landing gear vs undercarriage

landing gear and undercarriage both are nouns.

Word	Noun	Adjective	Verb	Adverb
landing gear	Yes	No	No	No
undercarriage	Yes	No	No	No

As nouns, undercarriage is a hypernym of landing gear; that is, undercarriage is a word with a broader meaning than landing gear:

landing gear: an undercarriage that supports the weight of the plane when it is on the ground
undercarriage: framework that serves as a support for the body of a vehicle

landing gear (noun)	undercarriage (noun)
an undercarriage that supports the weight of the plane when it is on the ground	framework that serves as a support for the body of a vehicle