Specific Fuel Flow - LS Series

Discussion in 'Chevy' started by TXFlyGuy, Apr 1, 2017.

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  1. Aug 2, 2017 #21

    BJC

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    I assume that the aircraft had a fuel flow meter of reasonable accuracy. How did you compute the power output?


    BJC
     
  2. Aug 2, 2017 #22

    TXFlyGuy

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    Taken from the GM factory published data. No corrections were made for atmospheric pressure. So it's an educated guess.

    Back to the drawing board...I was just informed that the fuel flow was 21 gph, at 7500 MSL. Had to make an extra fuel stop.
     
    Last edited: Aug 2, 2017
  3. Aug 3, 2017 #23

    pictsidhe

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    Power at that altitude and a wild guess at 20F above standard atmosphere temp would have been about 77% of sea level. Working your numbers backwards, you estimated 195hp? Corrected at 77%, that'd be 150hp, giving a BSFC at 21gph of 0.84! Either your engine tuner should be shot (not merely fired...) or the numbers are still wrong. No way should an LS3 at high throttle be that bad at 2900rpm.
     
  4. Aug 3, 2017 #24

    BJC

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    Based on manifold pressure and RPM?


    BJC
     
  5. Aug 3, 2017 #25

    TXFlyGuy

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    WOT, 2900 rpm.

    Edit: I just read where Holley claims that any engine at WOT will burn .5 pounds per hour per hp.
     
    Last edited: Aug 3, 2017
  6. Aug 3, 2017 #26

    TXFlyGuy

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    Agree. The ECU has not been tuned at all, apparently. They rushed to get the plane to OSH, and had a number of issues to iron out. I guess ECU programming was left on the back burner.
     
  7. Aug 4, 2017 #27

    Toobuilder

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    This is just a general statement and not pointing at this particular individual, but it is frightening to think how often the "rush to Osh" statement comes up. Its like we all try to be conscious responsible aviators most of the year but as soon as Osh looms we all collectively go insane for a month.
     
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  8. Aug 4, 2017 #28

    pictsidhe

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    That consumption would bother me on my aircraft, that's way out of tune, the plugs are getting checked and cleaned each stop?
     
  9. Aug 4, 2017 #29

    BoKu

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    I think Reno might be worse. Maybe not for as many people, but those who get it get hit hard.

    --Bob K.
     
  10. Aug 4, 2017 #30

    TXFlyGuy

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    We are all concerned over the fuel burn. This was on the trip from Ohio to OSH and back. The LS3 has only flown 2 long legs now since installation. A huge learning curve is underway.
     
  11. Aug 4, 2017 #31

    Toobuilder

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    So am I to understand that the airplane has a brand new, unproven engine installation (which isnt running correctly), and the owners thought it would be a good idea to strike out for The Big Show from Ohio?

    Is Osh within the Phase 1 test area for this airplane?

    Is it more impressive to limp into Osh 17 with excuses for bad performance, or confidently make Osh 18 with a well tuned airplane and reams of performance data to back it up?
     
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  12. Aug 5, 2017 #32

    TXFlyGuy

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    Swapped a Chevy V8, for a Chevy V8. This LS3 is well proven in multiple aviation applications.
     
  13. Aug 5, 2017 #33

    pictsidhe

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    They are usually set up a lot better. I'd happily fly behind a properly set up one, but yours wasn't.
     
  14. Aug 5, 2017 #34

    Toobuilder

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    The LS-3 is well proven, period. But a new engine in a homebuilt has to actually be proven as a system in that particular airframe. Thats the point of Phase 1 flight test. The same 540 is going back into my Rocket that I've been flying for the last 300 hours, and Ross' EFI has hundreds of thousands of hours of proven performance - but I can assure you that my airplane its not leaving eyesight of my home runway until a thorough flight test plan has been accomplished.

    Saying that a Chevy replaced a Chevy is going well beyond reasonable if used as justification for avoiding a return to Phase 1.
     
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  15. Aug 5, 2017 #35

    TXFlyGuy

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    The plane had the 40 hour fly off accomplished. Going to OSH was the first x-country trip for the LS3. Note that post #30 states..."two long legs...". That was the first time outside of the flyoff radius.

    Disclaimer: All of my info has come second, or even third hand. So the numbers might be a bit off. I will be at Titan in a couple weeks, and will get good data then.
     
    Last edited: Aug 5, 2017
  16. Aug 5, 2017 #36

    mcrae0104

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    deleted--upon closer reading, I see Tex answered what I was looking for.
     
  17. Aug 14, 2017 #37

    TXFlyGuy

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    Here it is...2600 rpm, 23 inches manifold pressure, 13 gph fuel flow. Not sure about the altitude.
     
  18. Aug 15, 2017 #38

    pictsidhe

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    Estimating 130hp, that'd be 0.55

    Edit, can't read: 0.6
    power estimation based on claimed sea level hp, manifold pressure and an estimate at temp at altitude.
     
    Last edited: Aug 15, 2017
  19. Aug 15, 2017 #39

    rv7charlie

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    Really difficult to even guess at HP without knowing the drag of the a/c design, speed, altitude, contribution of cooling drag to that particular a/c, leaning state......

    quote:Edit: I just read where Holley claims that any engine at WOT will burn .5 pounds per hour per hp. unquote

    Horse hockey. Air cooled (at full power; not the same thing as WOT) will be a lot worse than that, and water cooled will be significantly worse than that. Either type, WOT, at altitude (normally aspirated), properly leaned, will be significantly better than that.

    (Turbines will be worse; really no way around it...)
     
  20. Aug 15, 2017 #40

    pictsidhe

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    lotsa variables. piston speed makes a big difference. tex has his engine running at about the best bsfc piston speed, though. Assuming 4" stroke, it's at 1730 ft/min. Bsfc will start to drop spinning much faster. Car engines put out max power at several times the most economical piston speed. Toyota prius engines run under 0.4. I'm not sure if any other SI car engines do, yet. But modern ones do get in the 0.4s Tex's engine needs a **** good tune.
     

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