Turbine engines?
Discussion
Ok this has been bugging me due to limited spanner knowledge. How does one take the drive from a "jet" engine, I am talking about helicopters etc, taken that the power is from the central shaft, but how then do you take the drive shaft out of the exhaust? direct the gas away and take the driveshaft through a port in the side?
Recently saw an XJS with a Turbine engine fitted and although blatently daft was intreguing. (spelt wrong I think)
Recently saw an XJS with a Turbine engine fitted and although blatently daft was intreguing. (spelt wrong I think)
The entire shaft does not have to be in the exhaust flow. The exhaust flow is downstream of the combustion chambers. The forward end of the shaft, ahead of the chambers, would not be exposed to hot exhaust gases. I'm sure drive couplings, gearboxes etc can be linked in these areas - as is indeed the case with turboprop aircraft engines where the propellor reduction gears are usually at the forward part of the engine.
Turbine engines don't work well in cars, as they can't quickly change speed - they are designed to essentially run at constant speed. Converting that constant output to electricity, and driving some BIG motors has always seemed to be the way forward to me. There's stupendous torque to be had from electric motors.
Not sure if this is what you wanted, but I'll start from the top anyway.
The mechanical drive for the rotors in a helicopter (or to the transmission for a tank, a crude oil pump, a natural gas compressor etc) comes from something called the 'power turbine'. This is an separate turbine mounted down-stream of the main gas turbine engine bit, which is called the 'gas generator' or 'gas producer'.
There is no physical connection between the gas producer and the power turbine in this configuration, the 'coupling' is aerodynamic i.e. the expanding gases exiting from the gas producer are channelled via a duct to the power turbine. This gas then transfers some energy to the power turbine which can be used to drive the rotors or whatever via a gearbox. The power turbine is "blown" round by the exhaust gas. Using this method it is entirely possible, in fact it's often desireable to vary the speed of the output shaft without stopping the gas producer.
In the helicopter example if the gas producer shuts down for some reason the rotor blades continue to turn, but as there is now no power being put into them the pilot has to land pretty soon using a technique called auto-rotation.
The above is true of most gas turbines used to drive a mechanical load, although electrical generators sometime use a different configuration where the power turbine is physically connected to the same shaft as the gas producer. This is because an electrical generator will run at a constant speed dictated by the frequency of the utility grid it's connected to, it doesn't need the flexibility to run at different speeds. Also the increased rotating inertia of the solid coupling means the speed of the machine as a whole is less likely to be 'disturbed' by changes in load.
Sometimes the output shaft exits out the back by the exhaust, sometimes it exits out the front of the gas producer. In the configuration where the power turbine is 'free' of the gas producer this can be achieved by running a shaft up the inside of the main shaft of the gas producer. The gas producer shaft becomes a "tube" which rotates around the output shaft.
There are all sorts of seals between the static and rotating components, for example a 'laborinth seal'.
More ??
P.S. nice looking baby turbine on your 'chopper pdv6 !!
The mechanical drive for the rotors in a helicopter (or to the transmission for a tank, a crude oil pump, a natural gas compressor etc) comes from something called the 'power turbine'. This is an separate turbine mounted down-stream of the main gas turbine engine bit, which is called the 'gas generator' or 'gas producer'.
There is no physical connection between the gas producer and the power turbine in this configuration, the 'coupling' is aerodynamic i.e. the expanding gases exiting from the gas producer are channelled via a duct to the power turbine. This gas then transfers some energy to the power turbine which can be used to drive the rotors or whatever via a gearbox. The power turbine is "blown" round by the exhaust gas. Using this method it is entirely possible, in fact it's often desireable to vary the speed of the output shaft without stopping the gas producer.
In the helicopter example if the gas producer shuts down for some reason the rotor blades continue to turn, but as there is now no power being put into them the pilot has to land pretty soon using a technique called auto-rotation.
The above is true of most gas turbines used to drive a mechanical load, although electrical generators sometime use a different configuration where the power turbine is physically connected to the same shaft as the gas producer. This is because an electrical generator will run at a constant speed dictated by the frequency of the utility grid it's connected to, it doesn't need the flexibility to run at different speeds. Also the increased rotating inertia of the solid coupling means the speed of the machine as a whole is less likely to be 'disturbed' by changes in load.
Sometimes the output shaft exits out the back by the exhaust, sometimes it exits out the front of the gas producer. In the configuration where the power turbine is 'free' of the gas producer this can be achieved by running a shaft up the inside of the main shaft of the gas producer. The gas producer shaft becomes a "tube" which rotates around the output shaft.
There are all sorts of seals between the static and rotating components, for example a 'laborinth seal'.
More ??
P.S. nice looking baby turbine on your 'chopper pdv6 !!
The other way of getting the power out is to use a shaft exiting the front of the engine and then turn it 90 degrees to enter the gearbox. This arrangement is used by the RTM322 used in Merlin and Apache helicopters. If you view the cross section here you can see the shaft exiting in front of the compressor.
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