No, that's not what I am saying at all.
Assuming no frictional resistance, if a bus is accelerating at 2.5 m/s on level ground due to the torque of the engine
, and then the bus
pitches up due to a hill by 15 degrees, then assuming constant torque, the bus will no longer be accelerating, because the force due to engine torque
and the force due to gravity down the slope will be equal. The longitudinal reaction force in the bus (i.e. the force in the direction from the back
of the bus to the front of the bus) will be the same throughout this entire exercise, due to constant engine torque. Passengers will be pushed back
into there seats at about 0.255 g throughout this entire exercise.
Assuming constant torque:
Hill > 15 degrees = Deceleration
Hill < 15 degrees = Acceleration
The longitudinal reaction force will remain the same throughout, this is entirely due to engine torque!
The aircraft is essentially identical to this. At the beginning of takeoff roll, the thrust to drag ratio is maximized because there is no air
resistance, and the engines are producing maximum thrust. As the drag increases, the longitudinal acceleration will decrease somewhat. When the
aircraft rotates, the power the engines are developing stops going to accelerating the aircraft, but goes to making the aircraft gain height.
There will also initially be an increase in reaction force from the floor, as the aircraft takes off and its velocity changes from horizontal to
diagonal, and then later a decrease in reaction force from the floor as it is climbing (due to the being pitched up) but not accelerating. Due to a
decrease in friction against the floor, an increase in force the straps or bracing has to accommodate has likely increased.
However, the longitudinal reaction force (i.e. what the cargos feel longitudinally) will go from being from aircraft acceleration, to fighting
gravity, but will be fairly similar in magnitude throughout. The angle of attack would be non-zero after rotation, this is the only other reason I can
think of which would increase the force on the straps as it would increase the longitudinal force by a relatively small amount.
Point is, longitudinal reaction force is mostly dependent on the thrust-to-drag and thrust-to-mass of the aircraft.
edit on 9/5/13 by C0bzz
because: (no reason given)