Just a thought that hit me today. Why are no large, long-range passenger turboprops being built? I'm thinking of something with around 160-200 seats, in other words a bit larger than a 737, and cabable of transcontinental US routes as well as trans-atlantic flights. After some quick studies of most of the largest turboprobs, I find a few which are, or were, capable of cruise speeds almost as good as those of modern jets. A few examples:

 

Lockeed Electra - 325 knots

Ilyushin Il-18 - 337 knots

Lockheed C-130J -  348 knots

Antonov An-10 - 350 knots

Dash 8 Q400 - 360 knots (it's not that large though).

Saab 2000 - 370 knots (not that large either)

Tupolev Tu-114 - 415 knots

Airbus A400M - 421 knots

 

Isn't turboprops more fuel efficient than jets? Just take the A400M - it's a modern plane and it's also the fastest on the list, just about 30 knots slower than the 737. So, I ask myself, why are the only passenger turboprops built today commuter aircraft? If the A400M could be pushed to be just a little bit faster (the rather bulky airframe, which wouldn't be needed for a passenger aircraft, has to slow it down quite a bit) it would be as fast as a 737. And with the savings in fuel costs in mind, wouldn't the airlines be quite happy with a new, large type of turboprop to replace some of their jet aircraft?

 

Your thoughts? ^_^

 

PS: Sorry for any grammar mistakes, my english is not perfect and it's really late where I'm sitting... :rolleyes:

Mainly for long distance flying you are interested in performance at altitudes of 30.000+ feet. Turboprops aren't anywhere near in capability for this kind of operation. There are also things like engine power in relation to weight etc. Flying long distance means flying a heavy plane with lots of fuel. Takeoff and climb performance will be much better in a jet as well.

Flying at 330 knots at 40000 feet is a much faster ground speed then flying at 330 knots at 25000 feet. Even though turboprops can come close to speed in knots to a jet they are actually flying at a much slower ground speed at lower altitudes

 

 

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 330 knts gs at 40000 ft is no difference than 330knts gs at 1ft. IAS will depend on many variables. Wind speed direction etc.

You are seeing a business case decision in my eyes.

 

While you can bring lots of good points up for props on the short and maybe even medium range sectors, the ones for the long-range ops look different. Since you are competing on various levels, from the actual unit price, to maintenance and training, weather avoidance capabilities and the environmental factors like the noise produced or the ability to land short, you also have to consider how much time you lose or gain when using this or that 'cheaper' plane over lets say a modern jet.

 

You are comparing top speeds by the way, which may not reflect the actual ones in the everyday ops. Also, every one of those values needs at least an indicator for how efficiently this speed can be flown. The A400 may not offer superb cruise efficiency since it was designed with the main focus on allowing for certain missions, bulky cargo and a more or less narrow market where fuel costs are a factor but the 'do we have a plane for that job?' most likely being a larger one. Also, passenger transport (price sensitive!) with four engines 'just' to keep the cruise speed up? Nah, doesn't look like an airline's dream plane.

 

Current commercial passenger transport examples. People will try to find out if it makes sense to buy a Q400 or a much slower ATR. The Q400 can compete with jets when the enroute parts don't get too long. The terminal area and reaching cruise alt times then make up a large part of the journey and a loss of a few knots on the cruise speed will not affect the trip length that much.

 

Now, if you are losing those few knots on some fictional 3000nm trips, you are really losing time. And even if a prop can be turned around quicker and even if the maintenance of the thing is cheaper, the jet may enable the airlines to fly some more flights (and therefore a paying payload) because it added up the speed advantage to soon have one more flight within the same time span. And that's money being made.

 

Now that's a rough look at it and I think you have a point when seeing that the current prop manufactures are planning on larger variants or even a future size of a small 737. Small jets rarely sell good, large props (as compared to current sizes) might. As long as a prop is able to fly cheaper while not losing to much time on the sector in comparison with the jet, it will have a market. Same goes for special ops like city airports (think noise), short field landings or adverse conditions, remote and unpaved airstrips and so on. Having in mind that this special market may not be that big, so the time thingy gains the most weight.

 

Side note. There once was a great plane being sold. A STOL master, and a relatively quiet one. 50+ seats. Not that big of a market though. Special mission profile.

 

Back to normal ops, the longer the enroute segment, the less likely an airline might pick the slower prop. The slowness adds up too much and the prop therefore has to operate even cheaper to make at least the same money. And the faster you design that prop, to enable a larger margin, the less likely it is to be cheap. Take the Q400 vs ATR example, the Q400 is some 20%+ more expensive to operate. Or more. So that has to pay off in e.g. being able to fly more or different ops (expanding the network coverage).

