The wing theory hasn't changed much since the 1920s but the math is now easier
just letting the "zeros and ones" computer to do the calculations.
We've known the elliptic wing distribution (which is the optimum induced drag
profile)
is easily achieved by building an elliptical wing profile (Spitfire, P-47,
and others). But technically was costly in time and technique, (until
composites
of course).
For production the rectangular tapered wing was easier to build and just put in
a bit of twist to achieve the elliptic lift distribution but unfortunately it
was best suited to a specific wing loading. If cruise altitude, aircraft
weight,
or G forces changed, drag was affected.
One of my aero instructors was Professor Bondi, who was on the 727 wing
aerodynamic
team. Once the 727 was stretched, reengined and modified, the aircraft was
flying higher, with a heavier wing loading. Hence the team had to find a fix
but, had to do it without changing the base wing structure. It became a massive
push for finding an aerodynamic gimmick that would break through the high
altitude overloaded wing modifications. With the 747 and 737 coming online,
the 727 was dropped by Boeing and the rest is history. The design teams found
that they could make some improvements through wing tip design. Boeing wasn't
happy with changing anything that required extra structural changes.
For non swept straight wings of constant chord three things stood out. Tip
tanks
of a roundish shape were OK and decreased higher angle of attack drag, but
a swept up tip tank like the Cessna 310 worked a bit better, but so did an ugly
flat plate (or fence), and a sloped up angled flat plate over 45 degrees was
a benefit when fully loaded. These changes didn't help on the airliners as much
as the lower slower aircraft. Increasing the flat plate upper height worked
slightly better if installed vertically. Then Hoerner (in the late 40s)
extended
a straight constant chord wing and squared it (which also added wing area)
giving it a slight under camber which improved heavier loading tolerance and
decreased the drag due to lift but added parasite drag at the higher subsonic
speeds. Hoerner's WWII experience indicated a slight decrease in the tip vortex
and gave a 1-2% improvement in drag reduction. Especially on a straight
wing like the Fieseler Storch which he was working on. However, as Professor
Bondi pointed out, the Hoerner tip also increased wing area, so which was
actually
better? The extra wing area or the shape of the tip. Most aircraft
manufacture's
such as Piper and Cessna slightly changed their tips to a swept up
design but a composites company out of Texas who I can't remember the name
modified
the tip further creating a downturn and a larger droop such as was done
on to some aftermarket STCs on the Piper short wing and Hershy bar wing Cherokee
aircraft.
Today with our greater computer capability, you have found that efficiencies can
be found through adding these "aerodynamic gimmicks" to allow some fixes to
overloaded or poor designs.
Just like any manufacturer, we builders are not excited about modifying our
completed
aircraft. But modifications can be tested if you are willing to carve
some foam, glue onto the wing a mod and see how it works, then tear it off,
sand,
and repaint when done.
I prefer to go after the max drag producers. Cooling drag and fixed gear drag.
Most techniques we need are in the NASA or NACA wind tunnel tests and follow
on experiments done over the years. That makes the computer programs we have
far more fun to just look at ways to fix those pesky draggy parts like cowl
inlets/outlets
and wheel pant/gear leg improvements. Granted, engine cooling is
a very time consuming data issue but cooling exit ideas and movable flaps that
can enhance climb and streamline cruise.
I'm one day am going to look at a plug in for the belly cowl exit incorporating
a couple cowl flaps and perhaps a landing light that is retrofittable for the
trigear. Wheel pants I took care of and made them improve mx and inspection
and drag so I am sufficiently pleased enough to call them "Damned Adequate".
Now to get some time this fall to work on my simple add on cowl exit.
Keep on plugging. You all are having great discussions, and although not
immediately
applicable are interesting.
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com>
On Behalf Of Area-51
Sent: Saturday, August 12, 2023 6:30 AM
Subject: Europa-List: Re: The Obsidian Files - Wing Tips
Yes, it is truly amazing the amount of mathematics a computer can quickly deal
with these days. The Hoerner style chamfer tips are great; very unexpected
result.
Didn't even think to include tip tanks guess that would only apply to highly
specialised
long-haul versions of the Europa
how much fuel could a europa possibly support... 280 litre perhaps , +%~ ,
28-35
hours endurance... 2500-2800 miles .... fly around the world easy!!!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511245#511245
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