Conference vmszoo::rc

    Tom,
    
    Usually, the difference in tip-versus-root airfoil percentages is
    there create the same effect as washout without having to actually
    alter the incidence at the tip..., that is, incidence angle remains
    constant from-root-to-tip but the thicker tip section tends to hang
    on after the root section stalls, preventing tip stalls [snaps].  As 
    to how this is calculated, I'm afraid I have to plead ignorance...I 
    haven't the foggiest notion!
    
    Adios,	Al

    TOM,
    
    I always heard it, just as CASEY said it, that an increase in
    percentage thickness at the tips delayed tip stall and prevent unwanted
    airshow snap maneuvers at landing altitudes and airspeeds; BUT,
    if you will look at some other modelers' rather popular (winning)
    designs, you can find just the opposite. DeBolt used to thin his
    airfi airfoils when he was using tapered NASA Laminars. I believe
    Ron Chidgey might have on some of his CITRONS and TARBABYS, etc.
    'Course they might make up for this with higher approach speeds.
    I figure they did it to knock off weight at that long wingspan to
    hold down POLAR MOMENTS (make rolls and stopping rolls respond faster
    to control inputs). ALso, it would just plain make for a lighter
    wing. Al, how do they do it on the MIG 3? If anyone has any books
    on airfoils, etc, by CHARLES HAMPTON GRANT, they would probably
    explain.
    
    There's always some reason for doing things, even if it seems to
    completely contradict everything we understand. A beuatiful example
    is the P-38. When the idea of contra-rotating propellors (one prop
    on each engine of a two-engine, non-centerline set up) is seen on
    aircraft, all that I have seen are exactly opposite of what the
    P-38 used. I'm going to find an old '38 jock and find out the straight
    skinny on this (namely, single engine torque performance)
    
    By the way, has anyone noticed the priority model airplane nuts
    have. Notice the RC NOTES are attacked immediately after arriving
    at work (that's before the COMPANY'S BUSINESS)???????
    
    

    Don,
    
    The MiG-3 has a constant root-to-tip percentage with 2-degrees of
    washout built into the wing.
    
    Adios,	Al

    re -.2 & attacks: I get my coffee & muffin, fire up the tube, read
    the mail & file then start work. (give me time to fuel the engine).
    
    md

    Re-.3
    
    It only looks that way if you start at 8:00.  If you are like me,
    you start at 7:00, do mail and other quick "Company Business", then
    I check RC notes if my schedule dictates (read: the aligators are
    quiet) the time. :^) :^)
    
    Chris
    
    Al, 
    
    2 degrees of washout does not seem like enough do anything, how
    much is 2 degrees (lots,not alot, not very much)?   I would  also
    guess that this would act like negative incidence on the tip, right.
    Would this help inverted flight?
    
    Chris Again

    Hey Chris, What's it mean then if you start at 6:30??
    
    
    My real need is in the determining of what is correct for any one
    given airfoil. The theory is sound.  
    
    Any twist is a wing either planned or unplanned is a compromize
    when it come to manuavers.  Most if not all pattern designs use
    the "two" different airfoil approach rather than building in
    wash out. What's been printed here makes sence. You get the landing
    speed security without the detriment of having washout.
    
    It would be nice if someone could speak to a formula to determine
    a wingtip airfoil thickness given you have a root airfoil.
     
    That's what I really need. If none can be found I guess I'll do
    some comparisons and try and come to some common ground.
    
    
    						Tom

    Okay,
    
    Tom, you got me on that one.  Could I impress you by saying I'm
    a manager and come in before 10:00.  Oh, also I usually stay till
    5:00.  Makes for a loooonnngg day!  :-) :-)
    
    And I agree with you on the rationale of dual tapers.  Are the FK
    Aeroplane kits dual taper?
    
    Chris

    Re: .-2..., Chris,
    
    2-degrees washout is "quite" a bit, probably as much as you'd ever
    want to use.  It equates to jacking up the trailing edge ~3/8" at
    the tips of a 72" wing...and, yes, this amounts to negative incidence 
    at the tips, the purpose being to assure that the wingtips stall
    "last"  when the nose is raised thus preventing tip stalling while 
    landing or after takeoff when airspeed is low.  The effects of washout
    on inverted flight are negligible.  As Tom suggests in .-1, at speed,
    the primary result of washout is additional drag which is why many
    designers [including full scale] have gone away from washout in
    favor of using varying percentage airfoils at the root versus the
    tip.
    
    Re: .-1..., Tom,
    
    There more than likely is some formula for determining the amount
    of tip percentage variation for various applications but I am unaware
    of what it is or where to find it.  Rule of thumb, I don't think
    I've ever seen a variance of more than 3-to-4%.
    
    Adios,	Al

    Sorry I opened a bucket of worms on the morning habits of the work
    force............so.........
    
    If you're building an old fashioned wing (one with barn-door ailerons,
    you know, those that are cut into the wing and hang way out there
    near the tip) you could just build the wing straight and then
    TEMPORARILY jack the trailing edge of the ailerons up a smidgeon
    to give the round-house effect of washout, delaying tip stall. Then
    you can take that deviation out and smooth the trailing edges if
    no visciousness appears. 
    
    Some modelers (and full sized birds, too) used to put wedge shape
    sections on the leading edge of their wings, close to the fuselage
    to cause the INNNER sections to stall first, giving roughly the
    same effect as washout. (the T-33 was like this).
    
    Some guys with T.E. (strip ) ailerons sometimes use them as FLAPERONS,
    drooping the whole aileron for flaps for landing and takeoff. Of,
    course, this promoted ADVERSE YAW, with possible low speed stall
    and snaps. EVERYTHING HAS A TRADEOFF, it seems! 
    
    ANYONE FOR SELECTIVE BOUNDARY LAYER CONTROL?????
    
    don