Re: Engine start process questions

Date:         16 Jun 97 21:35:40 
From:         jwizardc@aol.com (JWizardC)
Organization: AOL http://www.aol.com
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Whoo Boy, what a set of questions!

1) The engine start RPM is set by the limitations of the engine starter as
opposed to the actual engine. Small (electric starting) turbo-props use
15-20% of RPM to get start as opposed to a given number. Since the advent
of the turbojet and 'modern' turboprops, engine RPM is given in % rather
than actual numbers. Who really needs to remember that the Allison
turboprop used in the Lockheed Electra spun at 13,480 RPM at normal power,
or that the JT8D-7 N1 spins at 9,580 and N2 at 14500?

2) The air is ducted to the starter motor via the same ductwork that
extracts the bleed air from the engine for air conditioning,
pressurization, and anti-ice duties. There is a simple valve that opens to
allow the air to get to the engine.

3) The fuel is injected into the engine via a fuel cutoff lever or switch
in the cockpit, which (in some cases) simultaniously applies ignition.
During cruise flight, the engines are like diesels - they don't require
spark plugs. During takeoff, climb, landing, and turbulence/rain a low
power ignition is left on as a backup.

4) No, the pilots don't have one hand on the fire handle. From starter
engagement to fuel turn-on, the pilot has his/her hand on the starter
motor switch. After fuel turn-on, the pilot's hand should then stay on the
fuel cutoff switch/lever, since any problem after fuel turn-on will most
likely be solved by simply removing the fuel from the engine.

5) The last part of the start cycle is the pilots ensuring that the
starter has indeed disengaged at the proper engine RPM. If it doesn't, the
engine's acceleration could spin the starter motor beyond it's limits,
which is listed in the operator's manuals as 'bad'. If the starter hasn't
disengaged, as indicated by the pneumatic pressure failing to rise back
up, or the electrical load from the starter being indicated, the pilots
would shut the engine down to prevent damage to the starter and possible
engine damage.

There are, of course, several variations on the basic theme - 'hot'
starts, 'hung' starts, etc. All these are practices 1-2 times per year in
flight simulators to keep the crews up to speed on their non-normal
procedures.

-jc

TheFNG