Yes, thats all correct. The downforce of the tail just perfectly balances
the CG being in front of the Aerodynamic Center. That creates a stable pit
ch attitude. Actually the negative CM of the wing is one of the factors th
at determine the Aerodynamic Center. Once the tail is gone, the aerodynami
c center of the entire aircraft will move back to the wings center of press
ure, which is behind the CG causing the aircraft to pitch nose down. At th
e same time, the CG has moved forward since 20 lbs on the tail is now missi
ng. Bad JuJu. The tail was creating a positive CM, which is no longer the
re. If the tail is normally creating downforce, then losing that downforce
will cause the plane to pitch down. Just think what happens when you push
the stick forward. You are lessening the downforce on the tail, which cau
ses the aircraft to pitch down.
Glenn
From: mikenjulie.parkin@btinternet.comTo: europa-list@matronics.comSubject:
Re: Europa-List: Europa Tailplane - Mod 73Date: Sun, 15 Jul 2007 21:24:08
+0100
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 strictl
y correct. It may be that you are correct with relevance to the europa, bu
t 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 th
e CofG the wing would be in a stable configuration. That is without any opp
osing forces the aircraft would pitch down. On the other hand, if the AC w
as 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 tail
plane. Overall the aircraft would be stable as long as sum of wing and tai
lplane Cm/Cl curves have a negative slope.
The point is that if the wing AC is forward of the CofG with no other force
s 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 i
s 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 tail
plane 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 neg
ative 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 Aerody
namic Centre which is approximately 25% chord in subsonic flow.
regards,
Mike.
----- Original Message -----
From: glenn crowder
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 ai
rfoil. This is whyaerobatic aircraft are designed with symmetrical airfoil
s - zero pitching moment.
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