Gas Turbine Technical Question

cking (SEa King???).

Oh yes the most wonderful flying machine ever, closely followed by the 767, of course!

Rgds Cking

Thanks, cking (SEa King???). No wonder the damn things were so hard to turn over. With our early RAAF Hercules, all four props had to be pulled round to line up an oil filler after every flight!

Bri

we used to park the props with No 1 blade at the top to stop the oil draining out of the pitch housing if the aircraft was parked up for any longer than overnight….it also reduced the risk of the props being hit by errant ground equipment as well.

Yes, proteus was a free turbine (or gas coupled) and the Allison is gear-coupled. Rotate a T56 prop and all the gears/shafts, compressors and turbines etc. rotate as well. Rotate the prop on a free turbine and only the power turbine and shaft rotate with it.

that would be the allisons on hercs up to the H model…… J model has an allison which is a free turbine. 😀

The Allison’s have a centrifugal prop brake that stops the blades “windmilling” It is mounted on the rear of the reduction gear box. I changed one on the Met reserch flight’s Herc (Snoopy) back in my youth. That was the only big job I ever did on a C-130.

Rgds Cking

Thanks, cking (SEa King???). No wonder the damn things were so hard to turn over. With our early RAAF Hercules, all four props had to be pulled round to line up an oil filler after every flight!

Bri

Please dont think I’m trying to hi-jack this post , but “Hello !” Uncle Keith!!! How are you ?:eek:

Hi-jack all you like. Thanks to everyone on here, I have the info I needed. 😀

Slightly off-piste, I know, but it always puzzled me:

the Allisons (wrong spelling?) in the Lockheed Hercules were as stiff as hell.

Bri :confused:

The Allison’s have a centrifugal prop brake that stops the blades “windmilling” It is mounted on the rear of the reduction gear box. I changed one on the Met reserch flight’s Herc (Snoopy) back in my youth. That was the only big job I ever did on a C-130.

Rgds Cking

Please dont think I’m trying to hi-jack this post , but “Hello !” Uncle Keith!!! How are you ?:eek:

Slightly off-piste, I know, but it always puzzled me:

1. Why the Proteus engines in the Bristol Britannia ‘wafted’ the props around slowly, and the props could be turned easily by hand.

2. But the Allisons (wrong spelling?) in the Lockheed Hercules were as stiff as hell.

Was the Proteus a free turbine but the Aly geared?

Bri :confused:

Yes, proteus was a free turbine (or gas coupled) and the Allison is gear-coupled. Rotate a T56 prop and all the gears/shafts, compressors and turbines etc. rotate as well. Rotate the prop on a free turbine and only the power turbine and shaft rotate with it.

Slightly off-piste, I know, but it always puzzled me:

1. Why the Proteus engines in the Bristol Britannia ‘wafted’ the props around slowly, and the props could be turned easily by hand.

2. But the Allisons (wrong spelling?) in the Lockheed Hercules were as stiff as hell.

Was the Proteus a free turbine but the Aly geared?

Bri :confused:

A Free power turbine generally means a turboshaft engine where the drive is taken to the rotor head via a reduction gearbox.

Keithmac

I’ll have to add my 2 cents here.
A free power turbine engine is an engine with a compressor/turbine section in the normal sense with an added turbine behind that which is connected to the drive/propellor. This turbine runs independantly of the rest so allowing the compressor to run at a more optimum rpm. A normal turbine will extract about50% of the thrust out of the gas stream to turn the compressor. The free power turbine will extract the rest for the drive. Depending on configuration (turbo-prop, helicopter etc) about 10% of the gas stream velocity remains over as thrust.

Quite where these two terms originated is something of a mystery, but I suspect the dreaded hand of our beloved CAA!

I lecture in Aircraft Engineering for a well known aviation training organisation, and I can assure you that this terminology has been around for quite some time, we teach it, it’s in our notes and has been for a long time. We also have questions (possibly the same ones) in our gas tubine examination bank.

As it’s also in the National Certificate Examinations I would suggest that it should also be in their notes or included in the study material that they refer to.

Next question – where is this written down? Book quote?….

I have had a reply from Rolls Royce Aero engines, and they have not heard of those terms being used. (Except Free power turbine). Quite why the question setting people couldn’t have used common terms is beyond me….. Turbo Prop, Turbo Shaft, Free Power Turbine, etc.

However – THANK YOU to the two on here AND the PM – you have ome to the same conclusion as us AND RR, so by default, it must be correct. Misleading question though!

Finally, expect this thread to be viewed by ALOT of guests tomorrow as I direct the students to have a look!

The question has pretty much been answered But to add:

A Gas coupled engine can be either a Free Turbine Turboprop or a Turbo shaft with a Free Power Turbine. In both of these engines there is no mechanical linkage between the Gas generating part of the engine and the turbine which drives the propeller or in the case of a Helicopter the gearbox.

A gear coupled engine is an engine where the gas generator is coupled to the output drive by mechanical means.

A Free power turbine generally means a turboshaft engine where the drive is taken to the rotor head via a reduction gearbox.

A good indication of the type of turboprop can be gained by looking at the engine when it is stationary, almost all free turbine turboprops automatically feather the propellers on shut down.

Keithmac

Sorry… I should have also added that the third part of the question was to describe a FREE POWER TURBINE….. (We know what that one is… – Our best guess would be that:

The gas coupled turbine IS a free power turbine…

A gear coupled turbine would be a turbo prop…

Gas-coupled could be a free turbine. Gear-coupled is self explanatory – I hope 😉