From: David Lednicer <dave@amiwest.com>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Oh Barnaby...
Date: Tue, 17 Jun 1997 09:21:45 -0700

Mike Menefee wrote:

> Vari-Eze canard.  Originally it needed to be long in order to give
> the elevons some authority.  True?  Well, the elevons are LONG gone...
> It seems to me we now have a thick airfoil whose properties don't
> match the profile of the main planes well.  Should they not be similar?
> I mean in their speed ranges...  you know, at what speed they perform
> well and badly and all that.
>
> Could we benefit from designing a much shorter canard with a longer
> chord, internal elevator hinges and lighter construction?  By benefit
> I mean similar slow flight characteristics, but improved top end (and
> no rain degradation).

	Canard aircraft designs (and Rutan ones in particular) are "tuned" so
that the canard stalls before the main wing.  This results in the need
for a high aspect ratio canard surface, to get the correct lift curve
slope on the canard relative to the main wing.  Hence, you are stuck
with the narrow chord, long canard.  In most flight conditions, the
canard is highly loaded, so you need a lot of structural depth.  This is
why the canard airfoils are so thick.  There is no escaping this.  The
EZs have external elevator hinges because the canards are really slotted
flaps.  Some canard aircraft (Quickies, Dragonflys, etc.) use a simpler
plain flap on the canard.  The EZ's canards are slotted because this is
necessary to produce the canard maximum lift required.

	Bottom line: canard aircraft are configured like they are for a
reason.  Don't mess with the design details unless you really understand
what drives them to be like they are.

-------------------------------------------------------------------
David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:   dave@amiwest.com
2133 152nd Ave NE          |   tel:     (206) 643-9090
Redmond, WA  98052  USA    |   fax:     (206) 746-1299

From: David Lednicer <dave@amiwest.com>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Why Canards
Date: Thu, 29 Jan 1998 14:53:21 -0800

Ken Brimmer wrote:
> The plane is much more efficient than convential A/C.  My plane with a
> 113 hp Lyc. cruises at 170 mph.

	So what?  Mike Arnold's AR-5 goes 214 mph on 65 hp!  This is simply a
measure of the aircraft's parasitic drag.  The Long EZ's equivalent flat
plate drag area is about 1.8ft2.  The Lancair 200's is reported to be
1.61ft2.

> My plane will not stall is there any plane out there that
> can say that?

	I can limit the elevator authority on a conventional aircraft (like the
Cherokee is rigged) of move the CG way forward and you wouldn't be able
to stall it either.  If you don't build your EZ right, stalling it has
much more serious consequences than stalling a conventional aircraft.

> My plane carries 46+ gals of gas so that gives me a range of 8 hrs.
> thus over 1300 miles range.

	True, but I could design a conventional configuration to have the same
amount of fuel.

	Having both surfaces lifting does not give a canard any advantage,
period.  In fact, it makes it more difficult to get a low induced drag
configuration.  If the canard has roughly an elliptical load, the wing
can carry almost no load inboard to get a net elliptical load for the
aircraft.  This produces very high root bending moments on the wing, as
all of its load is outboard.  Even worse, to get no CG shift as the fuel
burns off, the fuel must be stored on the CG.  This means a big strake,
which can't produce any lift, as it is part of the inboard wing.  This
adds up to tons of wetted area that does no work and adds lots of drag!

	Burt Rutan gets a lot of credit for coming up with decent flying
canards (and for developing the moldless composite construction method).
However, there are few advantages to the canard configuration.

-------------------------------------------------------------------
David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:   dave@amiwest.com
2133 152nd Ave NE          |   tel:     (206) 643-9090
Redmond, WA  98052  USA    |   fax:     (206) 746-1299

From: David Lednicer <dave@amiwest.com>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Why Canards
Date: Tue, 10 Feb 1998 09:05:24 -0800

MTSP wrote:

> Deep stall is not limited to canards. The BAC111 got in one during
> flight test and crashed. Long EZ's have also gotten into them, one
> happened in Az in 1996. Common denominator is aft cg.

	No, not quite!  On T-tail aircraft, with highly swept wings, the
problem comes about as a result of the configuration's geometry and can
happen at any CG.  Examples of the HP Victor, HS Trident, BAC1-11 and
Tu-134 have all crashed from deep stall.  The BAC1-11 and Tu-134 crashed
on the same day.  In all cases, they reached an angle of attack where
they were stalled and in trim and lacked the control power to recover.

	On canards, the driver is often rigging angles.  If you misrig a Long
EZ (set the wing at the wrong incidence), you can get deep stall at any
CG.  This is a result of the aft wing stalling first, instead of the
canard.  The Neutral Point is now quite a ways forward, and like with
the T-tail aircraft, the aircraft is in trim and lacking the control
power to recover.

