There's an interesting thread over on uk.rec.boats.paddle that we might
enjoy looking at. The (serious) question was posted: why do ruddered boats
have the rudder on the front?

One POV was that having it on back protects it in a collision....good
thought. Another offered POV was that the hull shape needs that laminar flow
to work, and a front rudder will disrupt that, destabilising the waterflow.
But then the question was posed about canard wings on aircraft, which are
basically rudders on front. They don't destabilize the airflow.

So lets toss that around here, too.....just why ARE the rudders on the back
of boats? Anyone ever experimented with a front-rudder?

--riverman

On 10-May-2004, "riverman" wrote:

But then the question was posed about canard wings on aircraft, which are
basically rudders on front. They don't destabilize the airflow.

Destabilizing the airflow isn't the issue. Destabilizing the aircraft is!

A pilot can't control a plane with a canard. You need fly-by-wire (i.e. a
computer to control the canard). Humans can't react fast enough. The Wright
brothers had a forward horizontal stabilizer on their first aircraft and it
quickly disappeared from aircraft design until small, fast computers came
around. (ditto forward-swept wings, negative dihedral [with exceptions - the
F4 comes to mind; not sure on its avionics.]). Aircraft that had these
characteristics were usually termed "widowmakers".

So lets toss that around here, too.....just why ARE the rudders on the back
of boats? Anyone ever experimented with a front-rudder?

If you put the rudder on the front, the kayak will not have good directional
stability, as any deflection of the rudder will result in the forces on the
rudder increasing and the deflection increasing (i.e. it "runs away"). The
paddler will have to be very quick to react to any deviation from the intended
course. If the rudder (or skeg) is on the stern, a deviation in course results
in an increase in the force on the rudder and it moves _back_ to the initial
course - it is self-correcting.

Take a skegged kayak and paddle it backwards with the skeg deployed. You'll
see the effect quite quickly. Alternatively, trim a kayak with a heavy load
forward pushing the bow down. It will be harder to control (track) than a
kayak trimmed heavy in the stern.

BTW - there are a few folks that hypothesize that the baidarka's flexibility
and bifurcated bow allowed for the paddler to twist the baidarka and use the
lower part of the bow as a forward rudder. However, modern materials make
baidarkas too stiff to reproduce the effect - sealskin is a lot more stretchy
than painted/coated cotton, nylon or polyester.

Mike

But then the question was posed about canard wings on aircraft, which are
basically rudders on front. They don't destabilize the airflow.


Destabilizing the airflow isn't the issue. Destabilizing the aircraft is!

A pilot can't control a plane with a canard. You need fly-by-wire (i.e. a
computer to control the canard). Humans can't react fast enough. The Wright
brothers had a forward horizontal stabilizer on their first aircraft and it
quickly disappeared from aircraft design until small, fast computers came

Not true! Canards are not rudders they are wings providing lift. They prodive
stability holding the nose up. They are set to loose lift at an angle slightly
less then the main wing. That way when the nose comes up lift is lost and the
nose comes back down. This helps keep the plane more stable not less. Also
the plane is less likely to stall. No computers in those little one and two
seaters from Rutan.

http://www.rutanaircraft.com/

On 10-May-2004, ospam (MBOSCHERT) wrote:

Not true! Canards are not rudders they are wings providing lift. They prodive
stability holding the nose up. They are set to loose lift at an angle slightly
less then the main wing. That way when the nose comes up lift is lost and the
nose comes back down. This helps keep the plane more stable not less. Also
the plane is less likely to stall. No computers in those little one and two
seaters from Rutan.

What happens when the canard loses lift first in level flight? Then the nose
dives and keeps diving. Nice that it prevents a stall, but most aircraft rely
on the horizontal stabilizer to force the nose up. Loss of lift puts the plane
into a dive from which it recovers by increasing speed and a return to a downward
force from the H stab. That doesn't happen with a canard.

Are Rutan's canards fixed or variable? If you look at an aircraft like the Viggen,
then you're looking at a canard that can seriously destabilize an aircraft. That
gives it maneouverability under control.

http://www.rutanaircraft.com/

"We'll be adding more information about the planes soon."

