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Thread: Small turboprop engines..?

  1. #1
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    Small turboprop engines..?

    I've noticed this small turboprop engine a while ago and it said the engine would be available end of 2012. Knowing that the Czech have a long tradition of good turboprops it might turn out to be a nice powerplant but I was wondering what other similar engines are already available in the world..?

    PBS Velká Bíte

    TP100 Turboprop engine

    55kg
    180kW shaft power
    5394N with AV723
    Ceiling 6000m/9000m

    I wonder why they didn't write down the fuel consumption..?

  2. #2
    Registered User Himat's Avatar
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    Re: Small turboprop engines..?

    Quote Originally Posted by DangerZone View Post
    I've noticed this small turboprop engine a while ago and it said the engine would be available end of 2012. Knowing that the Czech have a long tradition of good turboprops it might turn out to be a nice powerplant but I was wondering what other similar engines are already available in the world..?

    PBS Velká Bíte

    TP100 Turboprop engine

    55kg
    180kW shaft power
    5394N with AV723
    Ceiling 6000m/9000m

    I wonder why they didn't write down the fuel consumption..?
    In the datasheet on the two turbojet variants with the same "core" the fuel consumption is stated and a performance graph shown. Depending on wich you look at the very best spesific fuel consumption is between 1,09 and 1,2 kg/(daN/h). If you study the TJ100C datasheet you find that it uses 0,12kg/(N/h) at 70% power wich is the max continius power.

    If the turboprop uses a similar amount of fuel at the same power setting it will use: 700*0,12 = 84kg/h
    A 84kg/h fuel burn to get 129kW shaft power is rather "thirsty" compared to reciprocating engines.

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    Re: Small turboprop engines..?

    Quote Originally Posted by Himat View Post
    In the datasheet on the two turbojet variants with the same "core" the fuel consumption is stated and a performance graph shown. Depending on wich you look at the very best spesific fuel consumption is between 1,09 and 1,2 kg/(daN/h). If you study the TJ100C datasheet you find that it uses 0,12kg/(N/h) at 70% power wich is the max continius power.

    If the turboprop uses a similar amount of fuel at the same power setting it will use: 700*0,12 = 84kg/h
    A 84kg/h fuel burn to get 129kW shaft power is rather "thirsty" compared to reciprocating engines.
    Yeah, that would be quite 'thirsty' for some 160 hp continuous to consume 84kg of fuel, in weight terms it would be more than 100 L per hour for a reciprocating engine... Are all of them turboprops that 'thirsty'..?

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    Re: Small turboprop engines..?

    Turbines get less thirsty the better their compression ratio gets. Small turbines universally run at fairly low compression ratios. Until you're seeing tens of bar in the core, you aren't even starting to get into where turbines rule.

    That also doesn't say that it can't be done. It can be done. Just.. nobody has yet.

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    Re: Small turboprop engines..?

    Quote Originally Posted by DangerZone View Post
    Are all of them turboprops that 'thirsty'..?
    Not just thirsty but expensive to buy. With an experimental you can't make money with the airplane or writeoff expenses like you could on a KingAir so the turboprops just don't make financial sense except for rich guys looking for a "Wow" effect. Are you looking to Wow your friends?
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    Re: Small turboprop engines..?

    Quote Originally Posted by nerobro View Post
    Turbines get less thirsty the better their compression ratio gets. Small turbines universally run at fairly low compression ratios. Until you're seeing tens of bar in the core, you aren't even starting to get into where turbines rule.

    That also doesn't say that it can't be done. It can be done. Just.. nobody has yet.

    There is a good set of reasons for that though.

    High pressures mean high temperatures and stresses - leading to increased thermal cycling and creep. The risk of failure due to incorrect maintenance and inspections goes up dramatically. The cost of good heat resistant materials is prohibitive, and operations in less than ideal conditions easily removes coatings off internal components anyway, before you even start on corrosion mechanisims, etc etc etc.

    So my guess is the payback isnt there yet for very small turbines, with current costs of materials technology. It will come, but it's probably a long way off for really small turbines.
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    Re: Small turboprop engines..?

    Does anyone know the proposed price of the turboprop?

