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I have read this question:

Why do turbine engines work?

The compressor generates a certain volume of air at a high pressure. In the combustion chamber, this air is heated - this leads to a much larger volume of air. Looking at a section of the turbine (tapering to smaller section as compressor stage approaches combustion stage) we see that this further encourages high density mass flow into the combustion stage. At the exhaust stage the pitch of the fan blades is such that work is done by the fast moving air without causing a large pressure drop. In other words - it is "easier" for the air to go out the back. But since there is far more air coming out the back (added a lot of volume by burning fuel) the fast that it is working "less hard" on the way out doesn't stop the engine from producing power / thrust.

This is a very nice explanation why turbines work.

Though, I have not found any description on this site why turbines are more effective then propellers on airplanes. As I understand most of modern airplanes (that fly at high speeds) have turbines instead of propellers, and I have not even found to what extent turbines are better then propellers. As I understand, turbines give more throttle then propellers, but i have not found any explanation why. Or the given throttle per used fuel is more efficient.

I have found this:

https://en.wikipedia.org/wiki/Turboprop

This combines a propeller with a turbine. But it still gives no explanation why turbines would be more effective then propellers (if they are at all).

Question:

  1. Why are turbines more effective than propellers on airplanes?
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Turbine engines are not necessarily more efficient or useful than propellers. The topic is complicated; I will briefly sketch out the big issues here.

If you want to go trans- or supersonic, you cannot use propellers because the propeller tips go trans-sonic before the rest of the plane does and when they do, their propulsive efficiency falls dramatically. Jet engines are the only way to go in this operating regime.

If you want to go slow in a small plane, propellers (driven by piston engines!) are far more efficient than jets because when you scale a jet engine down in size and thrust, its propulsive efficiency falls quickly and its operation is so uneconomic as to be uncompetitive compared to piston-driven propellers.

If you want to fly a very large plane high and fast, piston-powered propeller propulsion is impractical because when you scale up a piston engine, you scale up all the fundamental problems of internal combustion engines and they become uncompetitive compared to jet engines.

You can marry the advantages of props and turbines by discarding the piston engine and using the turbine engine to drive a propeller instead; this is a very efficient means of propulsion as long as you don't have to exceed about 450 MPH.

Finally, note that you can get even more efficiency and performance out of a propeller-driven turbine by tucking the prop into a close-fitting annular shroud right in front of the turbine engine. To make up for the smaller prop diameter this requires, you add more blades to the "fan" and now you have the high-bypass turbofan that currently dominates the jet transport business.

TO SUMMARIZE: transsonic and supersonic flight = no propellers, jet turbines only

fast subsonic flight, big plane = high bypass turbofan

slow and small planes = no turbines, pistons & props only

medium sized planes, subsonic speeds = turboprops

There are exceptions for special-purpose planes (like for the military) where the tradeoffs between performance, purchase cost, and cost of operation are different.

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  • $\begingroup$ why would "propellers efficiency fall dramatically when their tip reaches trans-sonic speed"? $\endgroup$ – Thomas Aug 21 at 5:01
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    $\begingroup$ @Thomas, this is because the shock waves that are created in the trans-sonic regime severely upset the airflow over the propeller blades and they begin producing lots of noise and much less lift, which means less thrust and lots of wasted power. $\endgroup$ – niels nielsen Aug 21 at 16:02
  • $\begingroup$ Do you maybe have the privilege to help me migrate this question to Engineering? $\endgroup$ – Árpád Szendrei Sep 12 at 21:49
  • $\begingroup$ I do not know how, sorry- but you can just cut & paste, yes? $\endgroup$ – niels nielsen Sep 13 at 1:26

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