Hi Bob Tait


I have passed my AGK exam, but I still have some confusions about it. Here are the questions.
1.Does geared supercharger have waste gate?
2.In my opinion, no matter whether it has Supercharging or not, each engine has only one critical altitude. But it could have a lot of full throttle heights for each manifold pressure. For example, manifold pressure 14 has its own full throttle height, manifold pressure 18 has its own full throttle height, manifold pressure 24 has its own full throttle height, and so on. Is this correct?


And, I am learning ADY now. I have some questions about it too.
1.Asymmetric Blade Effect: Why the downgoing propeller blade will have a greater angle of attack than the upgoing blade?
2.Is the total reaction perpendicular to the chord line?
3.Does the drag that is resolved from total reaction include the induced drag?

Thank you

GENERAL KNOWLEDGE
1. No, a geared supercharger always runs the compressor at a fixed ratio of engine RPM. It is necessary to change the throttle position to prevent overboosting at low altitudes.

2. That's correct. Every value of manifold pressure has its own full-throttle height. Critical Altitude is simply full-throttle height for rated boost. That is, the greatest height at which 100% power can be maintained.

ASYMMETRIC BLADE EFFECT
1. See the diagram Fig 4.10 and Fig 4.11 in my Aerodynamics book.

2. All of the aerodynamic forces acting on the wing can be resolved to a single resultant force called the total reaction. It is considered to act through the centre of pressure and approximately at right angles to the chord. The total reaction can then be resolved into two component forces, one acting at right angles to the relative airflow (lift) and one acting parallel to the relative airflow (drag).

3. Remember that most diagrams you see represent the wing only as though it was mounted in a wind tunnel. That can be very misleading. If you consider the aerodynamic forces acting on the whole aircraft, you also see that the whole aircraft has a total reaction (and a centre of pressure) that is not in the same position as that on the wing alone. Many aircraft create some lift from the fuselage and/or tail plane (or even the cockpit canopy). For example, if you are considering a vector diagram for the aircraft in a glide, you would have to consider the lift and drag created by the whole aircraft - not just the wing. This also applies when we talk about the lift/drag ratio. It's the maximum lift/drag ratio of the whole aircraft that determines maximum still air gliding distance or maximum still air range.

But I asked the question about the relationship between total reaction and chord line on the QUORA few days ago. A professor gave another explanation

That's correct. The total reaction may not necessarily be exactly at right angles to the chord in the case of a cambered wing operating below the stalling angle of attack. However it is approximately true for most GA wings. In fact the direction of the total reaction changes with angle of attack changes. Thanks for your feed-back - it is most appreciated.

Thanks for the detailed explanation and your patience.