From: doshay@ursa.arc.nasa.gov (David Doshay)
Subject: Re: Canard Pros -n- Cons
Organization: NASA-Ames Biocomputation Center
Date: Tue, 15 Sep 1992 17:25:11 GMT

In article <1992Sep15.001530.4005@anasazi.com>, best@anasazi.com (Mike Best) writes:
|> In article <1992Sep12.001808.17457@news.arc.nasa.gov> doshay@ursa.arc.nasa.gov (David Doshay) writes:
|> >Just as there are huge differences in the flight dynamics of conventional
|> >configuration aircraft, the same is true of canard configured aircraft.
|> >The Cozy IV may look a little like a Velocity, but the designers had very 
|> >different goals, and hence details like landing speeds are different for
|> >the planes. The Cozy and Rutan designs are far more a handfull than the
|> >Velocity.
|> 
|> In what manner are they "more of a handfull"?  I know they are harder to
|> build (:)) but my flight experience with the Long EZ and Defiant have
|> demonstrated to me that they are among the most forgiving and, dare I
|> say it, EZ planes to fly.  However, they do land quite fast!
                                       ^^^^^^^^^^^^^^^^^^^^^^^
I was primarily refering to the landing speed.

|> 
|> >Your question about stalling the cannard while landing is a good one, but
|> >is info that is seldom discussed. People talk about the period of the 
|> >oscillation, but never the amplitude.
|> 
|> >The part about efficiency (both surfaces lifting) turns out to not be true in 
|> >actual practice.
|> 
|> Interesting, are you saying that both surfaces do not simultaneously lift?
|> If so, are they always in some ocillation behavior?  I have not noticed 
|> anything like this in practice (at least I couldn't observe this).
|> 

Both surfaces do lift, but the induced drag penalty due to the high loading
of the canard cost more than is gained by the extra lift, as compared
with the very small induced drag and the downloading from a tail on a
conventional aircraft. There is a paper by Tad McGeer and Ilan Kroo published
in AIAA Journal of Aircraft, something like '84 or '85, titled "A Fundamental
Comparison of Canard and Conventional Aircraft" that does a reasonable job of
comparing the basic designs. For small static margins the conventional 
configuration is more efficient.

The oscillation occurs as the canard stalls. The nose pitches down till the
angle of attack on the canard decreases enough for the canard to generate
the lift required to make the aircraft pitch up again. If the pilot continues
to hold full back pressure, there will be a series of pitch oscillations.
Because we generally want to land slowly to be friendly with the physics
kenitic energy = 1/2 m v^2, a full stall landing is considered nice. The
previous poster was asking about the magnitude of the pitch down at full
stall. If the stall of the canard does not result in pitching down past wings
level, then a full stall landing is OK, but if the pitch down takes the plane
much futher around, the nose-gear forces may be excessive.

All this said, I will add that I like canard designs for other reasons,
and those were posted earlier.

David		doshay@soma.arc.nasa.gov

The thought police insist I tell you:
my thoughts, not NASA's
Newsgroups: rec.aviation