Glen and Ron P.
I am a pilot and not an aerodynamicist. However, having just blown off
the dust from my old aerodynamics textbook, what you are saying is not
strictly correct. It may be that you are correct with relevance to the
europa, but it really does depend on where the C of G is!!
If one considers the main wing, if the Aerodynamic Centre (AC) is aft of
the CofG the wing would be in a stable configuration. That is without
any opposing forces the aircraft would pitch down. On the other hand,
if the AC was forward of the CofG without any opposing forces the
aircraft would pitch up.
As the stabiliser is well aft of the aircraft CofG it is always
stabilising. But it is possible to have a de-stabilising wing with a
stabilising tailplane. Overall the aircraft would be stable as long as
sum of wing and tailplane Cm/Cl curves have a negative slope.
The point is that if the wing AC is forward of the CofG with no other
forces affecting it the aircraft will pitch up, not down.
Most aeroplanes I have flown 'balloon' on flap selection, particularly
with the first notch of flap. However the nose down effect of selecting
flap is caused by a rearward movement of the Centre of Pressure which
creates an increased moment about the C of G which requires the
adjustment of the tailplane trim - all be it with a slightly increased
nose down attitude. Much the same I suppose as saying the pitch down is
caused by an increase in negative Cm.
Having said all that looking at the diagram in the aircraft handbook in
the weight and balance chapter as a rough guestimate it would appear
that the C of G of our europas (58-62.5in AOD) would always be forward
of the Aerodynamic Centre which is approximately 25% chord in subsonic
flow.
regards,
Mike.
----- Original Message -----
From: glenn crowder
To: europa-list@matronics.com
Sent: Sunday, July 15, 2007 4:32 PM
Subject: RE: Europa-List: Europa Tailplane - Mod 73
Hi Mike - yes the aircraft will always pitch down with a non
symmetrical airfoil. This is why
aerobatic aircraft are designed with symmetrical airfoils - zero
pitching moment.
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