 

At the end of the month, you are asking for how many paying payload got transported, at which costs. The obvious choice on just going for the cheaper flying plane therefore isn't the only factor.

 

If you want to know more about how feasible a larger prop plane is or might be, perhaps this article can help. http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_08_05_2013_p38-601644.xml

 

Short version. If you can find folks buying them, someone will build them.

 330 knts gs at 40000 ft is no difference than 330knts gs at 1ft. IAS will depend on many variables. Wind speed direction etc.

Eh?  Methinks you misunderstood Matt's comment, he was comparing airspeeds not groundspeeds.  330kt IAS at 40,000' is about 595kt TAS whereas 330kt IAS at 25,000' is about 495kt TAS, and for your other example 330kt IAS at 1' is 330kt TAS.  With no defined wind component, Speed over Ground equals TAS, so there's a 100kt difference between 25,000' and 40,000', and a 265kt difference between 1' and 40,000'.

The speeds listed are clearly ground speeds though, thus whatever altitude these aircraft operate in doesn't have any effect on them. 

Eh?  Methinks you misunderstood Matt's comment, he was comparing airspeeds not groundspeeds.  330kt IAS at 40,000' is about 595kt TAS whereas 330kt IAS at 25,000' is about 495kt TAS, and for your other example 330kt IAS at 1' is 330kt TAS.  With no defined wind component, Speed over Ground equals TAS, so there's a 100kt difference between 25,000' and 40,000', and a 265kt difference between 1' and 40,000'.

he said ground speed

Not to mention that jets are more comfortable and quieter than turbo props, something that is rather important for long flights.

he said ground speed

Yes he did.  His dependent variable was groundspeed, his independent variables were indicated airspeed and altitude... Matt is still correct is his statement that 330kt at 40,000' is a higher groundspeed than 330kt at 25,000'.

Not wanting to bug you folks discussing the 'he meant' issue. But the value being of interest would be true airspeed (TAS). In zero winds, that would equal the ground speed of course. The OP seems to make use of KTAS.

 

When comparing the planes and speeds though, it would be vital to know if you are looking at max values, the 'eco' ones or a mixture or both. From a short look on the first post, I think we are seeing the latter (mix). Still, it gives an impression about how fast props compare to normal jets. Today's Jets aren't fast, Concorde was. :wub:

 

Good point on the cabin noise difference from Alex. Modern renditions like a Q400 feature some noise cancelling tech.

During flight, microphones concealed throughout the cabin transmit noise information to a special on-board computer that also receives the propeller speed. The computer continually analyzes this information and signals devices called Active Tuned Vibration Absorbers (ATVAs) mounted on the fuselage frames. The ATVAs then produce out-of-phase counter vibrations, so that the original vibrations are significantly reduced.

http://www2.bombardier.com/q400/en/quiet.jsp

Yes I was saying that traveling at 330 knots at 40000 feet would be IAS and that would have a faster speed over the ground compared to flying at 330 knots IAS at 25000 feet.

 

On long haul I do in some cases choose one airline over another because a flight can be an hour shorter if the airlines is operating a 767 compared to a 737. If it was a long haul turboprop I would never choose that as that would be a much longer flight. 

 

I remember in the past comparing Air Canada and Westjet routes and found Air Canada's routes where in some cases an hour shorter with the 767's compared to Westjets 737's on flights over 5 hours. So I booked with Air Canada on those long haul routes instead. 

 

Performance is definitely a consideration for the business traveler as time is money. 

Another point to consider is that turbo props have "propellers!"

They have velocity problems, in that if they spin too fast the tips go supersonic. So they are power limited.

They can only be powered by simple jets or low ratio bypass engines. And, because the propellers are "exposed" they are also altitude limited.

Just look at the a/c that were developed to cross the Atlantic: The Brabazon, The Britannia, Constellations fitted with turbo props etc. All of them proved slower and less efficient than jets.

On the other hand they are much more efficient than jets for short hops not requiring altitudes above FL240.

Will props ice up?  Sorry if it's a dumb question... :unsure: 

Will props ice up?  Sorry if it's a dumb question... :unsure: 

 

Yes they do and they have de-icing......Sometimes when de-iced the ice breaks off and can smash up against the aircraft. Sounds scary but it is normal.

 

 

Which reminds me of the other point no one mentioned....Props are noisy so if I was to choose a low cost long haul route a prop would drive me mad.

 

Boeing just delivered its first low cost 787 so I would prefer this as it is the quietest long haul low fare aircraft out there:

 

http://www.stuff.co.nz/travel/9294896/Inside-Jetstars-Dreamliner