fixed vs. rectracts ... Drag and turbulence

[Mike Mueller]

 Hey Dean, Jim Martin was a great pilot! Good to hear he's still around.
Mike

-----Original Message-----
From: Dean Pappas [mailto:d.pappas at kodeos.com]
Sent: Monday, July 21, 2003 12:32 PM
To: discussion at nsrca.org
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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