Boxer Diesel Weight

Discussion in 'Subaru' started by flyboyjohn7, Apr 18, 2009.

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  1. Apr 26, 2014 #21

    stol

    stol

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    Scary is an understatement.......

    I have seen dozens if not hundreds of broken diesel cranks, be it Cats, Cummins, John Deere etc, etc and that is almost exactly where they all seem to break....
     
  2. Apr 26, 2014 #22

    rv6ejguy

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    We did a turbo system on an atmo Landcruiser diesel many years ago. The crank was huge. It looked indestructible but after only about 30,000 km, it snapped like a twig, just behind the #4 throw. Even though diesels have very low specific output, the stresses on them seem a lot higher. People often think diesels last forever. That hasn't been my experience in all cases, especially where people have turned the boost way up over factory specs. Plenty of blown head gaskets too.
     
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  3. Apr 27, 2014 #23

    akwrencher

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    So true. A well designed diesel will last thousands of hours. I personally know of some that ran more than 50 thousand hours, and one detroit genset that ran 24 7 for over 17 years. However, they will break if pushed to far beyond their limits. I can't imagine designing a crank for a diesel that looked like that, no matter what the "numbers" said, it just doesn't make sense.......sometimes TLAR is a good way to check yourself, especially when it doesn't......
     
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  4. Apr 27, 2014 #24

    Dan Thomas

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    Just one more example of engineering taken too close to real-world operating conditions.

    When I was a young guy I started building stuff like boats and whatnot. In a Mechanics Illustrated magazine there were the plans for a small, snappy little powerboat ideal for the kids. The designer said it was built stout and strong, because "if there's some way to break something, a kid will find it."

    The parallel here is that what works on the test track at the factory doesn't always stand up to ignorant consumer abuse. Give the car to a teenage male and see what breaks first, and fix that. Then let him drive it some more...


    Dan
     
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  5. Apr 28, 2014 #25

    cheapracer

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    :gig: Reminds me of things that are "Idiotproof" - then along comes a bigger idiot!
     
    Last edited: Apr 28, 2014
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  6. Apr 28, 2014 #26

    akwrencher

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    I wasn't trying to knock good engineers though, a well designed part can and should be stronger and lighter than a heavy bulky guestimate, but you can't cut the line too close. As Dan pointed out, what works on the test track.......

    I really do hope someone comes up with a well designed diesel light enough for modern aircraft standards someday. Would be sweet.
     
  7. Apr 28, 2014 #27

    cheapracer

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    This is promising but the company seems less than interested in moving forward ...

    Diesel Air Limited
     
  8. Apr 28, 2014 #28

    BJC

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    Probably more an issue of flawed assumptions and incomplete understanding rather than math ....
     
  9. Apr 28, 2014 #29

    rv6ejguy

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    At least their specs seem to make sense but as with most lightweight 2 stroke diesels, the BSFC is no better than a Lyconental running LOP. The only advantage would be the ability to run on diesel and presumably jet fuel. Their long term reliability is not proven at this time.
     
  10. Apr 30, 2014 #30

    pengyou

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    Does anyone know the reason for them snapping? i.e. do they seem to snap under high rpm apps, high torque apps, or is it just hours of use? Do they require more maintenance than normal engines?
     
    Last edited: Apr 30, 2014
  11. Apr 30, 2014 #31

    stol

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    Diesel crankshaft breakage is often attributed to just a few reasons. Design flaws, material flaws and most often operating habits usually are the major contributing factors..
     
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  12. Apr 30, 2014 #32

    rv6ejguy

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    Many people seem to think they can turn the boost up on diesels to any figure and it will have no impact on engine life. Use of aftermarket chips or reflashes is very common in the light truck and automotive world. Diesels may generally be built strong but have their mechanical limitations just like gasoline engines even if they don't have to worry about octane. I hear people on aviation forums routinely thinking they can just add more boost to an auto diesel to improve the power to weight ratio or use them in a direct drive layout, perhaps not realizing the limitations of the engine or the turbos at higher altitudes.
     
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  13. Aug 13, 2016 #33

    drdrainb

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    there is a guy who put one of these in a 2-seater 'pusher' style aircraft, looks just like the LH-10. here's the specs he emailed to me:

    311 Lbs., flight ready

    150hp, stock. he is limited to that power level because of his shaft drive extension. i think it has a couple CV joints in it.

    4.2 gph at full power

    2.6gph at econ. cruise.

    i'll post some pics if i can figure out how? lol.
     
  14. Aug 13, 2016 #34

    drdrainb

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    ULM12.jpg 20140322_191510 (1).jpg
     
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  15. Aug 13, 2016 #35

    drdrainb

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    this engine was used to race the pike's peak rally. the guy had the engine tuned with custom ecu & turbo to 180hp, with no ill effects. he's pushing the engine to 100% power for almost the entire race. this level of stress wouldn't be necessary in an aircraft. the turbo only needs to give a slight boost, & then ecu & waste gate set to 'normalize' for higher altitudes. effectively, you only need to accomodate for the lower pressures at higher altitude. there are turbo's built for this kind of situation.
     
  16. Aug 13, 2016 #36

    drdrainb

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    jet A, and kerosene AND diesel all have vapor & flashpoints WAY LOWER than gasoline, and are accordingly MUCH safer. but if i were running this engine I'd run offroad #2 low sulfur diesel in it. mainly because it's only like $1.60 per gallon. yes, diesel is heavier, but... 4.2 gph burn? at 150hp???!!! forget AVGAS.
     
  17. Aug 13, 2016 #37

    drdrainb

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    gemini diesel & diesel hawk both weigh about the same as their power equivalent avgas counterpart. especially the gemini. in fact... i think the gemini might be slightly lighter. the Gemini 125hp weighs 174Lbs. But... produces the same torque as an 0-320! ... which means you could probably pull a prop off an 0-320, put it on a gemini 125 & get the same performance as the 0-320.
     
  18. Aug 13, 2016 #38

    drdrainb

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    there's a website where they sell 'vanogan' vw van conversion parts. i noticed that that site offers a 'low porfile' oil pan. maybe that would do the trick?
     
  19. Aug 13, 2016 #39

    cheapracer

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    Thanks for your info drdrainb.
     
  20. Aug 13, 2016 #40

    rv6ejguy

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    The fuel flow and/or hp numbers are nonsense. 27.3 lbs./hr and 150hp equates to a BSFC of .182 lbs./hp/ hr. which is MUCH lower than the most efficient stationary CI engines built.

    If this is direct drive, he won't be making 150hp out of this engine at 2700 ish prop rpm, not even close.

    You understand that most light diesels run 70-100 inches Ab manifold pressure to make stock hp at sea level right? The turbo is working quite hard to make 70 inches at 12,000 feet or so- pressure ratio around 3.7.

    The Gemini and DH diesels are 2 strokes. Compare apples to apples. Neither of these engines have any significant service history either.

    The 125hp Gemini does not make the same torque as an O-320 since it has 35 less hp. HP= Torque X rpm/ 5252. Hp is the deciding factor in aircraft performance since it defines RATE of WORK.

    A 15 minute run up Pikes' Peak hardly validates the long term reliability of this engine which has quite a history of broken crankshafts in stock form even. Many light diesels like the SMA, Thielert and WAM have had numerous reliability issues far short of TBO/TBR when they were released.

    We'll see how this one fares at the 500 hour mark.

    The airplane and engine installation looks cool though...
     
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