an eagle $\endgroup$
    – TomMcW
    Jul 26, 2017 at 18:23

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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.

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  • $\begingroup$ @ymb when I said already noted, I was referring to my statement in second para, not that in the patent. $\endgroup$
    – aeroalias
    Jul 26, 2017 at 16:56
  • $\begingroup$ as shown below Is there supposed to be an image? $\endgroup$
    – TomMcW
    Jul 26, 2017 at 18:20
  • $\begingroup$ @TomMcW I think "shown below" refers to the quoted text. $\endgroup$
    – FreeMan
    Jul 26, 2017 at 20:02
  • $\begingroup$ @TomMcW I've edited it slightly. Hope it makes better sense now. $\endgroup$
    – aeroalias
    Jul 27, 2017 at 0:09

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