Q163) Which statement about minimum control speed is correct?
A) VMCA may not be lower than VMCL
B) The nose wheel steering control may used to determine VMCG.
C) Crosswind is taken into account to determine VMCG.
D) VMCA depends on the airport density altitude, and the location of the engine on the aeroplane (aft fuselage or wing). (mark scheme answer)
->I do agree with D but in my book it also states that VMCG is affected by cross-wind, making VMCG increase when the cross-wind comes from the side of the inoperative engine during the take-off run (C).
JAA Regulations give specific definitions for terms such as VMCG, VMCA and VMCL. None of these inlcude any crosswind. Qustions in the exams relate to these specific definitions. So although a crosswind may make it more difficult to stay on the centre line following a critical engine failure, it will not change the value of VMCG as defined in the regulations.
A similar problem arises with questions relating CofG position and VMCA. Forward movement of the CofG will reduce the minimum speed at whcih it is possible to maintain control in the air following a critical engine failure. But the legal definition of VMCA includes the words "with the CofG at the most unfavourable position". So the actual CofG position does not affect the value of VMCA as defined in the regulations.
93) If flaps are deployed at constant IAS in straight and level
flight, the magnitude of tip vortices will eventually : (flap
span less than wing span)
A) increase.
B) remain the same.
C) increase or decrease, depending on the initial angle of attack.
D) decrease. (according to the mark scheme)
Most aeroplane flaps do not extend over the full span of the wings.
If flaps are extended and the aeroplane remains in level flight then the lift force must be unchanged in magnitude. But because the flaps do not extend all the way to the wingtips, the lift force must have moved towards the wing roots. This means that the pressure differences above and below the area of wing close to the tips must have reduced.
It is this pressure difference above and below the wingtips that drives the air into the wingtip vortices. So will less pressure differences close to the wing tips, the strength of the wingtip vortices will be reduced.
101) If the altitude is increased and the TAS remains constant
in the standard troposphere the Mach Number will:
A) decrease.
B) not change.
C) increase or decrease, depends of the type of aeroplane.
D) increase. (according to the mark scheme)
According to the diagrams relating IAS, MN and TAS with altitude for an isothermal layer, if TAS stays constant and altitude is increased, MN also stays constand and IAS decreases.
Mach number is the TAS expressed as a fraction of the Local Speed of Sound (or LSS). Mach = TAS/LSS.
LSS is proportional to the air temperature. So if air temperature decreases then the LSS also decreases. As altitude increases in the ISA Troposphere the air temperature decreases. This causes the LSS to decrease.
So if an aeroplane climbs at constant TAS in the iSA Troposphere, the decreasing LSS causes the Mach Number to increase.
As an example
661 knots TAS at ISA msl (where LSS = 661 knots) = Mach 1
661 knots at 36000 feet (where LSS = 573.25 knots) = Mach 1.153
You should be aware of the ECTM lines, which describe the variations of EAS, CAS, TAS and Mach Number with increasing altitude. If not then please review your course notes. If your notes do not cover the subject please send me a PM for details.
225) What is the effect on induced drag of weight and speed
changes ?
A) induced drag increases with decreasing speed and induced
drag increases with increasing weight
B) induced drag decreases with increasing speed and induced
drag decreases with decreasing weight (according to the mark scheme)
C) induced drag decreases with decreasing speed and induced
drag decreases with increasing weight
D) induced drag increases with increasing speed and induced
drag increases with decreasing weight
I would say that A and B say the exact same thing:
-if induced drag increases with decreasing speed, it obviously decreases with increasing speed.
-if induced drag decreases with decreasing weight, it obviously increases with increasing weight.
You are correct. A and B are effectively saying the same thing and they are both correct.
330) Which statement is correct about the gust load on an
aeroplane (IAS and all other factors of importance
remaining constant) ?
1. the gust load increases, when the weight decreases.
2. the gust load increases, when the altitude increases.
A 1 and 2 are incorrect.
B) 1 is incorrect and 2 is correct.
C) 1 is correct and 2 is incorrect. (according to the mark scheme)
D) 1 and 2 are correct.
In this type of question the term “gust response” means the degree to which the load factor is changed by the gust. You should be aware of a number of calculations in which the load factor in a gust can be estimated using the equation
Load Factor in gust = Load factor before gust x (New CL / Old CL)
For straight and level flight prior to the gust initial load factor would be 1 so the equation can be simplified to
Load Factor in gust = (New CL / Old CL)
We can use this equation to see how changes in weight would affect gust response. Let’s assume that we have two identical aeroplanes. Aeroplane B is twice as heavy as aeroplane A.
If they are both flying at the same EAS then aeroplane B must be generating twice as much lift as much lift as aeroplane A. But with the same EAS they both have the same dynamic pressure, so the CL and hence angle of attack of B must be twice that of A.
If they both hit the same gust they will both experience (approximately) the same increase in angle of attack and the same increase in CL.
Let’s suppose that
Initial conditions are CL A = 1.0 and CL B = 2.0
Increase in CL is 0.5 in both cases.
For aeroplane A
New load factor = New CL / Old CL) = (1.5/1.0) = 1.5
For aeroplane B
New load factor = New CL / Old CL) = (2.5/2.0) = 1.25
So the increase in load factor (gust response) of the heavier aeroplane was only half that of the lighter aeroplane.
This gives us the general statement that gust response decreases with increasing weight. If you think back you may find that you experienced this when doing your PPL flying. If the ride with the instructor on board was much smother than flying solo, it wasn’t (just) your bad flying. The weight of the instructor reduced the gust response.
So statement 1 in your question is true.
The second part of the question is more problematic because it does not include enough information. But if an aeroplane at constant weight and flying at constant speed hit a gust of a constant speed at two different altitudes, the change in angle of attack and CL would be the same in both cases. So the gust response would be the same in both cases. But all of this assumes that we are using the same type of speed (EAS, CAS TAS) for both the aeroplane speed and the gust speed.
So statement 2 in your question is incorrect.
As with all JAR questions there are a number of (often un-stated) simplifying assumptions at work. As indicated by some of the previous post in this thread, it is also possible to use different interpretations of terms such as “gust response”. But those that I have used above are the ones that will get you the correct answer in the JAR POF exam.
If we were to interpret the question as meaning “the maximum gust response” or “maximum load factor attainable in a gust” then increasing weight and increasing altitude would both decrease the maximum gust response. So statement 1 would still be true and statement 2 would still be untrue.
What happens to the IAS of maximum rate of climb when the temperature decreases at low altitudes?
A) Increases
B) Decreases
C) Doesn't vary
D) First a) and then b)
The first point to note is that the questions is not asking about the “maximum rate of climb. It is asking about the “IAS for maximum rate of climb”. This speed is Vy.
The qualifying term “at low altitudes” has probably been included in this question to eliminate the possibility of shock induced separation and shock stall.
Vy, the speed for maximum rate of climb is the speed at which excess power is maximum.
This is because Rate of climb = Excess Power / Weight
Decreasing temperature will increase air density. This is the equivalent of a decrease in pressure altitude (it is actually a decrease in density altitude).
This will cause the following
1. The Power Available curve will rotate anti-clockwise about the origin.
2. The Power Required curve will move down and to the left, sliding
along a tangent drawn from the origin.
The overall effect of these changes will be a slight increase in the IAS equating to Vy.
With an increase in altitude we would see Vy gradually decrease to equal Vx at the absolute ceiling. The situation in this question is the opposite. Density altitude is decreasing so Vy increases, causing it to move away from Vx.