Tandem-wing Airplanes

"Marc J. Zeitlin" wrote in news:47a60ac9$0
:


Dan_Thomas wrote:

Seems to me that lifting tails are, and have been, illegal for
long time.

This is not true. There are no regulations that prohibit lifting
tails, or in fact in any way prescribe which way the lift vector needs
to point on any lifting surface.

... The regs call for the aircraft to automatically settle into a
glide if the power should fail,to prevent stalling.

What reg would that be? What airplane does NOT glide when the power
fails? Your plane is trimmed for whatever speed you're flying - chop
the power, and you'll continue to fly at that speed, albeit
descending. There may be some trim changes on aircraft that have
their engines mounted substantially above the CG (Lake Buccaneer, or
the equivalent) or that have substantial thrust angles, but the
principal holds.

Stalling and gliding are independent activities - one is not related
to the other. You can stall while gliding or under power, and you can
glide while unstalled or stalled.

... A lifting tail just won't do this. As the airplane slows it
will drop, raising the nose, and the airplane will stall, and
almost certainly enter an unrecoverable spin.

That's incorrect. In a conventional tailed aircraft, the tail may
have a downforce, no force at all, or an upforce, depending upon the
design of the aircraft, the relationship of the aerodynamic center to
the CG, and the flight regime. There is no intrinsic reason why a
lifting tail (or a tail that in a given situation is producing no
lift) would cause the aircraft to do what you state.

... If the pilot does manage to establish a glide, the nose will
drop further as glide speed increases, opposite to what we know
in our airplanes, and totally unstable.

Incorrect. The pitch stability of an aircraft is not determined by
whether or not the tail lifts - it's determined by the relative
position of the aerodynamic center and the CG (CG always ahead of AC),
and the relative angles of the front and rear wings. See:

http://www.av8n.com/how/htm/aoastab.html

As long as the front wing is operating at a higher angle of attack
than the rear wing - tail, wing, 2nd wing of a tandem; makes no
difference - which is usually achieved by correct settings of the
angle of incidence and ensuring that the front wing has a higher lift
curve slope than the rear wing, then the aircraft will be statically
stable in pitch.

The above web site has some VERY good explanations and pictures of
these situations, including canards. Consider a tandem aircraft to
merely be a canard or conventional aircraft that has it's tail/canard
to be about the same size as the other wing.

... Some early airplanes were built this way, and after they'd
killed enough pilots the designers decided to make things
differently.

Hmmm. I wonder how my COZY MKIV canard aircraft maintains pitch
stability, then, and in fact is extremely stall resistant. Scaled
Composites' "Proteus" aircraft is essentially a tandem wing airplane -
the front and rear wings are very close in size. The Piaggo Avanti
has both a canard flying surface AND a tail.

There are numerous examples of tandem, canard, and three surface
aircraft that are completely stable in pitch, and have benign stall
characteristics.

See FAR 23 (U.S.) or CAR 523 (Canadian) for the details.

Yes, see 23.302, which specifically references the canards and tandem
wing aircraft. If they were "illegal", as you claim, there shouldn't
be any reference to the rules with which they must comply. There are
no other part 23 FARs that state what you claim.


Phil J wrote:

OK, this makes sense.

No, actually very little of what's been written in this thread makes
any sense. There's a lot of misinformation about what makes aircraft
work. The web site I pointed to above, while not perfect, has some
excellent explanations of many aerodynamic points about which there is
much misinformation, confusion, and clears up a lot of things that
people know that just isn't true.

Kyle Boatright was just about the only one to write something that
made aerodynamic sense.


Beg yer pardon, but I posted pretty muc the same thing as you but in my
native tongue..

Bertie