J Johnson, A center mounted tail on a canard has virtually no
  lever arm
  length and would be huge, if moved back wetted area and CG
  problems are a
  concern. The wing tip rudders deflect outward only on most
 designs and
  affect drag far from the CG to yaw the aircraft, and a 2 degree
  incidence is
  believed to turn drag into a small thrust vector when not deflected.

  george grimes

 George, I think we're in agreement! Having the tail right near
 the props is not going to have alot of effect [hence the thought
 of extending the tail [empennage] . Control of asymmetric thrust using
 drag /tip rudders seem's to be counter intuitive in that during single
 engine operations one needs ever ounce of thrust they can get..

 I think the better option here [my opinion only] would be to create
 some form of a dual props in an axial config, best of both worlds
 so to speak.

 Fwiw

 J. Johnson

 You guys are missing a little something. The Rutan rudders move only
 out. They do more with drag than they do with side force.
 Since the lever arm is so great a little bit of drag goes a long way.
 Pardon the pun :)

 Sort of like th split ailerons on the Northrop flying wing.

 Paul Lamar

Paul, I'd noted in my previous email that I wasn't to excited about drag rudders
to compensate for asymmetric thrust. I did some napkin math.

Assumptions:

Engine thrust = 400lb's [assume at lower speed near a 'realistic' Vmc]
Engine is 40" offset from A/c centerline.

I checked and a cozy wing is 28'1" so 1/2 span is 168"

400lbs x 40" = 16,000 in-lbs [1,333 foot pounds yaw force.]

16000in-lbs / 168" = 95lb's drag [at the wing tip]

If we do the math we come out w/ a needed drag of ~95lb's at the tip to
compensate for the asymmetric thrust. No counting any extra drag from the
feathered prop, which would exacerbate the issue.  That means for round
numbers we're looking at losing 1/4 of our thrust just to maintain directional
control..  I'd count this as un-acceptable if it was my design.. but then maybe I'm
missing something?

J. Johnson

Yes. Very good.  I'll buy your math.

To get 95 pounds of drag at 100 MPH you would need a rudder of
3.6 square feet perpendicular to the air stream so I agree. Rudder
drag alone is not going to get it all.

Lets add in the lateral restoring force from the vertical tip fins
in the horizontal plain about the CG.

Lets say it is 100 MPH ten degrees yaw.
The aspect ratio of the vertical tip fin and rudder is close to
6:1 so C sub L of the vertical tip fin is close to one. Dynamic
pressure is 26 pounds per square foot at 100 MPH. I would need a
good drawing to be more precise.

The CG is somewhere up there between the canard and the main
wing. Give it 40 inches in front of the vertical tip fin 1/4 cord
point. The size of the vertical tip fin, lets assume, is 4 feet by 2 feet.

Lets say they are 8 square feet each (2 fins) so we have a restoring
moment of 16 square feet times 26 pounds per square foot at 100 MPH
or 16 times 26 pounds times 40 inch 16,640 inch pounds  or 1386 foot pounds.

The aero drag on each vertical fin cancels out leaving the good drag
from the one rudder deflection.

Total restoring force is now 1366 foot pounds from the tip fins and
1,333 foot pounds max from rudder drag or about 2700 foot pounds total.

IMHO the stabilized yaw angle will be somewhere  around 8 degrees plus
or minus 2 or 3 degrees. There will be some lower speed down to take off
speed where this is not going to work and the airplane will spin. Common
on all conventional twins except huff and puffs.

Minimum engine out control speed or some such.

You either pull the power on the good engine and crash straight ahead
or kiss your ass goodbye :)

Paul Lamar

Been done in Venezuela with coaxial props and Suzuki engines. I believe it
has been flying for several years.

The Leon brothers, Ruben and Carlos's twin Suzuki powered Cozy from
Venezuela, they flew this plane all the way to Oshkosh!
They squeezed two  engines side by side, coaxial drive shafts turning
counter-rotating propellers,  at 8000 ft it will do 110kts on a single engine.
(http://www.infortel.com/cozy/)

Rich