Hi Group
I have been following this thread with interest.
I have been picking the brain of an ex Grumman X-29 FSW lead wind tunnel
engineer
as far as our Europa wings trying to move fore or aft, and all I know at the
moment (pun intended) is how much I don't know.
He asked a few pointed questions about the Europa, can you help me out with
answering
them?:
**** What percent chord is the main spar at?
**** What wing section does the aircraft use?
**** What is the relationship (distance) between the main spar and the aft
fitting?
Once I provide him with these details, he will come back with his take on the
subject.
I will post his answer along with other comments he has made already.
Thx.
Ron Parigoris
BTW Frans, I have always thought of a Gyrocopter as an aeroplane with a big
pancake
of a wing above you. When you spin up the blades, they don't allow much in
the way of airflow through the spinning blades. Think of a big disk you put
at a positive angle of attack above you. Kinda neat concept, not very efficient,
takes a lot of pushing energy to keep your rotors spinning up to make it act
like a solid disc.
Here is an E-Mail I sent:
Hey Guyz
A Europa member was trying to explain to another member why at high angles of
attack
the wings want to sweep forward.
There are other members that tried to explain in words, one just said well, it's
the same reason why a Gyrocopter rotor spins in the direction that it does which
with little thought seems to be spinning in the wrong direction.
Attached is a diagram that is a pretty good visualization.
Ron P.
Here's his reply:
No its not (a good visualization)
You have to apply real numbers to those phoney scalers on that figure.
At high AOA the drag is significantly higher than shown, but lift not so much
so.
This would pull the L/D resultant much father aft.
Those two plots are implying that the L/D of a wing is the same at cruise and at
high AOA which we all KNOW is not true! (the reason you never fly a high
performance
sailplane near Cl Max!)
There is one good reason for putting fwd sweep in a wing planform. It allows
less
use of washout to keep the tip from stalling. If the wing is swept TOO far
fwd, the twist actually reverses! The root must be a lower AOA than the tip,
sometimes by a lot.
The biggest DISADVATAGE to FSW planform wings is structural divergence. Load
the
wing up, and without a sufficiently strong wing box structure, the wing tip
will twist to a higher AOA producing more twist repeat as necessary until
failure
(catastrophic I might add!)
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=403743#403743
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