Generally true but your last comment about a rearwards component of Lift isn't quite right.
It depends on what you mean by 'Lift'. If you're referring to the Total Reaction ie the sum of the aerodynamic forces produced by a wing, then yes, you could say it the way you did.
What you have really referred to is the Total Reaction ie total aerodynamic force produced by the wing. This total force is what gets resolved into a component called Induced Drag acting parallel to, and rearwards along, the flight path, and another component at 90 deg to the flight path called Lift. There can be no rearwards component of the part called Lift - by definition it acts at 90 deg to the flight path.
Consider an aircraft in a steady vertical climb BUT ONE THAT HAS HAD ITS WINGS REMOVED.
Thrust has to counter both Weight, and whatever Drag is present (all parasite drag since no lift is being produced to cause induced drag to be present).
Now add some wings BUT keep the aircraft attitude in an orientation that prevents the wings producing Lift. Like the no-wing case, there still won't be induced drag. There will still be all the other parts of Drag that afflict the structure and are lumped together in the term Parasite Drag, so Thrust must still be used to counter both (parasite) Drag & Weight.
If the aircraft attitude is changed so that the wings now produce Lift (ie a force at 90 deg to the flight path) then there will also be some additional amount of Drag: Induced Drag. This would also have to be overcome by Thrust in order to maintain speed. Bear in mind that any force at 90 deg to the vertical flight path will cause the flight path to deviate from vertical.
The Lift & Drag being produced are components of the total aerodynamic force the wing produces. That total force is what has a component acting back along the flight path - Induced Drag - plus the desirable Lift.
You could also consider it like this:
We're concerned with unaccelerated flight so that means the sum of all forces in any direction must be balanced by some combination of forces acting to produced an equal size force acting in the opposite direction. Straight & Level flight is the easiest example of this: Lift = Weight, Thrust = Drag. You could could draw a line at any orientation through the aircraft and all the forces on one side of the line will be exactly opposed by the combination of all the forces on the other side of the line.
This applies to unaccelerated motion in any direction: Forward, backward, sideways, vertical or whatever.
In an unaccelerated climb it still applies. All forces on one side of a line must be balanced by all forces on the other side.
Think of a horizontal dividing line: All 'upwards/forwards' forces must be balances by all 'downwards/backwards' forces. Thrust & Lift are the only upwards or forwards forces, and Drag & Weight are the only downwards or backwards ones.
Each group of forces can be combined into a single resultant using standard vector addition. The resultant has the same effect as combination of each of the forces from which it was made.
The Drag/Weight resultant MUST be balanced by a resultant caused by Lift & Thrust. The only way to make a Lift/Thrust resultant that balances Drag/Weight resultant is for Thrust to be larger than Drag & for Lift to be less than Weight. This is because the angles between the four forces varies, therefore the size of each force must vary to keep the resultants the same.
A diagram makes it soooo much easier to explain...
Last edited by Tinstaafl; 26th Dec 2003 at 00:08.