Turbo - prop/fan/jet ?

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Re: Turbo - prop/fan/jet ?

Post by ETOPS »

:smt021
AuxBatOn wrote: It is obvious. If it uses Newton's third law to push itself though the air, it's a jet.
Then obviously a turboprop is a jet. Even on a revers-flow turbine like a PT6A (38-45R), the exhaust gas jets exiting the engine produce up to 36% of the overall thrust. Hardly negligible in my opinion. Check the site if you don't believe me (http://www.pwc.ca/en/engines/pt6a note the *** at the bottom of the Features section).
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Re: Turbo - prop/fan/jet ?

Post by AuxBatOn »

I know that there will be residual thrust simply because it's impossible to extract and transfer all the energy from the turbine to the shafts (sts), but I do not see anywhere your 34% figure. On a typical turbo-prop it's normally less than 10%.

The thing is that there is no nozzle, the prop is NOT an integral part of the gas turbine and the basic design allows propulsion by the transfer of energy via the turbine, to the shaft, to the propeller. It is NOT a jet.

I flew an airplane powered by a PT-6-68. It produced a grand total of 100 lbf of thrust on a 1700 SHP engine. (oh, and there is no simple conversion between Force and Power).
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Re: Turbo - prop/fan/jet ?

Post by ETOPS »

The difference between 1090ESHP and 700SHP is ~36%.
AuxBatOn wrote:(oh, and there is no simple conversion between Force and Power).
Its not "simple" (I'm assuming you mean a fixed coefficient). It involves the flight velocity. Exhaust thrust [N] times flight velocity [m/s], divided by the prop efficiency [non-dimensional] equals the difference between ESP and SP [Nm/s] (watts [W]). I'm not sure what flight velocity and prop efficiency P&W used, but those are the numbers.
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

Alright, Propfan-Turboprop-Turbofan... We all understand there is no PURE jet engine anymore, and propfan (yes an engine with a Propeller!) is the future. According to Boeing and Airbus, after their, respectively, B787 and A350, they will work on building transport airplane using a Propfan. Of course other option are studied, but right now this kind of turbine engine can make the company save 30% of fuel, with similar cruise speed, and with much better take off and landing performance.

The turbine engine will definitely survive for a while, being the most efficient engine that can work even if you put agrofuel is the tank. However the time of turbojet engine is finished, and nowadays some propeller airplane can even be faster than some of the turbojet transport aircraft of the past, and with definitely more range, more equipment, more technology.

Since the TurboJet Boeing B-52 Stratofortress and the Turboprop Tupolev TU-95 after WW2, (both with similar performance) engineers understood or at least felt that the propeller airplane was not ready to die. They were right, Tubojet did, not Turboprop.

On the vocabulary side (some in this website want to be accurate), Turbojet gave "jet" to the modern airline pilot vocabulary, jet synonymous of "modern", "Rocket", "future", well, the pinnacle of aviation. Jet time, Jet pilot, Jet lag, Jet set you name it. In fact the first jet engine was created in the 12th century in ancient China to scare away the evil spirit (fire works) which became skyrocket later. A balloon that explods could be considered as a jet engine, Turbine engine is something else, and it's what matters.

On the technology side, concerning the Turboprop engine some say there is no power (or thrust) from the propelling nozzle, some say a very small amout, others say quite a lot, other say it varies depending on the turboprop brand/model. And depending on the answer it should tell us wether it is a jet engine or not? Come on, nowadays TurboJet is hasbeen, Propfan (propeller airplane) is the future, jet time is over rated, it is turbine time anyway. What should matter is what kind of airplane you have flown for the chief pilot. Bush Airplane? Large transport? Modern? Weight? Equipment? PIC time? Multi engine time? You can be a "jet pilot" (I don't like this vocabulary, it sounds a bit like public and journalist vocabulary) and being a safety pilot or a non-experienced copi on a single engine very light jet, and you can be a "propeller pilot" as a well experienced captain on a large transport turbine/propeller airplane with modern equipment.
"Jet time" is a bit overrated, in addition to be a bit confusing.
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Re: Turbo - prop/fan/jet ?

Post by David Hasselhoff »

ETOPS wrote:The difference between 1090ESHP and 700SHP is ~36%.
AuxBatOn wrote:(oh, and there is no simple conversion between Force and Power).
Its not "simple" (I'm assuming you mean a fixed coefficient). It involves the flight velocity. Exhaust thrust [N] times flight velocity [m/s], divided by the prop efficiency [non-dimensional] equals the difference between ESP and SP [Nm/s] (watts [W]). I'm not sure what flight velocity and prop efficiency P&W used, but those are the numbers.

African or European Swallow?
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Re: Turbo - prop/fan/jet ?

