Original Posted By: "Oscar Zuniga"
Oscar Oscar Oscar,Stand off of the LEFT wing tip about 30 feet and look at the airplane. Itshould have the nose left and the tail right. From this perspective, thepitching moment of the airfoil would be anticlockwise. In other words, thecenter of pressure, defined as the point under the wing's airfoil where allthe air can be assumed to act, is aft of the center of gravity, the point atwhich all the mass can be assumed to be positioned. If the center ofgravity is positioned at 19.5" aft of the leading edge and the center ofpressure is located at the 25% or the 1/4 chord point, as it is on mostairfoils, then a rotation is set up where the wing wants to flip nose overand over. We see this when the wing comes off of our Sleek Streak rubberpowered 25 cent model that we flew as kids. The wing flips over and over onthe way down.Therefore, the stabiliser acts downward to counter this rotation. Actingdownward means that it acts as an inverted wing. Lowering the leading edgeof the stabiliser works to increase ITS angle of attack, giving it more biteinto the air helping to force the tail down. We, in effect, "washed in" thestabiliser.Taking it further, assume a ship that looks like a Piet weighs 1000 lbsloaded to fly. At our flight speed, the pitching moment of this ship'sairfoil is rather large requiring a 100 pound aerodynamic downforce at thetail to keep the nose from tucking under. The wing now has to lift not onlythe 1000 pound weight of the ship but also needs to "lift" against the 100pound downforce of the stabiliser. Therefore, the wing is providing 1100pounds of lift to fly a 1000 pound airplane. Lift is not free and the twopenalties are imposed is in the form of additional parasite drag due to thewing being sized to carry 1100 pounds instead of 1000 pounds and, moreimportantly and more significantly, the induced drag is commensurate with1200 pounds of lift not 1000 pounds of lift like you might think. Wait,1200 pounds? That is 20% higher induced drag than one would think! Yes,1200 pounds because you are producing 1100 pounds worth of induced drag atthe wing and 100 pounds worth of induced drag at the stabiliser. Inducedrag is induced drag, it results whether the lift vector is up or down andthey do not cancel each other out!The reason Burt Rutan revived the concept of the canard is so that bothairfoils are working the same way and not against each other. Put the tailin the front and now it can lift to hold the nose up. If the ship wieghs1000 lbs, now you can have the wing holding up 900 pounds and the canardholding up the 100 pound pitching moment yielding a total induced dragcommensurate with 1000 pounds of lift, the ships weight, which is 5/6 of thecase of the tail mounted stabiliser, a significant drag reduction. The wingarea can be now be reduced as it only holds up 900 pounds vice 1100 pounds,saving weight, which reduces the induced drag, increases the range and/orpayload, etc..Flitzer los!ChrisChrisBraumeister und Inspektor der Flitzer und Flitzermotoren----- Original Message -----