Why do turbofans even exist when turboprops are more efficient and produce longer range?
>>891010
"The cowl around the turbofan's large fan allows it to perform better than an open propeller at high speeds..."
http://aviation.stackexchange.com/questions/4966/what-is-the-difference-between-a-turbofan-and-a-turboprop-engine
>>891010
> produce longer range
The Dash 8 400 series can take 68-86 people up to 1567 miles at 414 mph.
A comparably sized jet, the E-175 for example, can carry the same number of people up to 2400 miles at 553 mph.
An ATR 72-600 can carry about the same number of people less than 1000 miles at a cruise speed of 316 mph.
>>891010
Turboprops are shorter range, though, OP. Turboprops are more fuel-efficient and cheaper to run but have shorter range, hence their being used on smaller regional lines
A powerful enough turboprop to power an long liner is too loudly for airports norms.
But this is going to change with next technology like open rotor. Google it.
jet power still has better power to weight ratio and high altitude performance.
>>891091
They have no chance of being a better solution than top-mounted, next generation, ultra high bypass turbofans.
>>891027
with the same amount of jet fuel?
>>891372
The dash 8 400 series goes farther on 1 lb of fuel that the E-175 which in turn goes farther on 1. Lb of fuel than the ATR-72
Propellers are beautiful
>>891010
Have you looked at time between overhauls, maintenance costs, etc.?
>>891010
FOD
Foreign Object Damage
>>891079
>Why do turbofans even exist when turboprops are more efficient and produce longer range?
They're not too different.
One has a nacelle and more blades, the other has an open prop.
Both get 90+% of their thrust from the propellor/blade (provided it's a high bypass turbofan)
All modern turboprops have a gearbox, but geared turbofans are also in production.
Gearbox adds complexity and a turbofan has less need for a gearbox because it has less to worry about the blades/props going supersonic thanks to the nacelle. The nacelle adds effiency at higher speeds and it dampens some of the sound.
The main reasons are that a gearbox is more complex and turboprops are louder generally speaking and big ass props take up a lot of space.
And geared turbofans are quieter, smaller and just as fuel efficient.
Mostly sound regulations
Why don't turboprop planes use the thrust created by the turbojet itself in addition to that of the prop? The exhaust is usually aimed away from the long axis of the plane.
fewer moving parts in a jet
>>894292
Turbines used in turboprop engines are tiny compared to turbofan cores.
>>894292
A lot of them do
>>894091
Foreign Object Debris
go back to your lbs baka desu senpai
is this just a meme now? I feel like the last thread answered the question pretty well
>>894094
wait WHAT? I don't know jack shit about jet engines (I don't spend much time on /n/) but I was convinced turbofans got most of their thrust from air exploding out the back as it expanded with heat
>>891079
>more-efficient
>shorter range
That doesn't make sense. Greater efficiency means you can fly further on the same tank of fuel.
>>894292
At low speeds, propeller thrust is more efficient than jet thrust. So they usually have extra turbine stages to convert exhaust pressure to shaft power, so the left over thrust is negligible.
>>896731
smaller fuel tanks because big fuel tanks would be too heavy such a weak method of propulsion
>>896731
That's only one way of looking at efficiency. Most modern turboprops have Vne's of 240-270 KIAS. On short flights, for example IAD-CHO or PHL-ABE where the distances are so short that an aircraft will rarely go above 10,000 msl and are therefore restricted to 250 KIAS for the entire flight.
This is where turboprops are more efficient than a jet. They can complete the flight in roughly the same amount of time as a jet and do so using less fuel. Even if they did get above 10,000 feet and the jet was able to go as fast as it wanted to, the short distance of the flight would mean only arriving maybe 3-4 minutes sooner, and again all the while burning a lot more fuel.
>>896728
That was the really old jet engines and current military jet engines. The current airliner engines are basically already turboprops without the gearbox shit.
>>896728
That's a turboJET, which as >>897105 says, are now mostly used by the military. They're too loud and inefficient for commercial use. TurboFANs are used in most planes. Just look at the shape of the engine to see the difference, turbojets are long and thin while high-bypass turbofans are shorter, but have a large diameter. They're wider because they generate most thrust by being a ducted fan, which just happens to be powered by turbines. The blades generate most of the thrust, the actual jet turbines in the middle turn the blades.
Military jets (mostly fighters, transports use turbofans for efficiency - and therefore range) use turbojets for the much higher thrust, afterburning capability and because they work above mach 1, unlike turbofans.
>>897112
At the risk of pedantry, most military combat aircraft do use turbofans; they are of the low-bypass "leaky turbojet" variety. As you stated, high-bypass turbofans don't work well at all supersonically, due to the fact that the fan in a turbofan engine is designed to speed up a lot of air by a small amount.
>>891010
Because turbofans can operate at higher a airspeed and at higher altitudes. Turboprops utilize a propeller, which relies on more dense air to produce thrust, which is found at lower altitudes. They are a compromise, though, as the turboshaft engine that the propeller is connected to relies on colder inlet air temperature (for lower specific fuel consumption and engine percent power limitations), which is found at higher altitudes.
A turbofan engine on the other hand is more useful in a different flight regime. They are useful for high subsonic cruise ( <Mach .85 or so) and operation at high altitudes. While thrust available decreases with altitude, it does not decrease with velocity (in subsonic regimes). This means that the aircraft can go faster without a decrease in thrust available, unlike a turboprop.
To sum it up, a turboprop is limited to slower airspeeds in more dense air, while turbofans are not. Turbofans are, however, less fuel efficient, so often times regional aircraft will use turboprops.
Turpoprobs aren't more efficient at higher altitudes. PAX don't like them for the most part.
