Hi,
I've just done the Aerodynamics exam and got 90%, which I'm very happy with considering preparation for this one was a bit rushed. Thought I'd share where I tripped up in the hope it'll help someone else.

Purpose of design features; There was a question asking what vortex generators were there to delay. I answered turbulence, where I'm guessing the correct answer would have been separation of the boundary layer (which would lead to turbulence?).

The KDR lists Lift - which isn't all that helpful in letting us know where we went wrong!!! My guess is a question comparing an aeroplane in a climb to one in straight and level flight but with the same IAS, would the one in the climb have more, less or the same AOA. I reasoned that since there is less lift in a climb compared to level flight at the same speed, there would be a lower AOA. Am I getting that twisted???

Factors affecting turn performance: There was a question about Thrust, Drag, Lift and weight forces relative to each other. in a level balanced turn. I had L more than W but T equalling D. My reasoning at the time was that at a constant speed Thrust has to equal speed but extra lift is needed for the horizontal component of the turn. Thinking about it again you need more thrust to generate the extra lift, there's more drag involved because of the higher AOA but maybe thrust is increased more??

Factors affecting stability and control: Again a few questions this could have been. Pretty sure there was one asking about the effect on longitudal stability of an increase in angle of attack. I think I thought about the centre of pressure moving forward, giving it a longer arm from the tailplane which would make it more stable. if that was indeed the question and answer I selected, I'm now thinking that moving the Cop forward would bring it closer to the centre of gravity, which would make the plane less stable ????

Wouldn't it be nice to be told a bit less vaguely where you're going wrong!!! I guess there's some logic in their method somewhere.

Hopefully I haven't just broken any rules about publishing exam questions. If so my defence is that my recall is a bit fuzzy and I'm not guarantying that I've quoted exactly.

Just been looking up the references given on the KDR in the Day VFR Syllabus which is a bit of help in some but still not much in others. The question I got wrong regarding "Factors affecting turn performance" comes up in the syllabus 2.6.6.4(b) as State why:(b) an aeroplane tends to overbank in level and climbing turns and not in descending
turns.
Ok. There was a question which I remember as asking what aileron input is needed during a level turn. My understanding after reading and re reading your text is that during a level turn ailerons should be in the neutral position, which I'm sure was my answer in the exam. ?????

Graeme. 90% is a good result so I wouldn't beat yourself up.

For the aircraft to be climbing, Lift must be greater than weight.

In a level turn, the outside wing has to travel quicker than the inside wing, thus producing more lift and creating a tendency to over bank, in a climbing turn same happens but also at the top of the turn if the angle of bank was held constant, then you would over bank due to the angle of the aircraft in relation to the horizon changes from the bottom to the top of the turn (i am sure there is a picture of this in Bob's book). In a descending turn, this effect is opposite.

for a plane to be in any kind of level flight, weight must equal lift, if lift was greater, then you would be climbing. I think the gotcha here is that you need back pressure in a turn to hold altitude, but all this is doing is increasing lift so it still equals weight.

cheers
Ben

Good reply, Bungee.

I agree, in a level turn the outside wing is travelling faster and therefore will tend to generate more lift hence a tendency to over bank. In a climbing turn, the effect is more significant because you need to continually roll out of the turn to maintain the same bank angle and if you don't, the bank angle will get progressively steeper as you turn.

Just need to qualify a couple of points in your post though...

It would be better to say that for an aircraft to be climbing the forces acting against the climb need to be balanced by the forces acting to maintain the climb. In other words, thrust and lift which are acting to maintain the climb need to balance the forces of weight and drag which are acting against the climb. Lift will actually be less than weight in a climb, even if it is a climbing turn since a component of the thrust will be acting upwards and helping to support the weight. You can see this more clearly if you consider a vertical climb - there will be no lift required at all; it is all thrust.

In a constant level turn, the lift will be more than the weight since the lift vector is now at an angle to the vertical and no longer acting directly against the lift. You need more lift so the vertical component of it still matches the weight (which is what I suspect you meant).

You can get this increased lift by flying faster in the turn at the same angle of attack (assuming you have the excess thrust available to accelerate to the higher speed) or by increasing the angle of attack (i.e. back pressure on the control column). In either case, there will be an increase in drag which will need be matched by more thrust if the airspeed is to remain the same.

Cheers,

Rich

Thanks Richard... that's why you're on the big bucks!