fixed vs. rectracts ... Drag and turbulence

[Karl G. Mueller]

Wayne,

Put Wheel Pants in capitol letters. Without the wheel pants you
loose all the advantage of the fixed gear. In knife edge wheel pants
act like little air foils and add to the performance of the aircraft.
The amount of drag added to below the wing in a vertical down line
will keep your aircraft from pitching to the canopy ( We know that 
almost all pattern ships do, some more, some less )as much as 
it would without the fixed gear. These are some of my findings.

Karl G. Mueller
kgamueller at rogers.com

  ----- Original Message ----- 
  From: Wayne Galligan 
  To: discussion at nsrca.org 
  Sent: Monday, July 21, 2003 2:39 PM
  Subject: Re: fixed vs. rectracts ... Drag and turbulence


  THANKS DEAN....       So a properly set fixed gear setup(with wheel pants) should have a better or cleaner air flow(less turbulence then the retract cutout).

  WG

    ----- Original Message ----- 
    From: Dean Pappas 
    To: discussion at nsrca.org 
    Sent: Monday, July 21, 2003 1:32 PM
    Subject: RE: fixed vs. rectracts ... Drag and turbulence


    Hi Wayne,

    Here's what little I know from both a theoretical and practical basis.

    In general, our open wheel wells stink! 
    They are draggy and may cause all kinds of turbulence.
    Some ar worse than others, and there is no easy way, short of a flight test or wind tunnel,
    of telling which setups will be cleaner. 
    Tricycle-geared retracts are generally better than tail-draggers because the wheel wells are aft
    of the wing's high-point.

    According to one "real" aerodynamicist I spoke to, the best setups for drag reduction are in order:
    1) retracts with good tight fitting doors. 
    2) cleanly faired fixed gear.
    3) retracts the way we presently do them.
    4) crude fixed gear.
    5) and retracts with poorly fitting doors can possibly end up being horrible!

    As far as turbulence goes:
    Our open wheel wells in the leading edge made this guy cringe!
    He warned that poorly located fixed gear can cause turbulence with the flow under the wing root.

    Now from a practical point, I can recount my own experiments and one done by Jim Martin
    about a million years ago. (okay in the early seventies!)

    I have taped the wheel wells over and put small streamlined tires on both my JEKYLL ( about 4 years ago) 
    and an old tail-dragger TIPORARE (after the Tangerine contest in '83). Both planes showed no discernable speed
    difference, but there was no fancy instrumentation. The JEKYLL flew the same, but I thought that
    the TIPO (named TURNARARE) rolled more nicely. I thought that the transition, as I started to apply 
    the down pressure in a slow roll, went more smoothly. I eventually discovered that a slack piece of tape 
    across the wheel well in the area of the wire strut gave me the same benefit. Other builders make very 
    shallow and narrow troughs for the wire, probably for the same reason. Since I fly from fairly rough grass,
    the tape allowed more strut bend without binding. 

    Experiments with big P-51 style gear doors on the Jekyll showed that it was affected horribly by turbulence
    with the gear down, with or without the wells taped over. Result? Pants and legs should be as small as practical.

    Jim Martin (team member in '73) put heavy duct-tape over the  wheel wells of his BANSHEE when he forgot
    the air pump for his Rhom-Airs. Just last year, he told me that he thought the plane flew maybe a tiny bit 
    better, despite the heavy tape. 


    I hope this muddies the waters adequately,
        Reagards
        Dean P.

      -----Original Message-----
      From: Wayne Galligan [mailto:wgalligan at goodsonacura.com]
      Sent: Thursday, July 17, 2003 4:23 PM
      To: discussion at nsrca.org
      Subject: fixed vs. rectract l.g.


      Ok now. lets get down to the aerodynamic aspect of the rectract vs. fixed gear.  Anyone have some valid plus/minus on the two.  

      WG
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