Post by ETOPS »

One of each, both using their dorsal guiding feathers.
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Re: Turbo - prop/fan/jet ?

Post by iflyforpie »

ETOPS wrote:One of each, both using their dorsal guiding feathers.
But African Swallows are not mygreatory...
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Re: Turbo - prop/fan/jet ?

Post by trampbike »

Hedley wrote:This thread is desperately in need of Venn Diagrams! :wink:
There you go:
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

nicely done trampbike.

However some consider turboprop engine a jet engine. Furthermore when I watch a turbojet, turboprop, tubofan engine, I find the turboprop and turbojet engine very similar, while turbofan has quite a different design...
A turboprop engine is a jet engine attached to a propellor. The turbine at the back is turned by the hot gases, and this turns a shaft that drives the propellor. Some small airliners and transport aircraft are powered by turboprops.
Like the turbojet, the turboprop engine consists of a compressor, combustion chamber, and turbine, the air and gas pressure is used to run the turbine, which then creates power to drive the compressor. Compared with a turbojet engine, the turboprop has better propulsion efficiency at flight speeds below about 500 miles per hour. Modern turboprop engines are equipped with propellers that have a smaller diameter but a larger number of blades for efficient operation at much higher flight speeds. To accommodate the higher flight speeds, the blades are scimitar-shaped with swept-back leading edges at the blade tips. Engines featuring such propellers are called propfans.
http://inventors.about.com/od/jstartinv ... gine_2.htm


To your funny diagram you could have added the propeller an non-propeller aircrafts, because it's all what it was about right? It has its importance if you read many of the post in this thread, saying "if it has a propeller it is not jet!"
Because in fact a propeller airplane can have:
-a piston engine,
-turboprop engine (ingeneers say it is a jet engine)
-jet engine (according to avcanada vocabulary), the propfan.
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Re: Turbo - prop/fan/jet ?

Post by Pretend-A-Jet »

Its all BS, all of this "time" stuff.

"Multi Time" - The only time flying an airplane with more than one engine makes a difference is when one of the engines quits. Multi time should be worthless unless you've had an engine failure.

"EFIS Time" - You're just displaying the same stuff on a computer screen instead of dials. How much time does it take to get used to it? None really. Learning a new FMS is the most difficult thing, but having EFIS time doesn't mean you know it already. What is efis anyway, is a Beech 1900 with a computer screen depicting an attitude indicator an EFIS equipped airplane, or does it need to have EICAS to be considered EFIS.

"Jet Time" - Flying a plane is flying a plane. In a jet (yes, a jet, one without any propellers) you can't push the prop levers forward and slow down real quick, so you have to think ahead a bit, but you still pull the power back just like any other plane. Maybe it takes a little getting used to, but nothing you can't knock off during line indoc.

I'd repeat my 5000 hour idiot theory, but I think I've done that one a few times already.
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

"Multi Time" - The only time flying an airplane with more than one engine makes a difference is when one of the engines quits. Multi time should be worthless unless you've had an engine failure.
Yes I hear you. To get the idea we could compare piper seminol flight time and PC12 flight time. The PC 12 will be more complex to operate.
Still... You would need an initial and recurrent training in both airplane, and during this training you won't deal the same way with an engine failure... Multi time is still somewhat multi time.
"EFIS Time" - You're just displaying the same stuff on a computer screen instead of dials. How much time does it take to get used to it? None really. Learning a new FMS is the most difficult thing, but having EFIS time doesn't mean you know it already. What is efis anyway, is a Beech 1900 with a computer screen depicting an attitude indicator an EFIS equipped airplane, or does it need to have EICAS to be considered EFIS.
100% agree on that one. When I got my training on the efis, then NG (efis and ng considered as Boeing vocabulary), it was the smoothest and confortable transition I have ever had. Conventional instrument are tougher to deal with. I have never understood all the fuss about "glass cockpit time". It just makes every thing easier and safer (situationnal awarness).
yes, a jet, one without any propellers
A propfan is a "jet" airplane equipped with propeller. Other than that, agree with you. A good pilot will equally do well in a Q400 or CRJ, making a difference is pointless.
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Re: Turbo - prop/fan/jet ?

Post by Gannet167 »

This is a straw man argument. The main conjecture is about terminology. It's a fight over the nomenclature. Without going full nerd ahead on the engineering nuances of this engine or that - the distinction is between operating two broad categories of aircraft. Generally speaking, flying a "jet" is quite different than flying a "prop" -- generally speaking. There are always going to be exceptions. People joke about the Citation 2 Jet having bird strikes on the tail because it's so slow. And yet the Q400 and A400 (allegedly) are pretty good performers.

