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This story was intended to follow story number 1104 on the 08/08/2021. Do read that story prior to this.

The Modern Gas Turbine Propellor Engine.

Following my story on fuel I will also write about the PT6 engine. In addition I figured I’d get a heavy jet pilot to write about the gas turbine engine that he sits behind, well so to speak. They are no longer pure jets for these days for they too run propellors. Except they are called a high bi-pass fan.

It is the PT6-34 that I have spent most time sitting behind. It delivers 750 hp at max output. In the previous story I said they burned 170ltrs an hour but that was cruise not full power. My error. It is 240 with turbine kero and about 8 less with diesel. I don’t remember each variant of engine and it is not necessary because the arcs in the gauge are calibrated with a green arc for normal, yellow for caution or limited time and red for maximum limits.

There are three limits that must not be exceeded. Firstly and most importantly is max temp. and that being 800C. Remember water boiling point is only100c. Secondly max rpm. The turbines run at such high speed that rpm cannot be measured so it runs in percentage of rpm. 100% being 56,000 but it is permitted to run at 104%. Yes, I do have the decimal point in the correct place. The third is max torque with is limited by the gear-box which is a two-stage planetary system and reduces the propellor to 2,200 rpm. Normally a pilot runs the propellor during cruise at 17 or 1,800rpm.
This is how it works. The air comes in the front, turns 3 axial compressors, then a centrifugal compressor. The compressed air enters the fire place where there is a continuous burn. This is followed by this hot air entering another two axial power compressors, one turning the axial compressing the ambient air as it enters the engine and an other providing power to the planetary gear box which reduces the rpm to the propellor. Then the exhaust gases are exhausted, one each side of the engine.

Now since the propellor is of no use at the rear of the engine it, the entire unit is turned around, reversed so the prop is now out the front. So what happens is the air comes in the rear, turns a big wheel and is exhausted out the front.
The engine is popular with pilots because they are easy to start, reliable, light weight (less than 400 Ibs) and do not have a large frontal service to create drag (which spares about 100hp).

I will write further articles on the radial engine, then heavy gas turbines in the A350 and A380. And because this is a Ford Forum and not a Peugeot publication I will get my grandson to write about the engine in the Boeing and that will please my American readers. Besides I prefer Boeing. Reducing power after takeoff and poling forward to level or descend is done by a human hand and not computer. Sudden and unexpected changes (computer driven) in power or attitude make me nervous.


For those who wish to see a more thorough explanation please go to the link below.

http://www.mautone.eng.br/apostilas/...g%20Manual.pdf