References to content-free web sites are not particularly useful.

Mike

On Tue, 11 May 2004 03:38:29 GMT, "Michael Daly" wrote:

On 10-May-2004, ospam (MBOSCHERT) wrote:

Not true! Canards are not rudders they are wings providing lift. They prodive
stability holding the nose up. They are set to loose lift at an angle slightly
less then the main wing. That way when the nose comes up lift is lost and the
nose comes back down. This helps keep the plane more stable not less. Also
the plane is less likely to stall. No computers in those little one and two
seaters from Rutan.

What happens when the canard loses lift first in level flight? Then the nose
dives and keeps diving.

No, the nose dives, airspeed increases, the canard starts lifting (flying) again and the cycle repeats until you contact
the ground.

Ken B.

riverman wrote:

So lets toss that around here, too.....just why ARE the rudders on the back
of boats?

A rudder is basically a brake. If you apply the brake on the front of
your boat, the front stops while the back keeps moving. This can make
for a wild uncontrolled spin-out.

OTOH, If you apply the brakes on the rear, your craft tends to be
stable. It's that simple.

Anyone ever experimented with a front-rudder?

I regularly sail backwards to get away from the dock, which is kind of
like having a rudder on the front. Leading with the rudder is
inherently unstable, although with a bit of practice it's no big deal.
The problem is once the boat turns a certain amount in the wrong
direction, no amount of steering will correct the problem - the boat
just continues to pivot about the rudder until you've done a full 180.

A related question: Why are darts designed with the heavy part in the
front and the feathers in the back?

-Walt

wrote in message
...
On Tue, 11 May 2004 03:38:29 GMT, "Michael Daly"
wrote:

On 10-May-2004, ospam (MBOSCHERT) wrote:

Not true! Canards are not rudders they are wings providing lift.
They prodive
stability holding the nose up. They are set to loose lift at an
angle slightly
less then the main wing. That way when the nose comes up lift is
lost and the
nose comes back down. This helps keep the plane more stable not
less. Also
the plane is less likely to stall. No computers in those little one
and two
seaters from Rutan.

What happens when the canard loses lift first in level flight? Then
the nose
dives and keeps diving.

No, the nose dives, airspeed increases, the canard starts lifting
(flying) again and the cycle repeats until you contact
the ground.

There is nothing upstable about the canard configuration at all. Bert
Rutan's highly successful canard designs have set new standards for
efficiency. The first non stop global flight was made by "Voyageur", another
canard design from Bert Rutan
See:
http://www.dickrutan.com/page2.html

The canard configuration was chosen for the first really successful man
powered aircraft designs the Gossamer Condor and Albatross, designed by Paul
Mcready's team
See:
http://www.dfrc.nasa.gov/Gallery/Pho.../ECN-12604.jpg

With the canard configuration both wings generate lift as opposed to the
conventional configuration where normally the tailplane acts downwards.

Regards,

Roy

The canard configuration was chosen for the first really successful man
powered aircraft designs the Gossamer Condor and Albatross, designed by Paul
Mcready's team
See:
http://www.dfrc.nasa.gov/Gallery/Pho.../ECN-12604.jpg

Love the low tech chase vehicles.

--Chris

A related question: Why are darts designed with the heavy part in the
front and the feathers in the back?

Because the pointy end sticks in a dart board much easier than that
feathers. I used to play darts competitively and I think in all the
tournaments and leagues I played in I only saw one person using darts with
feathers. I rarely play much anymore but I've still got about five sets of
darts. Darts have gone high-tech. All but one of the sets I have use a
tungsten barrel. The shafts are mostly aluminum but I've got a few nylon
shafts. Feathers are no longer used and have been replaced with plastic or
foil "flights" that come in a variety of shapes and in every color or
graphic on them imaginable. I've got both plastic tip and steel tip darts.
The steel tip darts have a retractable tip and moves slightly on impact
which significantly decreases the number of darts which bounce off a wire.