As I see it, the forward fuselage is likely creating some unneeded positive lift from the wing up wash and requiring more tail down force. This could help explain the noted excess horizontal tail negative angleIs it possible that the fuselage is creating some negative lift? That would explain a high wing incidence at higher speeds.
No, an aircraft does not need a horizontal tail because of a "nose heavy effect." Conventional aircraft require a horizontal tail because the combination of wing, fuselage, and propulsion produces a nose-down pitching moment. Most airfoils have a chord-wise distribution of lift that is centered aft of the aerodynamic center. This results in a net force that, if unopposed, will rotate the wing forward. The fuselage will also generate a similar, but smaller, force. The thrust produced by the propeller can be either stabilizing or destabilizing, depending on location.To obtain longitudinal stability, airplanes are designed to be nose heavy when correctly loaded. The center of gravity is ahead of the center of pressure. This design feature is incorporated so that, in the event of engine failure, the airplane will assume a normal glide. It is because of this nose heavy characteristic that the airplane requires a tailplane. Its function is to resist this diving tendency.
It is normal to have the wing at a higher angle than the tail, but not for the reason given. The wing and tail are producing forces in opposite directions, so it is natural for them to be angled differently. It is very important to prevent the tail from stalling, but that is very different than simply saying it has to be at a lower angle of attack than the wing. As to decalage making the aircraft "more self-stabilizing," I don't see it. That statement implies that decalage increases the lift curve slope of the tail, but that's not the case. The angle of incidence of the tail (and hence, the decalage) simply fixes the point along that lift curve where the tail is operating in the trimmed position.Decalage is the difference in incidence between the wing and horizontal stabilizer (the wing should always have a larger incidence angle than the stabilizer). A large decalage angle generally makes the airplane more self-stabilizing in pitch, but it also causes larger trim changes when airspeed is increased or reduced.
Something doesn't make sense. Those numbers work out to a lift coefficient of 0.54, which is at about 1° AOA for the 4412.We do know wing area = 138 sq. ft.
We do know weight = 950 - 1150 lb.
We do know speed at 5000 rpm = 82 mph at 4000 ft
We do know AOA = about 6 to the cord line
What we don't know is DRAG.
Yes took 3D effect into account. No the wing is not working very hard. Here is how you calculate:At 5 degrees alpha, 2-D Cl for a NACA 4412 is in the range of 0.8 to 1.0.
Eugene is reporting the estimated angle between the flattish bottom of the wing and the horizon, so the actual alpha is greater that the angle that he sees. I didn't calculate any numbers, but even a Cl of 0.4 sounds low. What Reynolds number did you use, how did you calculate total wing lift, and how did you reduce 2-D lift for 3-D real world?
It sounds to me like the wing is working really hard.