Neutral point (NP) of the airplane can be thought as the aerodynamic center
of the plane. It can be derived by some simple math and is dependent on the
amount of lift (positive or negative) and the position of the lifting
surfaces. So in other words, how big is your HS and wing and where they
are. For stability the CG of the plane should be ahead of the NP. When the
distance between the HS and the wing is small (short couple) like in the KR
the NP is close to the surface with the higher lift (the wing) which leaves
less static margin for the CG and hence the inherent pitch sensitivity.
There are many solutions to this:
Make the HS bigger and/or extend the tail?
Put a heavier engine?
But remember everything comes at a cost and any changes should be made with
care fully addressing the effects that change will have.
Just as a FYI, if you make the aft flying surface bigger than the front
(canard design) then the NP moves a lot aft and your static margin
increases. However, like I said before, everything comes at a cost.
Back to the fox hole.
Ameet Savant
e-Business Consultant
Information Management Services - State of Nebraska
[email protected]
"Dan Heath"
<[email protected] To: <[email protected]>
> cc:
Sent by: Subject: KR>Re: it's somethign
to do with the elevators,
krnet-bounces@myl
ist.net
06/02/2003 08:46
PM
Please respond to
KR builders and
pilots
RE: Also, If so, what could I do to overcome this? (fit a bigger engine,
put on more weight???)
Daz,
Actually it is not the elevator. It has to do with a characteristic that
I
have heard called "short coupled". This has been defined to me as the
distance between a point on the main wing ( I don't know what it is
called)
and the same point on the horizontal stabilizer, and the relationship
that,
to the mean chord of the main wing.
So you could have a plane that looked to have a short distance between the
two wings and it not be short coupled because the mean chord of the main
wing was very short.
I hope someone with more aeronautical engineering knowledge than I have,
will explain it better.
You can offset the C of G by moving the engine out farther, or put on a
monster engine. However, your results will vary.
N64KR
Daniel R. Heath - Columbia, SC
[email protected]
See you in Red Oak - 2003
See our KR at http://KR-Builder.org - Click on the pic
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