bookworm , ft, alf5071h
Where are you SR71?
Still with us J T ?
Great to have you joining the fray. You will find yourselves reviewing a lot of aerodynamic basics and may also come to grips with a major myth that has been perpetuated regarding directional stability for far too long.
Most text books continue to make the mistake that the horizontal forces on an aircraft in steady flight have someting to do with weight and the cg. Well in this case only a smidgen.
A few basics first to re-establish the detail of what we are discussing. That is Sideslipping when Asymmetric.
1. The horizontal forces on a twin engined aircraft in steady straight unaccelerated level flight can be accumulated and represented by just two distict forces familiar to us.
1.1 Component of Thrust - Acts straight along an aircraft centre line assuming equal thrust from engines. Vertical positioning of thrust line irrelevant to horizontal. NO relationship to weight or cg
1.2 Total Drag - Acts straight along an aircraft centre line. Equals Thrust. Vertical positioning of drag line irrelevant to horizontal. NO relationship to weight or cg
2. The horizontal forces on a twin engined aircraft having asymmetric thrust flying in steady straight unaccelerated level flight, wings level, can be accumulated and represented by just three distinct forces familiar to us.
2.1 Component of Thrust - Acts along a line parallel to an aircraft centre line. Vertical positioning of thrust line irrelevant. NO relationship to weight or cg.
2.2 Total Drag - Acts parallel to an aircaft centre line. Equals Thrust. Vertical positioning of Total Drag line irrelevant. NO relationship to weight or cg.
2.3 Fuselage Sideforce - Acts from the lateral centre of pressure normal to the aircraft centre line and towards the engine having least thrust. Verical positioning of Fuselage Sideforce line irrelevant. NO relationship to weight or cg.
3. The horizontal forces on a twin engined aircraft having asymmetric thrust flying in steady straight unaccelerated flight, small bank angle, can be accumulated and represented by just four distinct forces familiar to us.
3.1 Component of Thrust - Acts along a line parallel to the aircraft flight path. Vertical positioning of thrust line irrelevant. NO relationship to weight or cg.
3.2 Total Drag - Acts parallel to the aircraft flight path. Equals Thrust. Vertical positioning of Total Drag line irrelevant. NO relationship to weight or cg
3.3 Component of Lift. Acts from an obscure point along the vertical line from the cg and normal to the flight path horizontally towards the side having greatest thrust.Vertical positioning of Component of Lift force line irrelevant. Point of origin related to cg, NO relationship to weight.
3.4 Balancing force to Component of Lift. Acts from the lateral centre of pressure normal to the aircraft flight path and towards the engine having the greater thrust. Verical positioning of Fuselage Sideforce line irrelevant. NO relationship to weight or cg.
Note. 1 bookworm. Deliberate no mention of rudder to keep it simple. Don't care where it is and incidently there is no way for you to accurately trim rudder to nail the min drag you have been chasing in a performance climb. Re-engined Caribou was a classic. Difficult without a boom and vane. Yaw string too gross.
Note 2 The vertical levels/planes of the above forces do not coincide. Resulting vertical moments are well cared for by the aircraft's longitudinal stability. We are strictly horizontal here.
Now - can someone please explain where we can generate that balancing force to the Component of Lift ?? I can assure you that it does not come from the strengths of a family of Gremlins, Fiffinellas and their proginy - Widgets.
Challenge to all who pass this way.
Watch this space for the next exciting discourse on aerodynamics !!