    Thanks,

    Blue skies,

    Tom

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    Registered User Dan Thomas's Avatar
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    Re: Small turboprop engines..?

    Small turbines get pretty inefficient. It's more than compression ratio; it's that small diameter, too, that requires such high RPM and its associated friction and internal drag. Similarly, small propellers spun at high speeds are less efficient than large props at low speeds.

    The smallest practical turbines are found in light helicopters and put out more than 400 hp. They pay for themselves there with their lightness and compactness, both important characteristics for a helicopter, and last a long time. Piston-engined machines can't carry nearly as much payload. A piston engine weighs about two pounds per horse; a turbine weighs half a pound per hp, sometimes less.

    I saw a converted APU a fellow was trying to market at Arlington about 15 years ago. It came in two versions, 100 hp and 150 hp. The 150 hp version burned 18 gallons an hour, nearly twice what an equivalent 150 hp Lyc would burn at full throttle. As turbines get larger their numbers look a lot better than that.

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    Re: Small turboprop engines..?

    If this were the 1950's you'd be 100% on the money. This is 2012, where small, high power turbines are common. The problem is, they're small. Turbochargers are hilariously efficient at compressing air. But the problem is they don't flow enough air. A turbocharger that provides a couple of hundred horsepower on a car, only ends up providing tens of horsepower as a straight turbine.

    The rpm isn't a big problem. While they're limited by some of the same mach restrictions as propellers are, their diameter is much, much smaller.

    The problem with those is still compression ratio. They at best are getting 45psi. We'd need 45psi, on top of 45psi, on top of 45psi to get some real numbers.

    Those converted apus were likely very low compression turbines.

    I should go do the math. The biggest issue is the lack of easily staged turbochargers.

    And even if you DO do that, you are still stuck with a motor that abhors throttling.

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    Re: Small turboprop engines..?

    What turbines are good at are reliability, light weight per hp, run cheaper fuel, and fly at altitudes where you can take advantage of thin air. They are terrible at fuel consumption at low altitudes, are delicate if miss treated, expensive, and hard to make.

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    Re: Small turboprop engines..?

    Quote Originally Posted by nerobro View Post
    If this were the 1950's you'd be 100% on the money. This is 2012, where small, high power turbines are common. The problem is, they're small. Turbochargers are hilariously efficient at compressing air. But the problem is they don't flow enough air. A turbocharger that provides a couple of hundred horsepower on a car, only ends up providing tens of horsepower as a straight turbine.

    The rpm isn't a big problem. While they're limited by some of the same mach restrictions as propellers are, their diameter is much, much smaller.

    The problem with those is still compression ratio. They at best are getting 45psi. We'd need 45psi, on top of 45psi, on top of 45psi to get some real numbers.

    Those converted apus were likely very low compression turbines.

    I should go do the math. The biggest issue is the lack of easily staged turbochargers.

    And even if you DO do that, you are still stuck with a motor that abhors throttling.
    I think you've mixed up Turboprops and Turbocharged engines. They are not the same thing.
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    Re: Small turboprop engines..?

    Quote Originally Posted by Battson View Post
    I think you've mixed up Turboprops and Turbocharged engines. They are not the same thing.
    I have not. But the same things make a turbine engine work, and a turbocharged engine work. Turbocharged engines just have intermittent combustion, while a jet engine has a constant burner.

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    Re: Small turboprop engines..?

    My mistake. I was just confused by the comments about RPM and compression ratio, which would apply to a turbocharger but aren't applicable to a gas turbine.

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    Re: Small turboprop engines..?

    Quote Originally Posted by Tom Nalevanko View Post
    Does anyone know the proposed price of the turboprop?

    Thanks,

    Blue skies,

    Tom
    I talked to them at the Friedrichshafen EXPO two years ago and the price of the TJ100A was around 20k Euros. So this one would probably be more expensive because it has more parts and is more complex to produce.

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    Registered User flyvulcan's Avatar
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    Re: Small turboprop engines..?

    When I contacted PBS Velka directly a few years ago about the TJ100A for potential use on my Komet project, I was quoted around Euros40k. I understand that since then, a few people have also been quoted around 40k. Consequently, I half expect the turboprop engine to be in the region of $80-100k.

    Dave

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