P-Navajo

I know the differences between the TPE331 and the PT-6. The power turbine on the PT-6 is not connected to the gas producer turbine, but there is gearing between the power turbine and the prop. My reference is "Aircraft Gas Turbine Powerplants" by Jeppesen starting on pg.4-43. I can type more from it in here if you would like.
 
I see what you're saying now. I thought you were attempting to say a PT6 is geared in the same way that a piston engine would have gear reduction, which wouldn't be the case; that would be more like a Garrett engine.

All clear.
 
jtrain609 said:
I see what you're saying now. I thought you were attempting to say a PT6 is geared in the same way that a piston engine would have gear reduction, which wouldn't be the case; that would be more like a Garrett engine.
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Wrong again Jon.

Both the PT-6 and the Garrett have a gearbox between the output shaft and the propeller, EVERY turboprop engine does. The PT-6 has a planetary gearbox in the very front, otherwise the prop would be spinning at 33,000 RPM, not 1900.

The prop must be connected to something or it wouldn't turn. The "free turbine" part means that the power turbine is not conected to the gas turbine and compressor stages.

PT-6 = prop-gearbox-power turbine gas turbine-compressor stages

Garrett = prop-gearbox-turbine stages-compressor stages
 
The power turbine spins real fast. To keep the prop from spinning that fast, there's a tiny gear on that shaft which leads to bigger gears that lead to the prop. The prop doesn't spin as fast as the power turbine.

...I could see how some would say it's "geared".

*edit*
What USMC said.

-mini
 
The Cheyenne 400LS has TPE331s hanging off the wings. Ridiculously cool looking, too.
 

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We ended up moving on to other planes. The price was pretty low, but I think MX cost would have put our hourly operating costs a little to high. The pressurization would have been nice but I'll live strapping on O2. There are a few Chietains and Panther Navajos we have our eyes on.
 
Poopsmith said:
We ended up moving on to other planes. The price was pretty low, but I think MX cost would have put our hourly operating costs a little to high. The pressurization would have been nice but I'll live strapping on O2. There are a few Chietains and Panther Navajos we have our eyes on.
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Two words:

Pulse Oximeter.

-mini
 
jtrain609 said:
While amateurs are debating whether shock cooling exists, the professionals are taking pains to make sure they don't blow up engines.
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Obviously you're not up to par on the subject.

Several known authorities on piston engines have commented on this and backed it up with a slew of engineering tests. A&M did the latest which yielded clear results.
 
I am, in fact, up to par on the subject.

I trust business to create the best practices, because THEY are the ones that have to pay for engines eh?

You would, of course, agree that business creates best practices?
 
The airplane in question does not have PT-6's. It has the POS Lycoming TIGO-541. It is a 425hp geared piston engine that was used on a few of the big twin pistons back in the 70's. The airplane is a dog and one of the few airplanes I've been around that is truly dangerous on one engine. There is a reason less than 50 were produced. The TIGO-541's have a bad reputation, are hard to get parts for, and have a TBO on par with most big radial engines. You are very wise to stay away from the P-Navajo! The Mojave is a decent aircraft if you need a pressurized, piston PA-31.

Alex.
 
jtrain609 said:
You would, of course, agree that business creates best practices?
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No, on many ocasions they continue in destructive and/or unessacary practices. Despite Amflight's years of experiance, they have not equiped their airplanes with modern accurate instrumentation.


Everything I've seen has convinced me that you can't "shock cool" an airplane engine without deliberate and repeated abuse. This is backed up by several enginering studies by universities like Texas A&M.

The main problem with these engines is that they sit unflown for far too long, and when they are flown they are run too hot. If you keep your engines "cool" (under 350 CHT), then you don't need to worry about "shock cooling".
 
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