BUT GENERALLY speaking, if you take an average - props are slower, fly lower and operate differently. If you're going for a job interview to fly a 757, Challenger time is probably more relevant than King Air time. Better? Worse? those are other arguments to have. But the RVSM, MNPS, Oceanic, swept super critical wing, high speed, buffet boundary etc. considerations will transfer over well. Knowing how to feather the prop isn't going to help you much. So to make a broad classification, time on jets transfers well to flying other jets. All semantics aside, there will always be exceptions. C-130 Herc time is probably quite useful in an interview to fly a medium jet. Citation 2 time, Tutor time, maybe not so much.

The rest of the argument sounds like sour grapes. I've never seen a jet column in a log book either. So if someone asks you what jet time you have, I suppose you can manipulate that however you like.

AuxBatOn - I think you mean the -68"A" and if I remember right, only 80lbs thrust came out of the stacks. That was a fun airplane.
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

In this thread we really want to compare the King air to everything else. King air is the turboprop airplane, everything else is jet apparently...
If you're going for a job interview to fly a 757, Challenger time is probably more relevant than King Air 200 time.
Yes true, because the Challenger T/O weight is 43100 lb, king air 200 being at or below 12500 lb, considered as a light single crew aircraft. Compare the king air with an other light aircraft, a jet light aircraft, and you will see it won't be so important for Air Canada or Cathay wether you flew a jet light aircraft or tuboprop light aircraft.

In addition to not being the same weight at all, King air 200 is a bit of a bush airplane, able to land almost anywhere, nothing to do with a challenger.

To me comparing a 43100 lb T/O weight airplane with a light single crew 12500 lb doesn't make any sense. Escpecially when we use this comparation to justify a point of vue.

Challenger T/O weight is heavier than a Dash 8-300, heavier than a ATR 42, heavier than a Dornier 328, heavier than a saab 340, much heavier than a Embraer 120, Heavier than the CASA CN235...

An ATR42 (dash8...), or challenger experience to hire a new first officer on the B757? It depends on the chief pilot, and human ressources policy, and it depends aswell on the quality of the pilot. But really I am not sure it will make a huge difference. DHL in germany even hire F/O at 200 hours sometimes on the B757... So concerning DHL and the B757, ATR 42 experience or Challenger experience, I am sure they won't make a difference...
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Re: Turbo - prop/fan/jet ?

Post by Gannet167 »

I wasn't seriously implying that a Challenger pilot is all that well qualified for a 757 job (but better than a King Air). It's an example to make a point. Comparing these two very different aircraft makes total sense because they're so different - this is the point being illustrated. Generally speaking, these differences are what makes experience on one of them more relevant than the other for certain types of jobs. A Challenger moves a lot faster and flies quite differently than a Dash-8, so I'd say Challenger time is more relevant to a job on another fast moving, swept wing jet.
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

Ok I see.
Possible that some chief pilot would prefer Challenger time over Dash 8 time. Unfortunately sometimes they would ask time on type and type rating. If you don't have B757 time, for many companies they will check if you flew turbine aircraft or not, multi time or not, PIC time or not, 5000 Lb T/O weight or 50 000 Lb, but I am not sure they will get all excited if you flew a Challenger. Challenger corporate/charter, or regular scheduled airline flying a Dash-8, ATR 42..., for many airlines both profil really have their chance, considering that both of them have no B757 experience. Anyway a regional turbopro pilot (Dash-8-300?) most of the time have no more problem to acess the airlines (B757?) than a Corporate jet pilot (Challenger?) with Air Canada (B767) and Cargo Jet (B757) if we speak about Canada. In Asia/middle east they will ask time on type, In Europe time on type, or will hire their own cadet.

Dash 8 regional turboprop pilot profil, or Challenger jet pilot profil, to access a B757? Well that is the same most of the time if we speak about the real life.
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Re: Turbo - prop/fan/jet ?

Post by Gannet167 »

Yeah, I get that. It was an example, to make a point. I'm not talking about how to advance a career on 757's specifically. It could be any type. My point is, while people argue about whether a King Air is a jet or not, the reason a company is asking about your "jet" time is to see how much relevant experience you have to THEIR type. If the job is for a jet, jet time is more relevant - generally speaking. If the job is for a Bell 206, helo time will be more relevant. If you're being hired to fly a fighter, your fighter time is more relevant. It has more to do with it then how the engine makes power, it's about operating a complex machine. When you have X hours Jet time, it suggests that you'll know how to operate another jet (similar to your experience) without much difficulty. Whether a turboprop is a jet engine or not is semantics. Turboprop time, generally speaking, is different time.
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Re: Turbo - prop/fan/jet ?

