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Thread: GA Turboprop

  1. #81

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    Quote Originally Posted by steveinindy View Post
    That was my thought too. If I'm shelling out $125K for an engine, that's not what I'm going for.
    Do you mean that you would go for another turboprop engine or do you mean you would spend your money on a completely different non-turbine engine?

  2. #82

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    Ok this will be my last question:

    Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was), and it was FAA certified. Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??

    Assume even that after 4000 hrs of use the total cost of the engine will be lower than for the piston (assuming lower operating (fuel+maintenance) cost). I know that 4000hrs is almost a lifetime for a GA private pilot.

  3. #83
    steveinindy's Avatar
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    Do you mean that you would go for another turboprop engine or do you mean you would spend your money on a completely different non-turbine engine?
    Seeing as there's no good turbine engine for that price and the fact that the low to middle end of GA (which is what we're discussing here) is well served by much easier/cheaper to maintain piston engines....

    If I were looking to get a turbine (which I am for the larger design I am working on), the engine is going to run me for at a minimum for $150,000 to $160,000. That's for a 940 hp (at sea level) TPE-331-10 that's used and about half way through it's TBO cycle. New, it's closer to $400,000.

    By comparison, a high end turbocharged piston engine for the top end of what most people consider GA (TIO-540-AE2A) will run you about $150,000 new or about $120,000 for a factory rebuild. Unless you have to go freakishly fast (>275-300 knots) or really high (>FL280) to accomplish your "mission", there's no reason to pay more for an engine that is used and sucks more fuel under most circumstances (until you get up into the really high flight levels (>FL350)). It just doesn't make sense.

    The only reason I am going for a turbine is because of my desire to go very long distances (think Indianapolis to the northeastern islands in the Caribbean or Boston to LA without refueling ) and the most efficient way to do that is at high altitude and high speed. That more or less requires a turbine powerplant. Most people aren't looking for that sort of thing.

    So, if I were your "average" GA pilot and not my own heady blend of slightly crazy, for $125K I'm getting a new top of the line Lycoming and enjoying still being able to pass >80% of the planes at the local airport.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  4. #84
    steveinindy's Avatar
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    let's say close to what a diesel engine burns
    So like 3 gph less than a similar piston engine?

    Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was),
    The thing is that it is possible. The issue is that most GA pilots don't do the sort of flying that is suited to turbine engines to have that kind of efficiency. The average cross country flight for a GA pilot is somewhere between 100 and 200 miles. There's literally no benefit to it because even a ten or twenty knot difference in cruising speed over that short of a distance isn't going to make that much of a difference in time. Also take into account that to get to the "sweet spot" altitude for nearly any turbine is going to take you 30-50+ miles. For shorter flights, you'd literally go almost from cruise power to flight idle for the descent because top of climb and top of descent are going to be more or less the same point.

    Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??
    For low altitude "standard GA" flying? Yes. A turbine is simply a round peg trying to be crammed into the smaller square hole of GA in the majority of flights. I hate to say it (since I'm one of the "fans" of turbines on this forum) but you seemed to have picked an argument for your paper that's more or less defensible and anyone who knows much about flight operations or aircraft engines would be able to rip it apart.

    assuming lower operating (fuel+maintenance) cost
    Here's the problem: neither of those are cheaper. I'm actually looking at doing the training to become an A&P just so I can maintain my own engine because of the costs associated with turbine maintenance. In most places (unless you're operating at a field that has a LOT of commercial traffic and very little GA....think Honolulu), you're going to pay considerably more for Jet-A than 100LL.

    I know that 4000hrs is almost a lifetime for a GA private pilot.
    Google "cycle maintenance" or "calendar maintenance". If you have a low use rate, you still have to have it overhauled every few years (5 or 10 depending on the model) because one of the worst things you can do to engines is let them sit. It's asking for corrosion to not at least have it looked at.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  5. #85
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    Quote Originally Posted by kjensen View Post
    Ok this will be my last question:

    Hypothetically if that TP-100 had lower fuel burn than a piston, let's say close to what a diesel engine burns (I know that it's not possible, but let's just assume that it was), and it was FAA certified. Would you still stick to the piston even if the price premium was "only" 25-50% over the piston??

    Assume even that after 4000 hrs of use the total cost of the engine will be lower than for the piston (assuming lower operating (fuel+maintenance) cost). I know that 4000hrs is almost a lifetime for a GA private pilot.
    You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.
    Ryan Winslow
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  6. #86

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    Quote Originally Posted by steveinindy View Post
    So like 3 gph less than a similar piston engine?
    Yes, something like that. They say that diesel is about 20-30% less than gasoline, so let's assume that this hypothetical turbine engine burns 10-20% less than a gasoline piston, even at low altitude.

    For low altitude "standard GA" flying? Yes. A turbine is simply a round peg trying to be crammed into the smaller square hole of GA in the majority of flights.
    If you assume that a turbine burns less than a piston even at low altitude, would that change your opinion?

    I appreciate your information on this!

  7. #87
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    They say that diesel is about 20-30% less than gasoline, so let's assume that this hypothetical turbine engine burns 10-20% less than a gasoline piston, even at low altitude.
    LOL Eh....depends on where you're at. Around here, the difference is $0.17 a gallon at the airport we use ($5.90 vs $5.73).

    You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.
    What he said.

    If you assume that a turbine burns less than a piston even at low altitude, would that change your opinion?
    I strongly suggest you take some classes on statistics or how to formulate research questions because positing all these wild hypotheticals that are never going to happen just to suit your desire to prove that a turbine engine can be a "disruptive technology" for general aviation. I can argue that we might be able to lift 747 loads with a weed whacker engine but I'd have to frame it like "Would you think it was viable if gravity were suddenly reduced by 99.999999999999%?". Either way, any rational person who is well versed in the subject (or goes back and checks your citations) is going to leave you doing the academic equivalent of bleeding from your rectum with that sort of theorizing.

    Go to your professor and admit you picked a non-viable choice. It's a better choice than trying to BS an argument that- unless your professor drools uncontrollably or smokes joints the size of tampons prior to grading papers- will result in you failing the class. Most professors will support you coming to them and realizing that you've done enough research to know that what you thought initially doesn't pan out.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  8. #88
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    I talked to the Mistral people today at the AERO. The status is that the engines have successfully been flown, but the company is too short of money to certify them. They have changed their marketing concept and are now aiming at the homebuilt and experimental market. They claim that there are already some flying in the US. The price for the 200 HP engine is 45000 EURO and the 300 HP costs about 54000 EURO. I think we have to wait until Mistral finds a strong investor for seeing their engines certified.

  9. #89

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    Quote Originally Posted by Flyfalcons View Post
    You've asked for honest opinions and you've gotten them. Trying to reword the question to fit your desired result isn't exactly real research.
    I'm only trying to find where the threshold is, I don't have any favorite here. I will not ask anything anymore, my intention was not to create irritation.

  10. #90

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    Point taken. I will not post any more questions. Thanks all for the feedback, I really appreciate it.

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