-------------------------------------------------------------------
David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:   dave@amiwest.com
2133 152nd Ave NE          |   tel:     (206) 643-9090
Redmond, WA  98052  USA    |   fax:     (206) 746-1299

From: richardNOSPAM@Riley.net
Newsgroups: rec.aviation.homebuilt
Subject: Re: canard or conventional?  What's more effieient?
Date: Sat, 25 Sep 1999 00:19:59 GMT

On Fri, 24 Sep 1999 05:29:12 -0500, in <37EB5278.686C97C0@despam.this>, Dave
Hyde <nauga@despam.this> wrote:

>So the definitive answer is "it depends".  There is no one answer.
>
>And just to throw this in, there are some who insist that a _three_
>surface (conventional airplane with a canard used as a trimming surface
>only - not for maneuvering) _can_ be the most efficient...a la Piaggio.


(Biased answer from a canard manufacturer follows)

The one big "efficiency" advantage a canard has is useable space.  A
conventional layout makes you carry around a largely useless empennage -
you can't put anything in it because of CG, it just extra weight and
wetted area you have to drag around to hold the tail on.  Every cubic
inch in a canard is doing something.

Apart from that - Dave is right.  Every good design is a good compromise.
Different designers find different compromise points.

(and I once heard John Roncz refer to a 3 surface airplane as an
Aerodynamicists Full Employment Program.  See the "Eagle")

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: automobile engine
Date: Fri, 11 Sep 1998 12:11:13 -0500

Bruce A. Frank wrote:

> ??Putting a larger than spec'ed engine in a tractor config. will not
> lead to an aft CG. From what I have read, it requires more
> re-engineering to solve the aft CG "problems" in a pusher canard design,
> in which an over weight engine is to be installed, than to solve the
> forward CG problems created when installing an overweight engine in a
> tractor design.
>
> The tractor config aft CG caused flat spin  and "falling leaf" altitude
> loss are no less difficult to get out of than the deep stall of a canard
> (over weight rear engine thus aft CG) aircraft. But installing an
> overweight engine doesn't cause this phenominon in front engined planes.

To further elaborate for Juan,

An aft CG condition in any airplane is extremely dangerous and will
likely cause you serious and painful problems.

Most conventional layout aircraft are designed to fly normally with
a slight to moderate down load on the tail.  All of your support is
coming from the forward wing, and the tail is merely providing the
torque required to overcome the moment resulting from a center of
lift that is aft of the CG.  As the CG moves aft, the down load on
the tail gets less, and the overall efficiency of the aircraft gets
a bit better.  This is the famous "load you Bonanza aft and it cruises
faster" problem.  Many airplanes have the fuel located in such a way
that the CG also moves aft as the fuel is burned.  This can cause an
airplane that was within the limits on takeoff to be aft at landing.
If your speed get too low to hold the tail up it will drop without
any way to pick it back up, resulting in an extremely painful flight
mode.  ( Upside down and backwards )

Most Canard aircraft have been designed to ensure that the specific
loading ( pounds per foot of span ) is higher on the forward wing
than it is on the after wing.  We do not ever want the aftermost
wing on a canard design to stall, because the Center of Lift will
move far forward beyond the CG and recovery will be impossible.
This will usually result in impact with the terrain at a high rate
of descent.  To prevent this, the CG is placed sufficiently far
forward to ensure that the forward wing will always lose lift
FIRST and cause the Center of Lift to shift aft BEHIND the CG.
This is the same characteristic that causes canard aircraft to have
slightly higher landing speeds.  You must keep that aft wing away
from stall.  As the CG shifts aft, the after wing begins to carry
more and more of the aircrafts weight.  This increases the loading
on the after wing and DECREASES the loading on the canard surface.
Eventually you reach a point where the rear wing stalls first, or,
as in the stable deep stall configuration, at the same time.  When
that point is reached the aircraft may no longer respond to controls
in pitch and you are no longer flying, just riding.

Since one of the most common modifications to a homebuilt is to put
in a bigger engine than the designer did, in a futile search for more
speed, the tendency is to increase engine weight.  In a canard this
usually moves the CG aft.  The Quickie Too is a notable exception.
In the Quickie Too the O-200 upgrade moved the CG forward, and the
aircraft is still stable and safe to fly, although the landing and
stall speeds have increased noticeably.  With most canards, the only
remedy is excess advoirdupois bolted into the nose, all of which cuts
into the handling qualitys of the aircraft.  Failure to properly
weight the nose leads to an aft CG condition and could ruin your day.