On Tue, 24 Sep 2019 13:29:42 +0100, Roland Perry
wrote:

In message , at 13:19:12
on Tue, 24 Sep 2019, David Cantrell remarked:
On Mon, Sep 23, 2019 at 04:45:38PM +0100, Someone Somewhere wrote:

But it seems obvious that the best solution would be some kind of
(presumably) electrical tug that could take a plane from the gate to the
point where it needs to switch to using its own engines for takeoff.

Given that the engines (I believe) turn the generators that provide
electrical power, that point is the point at which the plane is
disconnected from ground power. They need electricity to power the
radios that let them talk to the control tower, run air conditioning,
make announcements to passengers, and so on.

Which is why many aircraft had an engine (aka APU) in the tail to
provide that.

Failing that, batteries, like the much lamented lithium ones in
Dreamliners.

Yes, airliners use the APU to power the lights, aircon, radios, etc
when they're on the ground without main engines running if there isn't
ground power. So even if the plane was towed to near the take-off
point by an electric tug, the APU would still have to run. The APU
also provides the power to start the main engines.