-------- Original message --------
Date: 6/22/18 3:34 PM (GMT-05:00)
Subject: RE: [Q-LIST] Re: Reflexor, Elevator and takeoff/landing angle
Your comments are always appreciated. The moments are incorporated in the modeling, so yes they do contribute, however all other things being equal, I can understand why you see the incompatibility. I can summarize the issue as follows. Control surface deflection (downward) increases the camber of the airfoil, thereby increasing the lift, but also increases forward pitching moment. Rotating the aircraft to a higher AOA increases the lift but GREATLY increases the forward pitching moment of the each airfoil. The magnitude of moment increase resulting from the AOA is more significant than the magnitude moment increase from higher camber, so the 4 degree AOA scenario accounts for overall lower forward pitching moment at the moment of flight. The numbers for my modeled wings are as follows (moments are relative to 25% chord).. Forward pitching sign-convention is negative.
For the case of 6.5 degree AOA takeoff with 17 degrees of down elevator, and 6 degrees of TE UP reflexor:
Canard 1.72 -0.165
Main Wing 0.46 -0.801
For the case of 4 degree AOA takeoff with 12 degrees of down elevator, and 2 degrees of TE DOWN reflexor
Canard 1.47 -0.113
Main Wing 0.45 -0.697
By normalizing each scenario’s Cm’s by a factor that makes total Cl=1.0 (for purposes of comparison), the 6.5 degree AOA scenario’s forward pitching moment is 105% that of the 4.0 degree AOA scenario’s pitching moment
Jay, something doesn’t add up. At constant gross weight and CG location, you cite liftoff at two different combinations of elevator and reflexor deflection that seem incompatible to me. In one, your reflexor is 2deg TE down and your elevator is 12deg down; in the other, your reflexor is 6deg TE up and your elevator is 17deg down. It seems to me that one or the other of these conditions will result in a rapid pitch change (rotation about the lateral axis) and will be unsustainable immediately after liftoff. Are you including airfoil pitching moments in your calculations? They are required for determining pitch equilibrium.