Alan,
Your analysis of the bar and reason for the aft socket pin is good
enough to build the plane or maintain it.
Understanding the lift affects is really a vector analysis exercise.
I studied a T-28 wing failure accident and we were lucky enough to have
a video of the failure. The wing failed at a speed of 270 KIAS and the
video clearly showed that when the badly corroded spar and skin failed
(main wing spar is at about the 1/4 chord) the wing went full up as if
it were folded and hit the pilot on the head killing him instantly not
aft at all. In another accident at an airshow the main spar failed
first and began to flutter, the pilot unloaded and the main spar failed
first, and the wing trailed aft because the wing twisted up and aft spar
and upper skin hung on longer. Tragic accidents but changes were made
and T-28s still fly on well, when properly maintained.
When building model airplanes as a kid and just experimenting with
tailless designs, using a Clark Y airfoil, it flipped nose up badly even
when the CG was on the CL due to the wing pitching moment. The same
test with a symetrical airfoil was a piece of cake. The symetrical
airfoil has no pitching moment until the flaperon was deflected then
whamo.
The wing lift vector is not perpendicular to the chord or angle of
attack but is drawn as such in many training documents. In the US Air
Force I was drafted to rewrite the aero portion of our pilot texts and
teach it for a year. I had to teach the test questions because most
pilots (the generals included) are not aerodynamicists they know that
the houses get bigger when pushing forward and smaller when pulling
back unless you pull too much back stick. Things like if the engine
quits, bail out, and you can never have too much fuel (unless you are on
fire) works in some cases, but not for us lowly piston engine guys who
do not have fuel dumps and ejection seats.
Our little bird will pull forward on the aft support at modest and high
angles of attack and when unloaded to 1 G or less will go to neutral and
then to compression.
Get it flying and enjoy the plane.
Regards,
Bud
----- Original Message -----
From: Alan Carter<mailto:alancarteresq@onetel.net>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, July 01, 2013 1:36 PM
Subject: Europa-List: Re: wing lift/drag pins
<alancarteresq@onetel.net<mailto:alancarteresq@onetel.net>>
Hello Frans.
Who is pulling it. Gravity
It will move is an arc towards the ground.
A wing is similar to a sail on a sailing boat.
You can not sail directly into wind you can get to about 30 degrees of
it.
Sorry Frans but at the moment i am still puzzled.
At the moment i am thinking this bar has three purposes,
1. to prevent the drag pulling the wing back, which is most of the
time.
2. two provide the rigidity to the structure so keeping the front pin
locked into its mounting.
3. to stop the wing coming "forwards" in abnormal wing loadings,
Possible very high A/A, near the stall, or gusts, or abnormal flight
attitudes.
This puts this bar in compression , tension and neutral loads
But i am willing to change my mind,as i have used up ask a friend, may
be its time to ask the audience,
Regards .
Alan
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