Deciphering Flutter Prevention Criteria Report

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by TinBender, Nov 17, 2011.

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  1. Nov 17, 2011 #1

    TinBender

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    I am looking at Airframe and Equipment Engineering Report No. 45 Simplified Flutter Prevention Criteria for Personal Type Aircraft.
    http://handle.dtic.mil/100.2/ADA955270
    I haven't used a typewriter in about 25 years. I can't remember for sure, but I think the older ones didn't have + signs. Are the drawn in "things" plus signs in this equation? These symbols are found on page 15 and 18. There are normal looking drawn-in + signs elsewhere in the report.

    equation.PNG
    Any insight would be appreciated.
     
  2. Nov 17, 2011 #2

    bmcj

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    I wonder if it was meant to signify "+/-", meaning that the value could be additive or subtractive to the overall oscillation effect.
     
  3. Nov 18, 2011 #3

    ClippedCub

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    Last edited: Apr 16, 2012
  4. Dec 1, 2011 #4

    TinBender

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    They are positively signs of addition. Peery explains it the best.
    Product_of_Inertia_Transfer_Theorem.PNG
     
  5. Dec 8, 2012 #5

    TinBender

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    Flutter Prevention Criteria Report No. 45

    Why a poor scan of a hand corrected copy should be the FAA approved official means of determining freedom of flutter is beyond me. What started as a quick exercise to learn Acrobat OCR became a lengthy rewrite. It got me involved with report #43, upon which this one is based. I found a few very frustrating formula errors published in that report that are giving me problems converting it to excel. The problem is compounded by a transposition error carried all the way through the spreadsheet computation example.

    I have completed my self-imposed task of reformatting and redrawing report 45. There is one equation noted on page 18 that is questionable. All drawings have been redrawn.

    I respectfully submit this draft to you for 'Peer Review.' Suggestions are encouraged.

    Regards,
    Jamie

    View attachment New Flutter Report 45.pdf
     
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  6. Dec 8, 2012 #6

    dcarr

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    Jamie,

    That is an awesome bit of work. Thank you so much for sharing!

    David
     
  7. Dec 8, 2012 #7

    SVSUSteve

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    Jamie, thanks for the work you put in!
     
  8. Dec 8, 2012 #8

    wsimpso1

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    It looks like I have some reading to do. Thanks for the effort!

    Billski
     
  9. Dec 8, 2012 #9

    Hot Wings

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    Very nice offering! I've done a bit of this kind of restoration work and know how much time it takes.

    Thanks for sharing praising-the-lord-smiley-emoticon.gif

    [TD="class: smiley"][/TD]
     
  10. Dec 9, 2012 #10

    pwood66889

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    Your point:
    "C. Free Play of Ailerons
    The total free play at the aileron edge of each aileron, when the other aileron is clamped to the wing should not
    exceed 2.5 percent of the aileron chord aft of the hinge line at the station where the free play is measured."
    has me taking my tape measure out to visit my `coupe tomorrow! The FAA just sent out an AD on that very topic!!
    Thanx^2!!!
    Percy in SE Bama
     
  11. Dec 9, 2012 #11

    BBerson

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    Reading the flutter report was interesting.
    I kept thinking about the Reno tragedy. My thought is that maybe these extreme racers trim tabs should be mass balanced. As mentioned in the report, trim tabs don't require mass balance when the tab linkage is irreversible. Would a mass balanced tab have prevented the tab flutter after the irreversible system failed? (from loose hinge screws, according to NTSB) This could have prevented the Reno tragedy, I think, with perhaps just a few ounces of lead.
     
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  12. Dec 9, 2012 #12

    djschwartz

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    Re: Flutter Prevention Criteria Report No. 45

    I don not think this report represents an "approval" of a method. It is a very useful advisory to designers. Many design reports of this type have been produced over the years but that job was moved from the CAA to NACA and then NASA along time ago. This old report simply sits in the FAA archive as does a lot of other old CAA material. It's actually a good thing that they didn't simply throw it out as it is still useful.

    The "approval" of freedom from flutter comes from flight test results, and as good as the information is in this and other newer reports, only careful, thorough flight test can ensure that the results have worked out as expected.

    Dave
     
  13. Dec 9, 2012 #13

    SVSUSteve

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    So would better selection of locations for the crowd....the lessons of the Ramstein Air Show debacle were not learned by the organizers of Reno apparently. We would have still lost a **** good pilot and a nice aircraft (I'll shelve most of my disdain for people risking these rare warbirds and "improving" them in the name of racing for the sake of civility)
     
  14. Dec 9, 2012 #14

    TinBender

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    Re: Flutter Prevention Criteria Report No. 45

    Agreed. That is the definitive method. However, I stand by my previous statement due to § 23.641 :
    (Edit:) In Post #5, I did have a typo and a misstatement. "Why a poor scan of a hand corrected copy should be an FAA approved official means of showing freedom of flutter is beyond me." So, technically, Dave, you are, as usual, correct. And I do understand your point. This is good design practice, but not proof.

    (d) Compliance with the rigidity and
    mass balance criteria (pages 4–12), in
    Airframe and Equipment Engineering
    Report No. 45 (as corrected) ‘‘Simplified Flutter Prevention Criteria’’
    (published by the Federal Aviation Administration) may be accomplished to
    show that the airplane is free from
    flutter, control reversal, or divergence
    if—
    (1) VD/MD for the airplane is less than
    260 knots (EAS) and less than Mach 0.5,
    (2) The wing and aileron flutter prevention criteria, as represented by the
    wing torsional stiffness and aileron
    balance criteria, are limited in use to
    airplanes without large mass concentrations (such as engines, floats, or
    fuel tanks in outer wing panels) along
    the wing span, and
    (3) The airplane—
    (i) Does not have a T-tail or other unconventional tail configurations;
    (ii) Does not have unusual mass distributions or other unconventional design features that affect the applicability of the criteria, and
    (iii) Has fixed-fin and fixed-stabilizer
    surfaces.
     
    Last edited: Dec 9, 2012
  15. Jan 2, 2013 #15

    airborne

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    Dual (fail safe) independent links to the tab, perhaps?
     
  16. Jan 2, 2013 #16

    BBerson

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    The Reno crash was from loose hinge bolts, that allowed flutter, that broke the link rod.
     

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