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The reason jet engines have that sort of exhaust is because the primary purpose of the gas turbine there is to dump all the excess energy into the exhaust to ma

The reason jet engines have that sort of exhaust is because the primary purpose of the gas turbine there is to dump all the excess energy into the exhaust to make it go fast (so that the plane can be pushed ahead by the reaction force). They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.). If you want to use a gas turbine for producing power, you will set it up such that most of the energy goes into the work generated, rather than the exhaust, so it would be a cooler, slower exhaust, similar to an IC-engine.

01HNNWZ0MV43FF 3y ago
Depending on the plane and engine. Big jetliners have high-bypass turbines where they do intentionally produce a lot of torque, to spin a large compressor fan, but most of the fan air does not go through the combustion step, it's just used to react off of.
- WalterBright 3y ago
  It's ironic how propeller airplanes evolved into jets for for thrust and back to propellers. (A ducted fan is still a propeller.)
  - pfdietz 3y ago
    We may go to unducted fans soon. The latest iteration of this concept has two sets of fans, one set of which doesn't rotate.
philwelch 3y ago
Other people have already mentioned the distinction between turbojets (what you’re describing) and turbofan engines, but I think there’s another inaccuracy: > They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.). The APU is a completely separate gas turbine that doesn’t rely on the main engines. As a consequence, the APU on an airplane will also have its own exhaust. > If you want to use a gas turbine for producing power, you will set it up such that most of the energy goes into the work generated, rather than the exhaust, so it would be a cooler, slower exhaust, similar to an IC-engine. Yes, obviously. At the same time, I was under the impression that turboprops and turboshafts on airplanes and helicopters still produced enough jet exhaust to represent a safety hazard, and in those applications you would also expect that most of the energy would go into the work generated rather than the exhaust. So is it just that this residential generator is even more efficient than the main engine of a heavy-lift helicopter? Is it because it’s a less powerful machine in the first place? I could continue to speculate about this but I don’t actually know.
- londons_explore 3y ago
  It's because to extract all the energy from the exhaust, you need huuuuuge turbine blades to extract the last little bit of energy from very slow moving air. So instead you extract most of the energy, and then use the last little bit as extra thrust in a plane/helicopter.

01HNNWZ0MV43FF 3y ago

Depending on the plane and engine. Big jetliners have high-bypass turbines where they do intentionally produce a lot of torque, to spin a large compressor fan, but most of the fan air does not go through the combustion step, it's just used to react off of.

WalterBright 3y ago
It's ironic how propeller airplanes evolved into jets for for thrust and back to propellers. (A ducted fan is still a propeller.)
- pfdietz 3y ago
  We may go to unducted fans soon. The latest iteration of this concept has two sets of fans, one set of which doesn't rotate.

philwelch 3y ago

Other people have already mentioned the distinction between turbojets (what you’re describing) and turbofan engines, but I think there’s another inaccuracy: > They produce very little power, just enough to power the Auxiliary Power Unit (that manages the plane electronics, air-conditioning etc.). The APU is a completely separate gas turbine that doesn’t rely on the main engines. As a consequence, the APU on an airplane will also have its own exhaust. > If you want to use a gas turbine for producing power, you will set it up such that most of the energy goes into the work generated, rather than the exhaust, so it would be a cooler, slower exhaust, similar to an IC-engine. Yes, obviously. At the same time, I was under the impression that turboprops and turboshafts on airplanes and helicopters still produced enough jet exhaust to represent a safety hazard, and in those applications you would also expect that most of the energy would go into the work generated rather than the exhaust. So is it just that this residential generator is even more efficient than the main engine of a heavy-lift helicopter? Is it because it’s a less powerful machine in the first place? I could continue to speculate about this but I don’t actually know.

londons_explore 3y ago
It's because to extract all the energy from the exhaust, you need huuuuuge turbine blades to extract the last little bit of energy from very slow moving air. So instead you extract most of the energy, and then use the last little bit as extra thrust in a plane/helicopter.