Post by SunWuKong »

Sure. I mean, there is nothing in your last post that doesn't make sense.
while people argue about whether a King Air is a jet or not
But I think the thread was more about Turbofan/turboprop flight time, not about the king air, or not about small airplanes versus big ones.
If the king air represents the turboprop aircraft, then the CJ1 represents Jet aircrafts. And as you know CJ1 experience doesn't really open more doors than king air experience...
Turboprop airplanes come from light single engine to 4 engines heavy transport airplane, slow airplanes to fast ones (mach 0.6, mach 0.7), old equipment to the best equipment you can imagine (fly by wire...), able to fly RVSM (it seems important to you...), glasscockpit... Some limited in altitude, others able to fly up to 41000 feet...
So my point was: jet time or not, well it doesn't really matter, keeping in mind that we compare what we can compare.

If we compare a heavy transport jet airplane with a light single crew turboprop airplane, sure the first one is more valuable for your career (well, depending on what you want...). But doing so we don't really compare turboprop value versus turbofan value in your resume, but more heavy multi crew aiplanes versus light single crew one's.

Again, if we compare the same kind of airplane, same weight, same year from the factory, the difference of the value becomes very slim, proving here that turboprop experience is valuable like any other. Even if you want to write down on your resume jet time on a cessna caravan, you still "only" have bush experience with a light single engine, non-pressurized single pilot airplane. It is obvious here that the problem is not jet or not jet, but what kind of airplane you flew. To understand it, take your first exemple with the Challenger and the King air, but this time let's say we compare a Dash8-300 versus a CJ1 (same difference of weight with the Challenger/king air), and try to get hired by Cathay... With Dash 8-300 experience you will have more chance to get the job... So if I follow your logic, we can deduct that turboprop is more valuable than jet time...
Again, if we truly want to know turboprop time value, compare it at least with the same kind of airplane, otherwise it is not turboprop time value you evaluate.


Image You can log captain multi jet time.
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Re: Turbo - prop/fan/jet ?

Post by fish4life »

ETOPS wrote:The difference between 1090ESHP and 700SHP is ~36%.
thats because 1090 is the power the engine produces, 700shp is sometimes a torque limit due to the gearbox (eg engines designed for hot & high performance) or the 700SHAFT HORSE POWER is the power left to deliver to the prop after dealing with the power loss due to friction in the engine, turning the engine to be able to suck in air etc... its kinda like comparing and old muscle car where the engine would put out 500hp but only get 400bhp at the wheels, that doesn't mean its shooting out 100hp worth of exhaust out the pipes.

ps whoever needed to ask this original question probably doesn't have enough time/ knowledge to be considered by an airline requiring "jet" time anyway
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Re: Turbo - prop/fan/jet ?

Post by ETOPS »

Your muscle car analogy betrays a lack of knowledge on the subject.
A quick study of how ESHP is calculated will clearly show that it has nothing to do with gearbox and/or parasitic losses.
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Re: Turbo - prop/fan/jet ?

Post by iflyforpie »

ETOPS wrote:Your muscle car analogy betrays a lack of knowledge on the subject.
A quick study of how ESHP is calculated will clearly show that it has nothing to do with gearbox and/or parasitic losses.
I thought ESHP was an arbitrary ten percent added to the SHP figure to account for the small amount of thrust added by the exhaust.

If the thrust is larger than that, the engineers screwed up and either made the exhaust too restrictive or didn't install enough t wheels...
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Re: Turbo - prop/fan/jet ?

Post by FlaplessDork »

5 pages of ridiculousness.
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Re: Turbo - prop/fan/jet ?

Post by trampbike »

What do you mean? This thread has some Venn's diagrams, therefore it has to be good. :wink:
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Re: Turbo - prop/fan/jet ?

Post by AMM »

Yeah...a color version would be nice.
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Re: Turbo - prop/fan/jet ?

Post by Gannet167 »

If you delete everything except the Venn diagram, it would actually add to the thread. Sadly, we shouldn't need a Venn diagram on this forum.
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Re: Turbo - prop/fan/jet ?

Post by rigpiggy »

I am too lazy to get out my manuals, but if you are going to use PWC at least read it.

PT6A- 11 the rated ESHP includes the thrust however the -11 was 525 ESHP/500shp with a thermodynamic rating of 670hp this allowed for improved hot/high performance
the-36 was rated 783/750

step up to the -38 series was 801/750 with thermo of 1090
the -42 was 903/850 -45 was 1070/1020
this was mostly due to improved compressor design and the second turbine wheel

the -50/60's are interesting in that they added the extra axial compressor and were able to push out 1798/1700+ in the -67 series. the b1900 shows 1279/1214 this reduced flat rating was for what reason?
"Beuller, Beuller"

as you can see at best you get 65hp on 1214 or roughly 5% more hp across the board.
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