Quote:
In a banked turn,weight is a constant,
Even this bit is arguably wrong. Weight is a force. F=M*A. In a turn the aircraft is subject to the sum of acceleration due to gravity AND the acceleration of the turn, so it's effective weight is increased. The wing needs to produce additional lift to support this, which is why it requires either a higher AofA or extra speed to maintain altitude.
I don't really have the inclination to get into this in detail, however (wiz) your explanation suggests a misconception. The fact that the aircraft has (after vector addition) an unbalanced force means that it will accelerate, in this case towards the centre of the turn. Its weight is unchanged.
Weight is not equal to the F in F = MA. (unless the object is in frictionless free fall of course).
In straight and level flight the aircraft is NOT subject to an acceleration due to gravity. It IS subject to a force due to gravity, but since equal and opposite lift is being applied the resultant force is zero and the aircraft is not accelerating.
One common problem with F=MA is that people get the idea it implies a cause; i.e. that a force exists BECAUSE a mass is accelerated. Then they try and apply that concept to weight, mass, and acceleration due to gravity and get themselves in a muddle. Objects have weight whether they are being supported or not and whether they are being accelerated or not.
Its often handy to re-express F=MA as A=F/M which gives us a better pointer as to what's going on; accelerations are caused by unbalanced forces, not vice versa.
[ Additionally, regarding the OP, a purist might argue any of the following:
- Fuel is being burnt, therefore mass is decreasing so weight is decreasing. Techically correct, but perhaps a bit pedantic and missing the point of the question.
- Actually, even in straight and level flight, lift is fractionally less than weight, (due to Earth Curvature, the aircraft must be following a curved flight path and is not therefore in a 'uniform state of motion' as Newton would have said). This effect is pretty negligable for most aircraft, although it becomes detectable for fast moving things (e.g. SR71) or spacecraft. However this is a depth of analysis beyond most interviewers so I wouldn't go there, nevertheless, strictly speaking there is NO steady flight phase where lift>weight. ]
pb