Shaft-bow in Turbo-props

[FL420]

? for MauleSkinner

You do this basically in one of two ways...spin the prop to blow out residual heat, so that the temperature differential isn't so great,

Since the engine is geared, do you happen to know how many "blades" you should turn to ensure you have released the residual heat?

or turn the prop enough to flip the engine 180 degrees, so that the hot (expanded) part is now on the bottom cooling and shrinking, and the cool (not expanded) part is now on top, heating and expanding, resulting in "un-bowing" the engine.
David

Related question. How many "blades" to turn the shaft 180 degrees?

BTW. This isn't only a problem with Garrett turboprops. I was once furloughed for a few weeks when one of the IAE V2500 turbofans developed a bow in the rotor in our last remaining A320.

 

[MauleSkinner]

Since the engine is geared, do you happen to know how many "blades" you should turn to ensure you have released the residual heat?

Related question. How many "blades" to turn the shaft 180 degrees?

Question 1: Just spin it til you're tired

Question 2: I figured that out one time based on the gear ratio, but found it was just easier to spin it til I was tired

Fly safe!

David

 

[TXDA2000]

FL420,

There are several different gearbox ratios. Look into the intake and watch the impellor go round, the prop doesn't move a whole bunch.

 

[Tram]

Coking of the fuel nozzels. It was demonstrated
that if you reduced combustion chamber temp
by spinning the props within a minute or so of
shutdown you could significantly reduce the
buildups on the nozzels.

Doesn't the purge valve that opens on shutdown also help prevent coking?

You heard from AirTran yet?

 

[belchfire]

Yea, I used to have get out and spin the props on a B-100 king air once in a while. I didn't realize that there was a nozzle coking issue involved, thanks.

Er, well, that's what the magazine said.
Seemed reasonable to a (then) Aztruck
driver...they had these charts (how fast
the thing cooled off spinning vs. not
spinnning )and everything!

We had a restriction on starting-the EGT
had to be below 200C. I know that if you
were going to turn really quickly (less than
6 minutes on a passenger op) if you didn't
spin them you had to do a vent run that
could be continued into a start.

With in excess of 6000 hours (counting
both engines) around TPE's I never had
a shaft bow...there was this one time...
never mind!

Tram-ah yes, in a perfect world, where the
cops are British and the chefs are Italian and etc.
yes. But in the real world, where you see smoke from un-burnt (okay, partially burnt)kerosene wafting out of the intake and exhaust you know that all of the fuel didn't get used up!