Turboprops

Since some time ago I wanted to write a small entry just to show the following graphic to point a very basic issue to non-engineers:

Efficiency vs. airspeed.

I have very often heard remarks about turbo propellers referring them as old or old technology, etc. I guess that this comes from seeing images of old aircraft with propellers and reciprocating engines, and now people being used to fly in turbofan engines.

However, turbo propellers are neither old nor a worse technology. As almost everything in engineering it all depends on what the requirements are and the price to pay for the solution. Then come the trade-offs. As you may find in the Wikipedia entry [turboprops] “they are mostly used where high-performance short-takeoff and landing (STOL) capability and efficiency at modest flight speeds are required”.

The first requirement is among the ones explaining why some military transport aircraft such as the C-295, the C-130 or the most modern A400M are equipped with turboprops.

The second requirement explains why some regional airlines employ turboprops for short-haul flights, when the distance can be covered at a bit lower speed without a big impact in the flight time.

If you take a look at the picture above, you could start roughly guessing what type of engine you would choose depending at what speed you would normally fly (then more requirements would come into play).

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