On Thu, 22 Sep 2005 21:01:34 GMT, (me) wrote:

Just what is an "inertial starter"?

I have seen references to them, mostly in literature about
airplanes built before the 1940s. But I have never seen a
description of one, or an explanation of how it is different
from any other type of starter.

In order to understand what an inertial starter is, you have to be
able to understand what an inertia wheel is. An inertia wheel is a
wheel that has most of it's mass out along the perimeter such that
it's mass tends to keep the wheel spinning. Gyroscopes utilized tiny
inertia wheels. A child's toy top is another example of an inertia
wheel.

It's hard to spin up such a wheel because of the mass, but once it's
spinning it tends to want to remain spinning.

Lots of early engines used inertial starters because very few had
electrical systems. The pilot or ground crewman would insert a hand
crank into the side of the engine and one or often two people would
struggle to wind the inertial wheel up to speed. While they're doing
this, you can hear the wheel begin to shriek as it gets going faster
and faster. It usually took two guys to get the inertial wheel on the
Me 109 up to speed.

Once up to speed, the pilot primes the engine, turns on the mags and
clutches in the engine to the inertial wheel. You can hear the sound
of the inertia wheel dramatically changing as it's dragged down by the
mass of the engine it's now turning.

Hopefully the engine starts before the inertia wheel has lost it's
momentum.

If not, it's back to the hand crank and spin it up again.

Get ahold of the old movie "Task Force" with Gary Cooper and Walter
Brennan. The early biplanes they "fly" are started using an inertial
starter. Two ground crewmen crank it to spin it up.

Corky Scott