InevitableRip8968 t1_irp3kxd wrote
Reply to comment by dyskinet1c in TIL that passenger jet engines produce most of their thrust from fan at the front, not from the jet exhaust, and that this is called a high-bypass engine. by Rilot
Turboprops are considered the most efficient of all the different turbines, burns less fuel than the rest. But you trade speed for the efficiency.
allergic2Luxembourg t1_irq5k04 wrote
That's an oversimplification. Turboprops are more efficient at certain altitudes and Mach numbers, and jet engines at others. Thus why turboprops are used in shorter-range applications and jet engines in longer-range. The industry is most certainly choosing the right engine for efficiency as one of the major driving factors (though weight is also considered).
LazerWolfe53 t1_irqnzjc wrote
I feel like altitude is missing from most of these conversations. IIRC the high bypass jet engines get most of their thrust from the jet at high altitude.
IvorTheEngine t1_irqpkyt wrote
And flying higher means the air is thinner, so there's less drag. So even if the engine is less efficient, the overall flight can be more efficient.
dyskinet1c t1_irqttx5 wrote
Turboprops are also limited to rotation speeds where the tips of the blades are below the speed of sound.
If the blades rotate above the speed of sound, the tips generate shock waves that reduces the efficiency significantly.
barath_s t1_iryxaky wrote
> Turboprops are also limited to rotation speeds where the tips of the blades are below the speed of sound.
Laughs in Tu-95 and XF-84 Thunderscreech
> the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H
> The tips of the fan blades of a modern turbofan also move at supersonic speed, so the supersonic propellers on the Tu-95 do not create a direct disadvantage.
also
> The Tu-95 is one of the loudest military aircraft, particularly because the tips of the propeller blades move faster than the speed of sound.
Doggydog123579 t1_irzbsw1 wrote
WHAT DID YOU SAY? I COULDN'T HEAR YOU OVER THE SOUND OF MY EARS MELTING.
barath_s t1_is0chgy wrote
SERVES YOU RIGHT FOR LOOKING AT THE ARK OF THE COVENANT BEING IN THE VICINITY OF THE THUNDERSCREECH
OlDirtyTriple t1_irp9mj9 wrote
They're also incredibly noisy. Passengers would need hearing protection.
8bitslime t1_irpcb1t wrote
The Q400 exists and passengers certainly don't wear any hearing protection. It does have a lot of features in the realm of noise reduction inside the cabin though, much more than a turbofan airliner.
camwhat t1_irqklnp wrote
I tend to fall asleep quickly in Q400s. Ironically most of my family does so
Zebidee t1_irpmmkf wrote
>They're also incredibly noisy. Passengers would need hearing protection.
What are you even talking about??
There's thousands of turboprop passenger planes operating every day without passengers wearing hearing protection.
barath_s t1_iryxkfd wrote
Probably talking about turboprops where the prop tips are supersonic. These tend to be noisy.
Such as the Tu-95 and XF-84 Thunderscreech
> the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H
also wiki for Tu-95
> The Tu-95 is one of the loudest military aircraft, particularly because the tips of the propeller blades move faster than the speed of sound.
Note that turbofan tips for modern engines may also be supersonic
Reascr t1_irpbxeq wrote
Turbofans are plenty loud too, you still need hearing protection for them. But commercial aircraft go heavy on sound deadening for passenger comfort, so even turboprop civilian aircraft aren't too bad.
Military ones though? Yeah you'll get hearing damage if you don't use something.
elmwoodblues t1_irpm20v wrote
WHAT?
FriendlyDespot t1_irplecs wrote
There are plenty of turboprop commercial passenger aircraft flying around, and while you can notice the difference, it's not really much louder inside the cabin.
Prophet_of_Entropy t1_irs2cs2 wrote
only when the props exceed the speed of sound. not every turbo prop is a thunderscreech https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
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