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Old May 10th 04, 04:19 PM
C J Campbell
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"Jay Beckman" wrote in message
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Hi All...

I came across a term the other day I'm not familiar with...

Back in WWII, when a new plane came off the assembly line, a WAC would

it up and "Slow Time" it.

What was/is "Slow Timing" an airplane?

Was it for single-engine fighters only, or was this something done to all

It was running the engine at reduced power to break it in after maintenance
had been performed on it. It was done even after such simple measures as
cleaning and gapping the spark plugs. You did not want to introduce the
engine to the high stress of combat flying until it had been run in for a
few hours. Slow-timing was not necessarily done in flight; there are
paintings and photos of rows of B-17s all sitting on the ramp slow-timing
their engines.

The engine was not run at a constant speed, but varied, and sometimes run on
just one magneto for periods of up to one minute (you can get an argument
going about whether running on one mag is good or bad for the engine).
Although all airplanes needed slow-timing, temperamental aircraft such as
the P-51 needed it more.

Modern engines still require a break-in period, using mineral oil for the
first 50 hours or so. It is still a good idea to slow-time a new engine on a
trainer aircraft, avoiding maneuvers such as touch and goes for a few hours
until the engine is broken in.