Honeywell TPE shaft bow (Garrett)

[kilpicki]

Just read in another forum the reason for pulling the prop through after shutdown.

Shaft bow and Wf nozzle salvation were mentioned.

I was told be an experienced Garrett man that its for the mentioned shaft bow but only a one blade pull through was required to move the shaft a min of 90 degrees and any more prop movement is just building muscle on your arm.

Lets hear from you Garrett men.

[ad81]

The way I understand is that we do it to draw cool air through the engine along with the whole shaft bow deal. I usually pull about 30 blades through myself, maybe a few more than needed but thats depends on who you talk to.

[Ballsssssss]

Read my response in the Beech 18 Turboliner thread in that other section.

Shaft-bow is BS. If the shaft is going to bow after shut down, how does turning it 90 degrees to change anything? Would it not just bow again seeing as it has not cooled a lick from being turned one blade? I could be wrong but I doubt it.

[kilpicki]

Fair enough, so the reason for prop turn is to purge fuel from the can and nozzle tips.

Wouldnt it be good to do as PWC and blow air through the fuel line/nozzles on shut down and purge them.

Sounds like a simple enough thing to do but maybe Garrett has a reason not to.

[Ballsssssss]

The Garretts do have a purge system that blows fuel out of the nozzles/lines but it is not 100% effective.

[Unit 969]

“As the engine cools following shutdown, it cools from the bottom up. This process, “convection”, results in a time frame within which the upper portion of the engine is warmer than the bottom. As such, the upper portion of the engine case and internal components are more thermally expanded than those nearer the bottom of the engine, creating a phenomenon most commonly referred to as “thermal distortion” or “shaft bow”.
“The intent of post-shutdown hand rotation of the engine is twofold; to accelerate cooling and to inhibit fuel nozzle coking . . . Garrett also recommends engines be pulled through as part of the preflight inspection to check for the presence of resistance to rotation, which is the detectable component of shaft bow. To attempt a start on an unevenly cooled, thermally unbalanced engine can lead to excessive wear at the internal air seals and, worst case, contact between compressor impellers and mating shroud surfaces.
“It should probably be noted that detectable thermal distortion is quite unusual outside the initial few hours of operation following maintenance actions which replace the inter-stage air seals within the engine. The condition is also quite random in nature since the eddy currents and associated thermal gradient are a function of many variables - - such as wind direction and velocity, outside air temperature, tailpipe configuration and residual turbine temperature.”
Thanks to:
Chad L. Haring
Senior Advisor and Pilot
Allied Signal Aerospace Company
Garrett Engine Division

[kilpicki]

969
Excelent thanks
Now we know the facts.

What about a commuter like a Metro doing lots of short hops and lots of starts. The engine is pulled through and this is enough to prevent this senario?

[ad81]

Awesome reply, I think I read that in the engine manual or some other Garrett publication at one time.