wrote:

Using three batteries, I have three "-" battery wires running to a negative terminal strip all "jumped on the terminal input side. Is it also best to ground the "-" terminal strip to the largest metal mass in the glider such as the elevator/aileron yoke?

I'm not going to answer that question since it is based on a
fallacy: the concept of "ground" is, except in important but
limited circumstances, a mere concept not a reality.

Arguably the most useful technique is to consider where the
current will flow and where voltage drops will be apparent.
And answering that requires knowledge of not only "what's
connected to what", but also the detailed wiring loom between
each component.

Note that the answers will be different depending on both
the magnitude of the current and also how fast the current
is varying. The latter is most clearly apparent when
considering antennas, RF and transient spikes caused by
pulsed loads.

I'm sure others will give you a more helpful answer.